I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't
pop
the breaker. Obviously the magnetizing current is higher with the variac
turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington


Just a WAG, but maybe the sliding contact has worn "flat" and is
touching too many turns of wire, creating a multiturn shorted winding
when set at the 30% position, thus causing the problem.

You didn't say whether your variac is a 0-100% kind or the kind which
can output more than 100% of the input voltage.

If it's the 100% kind, then maybe when it's set to 100% the contact arm
is no longer resting on the winding but is on a broader piece of metal
connected to the hot input.

More details please. If you plug it in at 100% and then lower it to 30%
do things stay OK?

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

--Well I'm clueless but this might be a good question for
sci.electronics.basics

--
"Steamboat Ed" Haas : Feeling like Bender in
Hacking the Trailing Edge! : a strong magnetic field...
www.nmpproducts.com
---Decks a-wash in a sea of words---

Grant Erwin wrote:
I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

it sounds like you have a short, or have the autoformer wired wrong.

The slider connects to the output side. The input goes across the windings
of the toroid, either at the ends for a 0 to 100% transformer or one end
and a tap for the 0 to 140% ones.

The slider should have no effect on the transformer at no load otherwise.

Jeff Wisnia wrote:

Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A
circuit with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it
didn't pop
the breaker. Obviously the magnetizing current is higher with the
variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good
working condition, in other words I don't believe this is faulty
behavior.

Grant Erwin
Kirkland, Washington



Just a WAG, but maybe the sliding contact has worn "flat" and is
touching too many turns of wire, creating a multiturn shorted winding
when set at the 30% position, thus causing the problem.

You didn't say whether your variac is a 0-100% kind or the kind which
can output more than 100% of the input voltage.

If it's the 100% kind, then maybe when it's set to 100% the contact arm
is no longer resting on the winding but is on a broader piece of metal
connected to the hot input.

More details please. If you plug it in at 100% and then lower it to 30%
do things stay OK?

It doesn't pop the breaker at 100%, and at the moment it's turned down to
60% and doing an electrolytic derusting job. After that's done I'll be
able to experiment more.

Mine can be wired either to 0-100 or 0-120%, I believe. I've had it both
ways. I used to use it to overdrive hot air popcorn poppers to get more
power out of them when using them to roast coffee beans. But now it's
wired 0-100%. It's possible there's a wiring error, but I don't think so.

Grant

On Oct 10, 8:29 am, Grant Erwin wrote:


I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.


Yet your experimental evidence suggests otherwise. With no load, the
variac should draw negligible current at any setting.

Grant, can you post of a picture of how it is wired exactly.

i

On 2007-10-10, wrote:
On Oct 10, 8:29 am, Grant Erwin wrote:


I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.


Yet your experimental evidence suggests otherwise. With no load, the
variac should draw negligible current at any setting.

Do you have a GFI somewhere in the 20A circuit?

By the way, check your USPS mailbox, I sen't you something.

cheers
T.Alan

On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin
wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Magnetizing current doesn't depend on the position of the slider.
Sounds like a short.

On 2007-10-10, Don Foreman wrote:
On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin
wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Magnetizing current doesn't depend on the position of the slider.
Sounds like a short.

my guess is that his output terminal is connected to hot terminal.

That would explain why it does not pop breaker at full voltage, but
pops the breaker at middle voltage.

i

Don Foreman wrote:

On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin
wrote:


I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington


Magnetizing current doesn't depend on the position of the slider.
Sounds like a short.

Many people have suggested to me that there is a short.

If you think of the primary side as having terminals L1 and L2, let's for the
sake of argument say that there are 100 coils between L1 and L2, numbered 1, 2,
3, ... 99, 100. The output terminals are connected between S (for slider) and
L2. As you vary the control, S should physically contact one of the coils e.g.
coil number 50.

Let's imagine that it is instead contacting coils 50 through 54. This would be
the short that people tell me I probably have, right? As I see it, that would be
equivalent to having a primary with 95 coils, and I *still* don't see where a
large increase in magnetizing current would happen.

I'm sure the problem is in my thinking - please show me where!

GWE

On Oct 10, 8:05 pm, Grant Erwin wrote:
Don Foreman wrote:
On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin
wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Magnetizing current doesn't depend on the position of the slider.
Sounds like a short.

Many people have suggested to me that there is a short.

If you think of the primary side as having terminals L1 and L2, let's for the
sake of argument say that there are 100 coils between L1 and L2, numbered 1, 2,
3, ... 99, 100. The output terminals are connected between S (for slider) and
L2. As you vary the control, S should physically contact one of the coils e.g.
coil number 50.

Let's imagine that it is instead contacting coils 50 through 54. This would be
the short that people tell me I probably have, right? As I see it, that would be
equivalent to having a primary with 95 coils, and I *still* don't see where a
large increase in magnetizing current would happen.

I'm sure the problem is in my thinking - please show me where!

GWE

If connecting coil 50 connects to itself, then you have the equivalent
of a secondary consisting of one turn connected to a dead short.

Dan

On Wed, 10 Oct 2007 12:05:24 -0700, Grant Erwin wrote:
Don Foreman wrote:
On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped the breaker. When I set it to 100% of output
voltage, however, it didn't pop the breaker. Obviously the magnetizing
current is higher with the variac turned down. The question is why?
What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Magnetizing current doesn't depend on the position of the slider. Sounds
like a short.

Many people have suggested to me that there is a short.

