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Old 25th February 2001, 02:33 AM   #1
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Okay I got 22 volts AC on output of my transformer. Put it through a rectifier and get 22 volts DC on output of rectifier should it not be closer to 30 Volts DC. I am stumped any ideas, maybe tomorrow I will put scope on it to see what is going on. Just seems bloody strange!
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Old 25th February 2001, 05:40 AM   #2
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Did you put capacitors on the other end of the rectifier?
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Old 25th February 2001, 05:54 AM   #3
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You may need a circuit to load the power supply. Some resistance?
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Old 25th February 2001, 09:09 AM   #4
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Need a bit more information, here. Is this power supply hooked to a load? A fairly heavy one, perhaps? It's possible that the load is drawing down the voltage because the transformer is unable to supply enough current to maintain the rail. The VDC=1.414*VAC(rms) relationship only holds for an unloaded (or very, very lightly loaded) power supply. We are also assuming full wave rectification, yes?
Another thought: Check your rectifier, you may have some burned-out diodes. If it's a monolithic rectifier bridge, you may have to replace the whole thing. Just for fun, drop in some junk-box 1N400x diodes, detach the load (if any), and see if the rail pops up. If it does, suspect the bridge. If not, swap out the caps. You may have a high resistance shunt inside one of your caps. If the caps don't do it (I've only seen this once or twice, myself), then suspect the transformer--possible problems with the windings. Oddities used to be common in the old days with high voltage transformers; arcs between the windings and such, things that would come and go depending on the load. These days, with solid state (i.e. much lower voltages), it's not so common. Good luck.

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Old 25th February 2001, 01:02 PM   #5
blmn is offline blmn  Brazil
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If everything was done right, it seems like a half-wave retification (just one diode working) with insuficient filtering, as the fellows said in this tread.

If the power transformer is damaged, you will percept overheat in case of short circuit or absence of voltage at one of the secondaries (if it has more than one).

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Old 26th February 2001, 01:57 PM   #6
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Default p/s

Haven't had a chance to check this stuff out yet but thanks for the replys gives me a place to start. And yes there is no load on the supply. All I had hooked up was the transformer and the diode bridge.
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Old 26th February 2001, 02:21 PM   #7
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Default bad news for me

Well turns out I have an open in the primary winding. Today I plugged it in and no voltage on output. Resistance check of windings confirms an open in primary. Guess thats the chance you take when you buy surplus! Think I will order a new one from Plitron. Once again thanks for your replys
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Old 27th February 2001, 06:22 PM   #8
Eric is offline Eric  United States
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Question Transformer

Hi Doktor: Sorry to hear about the bad transformer. I was puzzled when I read your post, I had assumed you got a new one from Plitron in the first place - and was wondering why a new transformer was giving you trouble! I've chosen a PLITRON #097060201 625VA dual 24V 13A toroid for my a40 amp. Still in the process of gathering parts for it ...
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