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Old 22nd February 2005, 06:13 AM   #1
dmh is offline dmh  United States
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Exclamation is this a good idea???

i have a unidentified power tansformer from a kenwood reciever. I want to test it for use in a chip amp.

question 1:
from tihe picture does it look like I have identified the wires correctly?

question 2:
what are the 2 unidentified wires?

all the information i have is that it was from a kenwood stereo (maybe KR series) and the number which is printed on the transformer which i have had no luck in tracking down.

I plan to test it with fuses and a DMM of course but is it a good idea to assume from the colors?

just wanted to check with you guys first as i know very little about transformers.
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Old 22nd February 2005, 09:43 AM   #2
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dmh,

I think your idea of checking the transformer with a multimeter first is a good idea....

using the meter you can determine which leads are connected to the primary winding and which are connected to the secondary winding.

also a tip: if you take off the pressed metal housing of the transformer, you may be able to see the different windings which could help you determine which wires go where.....

(unsure if you have already tried this - hope this is helpful)

-Dan
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Old 22nd February 2005, 12:32 PM   #3
boholm is offline boholm  Denmark
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Do not apply voltage at first.

First - use your DMM in position "ohms" to measure the wires on the right (on the picture). If you measure close to zero (a few ohms is alright) then you have found a pair = one winding. Strap them together or otherwise mark them, so you don't loose track og the wires.

Second - look at the gauge of the wires. I guess that the pairs with the red wires are the same, but you have to be sure. Different wires can mean different ampere outputs. Now you have the fases.

Third - Take a battery and have it ready to connect live and neutral. First you need something to tell you the polarity of the wires of the right side; a LED or a voltmeter (pref. analog - easier to see, if it goes to plus or minus). When this is connected you can connect the battery: Not constantly but just let the wire touch the battery. Look at your meter and mark the proper wire for plus.

Now you should be ready to test with mains on. Of course with proper precautions
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Old 22nd February 2005, 12:36 PM   #4
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First off, DON'T perform any test using mains voltages until you KNOW what the windings are.

Use the ohms range of your meter and record the resistance values between each combination of wires, and then post these readings here and we will be able to determine the next step.

Wire colours can mean absolutely nothing.

Cheers
Graeme
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Old 22nd February 2005, 01:25 PM   #5
paulb is offline paulb  Canada
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If you have another source of low-voltage AC (like another transformer), you can apply 6, 12 or whatever volts AC to what you think is the primary, then measure it and the other windings. If you're wiring up another transformer to do this, include a fuse (always!) and make sure everything on the AC power line side is insulated; it's pretty easy to touch something live by mistake while you're probing voltages.
p.s. I'd be surprised if your transformer has an Earth connection. I haven't seen one like that.
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Old 22nd February 2005, 01:39 PM   #6
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Quote:
Originally posted by paulb
If you have another source of low-voltage AC (like another transformer), you can apply 6, 12 or whatever volts AC to what you think is the primary, then measure it and the other windings. If you're wiring up another transformer to do this, include a fuse (always!) and make sure everything on the AC power line side is insulated; it's pretty easy to touch something live by mistake while you're probing voltages.
p.s. I'd be surprised if your transformer has an Earth connection. I haven't seen one like that.

This was to be the next step - I wanted to make sure the primary was properly identified first (12V ac into a 2V tap can give quite a jolt on a high voltage winding)

An interwinding screen is quite common, and this is normally the transformer "Earth".

Cheers
Graeme
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Old 22nd February 2005, 06:16 PM   #7
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Quote:
Originally posted by boholm
Third - Take a battery and have it ready to connect live and neutral. First you need something to tell you the polarity of the wires of the right side; a LED or a voltmeter (pref. analog - easier to see, if it goes to plus or minus). When this is connected you can connect the battery: Not constantly but just let the wire touch the battery. Look at your meter and mark the proper wire for plus.

Hi,

What polarity are you talking about? I thought transformers
are AC voltage devices....

Udi.
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Old 22nd February 2005, 06:26 PM   #8
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Can you take the cover off and take some more pictures?

Colors are arbitrary. Don't assume the black primary lead to be ground: in the US AC-wiring world, black is hot, white is neutral. Again, these probably have no corrolation, but just an illustration.

My guess for the outputs would be the red and and black are voltage pairs and use either the blue or white as a center tap (for ground). The other wire is probably a low-voltage winding to power some sort of startup circuit.
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Old 23rd February 2005, 06:40 AM   #9
dmh is offline dmh  United States
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Thanks for the tips
with my meter set on 1X I get these readings for resistance (grouped wires have continuity). What should I be able to tell from this?
Thanks again
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Old 23rd February 2005, 06:40 AM   #10
dmh is offline dmh  United States
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please disregard the pic in my last post. These values are more accurate.
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