If you think of the primary side as having terminals L1 and L2, let's for
the sake of argument say that there are 100 coils between L1 and L2,
numbered 1, 2, 3, ... 99, 100. The output terminals are connected between
S (for slider) and L2. As you vary the control, S should physically
contact one of the coils e.g. coil number 50.

Let's imagine that it is instead contacting coils 50 through 54. This
would be the short that people tell me I probably have, right? As I see
it, that would be equivalent to having a primary with 95 coils, and I
*still* don't see where a large increase in magnetizing current would
happen.

I'm sure the problem is in my thinking - please show me where!


Are you absolutely sure you've got it wired right? If you connect the
mains to, say, L2 and the wiper, that would do what you say (and probably
cause collateral damage, because it would be in a step-up configuration.)

Hope This Helps!
Rich

Rich Grise wrote:

On Wed, 10 Oct 2007 12:05:24 -0700, Grant Erwin wrote:

Don Foreman wrote:

On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin


I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped the breaker. When I set it to 100% of output
voltage, however, it didn't pop the breaker. Obviously the magnetizing
current is higher with the variac turned down. The question is why?
What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Magnetizing current doesn't depend on the position of the slider. Sounds
like a short.

Many people have suggested to me that there is a short.

If you think of the primary side as having terminals L1 and L2, let's for
the sake of argument say that there are 100 coils between L1 and L2,
numbered 1, 2, 3, ... 99, 100. The output terminals are connected between
S (for slider) and L2. As you vary the control, S should physically
contact one of the coils e.g. coil number 50.

Let's imagine that it is instead contacting coils 50 through 54. This
would be the short that people tell me I probably have, right? As I see
it, that would be equivalent to having a primary with 95 coils, and I
*still* don't see where a large increase in magnetizing current would
happen.

I'm sure the problem is in my thinking - please show me where!



Are you absolutely sure you've got it wired right? If you connect the
mains to, say, L2 and the wiper, that would do what you say (and probably
cause collateral damage, because it would be in a step-up configuration.)

I'm working with the thing right now, unfortunately. But I can confirm that
when I move the slider up to 100% the current goes up, and when I move the
slider down, it goes down. Nor does the current at 100% exceed the current
if I just plug the load (a car battery charger) into the wall directly, so
I really doubt it's stepping anything up.

I'm trying to take digital pictures right now.

Grant

On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin
wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Will happen if you hook the sucker up backwards. The "primary" goes on
the 2 ends. The "secondary" is one end to the wiper.

--
Posted via a free Usenet account from http://www.teranews.com

On Oct 11, 12:20 am, clare at snyder.on.ca wrote:
On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin

wrote:
I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

Will happen if you hook the sucker up backwards. The "primary" goes on
the 2 ends. The "secondary" is one end to the wiper.

I think this is very likely what is going on. If you have the primary
wired through the wiper, the current drawn will increase dramatically
as you turn the variac down to low values; at low values, it means
that the primary is essentially a short (although possibly not the
kind of short you were looking for).

Open the variac and check the wiring as soon as you can, because it
might overheat and destroy the insulation.

Best wishes,

Chris

Rich Grise wrote:

On Wed, 10 Oct 2007 12:05:24 -0700, Grant Erwin wrote:

Don Foreman wrote:

On Wed, 10 Oct 2007 08:29:49 -0700, Grant Erwin


I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped the breaker. When I set it to 100% of output
voltage, however, it didn't pop the breaker. Obviously the magnetizing
current is higher with the variac turned down. The question is why?
What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Magnetizing current doesn't depend on the position of the slider. Sounds
like a short.

Many people have suggested to me that there is a short.

If you think of the primary side as having terminals L1 and L2, let's for
the sake of argument say that there are 100 coils between L1 and L2,
numbered 1, 2, 3, ... 99, 100. The output terminals are connected between
S (for slider) and L2. As you vary the control, S should physically
contact one of the coils e.g. coil number 50.

Let's imagine that it is instead contacting coils 50 through 54. This
would be the short that people tell me I probably have, right? As I see
it, that would be equivalent to having a primary with 95 coils, and I
*still* don't see where a large increase in magnetizing current would
happen.

I'm sure the problem is in my thinking - please show me where!



Are you absolutely sure you've got it wired right? If you connect the
mains to, say, L2 and the wiper, that would do what you say (and probably
cause collateral damage, because it would be in a step-up configuration.)

I'm working with the thing right now, unfortunately. But I can confirm that
when I move the slider up to 100% the current goes up, and when I move the
slider down, it goes down. Nor does the current at 100% exceed the current
if I just plug the load (a car battery charger) into the wall directly, so
I really doubt it's stepping anything up.

I'm trying to take digital pictures right now.

Grant
Possibly the slider is touching inside the unit at that setting????
and shorting out.
Ken.

"Grant Erwin" wrote in message
...
I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it (consistently)
popped
the breaker. When I set it to 100% of output voltage, however, it didn't
pop
the breaker. Obviously the magnetizing current is higher with the variac
turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington
We used a lot of 20A variacs in the calibration labs where I worked. They
will occasionally trip the breaker when energized and I think this depends
on the part of the AC cycle present at the instant the switch closes.

It is not possible that you have the variac wired backwards as it would
dramatically raise the output voltage and the input current when turned
down.

