I built a test fixture for doing all kinds of different things. One of the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt

"Matthew Rossiter" wrote in message
.. .
I built a test fixture for doing all kinds of different things. One of the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt


No, because there is no centre tap on a variac. Electrically, it is just a
variable auto transformer. One output leg is common with one of the line in
legs.

Arfa

What if you used a secondary transformer with a Center Tap and used the
VARIAC to control the AC input? I guess that's a pretty simple question,
but just want to make sure I'm not missing something.



No, because there is no centre tap on a variac. Electrically, it is just a
variable auto transformer. One output leg is common with one of the line
in legs.

Arfa

"Matthew Rossiter" wrote in message
...
What if you used a secondary transformer with a Center Tap and used the
VARIAC to control the AC input? I guess that's a pretty simple question,
but just want to make sure I'm not missing something.


Yes, that would work. You would need to find a transformer with a 50v - 0 -
50v secondary ( or two 0 - 50v windings that you could hook in series ) that
could supply the current demand of the monitors that you want to power.
Then, as you say, you would connect the variac to the primary. This scheme
will have the added advantage that it will provide safety isolation that the
variac on its own, won't.

If you couldn't find such a transformer, you could use two single-secondary
transformers, with the secondaries hooked up in series, and the primaries in
parallel, to arrive at the same end result.

Arfa

I might as well ask. Can you recommend a good place to find a 1:1 Center
Tapped "High Current" Transformer?

Thanks.

Matt


If you used a 1:1 transformer rated at 110 volts or better with a center
tapped secondary you should be able to obtain the desired result.




No, because there is no centre tap on a variac. Electrically, it is just
a
variable auto transformer. One output leg is common with one of the line
in legs.

Arfa

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794

"Meat Plow" wrote in message
news
On Fri, 02 Mar 2007 21:41:12 +0000, Matthew Rossiter wrote:

I built a test fixture for doing all kinds of different things. One of
the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have
both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt

The output of a variable AC supply is almost always isolated from any
reference to any kind of "ground" you might be thinking of.

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794


I would have to disagree there. A variable AC source in the form of a
traditional variac, is an adjustable autotransformer, which means that one
of the line legs - lets call it "neutral" or "cold" - is common to both the
input and output, which means that the variable output is referenced to the
incoming supply, which is itself tied to ground at the local substation in
most countries, as far as I know. A variac does not provide any form of
electrical isolation, so the output from it *must not* be treated as
'bench-safe', unless its input is plugged into a proper isolation
transformer.

Arfa

ABSOLUTELY CORRECT.

It is NOT a transformer. = NO isolation.


On Sat, 03 Mar 2007 10:28:52 GMT, "Arfa Daily"
wrote:


"Meat Plow" wrote in message
news
On Fri, 02 Mar 2007 21:41:12 +0000, Matthew Rossiter wrote:

I built a test fixture for doing all kinds of different things. One of
the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have
both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt

The output of a variable AC supply is almost always isolated from any
reference to any kind of "ground" you might be thinking of.

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794


I would have to disagree there. A variable AC source in the form of a
traditional variac, is an adjustable autotransformer, which means that one
of the line legs - lets call it "neutral" or "cold" - is common to both the
input and output, which means that the variable output is referenced to the
incoming supply, which is itself tied to ground at the local substation in
most countries, as far as I know. A variac does not provide any form of
electrical isolation, so the output from it *must not* be treated as
'bench-safe', unless its input is plugged into a proper isolation
transformer.

Arfa

h wrote:
ABSOLUTELY CORRECT.

It is NOT a transformer. = NO isolation.





Well it is a transformer, it's just one that has one side of the
secondary tied directly to one side of the primary, hence no isolation.

You can get cheap 1:1 isolation transformers, they're sold for use with
older video arcade monitors. Any place that sells amusement supplies
should have them. I get most of my parts here
http://homearcade.org/BBBB/ Not sure offhand what current the
transformers are good for, but usually a few amps.

On 3 Mar, 15:34, Meat Plow wrote:
On Sat, 03 Mar 2007 10:28:52 +0000, Arfa Daily wrote:
"Meat Plow" wrote in message
news
On Fri, 02 Mar 2007 21:41:12 +0000, Matthew Rossiter wrote:

I built a test fixture for doing all kinds of different things. One of
the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have
both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt

The output of a variable AC supply is almost always isolated from any
reference to any kind of "ground" you might be thinking of.

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794

I would have to disagree there. A variable AC source in the form of a
traditional variac, is an adjustable autotransformer, which means that one
of the line legs - lets call it "neutral" or "cold" - is common to both the
input and output, which means that the variable output is referenced to the
incoming supply, which is itself tied to ground at the local substation in
most countries, as far as I know. A variac does not provide any form of
electrical isolation, so the output from it *must not* be treated as
'bench-safe', unless its input is plugged into a proper isolation
transformer.

Arfa

Was thinking of my Sencore PR57 which is a VARIAC as in (variable AC
supply) and it does have an isolated output, no big ****ing deal.

Yours then is exceptional. To assume a variac has an iso output is
asking for a nasty accident, as most have outputs connected direct to
line.


NT

"Meat Plow" wrote in message
news
On Sat, 03 Mar 2007 10:28:52 +0000, Arfa Daily wrote:


"Meat Plow" wrote in message
news
On Fri, 02 Mar 2007 21:41:12 +0000, Matthew Rossiter wrote:

I built a test fixture for doing all kinds of different things. One of
the
ideas I had in mind was using a Variac to adjust AC voltage for certain
types of monitors, one which requires two 45VAC inputs.

Would I be able to use a VARIAC to set the voltage to 90 VAC and have
both
terminals deliver equal 45VAC in reference to ground?

