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Old 25th August 2016, 04:15 AM   #1
donovas is offline donovas  South Korea
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Join Date: Jun 2014
Default current spike blowing out diodes?

sorry, this is a double post but i need as much help i can get asap.

im using psu board with dinky 1n4004 diodes in them, double bridge mode. and the tranformer is 200vac EI.

I have two setups like this and only difference is that on setup A the transformer is not varnished, (i meant to do it myself later) and has only one secondary tap of 0,27v, where as setup B has varnished tranformer and secondary taps of 0,9,12,27v.

on setup A, the 1n4004 diodes on the PSU spark and blow whenever i turn on the amp.

setup B runs fine, even when i transfer the PSU from the setup A. so i'm sure the difference of the transformers is causing the issue. board from setup B does the same thing in setup A

What is the issue?
and why is it happening?

thanks in advance.
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Old 25th August 2016, 08:28 AM   #2
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Location: The Jurassic Coast, England. GB
What is the current you are requiring on start up? How big are your tank capacitors that you are trying to charge? Circuit may help.
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Old 25th August 2016, 09:54 AM   #3
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
use a Mains Bulb Tester to power on any new or modified mains powered equipment.

Then you can measure some voltages even if the bulb is lit up.
It the current draw is very low, the bulb does not light up, although it may flash dimmly for a very short period at initial start up.
regards Andrew T.
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Old 26th August 2016, 10:19 PM   #4
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Location: gold coast
Are your diodes from a reputable source? I've had a bunch of 1N4007s and 1N5404s which couldn't handle transients and blew too. Best thing if you have a bunch of them is to throw them out.
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Old 27th August 2016, 12:23 AM   #5
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Location: Coffs Harbour
setup B runs fine, even when i transfer the PSU from the setup A.
I think the OP tells us that the power supply (that would include the diodes) is fine if only the transformer remained different on a swapover test. The appearance of varnish should be irrelevant if it is a commercial product so I suspect that the windings may be wrongly connected on the dodgy transformer. You need to verify that there is no connection between what you believe are primary and secondary windings and that the AC voltages are the same for each 0-27VAC winding.

Take care with mains AC on exposed wiring!
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