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Old 17th July 2005, 04:45 PM   #1
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Default Transformer Dual Primaries/Secondaries

I'm trying to figure out how to use 115v primary input and return 10v secondary output from a Triad VPL 20-1200. There are dual primaries for use with either 115v or 230v supplies and dual secondaries for either 20v or 10v output. After reading archived posts I thought that I would need to parallel the primaries to use 115v. Wouldn't that mean connecting BLK and BRN together to the hot lead and connecting WHT and BLU together to the common? To parallel the secondaries, wouldn't I connect RED and VIO together and YEL and GRY together? On testing, this scenario doesn't work. The only way I can get 10v is to connect the Primary side BLK to hot WHT to BRN and BLU to common and on the secondary side RED to meter, YEL to VIO and GRY to meter. To me this seems to be series connections on both primaries and secondaries and I'm getting 10v only because I'm driving half the expected input (115v on 230v primary connection). Sorry for the crude drawing and the lack of understanding. Thanks for any assistance.
http://home.comcast.net/~jharvill1/T...PL_20-1200.pdf
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Old 17th July 2005, 06:24 PM   #2
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Default Re: Transformer Dual Primaries/Secondaries

Quote:
Originally posted by cantskienuf
Wouldn't that mean connecting BLK and BRN together to the hot lead and connecting WHT and BLU together to the common?
Your use of the term common is a bit worrisome. By common I hope you mean neutral? Yes, it looks like BLK + BRN to hot and WHT + BLU to neutral.

Quote:
Originally posted by cantskienuf
To me this seems to be series connections on both primaries and secondaries and I'm getting 10v only because I'm driving half the expected input (115v on 230v primary connection).
Exactly.

Since that drawing was made by yourself and not Triad, maybe the ordering of leads, and in turn phase, are probably meaningless? Your solution may be as simple shorting YEL + VIO and RED + GRY and seeing what you get. In any case, your first step BEFORE THAT should be to wire the primaries properly and make sure you do indeed get 10V from each individual secondary.
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Old 17th July 2005, 06:55 PM   #3
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Clearly I'm not an electrician, so excuse my errant terminology. I've re-validated that the drawing is correct. Triad does not link to their drawing and I don't have a scanner for the hardcopy. When the primaries are wired parallel (BLK & BRN joined and attached to one side of the 115v AC line; WHT & BLU joined and attached to the other side of the AC line) I get 10v with the meter attached to RED & GRY, I get 10v with the meter attached to YEL & VIO, I get 10v with the meter attached to YEL & GRY and I get 10v with the meter attached to RED & VIO. The Triad hardcopy contains a Technical Note which states that "Primary and Secondary windings are designed to be connected in Series or Parallel. Windings are not intended to be used independently." I take this to mean that I must either jumper YEL to VIO for a series connection (which produces 20v) or I must connect RED & VIO together and YEL & GRY together in order to have a parallel connection. When I do the latter (what I believe to be a parallel connection) I get about 110mV. When I test each individual winding (RED & YEL and VIO & GRY) I get 190mV and 70mV respectively. I guess the other very real possibility is that my color perception is limited and I'm mis-reading the wires. If they exit the transformer in the same order as the drawing, I am correct. I can definitely tell that the YEL lead is the second from the top, so it tracks with the drawing, as did the exit pattern of the primary wires.
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Old 17th July 2005, 08:43 PM   #4
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Quote:
Originally posted by cantskienuf
I've re-validated that the drawing is correct.
Quote:
Originally posted by cantskienuf
I get 10v with the meter attached to RED & GRY, I get 10v with the meter attached to YEL & VIO, I get 10v with the meter attached to YEL & GRY and I get 10v with the meter attached to RED & VIO.
It is almost impossible for both of the above observations to be correct. Think about it; if the drawing is correct how is the 10V being generated between two isolated windings?

A couple of more tests would help. One would be to measure the DC resistance between all combinations of two secondary leads. Do this with the transformer unplugged.

Another is to make sure that some of the 10V readings are not being generated by inductive coupling in the xfrmr. Put something like a 10K resistor in series between a secondary lead and the meter and see what voltages you read.
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Old 17th July 2005, 09:10 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
I think Leadbelly is about right. Your drawing is probably wrong.
Test for continuity of every winding.
Then wire 110v into just one primary winding (you are now running at about half VA but for test purposes this is not a problem).
Now check the voltage at a pair of ends for one secondary and then check the other pair.

Unplug from the mains, reconnect the second primary ( they could be out of phase so you need to do this next bit very quickly).
If the primaries are out of phase then the transformer does not develop much flux in the core and the primary current is enormous and will overheat the primary VERY quickly.

Connect your meter to one already proved secondary winding and briefly plug the transformer back on. If you get the same secondary voltage then OK. If you get almost zero volts or the fuse blows then switch off immediately.
Reconnect the second primary the other way round and try the secondary voltage again.
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Old 18th July 2005, 06:55 PM   #6
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The source of the confusion was indeed my lack of color perception. I was able to pick up the VIO and YEL, but could not tell the RED from GRY and assumed the wires exited the transformer in the order shown on the drawing. Apparently, that is not the case. VIO and YEL do, but the others do not. I guess the drawing merely tells you what wires are associated with what secondary, not where to locate them. After conferring with someone who is not color-impaired, I've solved the riddle. Fortunately, I tested them with very short duration attachments on a GFCI circuit and didn't burn any windings. I think from now on I'll buy my transformers with labeled solder tabs instead of colored leads.....
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Old 18th July 2005, 09:09 PM   #7
macboy is offline macboy  Canada
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Quote:
The source of the confusion was indeed my lack of color perception.... I think from now on I'll buy my transformers with labeled solder tabs instead of colored leads.....
OK, a little off topic but still very DIY... what if you built a little color checker tool using a red LED and an green LED. Shine each LED onto the wire(s) in question, to see which one reflects more strongly. The wire that is brighter with red illumination is red and the one that is brighter under with green is green.
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