在 2000年4月12日星期三 UTC+8下�3:00:00，Kirk Lindstedt写�：
I believe Variac's are VARIable AC transformers. Not DC as you stated. I think
these are essentially autotransformers, ie a primary and no secondary winding.
Instead, they have a wiper on the primary that taps off different voltages based on
the position of the wiper. Similar to the old Lionel train transformers. You can
set an AC voltage and it somewhat remains constant within some varying loads.
Since there is no secondary winding, there is no isolation from the AC main power
like a true transformer. Hope this helps.

GaryH82012 wrote:

Price seemed good, so I bought an electronic device called a Variac at an
auction. It was described as a DC transformer, but I don't know. It plugs into
120 volt outlet and has the same style receptacle on the side for plugging
into. There are two meters on the front: AC volts (0-150) and AC Amps (0-10)
The needle on the AC volts moves when the big dial on the face is turned. I'm
guessing it puts out variable AC voltage and, under load, displays AC amps.
It''s about 12 inches tall by 8 inches wide by 4 inches deep. What can I use it
for ? Thanks for replys, Gary Hastings

You may visit our video on youtube https://youtu.be/x8MlqsF1nZE
https://youtu.be/qx6X4DMBQ70

A variac can only accept AC power input, but with Rectifier installed it can switch output from AC to DC.

Variac mainly used as a light dimmer, speed controller , machines for motor test and repair ,experiment machines for teaching or lab test and also industrial use.

Well, some people call it variac and others say variable transformer, we can understand from the name that it basicly used to give out constant adjustable voltage. For example single phase input 220v ,the standard output is 0-250v ,three phase input 380v output 0-430v. Please note that these are just standard output ,we can make the input and output range as your needs.
For frequency all good to use 50 or 60hz.

First lets check out the manual adjust type, as we can see it has four terminals on the front panel ,to connect in and output cables. And also a panel meter that display the output voltage. Which we can also use LCD display. Now on the top of it we can see a black wheel, the output voltage will goes slowly up or down while we rotate it.

Here is a motor drive type, we can see terminals and meters are same but a motor on top instead of the wheel. By using this type you can connect the motor to a control box to adjust the output from distance, like you can use a 10 meters or 20 meters wire to control the variac in another room. We now have AC and DC motors for option.

Now lets talk about the fancy motor type. Well we can see those meters display our output voltage and current. We can control the power on and off ,up and down by push button switches here. For example if we want the volt up we just press this button and when it reach the volt we can release it. The accuracy is 1 volt. Inside is the main switch control the power and coils and terminals for cable. Moreover, we install a temperature sensor inside which will cut off the power and make alarm noise when the temp. Hit 100 degrees.

For all variacs we can do max 1000kva now and we can install a rectifier to make the output switch from AC to DC.
For more information please visit our website Electric transformer manufacture or send me email :

On 2017-06-08, wrote:

A variac can only accept AC power input, but with Rectifier installed
it can switch output from AC to DC.

Yes -- but if that is done, it is usually built into a power
supply.

Variac mainly used as a light dimmer, speed controller , machines for
motor test and repair ,experiment machines for teaching or lab test and
also industrial use.

Anywhere variable AC voltage is needed -- including for testing
AC-powered equipment to see how well it performs at extreme voltages.

Well, some people call it variac and others say variable transformer,

Variac was the brand name used by General Radio, who may have
been the originator of the device, and certainly the maker of the best
ones which I have used.

Superior Electric called their version a Powerstat.

But all are simply a variable autotransformer, wound on a
toroidal core which concentrates a lot of magnetic field in a small
space.

we can understand from the name that it basicly used to give out
constant adjustable voltage. For example single phase input 220v ,the
standard output is 0-250v ,

The typical General Radio Variac for house line voltage has four
fixed taps, 20V, 100V and another 20V all in series, not counting the
variable tap. This can be wired with the 120 VAC at the two end taps,
so the variable will go from 0-120VAC, or it can be wired with neutral
at one end, and at 20V from the other end, so you can vary the output
voltage from 0-140 VAC (useful for some testing.) There are the two 20V
taps at the two ends for one reason -- the Variac can be panel mounted,
with the shaft coming in the bottom mounting plate, or it can be a bench
use one sitting on the bottom mounting plate with the shaft coming in
from the top. This allows you to wire for 0-140VAC in either situation,
even though the knob is turning CW or CCW for higher voltage depending
on viewpoint.