It is likely that you have the input leads connected backwards. In that
case, when turned down both output leads (the hot and the neutral) would be
120volts to ground and this might cause an input overcurrent depending on
what you have connected and its isolation from ground. I strongly suspect
this is the case if you can reliably reproduce the problem. If so, it
creates a serious unrecognized hazard and should be corrected immediately.
When the output is turned to zero, both output leads can kill you if you
contact one of them and are grounded.

Don Young

My bet you have the inputs on the wrong points.

The 'Mains' go across the whole coil.
The white wire connected to one end of the coil is zero volts out the
wiper. When the wiper (the output) is turned to the other end it is at the max.

The variac should easily idle on the power supply at any wiper value when no
load is attached. The output is the wiper.

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Grant Erwin wrote:
I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't
pop
the breaker. Obviously the magnetizing current is higher with the variac
turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington

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Treat it like a Pot (volume adjustment) - don't put it in series.

It is a transformer that has an input winding that one end is common
to the output. Often the input is not across the 100% winding but
a few turns short. That gives you the 120% more than the input because
the wiper sees ''120 windings'' when the input is press across ''100 windings''.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Grant Erwin wrote:
Jeff Wisnia wrote:

Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A
circuit with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it
didn't pop
the breaker. Obviously the magnetizing current is higher with the
variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good
working condition, in other words I don't believe this is faulty
behavior.

Grant Erwin
Kirkland, Washington



Just a WAG, but maybe the sliding contact has worn "flat" and is
touching too many turns of wire, creating a multiturn shorted winding
when set at the 30% position, thus causing the problem.

You didn't say whether your variac is a 0-100% kind or the kind which
can output more than 100% of the input voltage.

If it's the 100% kind, then maybe when it's set to 100% the contact
arm is no longer resting on the winding but is on a broader piece of
metal connected to the hot input.

More details please. If you plug it in at 100% and then lower it to
30% do things stay OK?

It doesn't pop the breaker at 100%, and at the moment it's turned down to
60% and doing an electrolytic derusting job. After that's done I'll be
able to experiment more.

Mine can be wired either to 0-100 or 0-120%, I believe. I've had it both
ways. I used to use it to overdrive hot air popcorn poppers to get more
power out of them when using them to roast coffee beans. But now it's
wired 0-100%. It's possible there's a wiring error, but I don't think so.

Grant

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Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit
with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't
pop
the breaker. Obviously the magnetizing current is higher with the variac
turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

Grant Erwin
Kirkland, Washington
Was there any load on the output?
...lew...

Lew Hartswick wrote:
Grant Erwin wrote:

I have a 20 amp variac. Yesterday I tried plugging it into a 20A
circuit with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it
didn't pop
the breaker. Obviously the magnetizing current is higher with the
variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good
working condition, in other words I don't believe this is faulty
behavior.

Grant Erwin
Kirkland, Washington

Was there any load on the output?
...lew...

No, no load whatever.

GWE

According to Grant Erwin :
I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

It sounds as though you are applying power between one end of
the winding and the wiper controlled by the knob.

The 20A Variac (if a genuine General Radio Variac, and not some
other maker) is likely to have several taps, and may even have windings
good for 240 VAC input.

You connect the input power to a pair of terminals according to
the voltage you have to feed it and the markings on the terminal plate.
(Typically a 0V at one end of the winding, and a 120V somewhere on the
way up from there. There may be a 140V terminal even beyond that, which
means that you can get overvoltage if you connect to the 120V terminal
and run the wiper past that.

The *output* (load) should be connected between the 0V terminal
and the wiper. Never connect the wiper to the input power.

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

With no load connected to the wiper, it should not pop the
breaker at *any* setting of the wiper. I've used these things for many
years -- Variacs, Powerstats, and other brands mixed in. *None* of them
have ever exhibited the behaviour which you have observed, but then I
never connected input power to the wiper either. I strongly believe
that you have input power connected to the wiper. And if so, with the
wiper set at 30%, and 120V input, you will probably have 360V (or more)
on the high end of the coil -- for a moment before the breaker pops.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Oct 11, 7:16 am, (DoN. Nichols) wrote:
According to Grant Erwin :

I have a 20 amp variac. Yesterday I tried plugging it into a 20A circuit with
its output voltage set to 30% of input voltage, and it (consistently) popped
the breaker. When I set it to 100% of output voltage, however, it didn't pop
the breaker. Obviously the magnetizing current is higher with the variac turned
down. The question is why? What's going on here?

It sounds as though you are applying power between one end of
the winding and the wiper controlled by the knob.

The 20A Variac (if a genuine General Radio Variac, and not some
other maker) is likely to have several taps, and may even have windings
good for 240 VAC input.

You connect the input power to a pair of terminals according to
the voltage you have to feed it and the markings on the terminal plate.
(Typically a 0V at one end of the winding, and a 120V somewhere on the
way up from there. There may be a 140V terminal even beyond that, which
means that you can get overvoltage if you connect to the 120V terminal
and run the wiper past that.

The *output* (load) should be connected between the 0V terminal
and the wiper. Never connect the wiper to the input power.

I believe the variac and my electrical circuits are both in good working
condition, in other words I don't believe this is faulty behavior.

With no load connected to the wiper, it should not pop the
breaker at *any* setting of the wiper. I've used these things for many
years -- Variacs, Powerstats, and other brands mixed in. *None* of them
have ever exhibited the behaviour which you have observed, but then I
never connected input power to the wiper either. I strongly believe
that you have input power connected to the wiper. And if so, with the
wiper set at 30%, and 120V input, you will probably have 360V (or more)
on the high end of the coil -- for a moment before the breaker pops.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

FYI

Claude Lyons in the UK has some info on their site - they have been
making variacs for a long time - many RS catalogue variacs where made
by them.

