Testing: -> Old Unmarked Power Transformers <-

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northsiderap

Well-known member
Joined
May 8, 2005
Messages
223
Location
Michigan
Lately I've been checking out power supply design, and I have an assortment of old unmarked power supply transformers to check out.

I have been measuring DC resistance and trying to draw out a schematic of which wires I think are supposed to go where... Then I have a beefy 50k I attempt to load the secondary with.

Sofar I have messed up a few transformers in a big puff of smoke and usually a nice 60hz buzzing sound... I'm starting to get shell shocked from all the fireworks.
:shock:
Anyone have any better way to test old unmarked power xformers? Tomorrow I'm going to use a 1 VAC generator if no-one has any better ideas...
 
I seem to remember that most power transformers follow a common color code.

The 1 volt generator is always a good plan and my prefered way around unknown transformers. The following is used in conjunction with the ratios as discovered with the 1 volt measurements.

This is from memory, so take with a large grain of salt.

Primary: Black
Filliment : Green
HT : Red
Bias : Blue or Yellow

Any center taps will contain the basic color, ie HT CT : red with yellow stripe.
or Red with White stripe etc.

I'm sure CJ will be here soon to clean this up. :?

Hope this helped.
Peace - Out, Irv
 
Forgot to add that I measure unterminated voltages, ie No Load.

I just terminate all wires on a screw type terminal strip and poke away with the meter and 1 volt gen. after I take my best shot at the primary, I'll power it up and measure volts again. This way if I guess wrong usually no magic smoke is released in the process.

You could also power up the transformer primary with a light bulb in series for current limiting and indication.

Peace - Out, Irv
 
[quote author="KingKai"]I seem to remember that most power transformers follow a common color code.
[/quote]
Not old russian ones. :wink:
For a common low voltage transformer primari dc resistance is bigger than secondaries.Also thicker wire means usually low voltage big amperage secondaries.
 
"Not old Russian Ones"

D'oh I hate it when my North-American myopic view gets in the way! :oops:

Well at least the light bulb should lessen the occurance of magic smoke emanating from the test subject. :razz:


Peace - Out, Irv
 
I'm in a similar situation. I have two old U.S. made power transformers that are potted and contain no information. It's hard to tell the colors of leads but it appears to be


2 Black
2 Green
1 Green/White
2 Red
1 Red/White
2 Orange
2 Blue

Does anyone have a rough idea of what all of these might be used for? I'm going to try the 1v generator idea assuming the black is the primary.


Ryan
 
KingKai said:
The 1 volt generator is always a good plan and my prefered way around unknown transformers.
The generator should be applied to a winding that has sufficient inductance. Applying it to a low-volt winding is bound to make measurements difficult.
That's why it's important to rough up the job by measuring the DCR and assessing the wire gauge.
 
That reminds me I have a couple big old transformers to throw away on junk day this month. I bought them back in the 70s as surplus. If I haven't used them yet, unlikely to ever.

JR

[update, yesterday I threw out both transformers and an old broken statue of a china man (missing his head). This morning the transformers are gone but the broken china man remains... apparently scavengers collected the transformers for scrap value.  [/update]
 
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