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Old 27th April 2002, 12:20 PM   #1
stigla is offline stigla  Norway
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Default Universal PSU ideas...

Hello All!

Story; I have recently found this gigantic 300W, 230 to 110 volts Isolating transformer from a dumped soda-pop automat I found in the forest (of all places!)

This I would like to use in a powerfull universal Power supply to have in my, ahem, 'test lab'

I don't have much experience in large powerful PSU's so I was wondering if anyone have got any ideas / shematics or something to witch I could put the transformer to good use.

I am thinking about adjustible output voltage... 1-50 volts for example. Nothing advanced. Though, a current limiting adjustment thingy is nice to have around. maybe 0-5A or something....

Any ideas are welcome....

Stig
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Old 27th April 2002, 02:05 PM   #2
UrSv is offline UrSv  Sweden
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As far as I see, given the high secondary voltage of 110 VAC, you would get roughly 150 VDC after rectifiers. This means that you have to get rid of 100 VDC at the current you want which means something like 250 W if the maximum current is around 2.5 A (which it is for 300 VA at 110 VAC I think. That makes the PSU kinda hot. I would find another transformer and use this one for something else...it would probably be cheaper (hint: check what people think about cost for heating houses with heatsinks here).

/UrSv
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Old 27th April 2002, 02:09 PM   #3
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you'd have to use a switching supply.
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Old 27th April 2002, 06:05 PM   #4
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Cool Tranformer

230 V winding connected to 115 AC will give about 55V AC out which is about 75 V DC which could be used for 50V regulated supply with big heatsink. Switching supply....... I don't think so.
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Old 27th April 2002, 08:36 PM   #5
stigla is offline stigla  Norway
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hmmm, well, we use 230V AC here where I come from....

It is obviously possible to open the tranny by removing some screws, so if the windings is not dipped in lack or something it may be possible to wind off some turns on the secundary to give around 50-60V AC out.... this will improve current-handling too!! Will investigate this further tomorrow.

Stig
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Old 28th April 2002, 01:47 AM   #6
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dont count on it improving current handling and you'd have to remove an awful lot to drop the secondary by that much ....

Harry,
Basic switching supplies do not have to be that complex and can end up very well regulated indeed.
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Old 28th April 2002, 05:25 AM   #7
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having thought more about it, that power transformer would not be very useful in a simple switching supply either.
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Old 28th April 2002, 12:56 PM   #8
stigla is offline stigla  Norway
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Opened up the tranny today, despite AudioFreaks advice....

Was easy, infact, the two windings (prim. and sec.) was completely sectioned, so the only hard work was to remove and re-install the E and I's... took some time.

Winded of some 60 turns I think, forgot to count :-( Added a smaller winding to be used in series if I had wound off too much.
When finished I wrapped the windings with plumbers teflon tape and put the E, I's back. (got 5 leftovers I couldnt get in...)

Anyways, I've now got a 57V AC out and a 19V AC out. Gives around 80 volts of DC... still a bit high or what?


Stig
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Old 28th April 2002, 01:02 PM   #9
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that could be of some use .... use the lower voltage winding for low voltage and the high voltage winding for higher voltages but the note still applies .... be careful of the current requirements you place on the transformer.
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Old 28th April 2002, 02:11 PM   #10
stigla is offline stigla  Norway
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Yeah, I'll fuse it ofcourse.

How about using f.ex. a LM 723 to control a transistor, f.ex a MJ15001 (140V, 15A max).... I can use the 19V winding to power the LM 723...

Or what about putting f.ex. three LT 350 in series, so that I don't go over the max Voltage rating?

Maybe using a LM317 HV to control a transistor?

I'm thinking like this. Anyone got any ideas / experiences?

Stig
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