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'[OT] High current transformer'
1999\01\25@190116 by Gabriel Gonzalez

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face
Sorry for this OT.

I'm looking for: info, ideas, pointers, etc.

I need to pass 40-60A thru a wire to insure the capacity, but where do I get
this much current without having to use a humungous load to drop the voltage
and control the current.

I thought on using a relatively large power transformer, replacing the
secondary winding with a few turns of really heavy gauge to get a low
voltage (0.5-1V maybe) at a high current.

What do you suggest?

TIA

Gabriel

1999\01\25@193932 by David Reinagel

picon face
> I'm looking for: info, ideas, pointers, etc.
>
> I need to pass 40-60A thru a wire to insure the capacity, but where do I get
> this much current without having to use a humungous load to drop the voltage
> and control the current.
>
> I thought on using a relatively large power transformer, replacing the
> secondary winding with a few turns of really heavy gauge to get a low
> voltage (0.5-1V maybe) at a high current.
>
> What do you suggest?
>
> TIA
>
> Gabriel
>
I did someting like this many years ago when we were testing the ground
voltage rise on some hospital equipment when we put a large current
between the equipment chassis and the earth ground.  We got a pair of
2.5VAC high current output filament transformer (rated for 20 amps
continuous output) and wired them in parallel (make sure the phasing
is correct so that the current outputs add to each other), and we
wired the primary in parallel to an variable transformer.  Using a
100-amp-to-50-millivolt shunt resistor (resistors made for measuring
currents) in series with the secondary and a meter across the shunt,
we would turn the variable transformer up until we got the desired
current.  These measurements were very accurate.

If you want to cheap, crude way to do it, get an old-fashion soldering
gun -- I found a 150 watt unit a few years ago new (made in China) for
less than $20 [if you need the company name ..., e-mail me privately and
I will look it up at home].  This soldering gun is basically a
transformer with a single winding on the secondary.  Replace the
soldering "tip" with the wire you are trying to test, plus a current
meter -- you probably will get a LOT of current -- maybe even too
much.  But you can do things to reduce that.

Dave Reinagel
cisco Systems, Inc.

1999\01\25@193941 by Sean Breheny

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What about getting a cheap soldering gun. AFAIK, most of these are simply
transformers similar to what you suggest, except that a wire with a
slightly higher resistance is used as the tip, , connected to the secondary
(usually only one turn of metal tubing).

Good luck,

Sean

At 04:45 PM 1/25/99 -0700, you wrote:
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1999\01\25@200934 by Reginald Neale

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Gabriel asked:

>I need to pass 40-60A thru a wire to insure the capacity, but where do I get
>this much current without having to use a humungous load to drop the voltage
>and control the current.
>

How about keeping the average power requirements down by testing the wire
with a pulse? You can charge up a bank of caps to supply lots of current
for a short time. Put a sampling resistor (calibrated shunt) in series with
your wire to monitor the current.

Reg Neale

1999\01\25@203014 by Gabriel Gonzalez

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No, the test has to be 40A (nominal) for 3 minutes.

Gabriel

-----Original Message-----
From: Reginald Neale <.....nealeKILLspamspam@spam@SERVTECH.COM>
To: PICLISTspamKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Date: Monday, January 25, 1999 6:04 PM
Subject: Re: [OT] High current transformer


>Gabriel asked:
>
>>I need to pass 40-60A thru a wire to insure the capacity, but where do I
get
>>this much current without having to use a humungous load to drop the
voltage
>>and control the current.
>>
>
>How about keeping the average power requirements down by testing the wire
>with a pulse? You can charge up a bank of caps to supply lots of current
>for a short time. Put a sampling resistor (calibrated shunt) in series with
>your wire to monitor the current.
>
>Reg Neale

1999\01\25@212101 by Dwayne Reid

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face
Gabriel Gonzalez wrote:

>I need to pass 40-60A thru a wire to insure the capacity, but where do I get
>this much current without having to use a humungous load to drop the voltage
>and control the current.
>
>I thought on using a relatively large power transformer, replacing the
>secondary winding with a few turns of really heavy gauge to get a low
>voltage (0.5-1V maybe) at a high current.

Exactly what I use.  I have on old spot welding transformer that puts out a
couple of volts unloaded and about 300 Amps shorted.  I use a variac to
control the primary if I am unsure of the resistance of the load.  For
repetitive tests, I replace the variac with a series light bulb of
appropriate wattage to give me the output current I need.  Note the light
bulb is in series with the Primary of the transformer.  It acts like a
ballast resistor and quasi-regulates the output current.  Sometimes I drive
the transformer / bulb combo from a variac.

Note that spot welding transformers are intended for short duty cycle use if
driven near full power.  I find that I can get about 60 -70 Amps continous
out of mine without the transformer getting too hot to touch.  Go anywhere
near the full rated current on a continous basis and you WILL generate a lot
of smoke and a bad smell.

Hope this helps.

dwayne


Dwayne Reid   <EraseMEdwaynerspam_OUTspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1999\01\26@014534 by Eric Borcherding

picon face
Gabriel,

Might I suggest 2 or 3 paralleled NiCAD High Capacity D cells.
If you need lower voltage drop each Cells with a diode.   You
can then trickle charge the cells with a low voltage small wall
cube.   Best not to use for too long a time - you may want thermal
switches on each to avoid a serious "venting"  I have done the pop
a 30A fuse with a D Cell trick.  Use Nicads - not NimH.   NiCads
still have an phenominal pulse load capacity.

Eric Borcherding

1999\01\26@044257 by Nigel Orr

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face
At 18:24 25/01/99 -0700, you wrote:
>No, the test has to be 40A (nominal) for 3 minutes.

Does it have to be AC?  Could you use a 12V auto battery?

Nigel

1999\01\26@145951 by Nigel Goodwin

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In message <002001be48bc$c701fb80$b9cbe994@tgo>, Gabriel Gonzalez
<tgospamspam_OUTCHIH1.TELMEX.NET.MX> writes
>Sorry for this OT.
>
>I'm looking for: info, ideas, pointers, etc.
>
>I need to pass 40-60A thru a wire to insure the capacity, but where do I get
>this much current without having to use a humungous load to drop the voltage
>and control the current.
>
>I thought on using a relatively large power transformer, replacing the
>secondary winding with a few turns of really heavy gauge to get a low
>voltage (0.5-1V maybe) at a high current.
>
>What do you suggest?

That sounds about the easiest way of doing it (unless you could find a
ready made transformer), it's how PAT machines (Portable Applianace
Testers) work, they pass a large current down the earth lead and measure
the resistance - this has the added benefit that if the wire is a bit
dodgy it actually blows it!. It's the large transformer that makes PAT's
hard to carry :-).
--

Nigel.

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1999\01\26@165330 by Gabriel Gonzalez

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Yes, AC only.

Gabriel

-----Original Message-----
From: Nigel Orr <KILLspamnigel.orrKILLspamspamNCL.AC.UK>
To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Date: Tuesday, January 26, 1999 2:37 AM
Subject: Re: [OT] High current transformer


>At 18:24 25/01/99 -0700, you wrote:
>>No, the test has to be 40A (nominal) for 3 minutes.
>
>Does it have to be AC?  Could you use a 12V auto battery?
>
>Nigel

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