This is their tech doc: http://www.claudelyons.co.uk/tech.pdf it
shows connections etc.

regards
Tim

I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.

I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.

I think my problem is with my breaker tripping too low or too quickly.
I'm contemplating adding one of those temp-varistors to the input,
the kind which have resistance about 1 ohm when cold, but .01 ohms
when warm. Those are supposed to work OK in damping variac magnetizing
inrush current.

GWE

Robert Swinney wrote:

Well . . .
How about it Grant ? You asked a question on RCM. You got some good answers, particularly those
alluding to your having the variac connected improperly. When are you going to 'fess up and let us
know what your problem was???

Bob Swinney

"Grant Erwin" wrote in message ...
Lew Hartswick wrote:

Grant Erwin wrote:


I have a 20 amp variac. Yesterday I tried plugging it into a 20A
circuit with its output voltage set to 30% of input voltage, and it
(consistently) popped
the breaker. When I set it to 100% of output voltage, however, it
didn't pop
the breaker. Obviously the magnetizing current is higher with the
variac turned
down. The question is why? What's going on here?

I believe the variac and my electrical circuits are both in good
working condition, in other words I don't believe this is faulty
behavior.

Grant Erwin
Kirkland, Washington

Was there any load on the output?
...lew...


No, no load whatever.

GWE

"Grant Erwin" wrote:
I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.

It does, but the core and windings aren't designed for that amount of
current, and will saturate. When that occurs, your input is looking at the
DC resistance of the winding instead of the inductive reactance of the core.

Just for fun, hook the AC main across both sides of the variac, use the
neutral as it is, and pull the AC OUT off of the slider, as follows:

http://sound.westhost.com/beg4-3.gif

Do you still have the problem when using that configuration?

Jon

In article ,
Grant Erwin wrote:

I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.

This part sounds wrong - the hot lead should be the fused lead, and the
neutral should be both not fused, and connected directly to the load.
Either way the described setup is connected is half-wrong, IME.

ie - hooked up as described, the fuse is in the wrong place, but the
connection to the load is right.

--
Cats, coffee, chocolate...vices to live by

Ecnerwal wrote:
In article ,
Grant Erwin wrote:


I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.


This part sounds wrong - the hot lead should be the fused lead, and the
neutral should be both not fused, and connected directly to the load.
Either way the described setup is connected is half-wrong, IME.

ie - hooked up as described, the fuse is in the wrong place, but the
connection to the load is right.


I see your point about the location of the fuse, but it doesn't explain
anything.

GWE

Jon Danniken wrote:
"Grant Erwin" wrote:

I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.


It does, but the core and windings aren't designed for that amount of
current, and will saturate. When that occurs, your input is looking at the
DC resistance of the winding instead of the inductive reactance of the core.

Just for fun, hook the AC main across both sides of the variac, use the
neutral as it is, and pull the AC OUT off of the slider, as follows:

http://sound.westhost.com/beg4-3.gif

Do you still have the problem when using that configuration?

That looks exactly like my configuration. And yes, I still have the
problem.

GWE

Grant Erwin wrote:
One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.

GWE

George, the fuse should be in the hot lead ALWAYS.
...lew...

According to TMN :

[ ... ]

Claude Lyons in the UK has some info on their site - they have been
making variacs for a long time - many RS catalogue variacs where made
by them.

This is their tech doc: http://www.claudelyons.co.uk/tech.pdf it
shows connections etc.

A good bit of information, but a couple of things to beware of:

1) Since they are in the UK, the default voltage is 240 VAC,
instead of the 120 VAC more common here.

2) Since they are a different manufacturer, the numbering of the
terminals may differ from the General Radio Variacs, or the
Powerstats (or other trade names) by other makers.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

According to Grant Erwin :
I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.

It *does* -- within limits. The problem comes when you have too
few turns and the magnetic structure saturates, thus drawing lots of
current. Thus popping the breaker at 30%, but continuing to operate
(perhaps drawing a bit of excess current) at 80%.

I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.

Now, *this* is wrong, at the least. You have your fuse in
series with the neutral rather than the hot, so if the fuse pops, the
whole circuit is floating at full line voltage, including both sides of
the load. The fuse should be in series with the black lead, and yes,
the white should continue on to the load as the neutral for the load
too.

I would advise opening the housing and making sure that it is
correct, too. I know that I got (for free) an enclosed Powerstat which
was terribly mis-wired. It took a while to get it right, because of
a too-crowded wiring area.

Now -- it *might* be possible that a damaged slider is bridging
multiple turns (more than two), but it still should be as likely to pop
the breaker at almost any setting of the knob -- unless the winding is
damaged by serious overcurrent at some point. I would strongly advise
you to open the case and see just how it is wired inside.

I think my problem is with my breaker tripping too low or too quickly.
I'm contemplating adding one of those temp-varistors to the input,
the kind which have resistance about 1 ohm when cold, but .01 ohms
when warm. Those are supposed to work OK in damping variac magnetizing
inrush current.

What kind of breaker is it? Normally, most home power
distribution panels have a combination of a thermal breaker, which will
trip within a few minutes at a certain level of overcurrent, and a
magnetic trip breaker which will trip almost instantly with severe
overcurrent.