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in 120
VAC between one end and that center tap, and get up to 240 VAC output
(at the cost of lots more current from the 120 VAC line than you feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

I've seen one such variable autotransformer (actually a
Powerstat, not a Variac) set up in a recording room at a South
American US Embassy, used to adjust for sometimes rather low power line
voltages. (Unfortunately, it was a large one and had a knob which
looked like a steering wheel, and a small kid walked up to it and spun
it clockwise, burning out the rectifier in a recorder.)

three phase input 380v output 0-430v. Please
note that these are just standard output ,we can make the input and
output range as your needs. For frequency all good to use 50 or 60hz.

Well ... I have two sizes of Variacs (2A and 7A) made for 400
Hz. Minimum frequency is 350 Hz before it saturates. (And 400 Hz is
normally used to power aircraft instruments because at 400 Hz, you don't
need as much weight of core.) The core is shorter but the same diameter
as the same current rating for 50-60 Hz.

For three phase, there are three identical units, stacked up and
using a common shaft. This gets heavy quickly. :-)

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) 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 in message
...
On 2017-06-08,
wrote:

...
The typical General Radio Variac for house line voltage has four
fixed taps, 20V, 100V and another 20V all in series, not counting
the
variable tap. This can be wired with the 120 VAC at the two end
taps,
so the variable will go from 0-120VAC, or it can be wired with
neutral
at one end, and at 20V from the other end, so you can vary the
output
voltage from 0-140 VAC (useful for some testing.) There are the two
20V
taps at the two ends for one reason -- the Variac can be panel
mounted,
with the shaft coming in the bottom mounting plate, or it can be a
bench
use one sitting on the bottom mounting plate with the shaft coming
in
from the top. This allows you to wire for 0-140VAC in either
situation,
even though the knob is turning CW or CCW for higher voltage
depending
on viewpoint.

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

The large rotating plate in the back is the heatsink for the brush and
is at output voltage. On some types the shaft is also at output
voltage and needs a well insulated knob and clearance from a panel
mounting hole.

-jsw

On 2017-06-09, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-08,
wrote:

[ ... ]

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits from
the data on the terminal block.

O.K. Found some illustrated in eBay auctions. W5H series is
normally 5A at 120 VAC, and this is 2A at maximum output voltage.
(The input and load currents add in the part of the winding below the
120VAC input tap.

The large rotating plate in the back is the heatsink for the brush and
is at output voltage. On some types the shaft is also at output
voltage and needs a well insulated knob and clearance from a panel
mounting hole.

The GR (General Radio) Variacs have a steel shaft with a black
Bakelite shell, so it is insulated from the rotor and brush assembly.
Now if somebody replaced the original shaft with a plain steel one, all
bets are off. :-)

And, of course, if you have a three phase assembly, the shaft
*must* be insulated, since it drives all three brush carrying rotors.

Here is a rather extreme 3-phase one on eBay:

Auction # 162543903031

It has two Powerstats wired in parallel per phase, for six in total.
Max 90 amps out @ 240 VAC.

The shaft appears to be bare metal, so there must be insulation
where each rotor connects to the shaft.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) 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 10 Jun 2017 03:00:12 GMT, "DoN. Nichols"
wrote:

On 2017-06-09, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-08,
wrote:

[ ... ]

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits from
the data on the terminal block.

O.K. Found some illustrated in eBay auctions. W5H series is
normally 5A at 120 VAC, and this is 2A at maximum output voltage.
(The input and load currents add in the part of the winding below the
120VAC input tap.

