RE: Trans label

Unmarked electrical components are either a treasure hunt or a potential source of flash heat when they are misused. To f i g u r e o u t unmarked transformer wires one good way is to test them with a very low AC voltage and measure the voltage induced on the other windings. This will help to uncover the turns ratio between the windings.

Step 1 is to use an OHM Meter to identify each winding and it's configuration (such as center-tapped with three leeds). Step 2 is to apply 1 or 2 volts AC to any winding. This is low enough that you will not cause any harm. Step 3 is to measure the voltage applied to the winding you selected and then measure the voltage on all the other windings. Step 4 is to calculate the ratios between all the windings. For example 12 VAC is 1/10 of 120 VAC, and 12 VAC is 1/20 of 240 VAC. Obviously if you apply 1 VAC to what is marked 12VAC, then if you find 10 times 1 volt (10 VAC) on a winding, you may begin to suspect that you have located the 120 VAC input winding. I believe this is pretty clear.

When you think you have it figured out, install a 1 AMP fast blow fuse on the power you want to apply to what you hope is the Primary winding. With no load on the transformer, if the fuse blows you have likely made a mistake. If you suspect the unknown transformer has multiple primary windings, you need not concern yourself with wiring the two primaries for the low current (no load) testing. Once you know what you've got, you will need to use any dual primaries in the proper manner before you place the transformer under full load in your application.

I guess if I'm not careful, they'll start calling me Mr. Transformer. The hard part of what I have suggusted is getting a low voltage transformer to dedicate to the testing process. If you can find a 240 VAC to 6VAC small transformer, you can wire it to 120 VAC and use the 3 VAC out for testing transformers.

David Howland



-----Original Message-----
From: DRigotti@... [SMTP:DRigotti@...]
Sent: Saturday, September 04, 1999 9:34 AM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] Trans label

From: DRigotti@...

Please help me....
I have a transformer that has a label marked like so:
12V 0V 12V
10A
NO other markings. Is it a 120VA (12VAC @10A) OR 240VA (24VAC @10A)?
Its about 3 1/2" all around and weighs 5 pounds.
I'm guessing its good for 12VAC @ 10 Amps OR 24VAC @5 Amps.
Thank You All!
Dave

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