Or is this breaker in the autotransformer's housing along with
the fuse? BTW -- is this a genuine General Radio Variac, or is it some
other brand? This can determine how the terminals are marked. I'll
just call it an autotransformer from here on until you assure me that
the brand is General Radio -- the only ones who made the Variac.

For that matter -- a 20A autotransformer is fairly large,
whether 120 VAC or 240 VAC, and those that I have seen have had an
enclosure (cage) with the terminal board of the actual autotransformer
exposed through a gap in the cage. If that is the case, then the
terminals which you see on the outside are all that you will have.
Typically, the wiper will be the middle of the numbered terminals -- or
on at least some GR Variacs, there is an illustration of the winding,
with the voltages marked for each, and the wiper as an arrow pointing to
the inside of the curve of the winding.

An exception to the above would be in the case of a
center-tapped winding, with 120V being the center tap, and 240V being
full CW, so you can use it as either a step-up or 0-full line voltage
autotransformer.

Hmm ... a possible source for the miswiring. Typically, these
are supplied so they can either mount on a panel, with the shaft coming
through the base of the autotransformer, through the panel, and then to
the knob, with the scale screwed to the panel. However, when used as a
bench autotransformer, the shaft stops at the base, and extends up
through the disc which carries the wiper, through the cage, to the knob,
with the scale screwed to the cage. In this case, the sense of fully
CCW and fully CW interchange. So the fuse, if permanently mounted and
connected to one end of the winding would be at the CW end of the
winding (full voltage) in one condition, and at the CCW end of the
winding (zero voltage) in the other condition.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

That is a typical design. It gives you the 130% on the output having the
wiper wipe beyond the input high end winding.

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Jon Danniken wrote:
"Grant Erwin" wrote:
I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.

It does, but the core and windings aren't designed for that amount of
current, and will saturate. When that occurs, your input is looking at the
DC resistance of the winding instead of the inductive reactance of the core.

Just for fun, hook the AC main across both sides of the variac, use the
neutral as it is, and pull the AC OUT off of the slider, as follows:

http://sound.westhost.com/beg4-3.gif

Do you still have the problem when using that configuration?

Jon




----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

DoN. Nichols wrote:

According to Grant Erwin :

I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.


It *does* -- within limits. The problem comes when you have too
few turns and the magnetic structure saturates, thus drawing lots of
current. Thus popping the breaker at 30%, but continuing to operate
(perhaps drawing a bit of excess current) at 80%.


I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.


Now, *this* is wrong, at the least. You have your fuse in
series with the neutral rather than the hot, so if the fuse pops, the
whole circuit is floating at full line voltage, including both sides of
the load. The fuse should be in series with the black lead, and yes,
the white should continue on to the load as the neutral for the load
too.

Yup. The fuse should be on the black wire.

I would advise opening the housing and making sure that it is
correct, too. I know that I got (for free) an enclosed Powerstat which
was terribly mis-wired. It took a while to get it right, because of
a too-crowded wiring area.

On mine, the wires go to very clearly marked terminals on the front. It's
pretty easy to see how it's wired.

Now -- it *might* be possible that a damaged slider is bridging
multiple turns (more than two), but it still should be as likely to pop
the breaker at almost any setting of the knob -- unless the winding is
damaged by serious overcurrent at some point. I would strongly advise
you to open the case and see just how it is wired inside.

I will. After I'm done using it. It'll be early next week.

I think my problem is with my breaker tripping too low or too quickly.
I'm contemplating adding one of those temp-varistors to the input,
the kind which have resistance about 1 ohm when cold, but .01 ohms
when warm. Those are supposed to work OK in damping variac magnetizing
inrush current.


What kind of breaker is it? Normally, most home power
distribution panels have a combination of a thermal breaker, which will
trip within a few minutes at a certain level of overcurrent, and a
magnetic trip breaker which will trip almost instantly with severe
overcurrent.

It's a Square D QO 20 amp breaker.

Or is this breaker in the autotransformer's housing along with
the fuse? BTW -- is this a genuine General Radio Variac, or is it some
other brand? This can determine how the terminals are marked. I'll
just call it an autotransformer from here on until you assure me that
the brand is General Radio -- the only ones who made the Variac.

It's almost certainly another brand, I'm just using 'variac' like kleenex,
to mean a generic autotransformer.

For that matter -- a 20A autotransformer is fairly large,
whether 120 VAC or 240 VAC, and those that I have seen have had an
enclosure (cage) with the terminal board of the actual autotransformer
exposed through a gap in the cage. If that is the case, then the
terminals which you see on the outside are all that you will have.
Typically, the wiper will be the middle of the numbered terminals -- or
on at least some GR Variacs, there is an illustration of the winding,
with the voltages marked for each, and the wiper as an arrow pointing to
the inside of the curve of the winding.

An exception to the above would be in the case of a
center-tapped winding, with 120V being the center tap, and 240V being
full CW, so you can use it as either a step-up or 0-full line voltage
autotransformer.

Hmm ... a possible source for the miswiring. Typically, these
are supplied so they can either mount on a panel, with the shaft coming
through the base of the autotransformer, through the panel, and then to
the knob, with the scale screwed to the panel. However, when used as a
bench autotransformer, the shaft stops at the base, and extends up
through the disc which carries the wiper, through the cage, to the knob,
with the scale screwed to the cage. In this case, the sense of fully
CCW and fully CW interchange. So the fuse, if permanently mounted and
connected to one end of the winding would be at the CW end of the
winding (full voltage) in one condition, and at the CCW end of the
winding (zero voltage) in the other condition.

