Transformer Test

sr1200 · Oct 18, 2016

I have a power transformer primaries setup for 120 secondaries are 2 yellows that output 6.3v, 2 orange that are supposed to put out 750v (and has a grey center tap) and 2 purples which output 5v.
If i set my DMM to AC and put a lead on each of the yellows, i get 6.3v. If i put a lead on each of the purples i get 5v. If I put a lead on each of the orange i get 0. NADA, nuttin, zip. HOWEVER if i check each orange individually i get roughly half of what is supposed to be coming out of it (380v apporx). I have a feeling the two secondaries are out of phase with each other, however, not sure if the CT has something to do with that. Anyone have any input on if this is normal or i have a bum TX?

CJ · Oct 18, 2016

you are exceeding your DMM voltage rating,

maybe

only a guess

center tapped transformers can be dangerous to meters, a transformer meant for a bridge circuit will have safe voltages between the two wires, so checking a CT xfmr from CT to outside leads is the way to go,

PRR · Oct 18, 2016

Agree. Most meters only good to 500V-600V. Past 1,000V they arc and burn. Perhaps some just shut-down over 500V to indicate that you are being stupid/dangerous. (Yeah, that's my right, but the meter-maker's right to not aid me.)

gswan · Oct 19, 2016

Depending on the type and quality of meter you are using, you may be exceeding the safety ratings.
This may help:
http://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

sr1200 · Oct 22, 2016

meter is pretty decent, AC goes up to 750 dc 1kv.
I spoke with the transformer manufacturer and they stated that if the ct goes to ground, this phenomena will occur and is correct in nature.

looks like i gotta start hunting another problem down. (see my next plea for help thread)