There is a gotcha with bridge rectifiers, it bit me yaars ago.
Borrowing the sketch below:
WHERE, if anywhere, are the 'grounds'?
----- Original Message ---
Your schematic should look something like the following, with a whole
lot more diodes:
(AC Input)
|
|--|>|--|>|--|>|--|--|>|--|>|--|>|--|
| |
| (-) | (+)
| |
|--|>|--|>|--|>|--|--|>|--|>|--|>|--|
| | |
(Negative) (AC Input) (Positive)
(output) (Output)
I'd guess you have one leg of the bridge turned around.
As i understand the test rig, the low/common
side of the variac is at 'ground'.
IF (note the IF....) the negative output is
'grounded' one string is trying to short the
variac wiper to 'ground', half the time.
This would not be an issue in the real
application, unless the secondary is
'grounded'.
best
dwp
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