The large rotating plate in the back is the heatsink for the brush and
is at output voltage. On some types the shaft is also at output
voltage and needs a well insulated knob and clearance from a panel
mounting hole.

The GR (General Radio) Variacs have a steel shaft with a black
Bakelite shell, so it is insulated from the rotor and brush assembly.
Now if somebody replaced the original shaft with a plain steel one, all
bets are off. :-)

And, of course, if you have a three phase assembly, the shaft
*must* be insulated, since it drives all three brush carrying rotors.

Here is a rather extreme 3-phase one on eBay:

Auction # 162543903031

It has two Powerstats wired in parallel per phase, for six in total.
Max 90 amps out @ 240 VAC.

The shaft appears to be bare metal, so there must be insulation
where each rotor connects to the shaft.

Enjoy,
DoN.


The rating of an autotransformer is generally NOT in amps, but in VA
(Volt Amps) All 4 of my variacs and powerstats are rated in VA or KVA.
They DO also have acurrent rating, but that is the maximum INPUT
current limit. I have them from 210/220va (210 on 50Hz, 220 on 60) to
3.5KVA, a mix of Powerstar and Variac brands..

If you have a 1200va powerstat it is food for 10 amps in at 120 volts
and only 5 maximum at 240 volts out.

"DoN. Nichols" wrote in message
...
On 2017-06-09, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-08,
wrote:

[ ... ]

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush
moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits
from
the data on the terminal block.

Try this. It's too big for me to check with my limited dialup
bandwidth or monthly cellular data allocation.
http://lcweb2.loc.gov/master/mbrs/re...og%20P258G.pdf

From my download of the Powerstat catalog C7002-1:

"CONSTANT CURRENT LOAD: Output that can be carried regardless of
output voltage setting.

CONSTANT IMPEDANCE LOAD: loads such as incandescent lamps or
resistance heaters in which the current drawn is approximately
proportional to the applied voltage, increasing to maximum current at
line voltage. These ratings apply only to units having maximum output
voltage limited to line voltage."

Their tech support confirmed the catalog's 5A Const I, 7A Const Z
rating of a Type 21 whose nameplate gave 3.75A as the limit.

When I tested a type 10 at its 3.0A Const Z rating an IR thermometer
indicated the brush temperature as 100C. It was driving a 24VAC 250VA
control transformer with a rectifier / capacitor output. The
combination is well matched and makes a decent 10A variable power
supply and battery charger. It will provide 15A briefly, until the
Powerstat and transformer primary overheat.

I added the output capacitor to stabilize the readings of digital volt
and amp meters.
http://www.ebay.com/itm/DC-0-30V-0-1...#ht_1505wt_868

-jsw

wrote in message
...
On 10 Jun 2017 03:00:12 GMT, "DoN. Nichols"

wrote:

On 2017-06-09, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-08,

wrote:

[ ... ]

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush
moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits
from
the data on the terminal block.

O.K. Found some illustrated in eBay auctions. W5H series is
normally 5A at 120 VAC, and this is 2A at maximum output voltage.
(The input and load currents add in the part of the winding below
the
120VAC input tap.

The large rotating plate in the back is the heatsink for the brush
and
is at output voltage. On some types the shaft is also at output
voltage and needs a well insulated knob and clearance from a panel
mounting hole.

The GR (General Radio) Variacs have a steel shaft with a black
Bakelite shell, so it is insulated from the rotor and brush
assembly.
Now if somebody replaced the original shaft with a plain steel one,
all
bets are off. :-)

And, of course, if you have a three phase assembly, the shaft
*must* be insulated, since it drives all three brush carrying
rotors.

Here is a rather extreme 3-phase one on eBay:

Auction # 162543903031

It has two Powerstats wired in parallel per phase, for six in total.
Max 90 amps out @ 240 VAC.

The shaft appears to be bare metal, so there must be insulation
where each rotor connects to the shaft.

Enjoy,
DoN.