Don, I haven't yet heard anyone say anything (besides the fuse being on
the wrong power line) that would indicate to me there is any miswiring.

People keep telling me the wall AC must be connected to the wiper. Well,
remember when I plug this in with it set to 100% and the breaker doesn't
pop, then I can turn it all the way down to zero and it still doesn't
pop. And if the wall power were connected that would surely pop the breaker.
So wall power isn't connected to the slider. Furthermore, when I turn the
dial to turn down the voltage, the voltage goes down. It all works just
like it should, in fact. Nothing is getting warm, everything's fine. Except
it has a heck of a magnetizing current. As I google around, I'm not the only
one who's had this problem. It appears to be worse when the slider is in a
low position, but maybe that was poor test technique.

I wish I knew more about Square D QO panel breakers. I think I read somewhere
that if one pops, it will have a tendency to pop again for some time, meaning
that once it pops everything I do after that may have been irrelevant.

A guy at my partner Karen's work place recommended I put a thermistor in
series with the input power, perhaps one like this:
http://www.ametherm.com/Data%20Sheets/MS32%205R020.pdf

Grant

According to Grant Erwin :
DoN. Nichols wrote:

[ ... ]

Now, *this* is wrong, at the least. You have your fuse in
series with the neutral rather than the hot, so if the fuse pops, the
whole circuit is floating at full line voltage, including both sides of
the load. The fuse should be in series with the black lead, and yes,
the white should continue on to the load as the neutral for the load
too.

Yup. The fuse should be on the black wire.

O.K. We agree here.

I would advise opening the housing and making sure that it is
correct, too. I know that I got (for free) an enclosed Powerstat which
was terribly mis-wired. It took a while to get it right, because of
a too-crowded wiring area.

On mine, the wires go to very clearly marked terminals on the front. It's
pretty easy to see how it's wired.

O.K. But where is the "front"? Is it in a rectangular box or
something similar?

Now -- it *might* be possible that a damaged slider is bridging
multiple turns (more than two), but it still should be as likely to pop
the breaker at almost any setting of the knob -- unless the winding is
damaged by serious overcurrent at some point. I would strongly advise
you to open the case and see just how it is wired inside.

I will. After I'm done using it. It'll be early next week.

O.K. You can even feel for damage to the winding by removing
the power and rotating the knob -- feeling for any hitch.

I think my problem is with my breaker tripping too low or too quickly.
I'm contemplating adding one of those temp-varistors to the input,
the kind which have resistance about 1 ohm when cold, but .01 ohms
when warm. Those are supposed to work OK in damping variac magnetizing
inrush current.


What kind of breaker is it? Normally, most home power
distribution panels have a combination of a thermal breaker, which will
trip within a few minutes at a certain level of overcurrent, and a
magnetic trip breaker which will trip almost instantly with severe
overcurrent.

It's a Square D QO 20 amp breaker.

O.K. I wonder if the 'Q' stands for "quick-blow"?


BTW -- is this a genuine General Radio Variac, or is it some
other brand?

[ ... ]

It's almost certainly another brand, I'm just using 'variac' like kleenex,
to mean a generic autotransformer.

O.K. What was what I was thinking -- and it can be important to
list the actual brand to get good information about terminal numbers and
such. The major other maker in the US was Superior Electric, which used
the name Powerstat IIRC.

If you *know* GR equipment, the knob used on them is a sure
giveaway as to the brand. :-_

[ ... ]

Hmm ... a possible source for the miswiring. Typically, these
are supplied so they can either mount on a panel, with the shaft coming
through the base of the autotransformer, through the panel, and then to
the knob, with the scale screwed to the panel. However, when used as a
bench autotransformer, the shaft stops at the base, and extends up
through the disc which carries the wiper, through the cage, to the knob,
with the scale screwed to the cage. In this case, the sense of fully
CCW and fully CW interchange. So the fuse, if permanently mounted and
connected to one end of the winding would be at the CW end of the
winding (full voltage) in one condition, and at the CCW end of the
winding (zero voltage) in the other condition.

Don, I haven't yet heard anyone say anything (besides the fuse being on
the wrong power line) that would indicate to me there is any miswiring.

However -- the tripping at lower settings, but not at higher is
not normal behavior for any autotransformer wired correctly.

People keep telling me the wall AC must be connected to the wiper.

I *hope* not. The wall AC should be connected to the ends of
the winding, or to one end and an appropriate tap. If it is connected
to the wiper, then that is exactly what will cause the problem which you
are experiencing.

So -- did you really mean to type that above? If you put a
"not" in front of the "be connected" then you are as you should be.

Let me try ASCII graphics and see whether this matches what you have
(after moving the fuse, at least) -- View with a fixed pitch font as
usual):

fuse
(Hot)-----o~o------------3
3
3
3
3
3
LINE 3-----------------0----------(variable hot)
3
3
3
3 LOAD
3
3
3
(Neutral)-------------+--3
|
+---------------------------------(neutral)

If it looks like this (other than your current fuse location) then it is
as it should be. However, if the line side goes to the wiper, you
*will* have problems similar to what you have reported.

Well,
remember when I plug this in with it set to 100% and the breaker doesn't
pop, then I can turn it all the way down to zero and it still doesn't
pop.

