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In Reply to: RE: transformer puzzle posted by DAK on July 25, 2015 at 14:19:05
Here's a photo of the transformer. The top four terminals are numbered 1,2,3,4 going from left to right. The bottom three aere numbered 5, 6, 7 going from left to right. The resistance between 1 & 2 is 2 ohms, and it is the same between 3 and 4. There is no continuity between the two pairs.The resistance betweem 5 and 7 is about 125 ohms and between 5 &6 and 6 & 7 it is about 60 ohms. My guess is those three are the center tapped secondary terminals. Problem is there is no continuity between any of them which is hard to understand considering the resistance readings I got.
When I tried hooking up ac to 1 & 2 it blew a fuse on the variac after not too much voltage was applied.
I have found a lot of different transformers at hamfest over the years but never had one act like this. Is it possible for it to be kerflooey and still get the resistance reading I did?
Edits: 07/25/15 07/25/15Follow Ups:
A resistance of 2 Ohms between terminals 1 - 2 and 3 - 4 is about right for a dual winding transformer. It's too high to be a low voltage filament winding. A resistance of 127 ohms between 5 and 7 is again about right for a high voltage "plate" transformer.
Is the transformer heavy (over 4 lbs)? If so, it is likely to be designed for 60 Hz applications. If not, it's probably a military 400 Hz transformer, although I haven't seen many potted 400 Hz transformers (they are more usually open frame with a icky epoxy material covering them).
Given that it blew the fuse when less than 117 volts was applied to terminals 1 and 2, it's likely to either have a shorted winding or to be a 400 Hz unit.
Well, it's a heavy sucker, definetly more than 4 lbs. Guess it probably has a shorted winding. Maybe I will try terminals 3 and 4 and see what happens as I have not done that. If that is no good i guess I have a door stop.
I have a few PT which statically test ok, but when powered up have poor performance. Probably a short to ground. regards, Dak
nt
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