The rating of an autotransformer is generally NOT in amps, but in VA
(Volt Amps) All 4 of my variacs and powerstats are rated in VA or
KVA.
They DO also have acurrent rating, but that is the maximum INPUT
current limit. I have them from 210/220va (210 on 50Hz, 220 on 60)
to
3.5KVA, a mix of Powerstar and Variac brands..

If you have a 1200va powerstat it is food for 10 amps in at 120
volts
and only 5 maximum at 240 volts out.

The core and winding's VA rating has a more comfortable margin than
the brush's current rating, the one I observe since replacements are
hard to find and expensive, and difficult to make because the carbon
is brittle. I could only mill into an edge, milling out chipped it
off.

The Powerstat chart gives both current and KVA ratings, at constant
current and constant impedance, for metal panel (heatsink) and
non-metallic or bracket mountings.

-jsw

"Larry Jaques" wrote in message
...
On Sat, 10 Jun 2017 07:51:41 -0400, "Jim Wilkins"
wrote:

"DoN. Nichols" wrote in message
...
On 2017-06-09, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-08,

wrote:

[ ... ]

I say "for house use" because there are also 240VAC industrial
versions, which have an additional (center) tap. You can feed
in
120
VAC between one end and that center tap, and get up to 240 VAC
output
(at the cost of lots more current from the 120 VAC line than you
feed
out at 240 VAC, of course.

The Superior Electric "Powerstat" is pretty much the same,
including similar voltage taps.

The maximum output current decreases considerably as the brush
moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated
for
only 4A at 120V in, 240V out. Trying to pull more current loads
it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits
from
the data on the terminal block.

Try this. It's too big for me to check with my limited dialup
bandwidth or monthly cellular data allocation.
http://lcweb2.loc.gov/master/mbrs/re...og%20P258G.pdf

From my download of the Powerstat catalog C7002-1:

"CONSTANT CURRENT LOAD: Output that can be carried regardless of
output voltage setting.

CONSTANT IMPEDANCE LOAD: loads such as incandescent lamps or
resistance heaters in which the current drawn is approximately
proportional to the applied voltage, increasing to maximum current
at
line voltage. These ratings apply only to units having maximum
output
voltage limited to line voltage."

Their tech support confirmed the catalog's 5A Const I, 7A Const Z
rating of a Type 21 whose nameplate gave 3.75A as the limit.

Is there much difference between them? How was that handled?

Huh? Those ratings all apply to the -same- unit, depending on how it's
used.

This shows an 'improved' model, full 10A, which apparently took the
place of the others.
http://pubs.acs.org/doi/abs/10.1021/...nalCode=iechad

The article is dated 1959. I have the 5A version of that rectangular
VARIAC with the handle and two-prong ungrounded outlet on top.

I buy them old, cheap and hopefully repairable at flea markets. My 3A
Powerstat 10Bs were salvaged from a brand new machine (~1975) that
fell off the customer's forklift and landed face-first on them. They
broke in different ways and I was able to reassemble a basket of them
into several good (?) ones.

The one I used to tame the buzz box welder transformer was on the
front panel from a 1950's power supply.

When I tested a type 10 at its 3.0A Const Z rating an IR thermometer
indicated the brush temperature as 100C. It was driving a 24VAC
250VA
control transformer with a rectifier / capacitor output. The
combination is well matched and makes a decent 10A variable power
supply and battery charger. It will provide 15A briefly, until the
Powerstat and transformer primary overheat.

I added the output capacitor to stabilize the readings of digital
volt
and amp meters.
http://www.ebay.com/itm/DC-0-30V-0-1...#ht_1505wt_868

Found a less expensive precision ammeter for your charging circuit,
in
case you're interested: http://tinyurl.com/y7bns73g

"Input impedance: 10Euro"

Thanks for looking, but I buy little stuff mainly from Amazon to limit
exposure of my credit card, and check my account afterwards.

I think a voltmeter that reads ##.## is good enough to determine the
State of Charge of batteries, though I couldn't pass up that 5-1/2
digit Fluke for $25. 5% accuracy from 1ma to 10A is probably fine for
current. I checked my 15-year-old truck battery at 200A this morning,
it wouldn't matter if it was really 180A or 220A. At the low end
knowing the key-off battery drain to within 10mA should show me if a
relay sticks closed.

