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Old 11th December 2002, 12:06 PM   #11
biff584 is offline biff584  United States
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That sounds right to me- it's very old variac and I don't know anything about it. Thanks alot.

-Brian
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Old 11th December 2002, 12:31 PM   #12
JohnG is offline JohnG  United States
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If it is a variac supplying a standard transformer, and you are measuring on the secondary of the transformer, you should not be having any serious problems.

I would also suspect a miswired or faulty transformer, assuming your "standard transformer" following the variac is NOT an autotransformer. Note that variacs are autotransformers and provide NO isolation.

Also, it is a bad idea from a safety standpoint to float the scope with an isolation transformer. It can put your entire scope at high voltage; knobs, probes, and everything. One touch and your DIY career (and all your other careers) could be over. The one time I have see this done in a semi-safe manner, the scopes were behind a plastic barrier and plastic sticks were used to work the controls. This was many years ago; we use amplified diff probes now.
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Old 11th December 2002, 06:37 PM   #13
biff584 is offline biff584  United States
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Just retested the power supply today- I didn't try to measure the output across the bridge- just across the cap's. Everything worked fine- no smoke.

-Brian
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Old 11th December 2002, 06:43 PM   #14
tiroth is offline tiroth  United States
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I suspect grounding one of the rails was to blame.
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Old 11th December 2002, 07:48 PM   #15
skaara is offline skaara  Slovenia
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Quote:
Originally posted by biff584
Just retested the power supply today- I didn't try to measure the output across the bridge- just across the cap's. Everything worked fine- no smoke.

-Brian

Isnt that the same?
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Old 11th December 2002, 08:08 PM   #16
biff584 is offline biff584  United States
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No- before I put the probe directly across the bridge, with nothing else connected to the bridge. This time I added the two filter caps, and placed the probe from one cap to the ground (center tap of transformer tied to earth ground).

-Brian
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Old 11th December 2002, 10:16 PM   #17
skaara is offline skaara  Slovenia
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oh

Its working, and only that matters
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Old 11th December 2002, 10:31 PM   #18
tiroth is offline tiroth  United States
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Quote:
Originally posted by skaara
Isnt that the same?
Well if you literally measure "across the bridge" you'll be grounding one rail!
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Old 11th December 2002, 11:54 PM   #19
biff584 is offline biff584  United States
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Yeah- I figured that one out the hard way!
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Old 12th December 2002, 12:22 AM   #20
grataku is offline grataku  United States
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Well if you literally measure "across the bridge" you'll be grounding one rail!

Uh?
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