Now *that* is new information. I don't remember reading that
before. That would suggest that you don't have the line connected to
the wiper, in spite of your sentence somewhere above.

And if the wall power were connected that would surely pop the breaker.
So wall power isn't connected to the slider. Furthermore, when I turn the
dial to turn down the voltage, the voltage goes down. It all works just
like it should, in fact. Nothing is getting warm, everything's fine. Except
it has a heck of a magnetizing current. As I google around, I'm not the only
one who's had this problem. It appears to be worse when the slider is in a
low position, but maybe that was poor test technique.

Strange. Is that repeatable -- popping the breaker when it is
first turned on -- only if you are at 30% or so?

I wish I knew more about Square D QO panel breakers. I think I read somewhere
that if one pops, it will have a tendency to pop again for some time, meaning
that once it pops everything I do after that may have been irrelevant.

Perhaps so.

A guy at my partner Karen's work place recommended I put a thermistor in
series with the input power, perhaps one like this:
http://www.ametherm.com/Data%20Sheets/MS32%205R020.pdf

That might do it -- or you might simply want to get a less
touchy breaker.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote:


snippage

It's a Square D QO 20 amp breaker.

O.K. I wonder if the 'Q' stands for "quick-blow"?

"Quick Open" actually. They are very good breakers, unlikely to be the
source of the problem.



snippage


I wish I knew more about Square D QO panel breakers. I think I read somewhere
that if one pops, it will have a tendency to pop again for some time, meaning
that once it pops everything I do after that may have been irrelevant.

Perhaps so.

I believe most breakers are designed to be fail safe where it they are
stressed and going to drift out of calibration they will drift towards a
lower trip point. Somewhere I recall reading that breakers are typically
rated to be accurate for about three trips before starting to drift.

He needs to put a clamp on amp probe with peak recording on the input
and see just what the peak is on startup. Either way, without a load on
the output there should be virtually no peak on power up regardless of
the variac setting.


A guy at my partner Karen's work place recommended I put a thermistor in
series with the input power, perhaps one like this:
http://www.ametherm.com/Data%20Sheets/MS32%205R020.pdf

That might do it -- or you might simply want to get a less
touchy breaker.

On the test bench we normally had a light bulb in series with the variac
which would light up and limit current to the unit being tested if it
had a short. When we were confident the unit was ok we flipped a switch
to bypass the light bulb.

As for the breaker, it's fairly unlikely a QO breaker will be "touchy",
but for the $8 or so I'd pick up another and swap it out. If there is no
change in the symptoms you just have a spare breaker on hand, always a
good thing anyway.

Pete C.

Grant - is the output of the variac connected to anything when its turned on
or is the output open?

Hul

Grant Erwin wrote:
DoN. Nichols wrote:

According to Grant Erwin :

I'm puzzled. For sure my wall voltage is connected properly. My
output voltage is showing about 95V (the item is in use at present)
with the voltage set a tad above 80%.

I'm not seeing how hooking up the wall voltage to the slider doesn't
get me a stepUP transformer.


It *does* -- within limits. The problem comes when you have too
few turns and the magnetic structure saturates, thus drawing lots of
current. Thus popping the breaker at 30%, but continuing to operate
(perhaps drawing a bit of excess current) at 80%.


I physically looked at the connections too. Unless the external terminals
don't match the wiring on the nameplate, the wall voltage (117VAC) is
connected across the input side. One side is directly connected (that's
the hot lead) and the other side (the white lead) is connected through a
fuse to the other input terminal. That terminal is also connected to the
output, as is the slider.


Now, *this* is wrong, at the least. You have your fuse in
series with the neutral rather than the hot, so if the fuse pops, the
whole circuit is floating at full line voltage, including both sides of
the load. The fuse should be in series with the black lead, and yes,
the white should continue on to the load as the neutral for the load
too.

Yup. The fuse should be on the black wire.

I would advise opening the housing and making sure that it is
correct, too. I know that I got (for free) an enclosed Powerstat which
was terribly mis-wired. It took a while to get it right, because of
a too-crowded wiring area.

On mine, the wires go to very clearly marked terminals on the front. It's
pretty easy to see how it's wired.

Now -- it *might* be possible that a damaged slider is bridging
multiple turns (more than two), but it still should be as likely to pop
the breaker at almost any setting of the knob -- unless the winding is
damaged by serious overcurrent at some point. I would strongly advise
you to open the case and see just how it is wired inside.

I will. After I'm done using it. It'll be early next week.

I think my problem is with my breaker tripping too low or too quickly.
I'm contemplating adding one of those temp-varistors to the input,
the kind which have resistance about 1 ohm when cold, but .01 ohms
when warm. Those are supposed to work OK in damping variac magnetizing
inrush current.


What kind of breaker is it? Normally, most home power
distribution panels have a combination of a thermal breaker, which will
trip within a few minutes at a certain level of overcurrent, and a
magnetic trip breaker which will trip almost instantly with severe
overcurrent.

It's a Square D QO 20 amp breaker.

Or is this breaker in the autotransformer's housing along with
the fuse? BTW -- is this a genuine General Radio Variac, or is it some
other brand? This can determine how the terminals are marked. I'll
just call it an autotransformer from here on until you assure me that
the brand is General Radio -- the only ones who made the Variac.

It's almost certainly another brand, I'm just using 'variac' like kleenex,
to mean a generic autotransformer.

