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Old 18th February 2010, 04:28 PM   #1
munorc is offline munorc  United States
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Default Identifying transformers

I have acquired a box of chokes transformers. I would like some help identifying some of them. Many are Thordarson, Stancor, Triad. Those I can find literature for.

One of particular interest id a Sangamo Push-Pull Output Transformer, Type H-171. I have not found any references for Sangamo so far. Can anyone ID?

Also, I have a few transformers that are unlabeled. I can determine the ratio but how do you determine any other specs? In addition to those, I have a friend with a box full of trannies that were pulled off of old amps and organs. Similar situation,

Once ID'd, what is the view on using "vintage iron"? Many of these are NOS, still in boxes. What should be done to qualify them to be safe to use?
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Old 18th February 2010, 05:22 PM   #2
munorc is offline munorc  United States
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make that "chokes AND transformers"
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Old 18th February 2010, 07:19 PM   #3
TheGimp is offline TheGimp  United States
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Warning, Potentially lethal High Voltages may be produced with some transformers, and line voltage is lethal.

How familiar are you with electrical/electronic theory? Power safety?

The inductors will be the easy part. Measure them on an inductance bridge.

The transformers will be a bit more difficult. If you can identify the windings by color code, you can make an educated guess, given you know enough about electrical theory and searching for old transformer manuals.

Those can be tested by applying a variac with in line fuse to the primary and measuring the outputs. That said there are probably thousands of winding ratios that you must make educated guesses at.

Once you have identified them as power transformers you probably should test them for insulation integrity with a HyPot test set. 2500V with no more than 2mA leakage current would be a good starting point. Once you are sure they are safe, I'l hook line voltage up to the primary and let them run with no load for a couple of hours to make sure they don't get hot. They will get slightly warm. Be sure to tape off the secondary leads at this point to avoid electrical hazards.

Output transformers can sometimes be identified by the wiring color codes as well.
You can measure the turns ratio with a signal generator and oscilloscope.

What is left will require testing with a signal generator and oscilloscope.

There are several threads about transformers that I suggest doing a lot of digging with the search engine.

I got a bunch of transformers from a TV shop that shut down. About half were shorted internally and dangerous.
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Old 18th February 2010, 07:55 PM   #4
munorc is offline munorc  United States
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Is there a help page for the specific search tool for this forum? I can find many threads on transformers but I have not been very successful with specific multi term searches.

I think a HiPot test is probably a bit out of reach, at the moment. I do have a couple of GR megohm bridges that I use for insulation testing on AC motors. They only have a max voltage of 550V, however.
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Old 18th February 2010, 08:02 PM   #5
TheGimp is offline TheGimp  United States
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The top toolbar has a search function. Also if you try to start a thread about a subject like "Transfomrer Identification" it will prompt you with a screen of similar threads you can look at.

Transformer codes

Transformer wiring

etc.

Someone pointed to a link to two jpg files called XFMR1.jpg and XFMR2.jpg that dealt with testing transformers, but I can't find the thread.

550V is a bit low for safety testing the isolation between primary and secondary, etc. These transformers can develop peak output voltages in the 700-1000V range and a leakage path to primary or core can be dangerous.

Last edited by TheGimp; 18th February 2010 at 08:10 PM.
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Old 18th February 2010, 09:33 PM   #6
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I found this article helpful:
diytube.com :: View topic - The Dumpster Transformer Topic
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Old 18th February 2010, 09:43 PM   #7
m6tt is offline m6tt  United States
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Only applies to US transformers, and only sometimes.

TRANSFORMER COLOR CODE (RMA STANDARD)

RETMA transformer lead color codes
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Old 18th February 2010, 11:19 PM   #8
BudP is offline BudP  United States
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Quote:
Only applies to US transformers, and only sometimes.
I know of at least nine differing ones, 7 of them are US based.

Bud
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Old 18th February 2010, 11:27 PM   #9
BudP is offline BudP  United States
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The safest way to test for turns ratio and absolute turns is to use a ten turn search coil. Look to see if there is enough space between core and coil, if you can see daylight for perhaps half the width of the coil, you are in. Take some thin insulated wire, preferably coil winding magnet wire and loop ten turns around the coil. Tape them on one side, hook an accurate ac volt meter up , apply a variac to the highest DCR winding and run the voltage up in the search coil to 0.100 volts. Measure all other windings and assume a couple of additional turns for the highest DCR winding and you have your absolute turns and turns ratio.

You can also do this with just one full turn of wire, if that is all the space you have, but it is not as accurate.

Bud
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Old 19th February 2010, 01:36 AM   #10
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Quote:
Originally Posted by TheGimp View Post

Output transformers can sometimes be identified by the wiring color codes as well.
You can measure the turns ratio with a signal generator and oscilloscope.
I use a variac and a volt-meter to determine OPT ratios and power transformers. 10 V is convient for OPTs, 12V for power trafos.

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