-jsw

On 2017-06-10, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-09, Jim Wilkins wrote:

[ ... ]

The maximum output current decreases considerably as the brush
moves
above the line voltage. My 10A 120/240V Powerstat 236 is rated for
only 4A at 120V in, 240V out. Trying to pull more current loads it
down.

O.K. That makes sense. I've never had to deal with that
problem. And I don't have one on hand to read the current limits
from
the data on the terminal block.

Try this. It's too big for me to check with my limited dialup
bandwidth or monthly cellular data allocation.
http://lcweb2.loc.gov/master/mbrs/re...og%20P258G.pdf

That is offensively big. 57 MB total download.

From my download of the Powerstat catalog C7002-1:

"CONSTANT CURRENT LOAD: Output that can be carried regardless of
output voltage setting.

CONSTANT IMPEDANCE LOAD: loads such as incandescent lamps or
resistance heaters in which the current drawn is approximately
proportional to the applied voltage, increasing to maximum current at
line voltage. These ratings apply only to units having maximum output
voltage limited to line voltage."

Those passages do not appear in this catalog. After failing a
search for the phrase "CONSTANT CURRENT LOAD" I backed off to just look
for "CONSTANT" (case insensitive), and the typical references were like
this example:

================================================== ====================
TYPES 217-2, 217U-2, Q217U·2 AND Q217UM-2

When series connected on 480 volt, 60 cycle single phase lines,
the output is 0-480 volts, 4.0 amperes. When open-delta con
nected from a 240 volt, 60 cycle three phase input, the output is
0-240 volts, 4.0 amperes. For a constant impedance load the
allowable output current at the maximum output voltage position
is 6.3 amperes.
================================================== ====================

So -- you are allowed more current at full voltage than anywhere else on
the winding. (Assuming input is also at the full voltage tap.)

And I disagree with them calling incandescent lamps and/or
resistance heaters "Constant Impedance". Easy to demonstrate with an
automotive lamp. Measure the resistance when cold, then attach to full
voltage and measure the resistance and from that and the voltage,
calculate the resistance. Lamps are commonly used for an approximation
of a constant current source -- and heater elements. I've seen the
latter in old tube radios to limit the surge into the filaments when
starting cold, and adapting to varying line voltage.

Their tech support confirmed the catalog's 5A Const I, 7A Const Z
rating of a Type 21 whose nameplate gave 3.75A as the limit.

When I tested a type 10 at its 3.0A Const Z rating an IR thermometer
indicated the brush temperature as 100C. It was driving a 24VAC 250VA
control transformer with a rectifier / capacitor output. The
combination is well matched and makes a decent 10A variable power
supply and battery charger. It will provide 15A briefly, until the
Powerstat and transformer primary overheat.

O.K.

I added the output capacitor to stabilize the readings of digital volt
and amp meters.
http://www.ebay.com/itm/DC-0-30V-0-1...#ht_1505wt_868

-jsw

O.K.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) 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 in message
...
On 2017-06-10, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-09, Jim Wilkins wrote:

[ ... ]

From my download of the Powerstat catalog C7002-1:

"CONSTANT CURRENT LOAD: Output that can be carried regardless of
output voltage setting.

CONSTANT IMPEDANCE LOAD: loads such as incandescent lamps or
resistance heaters in which the current drawn is approximately
proportional to the applied voltage, increasing to maximum current
at
line voltage. These ratings apply only to units having maximum
output
voltage limited to line voltage."

Those passages do not appear in this catalog. After failing a
search for the phrase "CONSTANT CURRENT LOAD" I backed off to just
look
for "CONSTANT" (case insensitive), and the typical references were
like
this example:

================================================== ====================
TYPES 217-2, 217U-2, Q217U·2 AND Q217UM-2

When series connected on 480 volt, 60 cycle single phase lines,
the output is 0-480 volts, 4.0 amperes. When open-delta con
nected from a 240 volt, 60 cycle three phase input, the output is
0-240 volts, 4.0 amperes. For a constant impedance load the
allowable output current at the maximum output voltage position
is 6.3 amperes.
================================================== ====================

So -- you are allowed more current at full voltage than anywhere
else on
the winding. (Assuming input is also at the full voltage tap.)