For that matter -- a 20A autotransformer is fairly large,
whether 120 VAC or 240 VAC, and those that I have seen have had an
enclosure (cage) with the terminal board of the actual autotransformer
exposed through a gap in the cage. If that is the case, then the
terminals which you see on the outside are all that you will have.
Typically, the wiper will be the middle of the numbered terminals -- or
on at least some GR Variacs, there is an illustration of the winding,
with the voltages marked for each, and the wiper as an arrow pointing to
the inside of the curve of the winding.

An exception to the above would be in the case of a
center-tapped winding, with 120V being the center tap, and 240V being
full CW, so you can use it as either a step-up or 0-full line voltage
autotransformer.

Hmm ... a possible source for the miswiring. Typically, these
are supplied so they can either mount on a panel, with the shaft coming
through the base of the autotransformer, through the panel, and then to
the knob, with the scale screwed to the panel. However, when used as a
bench autotransformer, the shaft stops at the base, and extends up
through the disc which carries the wiper, through the cage, to the knob,
with the scale screwed to the cage. In this case, the sense of fully
CCW and fully CW interchange. So the fuse, if permanently mounted and
connected to one end of the winding would be at the CW end of the
winding (full voltage) in one condition, and at the CCW end of the
winding (zero voltage) in the other condition.

Don, I haven't yet heard anyone say anything (besides the fuse being on
the wrong power line) that would indicate to me there is any miswiring.

People keep telling me the wall AC must be connected to the wiper. Well,
remember when I plug this in with it set to 100% and the breaker doesn't
pop, then I can turn it all the way down to zero and it still doesn't
pop. And if the wall power were connected that would surely pop the breaker.
So wall power isn't connected to the slider. Furthermore, when I turn the
dial to turn down the voltage, the voltage goes down. It all works just
like it should, in fact. Nothing is getting warm, everything's fine. Except
it has a heck of a magnetizing current. As I google around, I'm not the only
one who's had this problem. It appears to be worse when the slider is in a
low position, but maybe that was poor test technique.

I wish I knew more about Square D QO panel breakers. I think I read somewhere
that if one pops, it will have a tendency to pop again for some time, meaning
that once it pops everything I do after that may have been irrelevant.

A guy at my partner Karen's work place recommended I put a thermistor in
series with the input power, perhaps one like this:
http://www.ametherm.com/Data%20Sheets/MS32%205R020.pdf

Grant

wrote:

Grant - is the output of the variac connected to anything when its turned on
or is the output open?

Hul

I'll summarize: the variac (with no load) set to 30% output popped the 20A
breaker (Square D QO) in the wall panel. When set to 100%, it didn't pop the
breaker, and once magnetized, I could vary the dial all the way to zero
normally. The variac is in use and appears to control voltage as expected. Many
people have told me that the wall voltage must be wired to the slider, but it
can't be and isn't. My conclusion is that for whatever random reason this variac
has a greater magnetizing current with the slider in a low position than high.
Admittedly, I didn't test this properly. To test it properly I'd use several
circuits, and do a hundred or so tests repeated widely in time to ensure that
the breakers weren't stressed from being recently popped.

Grant

The slider is the output and is never connected to the mains.

You have a transformer. The primary is across the mains.
The secondary has a common line to the 'return white' main power line and the
primary.
The slider wire and a white from the return and common side is the load
connection - put a light bulb there or whatnot.

Not this way:
If power is applied - the black or white from the power panel to the
wiper it will burn out windings (or blow circuits.) if the wiper is
turned towards zero - as the wiper moves the hot to the neutral and
begins a copper short - forget the transformer. Bad way bud.

I've used them for years at least 40 and have a half dozen in the shop.
Had two on my train track. Have a large one in a power panel.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Grant Erwin wrote:
wrote:

Grant - is the output of the variac connected to anything when its
turned on
or is the output open?

Hul

I'll summarize: the variac (with no load) set to 30% output popped the
20A breaker (Square D QO) in the wall panel. When set to 100%, it didn't
pop the breaker, and once magnetized, I could vary the dial all the way
to zero normally. The variac is in use and appears to control voltage as
expected. Many people have told me that the wall voltage must be wired
to the slider, but it can't be and isn't. My conclusion is that for
whatever random reason this variac has a greater magnetizing current
with the slider in a low position than high. Admittedly, I didn't test
this properly. To test it properly I'd use several circuits, and do a
hundred or so tests repeated widely in time to ensure that the breakers
weren't stressed from being recently popped.

Grant

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"Grant Erwin" wrote in message
...
wrote:

Grant - is the output of the variac connected to anything when its
turned on
or is the output open?

Hul

I'll summarize: the variac (with no load) set to 30% output popped the
20A breaker (Square D QO) in the wall panel. When set to 100%, it
didn't pop the breaker, and once magnetized, I could vary the dial all
the way to zero normally. The variac is in use and appears to control
voltage as expected. Many people have told me that the wall voltage
must be wired to the slider, but it can't be and isn't. My conclusion
is that for whatever random reason this variac has a greater
magnetizing current with the slider in a low position than high.
Admittedly, I didn't test this properly. To test it properly I'd use
several circuits, and do a hundred or so tests repeated widely in time
to ensure that the breakers weren't stressed from being recently
popped.

Grant

Grant,
I dont think you have ever clearly stated:- does this failure occur with
no NO connection to the slider or do you have some load connected.

Also there are variacs around built for 400hz and aicraft use.

It would be great if you could take a photo of the whole thing and also
the name plate so we could understand what we are arguing about.


John G.