Thanks

Matt

The output of a variable AC supply is almost always isolated from any
reference to any kind of "ground" you might be thinking of.

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794


I would have to disagree there. A variable AC source in the form of a
traditional variac, is an adjustable autotransformer, which means that
one
of the line legs - lets call it "neutral" or "cold" - is common to both
the
input and output, which means that the variable output is referenced to
the
incoming supply, which is itself tied to ground at the local substation
in
most countries, as far as I know. A variac does not provide any form of
electrical isolation, so the output from it *must not* be treated as
'bench-safe', unless its input is plugged into a proper isolation
transformer.

Arfa

Was thinking of my Sencore PR57 which is a VARIAC as in (variable AC
supply) and it does have an isolated output, no big ****ing deal.


Sorry old boy - wasn't meaning to dis you ... I just wanted to make sure
that no one had a safety issue by not understanding the difference between a
double wound and an auto tranny. Thanks for the support in that other thread
further up though. That Aussie **** pops up on other groups as well. I think
it must be every time he runs out of money to buy his meds ...

Arfa

I'm having a little hard time finding a 1:1 Center tapped transformer with
some good power.

Hammond makes an 80CT transformer @ 4 amps
http://www.hammondmfg.com/165.htm - 165N80
but that would only give me 40VAC each tap, but pleny of current. Maybe
that's all I'd need, I don't know.

I think their 300 series would be a little under-powered.
http://www.hammondmfg.com/300series.htm - or am I reading the specs wrong?

I've been doing searches on google (and on ebay) but it seems finding a 1:1
center tapped transformer with plenty of power is hard. unless maybe I'm
not looking in the right place.

Just looking for a little help.

Thanks!

Matt



"James Sweet" wrote in message
news:IsjGh.170$ig.145@trndny01...
h wrote:
ABSOLUTELY CORRECT.

It is NOT a transformer. = NO isolation.




Well it is a transformer, it's just one that has one side of the secondary
tied directly to one side of the primary, hence no isolation.

You can get cheap 1:1 isolation transformers, they're sold for use with
older video arcade monitors. Any place that sells amusement supplies
should have them. I get most of my parts here http://homearcade.org/BBBB/
Not sure offhand what current the transformers are good for, but usually a
few amps.

Matthew Rossiter wrote:
I'm having a little hard time finding a 1:1 Center tapped transformer with
some good power.



You can use a pair of 1:1 transformers in series to achieve that.
Primaries in series and then secondaries in series. That will give you
center tapped 1:1.

What sort of motor is this that requires two transformer windings?

Doesn't the Electrohome G08 monitor require two 45Volt AC inputs?


"James Sweet" wrote in message
news:aAkGh.1977$Tf.1189@trndny03...
Matthew Rossiter wrote:
I'm having a little hard time finding a 1:1 Center tapped transformer
with some good power.



You can use a pair of 1:1 transformers in series to achieve that.
Primaries in series and then secondaries in series. That will give you
center tapped 1:1.

What sort of motor is this that requires two transformer windings?

Actually, it is not a transformer.

It is ONE coil of wire connected across the AC supply with a variable
tap. Output is tied between tap and (Hopefully) neutral of the AC
input.


On Sat, 03 Mar 2007 18:51:20 GMT, James Sweet
wrote:

wrote:
ABSOLUTELY CORRECT.

It is NOT a transformer. = NO isolation.





Well it is a transformer, it's just one that has one side of the
secondary tied directly to one side of the primary, hence no isolation.

You can get cheap 1:1 isolation transformers, they're sold for use with
older video arcade monitors. Any place that sells amusement supplies
should have them. I get most of my parts here
http://homearcade.org/BBBB/ Not sure offhand what current the
transformers are good for, but usually a few amps.

h wrote:
Actually, it is not a transformer.

It is ONE coil of wire connected across the AC supply with a variable
tap. Output is tied between tap and (Hopefully) neutral of the AC
input.




I think you should read up on autotransformers. Variac is a trade name
for a variable autotransformer, and they are in fact transformers. The
output of most of them can be adjusted *above* the incoming line
voltage, standard is about 10%. The one I have sitting here accepts 120V
input and outputs 0-140V so it is clearly a transformer.

For a bit more detailed info on the subject here's an article.

http://en.wikipedia.org/wiki/Variac

GET out your trusty ohmmeter and measure it before you make a fool of
yourself.

It is a single coil of wire with a tap.

Call it what you will it is NOT two coils of wire insulated from each
other == transformer

wrote:
Actually, it is not a transformer.

It is ONE coil of wire connected across the AC supply with a variable
tap. Output is tied between tap and (Hopefully) neutral of the AC
input.




I think you should read up on autotransformers. Variac is a trade name
for a variable autotransformer, and they are in fact transformers. The
output of most of them can be adjusted *above* the incoming line
voltage, standard is about 10%. The one I have sitting here accepts 120V
input and outputs 0-140V so it is clearly a transformer.

For a bit more detailed info on the subject here's an article.

http://en.wikipedia.org/wiki/Variac

On 17 Mar, 00:21, wrote:

GET out your trusty ohmmeter and measure it before you make a fool of
yourself.

It is a single coil of wire with a tap.

Call it what you will it is NOT two coils of wire insulated from each
other == transformer

It seems youre confused as to what constitutes a transformer.


NT

wrote in message
oups.com...
On 17 Mar, 00:21, wrote:

GET out your trusty ohmmeter and measure it before you make a fool of
yourself.

It is a single coil of wire with a tap.

Call it what you will it is NOT two coils of wire insulated from each
other == transformer

It seems youre confused as to what constitutes a transformer.

Have you never heard of an auto transformer? Most all variacs are auto
transformers.