I think what they mean is you will get the most current at full
voltage, but could draw the same 6.3A maximum current at a lower
setting if necessary. You can NOT get that current above line voltage
in the boost configuration, in that case the limit is 4A. I don't know
if you can pull it below the input tap in the boost configuration
where the volts per turn is higher.

At least that was the story when I was learning to design industrial
controls. The derating curves don't reduce to a simple, easily
remembered explanation or a single number on the label.

I've measured the iron loss on a few cores. It rises rapidly above the
spec sheet voltage and frequency, they don't make good speaker
crossover inductors.

Electrical engineers aren't taught the subtle imperfections of
components and electricians fall short on the theory. I sought to fill
that gap and become able to turn a scribbled schematic into a fully
documented working machine.

And I disagree with them calling incandescent lamps and/or
resistance heaters "Constant Impedance". Easy to demonstrate with
an
automotive lamp. Measure the resistance when cold, then attach to
full
voltage and measure the resistance and from that and the voltage,
calculate the resistance. Lamps are commonly used for an
approximation
of a constant current source -- and heater elements. I've seen the
latter in old tube radios to limit the surge into the filaments when
starting cold, and adapting to varying line voltage.


This is Staco's explanation:
http://isefaq.com/package/index.php?...nsformers.html

This addresses the limits to brush current, my concern when using them
for bench testing:
http://variac.com/ShortTermOverload.pdf

The brushes drop a volt or so which limits circulating current in
shorted adjacent windings. When I was looking for carbons to cut down
I found that brush composition should be more or less matched in
resistivity to the working voltage, to reduce motor commutator
sparking. Presumably the original designer chose the proper cross
section to control the current density.

In the 1980's I used a 4W night light bulb as the Zener limiting
resistor in a test fixture that had to operate from an input that
varied from ~20V to 80V. The 80V entered the rotating assembly
through slip rings so I couldn't just add an external power supply.
Today I could use a cheap switching supply to drop the voltage.

-jsw

"Jim Wilkins" wrote in message
news
"DoN. Nichols" wrote in message
...
On 2017-06-10, Jim Wilkins wrote:
"DoN. Nichols" wrote in message
...
On 2017-06-09, Jim Wilkins wrote:
..................

This addresses the limits to brush current, my concern when using
them for bench testing:
http://variac.com/ShortTermOverload.pdf

Specifically I was confirming the loosely specified time-current curve
of the breaker intended to protect the Variac brush, using the
short-circuit-tolerant arc welder transformer to boost the current so
that 15A from the Variac put 50A through the breaker. The transformer
has enough self-inductance that it needed a good fraction of line
voltage to reach 50A on the shorted output.
-jsw

"Larry Jaques" wrote in message
...
On Sun, 11 Jun 2017 13:00:34 -0400, "Jim Wilkins"
wrote:

[battery drain]
Audible/spark check. Disconnect battery, pull clock fuse/hood
light,
wait 1 minute, touch cable terminal to battery lug, listen for relay
clicks and look for spark. (In your case, listen for lack of relay
click. I love the headlight relay in the Toyota, ensuring that I
never have a dead battery from leaving the lights on when running in
from a stormy day. I first saw those in Japanese import pickups in
the '70s and thought they were a great idea. I think Mercenary
Bends
always had them, too.

(The aforementioned test is more risky nowadays with electronics in
every vehicle, but I've never fried anything. And most HIFI gear has
ferrite bead protection, too.)

This neatly solves the problem:
https://www.eevblog.com/forum/testge...-uni-t-ut210e/

It isn't the right choice for an electronic tech's bench meter that
may need to measure low milliAmps or microAmps accurately but it's
been fine for my vehicle and appliance diagnosis and repair, and solar
panel, battery and inverter testing.

I don't like having battery power exposed to accidents on shunts and
loads connected with stiff heavy cables, or bare banana plugs. That's
why I sprung for the expensive fine strand silicone-insulated wire and
lots of Andersons to connect it..

-jsw

On Mon, 12 Jun 2017 12:59:30 -0400, "Jim Wilkins"
wrote:

"Larry Jaques" wrote in message
.. .
On Sun, 11 Jun 2017 13:00:34 -0400, "Jim Wilkins"
wrote:

[battery drain]
Audible/spark check. Disconnect battery, pull clock fuse/hood
light,
wait 1 minute, touch cable terminal to battery lug, listen for relay
clicks and look for spark. (In your case, listen for lack of relay
click. I love the headlight relay in the Toyota, ensuring that I
never have a dead battery from leaving the lights on when running in
from a stormy day. I first saw those in Japanese import pickups in
the '70s and thought they were a great idea. I think Mercenary
Bends
always had them, too.

(The aforementioned test is more risky nowadays with electronics in
every vehicle, but I've never fried anything. And most HIFI gear has
ferrite bead protection, too.)

This neatly solves the problem:
https://www.eevblog.com/forum/testge...-uni-t-ut210e/

It isn't the right choice for an electronic tech's bench meter that
may need to measure low milliAmps or microAmps accurately but it's
been fine for my vehicle and appliance diagnosis and repair, and solar
panel, battery and inverter testing.

I don't like having battery power exposed to accidents on shunts and
loads connected with stiff heavy cables, or bare banana plugs. That's
why I sprung for the expensive fine strand silicone-insulated wire and
lots of Andersons to connect it..

-jsw

I got one of those, and they are pretty good. Another REALLY handy
tool is from Autel - MX101 and MX201. They plug into automotive fuse
panel, with fuse plugged into them, and they read out the current
being drawn by the circuit,The 101 is good for 30 amps with standard
ATO fuse, and the 201 good for 20 amps with the mini blade fuses.

wrote in message
...
On Mon, 12 Jun 2017 12:59:30 -0400, "Jim Wilkins"
wrote:

......
I got one of those, and they are pretty good. Another REALLY handy
tool is from Autel - MX101 and MX201. They plug into automotive fuse
panel, with fuse plugged into them, and they read out the current
being drawn by the circuit,The 101 is good for 30 amps with standard
ATO fuse, and the 201 good for 20 amps with the mini blade fuses.

I bought the Harbor Freight version, checked that it worked, and
fortunately haven't had a problem since then that needed it. I count
its cost as insurance.

On Sun, 11 Jun 2017 06:59:12 -0700, Larry Jaques
wrote:

On Sat, 10 Jun 2017 13:30:25 -0400, "Jim Wilkins"
wrote:

"Larry Jaques" wrote in message
. ..
On Sat, 10 Jun 2017 07:51:41 -0400, "Jim Wilkins"
wrote:

snip

"Input impedance: 10Euro"

Ain't Chinglish translations wunnerful?
I'm wondering about the package contents: 1 meter, 1 CABLUE.

They misspelled Kablooey. I'd be careful.

On Tue, 13 Jun 2017 07:06:00 -0500, Pete Keillor
wrote:

On Sun, 11 Jun 2017 06:59:12 -0700, Larry Jaques
wrote:

On Sat, 10 Jun 2017 13:30:25 -0400, "Jim Wilkins"
wrote:

"Larry Jaques" wrote in message
...
On Sat, 10 Jun 2017 07:51:41 -0400, "Jim Wilkins"
wrote:

snip

"Input impedance: 10Euro"

Ain't Chinglish translations wunnerful?
I'm wondering about the package contents: 1 meter, 1 CABLUE.

They misspelled Kablooey. I'd be careful.


ROFLMAO!! Indeed!

Ive got a half dozen various Variacs...some actual Variacs...some
Chinese, if anyone needs any.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus