What power supply is this and how does it work - diyAudio
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Old 11th May 2012, 02:39 AM   #1
srinath is offline srinath  United States
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Default What power supply is this and how does it work

I picked these up from an office sale.

Its got 42V dc X 27 amp, and 12, 5 and 3.3 taps with a few amps each. Obviously it was made to deliver 42vdc.

I am surprised to see such a small transformer and so many transistors, hard to see but the heat sink has like 10 of those.

Anyway hope I can use it or use parts of it for a chip amp project.

Thanks guys and gals.
Cool.
Srinath.
Attached Images
File Type: jpg Power_supply_front.JPG (67.8 KB, 500 views)
File Type: jpg Power_supply_back.JPG (56.5 KB, 480 views)
File Type: jpg Power_supply_fan.JPG (78.4 KB, 465 views)
File Type: jpg Power_supply_big_trafo.JPG (59.7 KB, 466 views)
File Type: jpg Power_supply_little_trafos.JPG (87.0 KB, 467 views)
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Old 11th May 2012, 04:35 AM   #2
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Modern power supplies use switching to combine voltage transformation and regulation into one step while reducing size and weight.
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Old 11th May 2012, 01:28 PM   #3
srinath is offline srinath  United States
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So I shouldn't go around pulling that thing apart, I need to use it as it is ?
Thanks.
Srinath.
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Old 11th May 2012, 02:07 PM   #4
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Usually they are designed to meet some special specifications, and has a +-5% adjust (a trimmer inside, but accessible from outside. Im sorry to tell you that youu cant modify it more than such limits. I tell you from my repairing and designing experience.

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Old 11th May 2012, 02:32 PM   #5
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You can pull it apart if you want. The heatsinks would be useful, but if it still works I would say it's more useful as-is.
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Old 11th May 2012, 02:46 PM   #6
macboy is offline macboy  Canada
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That is definitely a switching supply, no question.
If you had two, you could get +/- 42 V rails, as long as you made sure that the output is floating and not referenced to ground (i.e. the grounded plug). If you can adjust the voltage down to a little below 40 V that would be better (42 V is on the bleeding edge for most chipamps), but if you don't know how, it's probably better not to guess.

Since these rectify and filter the AC mains directly, you must be careful poking around inside. Those big capacitors can have over 170 VDC on them (350 V in 240 VAC countries!). There is sometimes a 'bleeder' resistor across those to drain the charge, but it can take at least several minutes to drain it after pulling the plug. Even still, you should must drain those high voltage capacitors with a large 100 ohm or so resistor across the terminals for several seconds. Don't touch anything until you know the high voltages are drained.
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Old 11th May 2012, 03:01 PM   #7
srinath is offline srinath  United States
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Default Modify it.

Quote:
Originally Posted by Osvaldo de Banfield View Post
Usually they are designed to meet some special specifications, and has a +-5% adjust (a trimmer inside, but accessible from outside. Im sorry to tell you that youu cant modify it more than such limits. I tell you from my repairing and designing experience.

Regards.
I am not trying to exceed its limits, I am trying to make it a smaller and lighter by eliminating the unneeded if there were any. Maybe that itself a dumb idea, its like making an amp lighter by ditching the heat sink.


Quote:
Originally Posted by macboy View Post
That is definitely a switching supply, no question.
If you had two, you could get +/- 42 V rails, as long as you made sure that the output is floating and not referenced to ground (i.e. the grounded plug). If you can adjust the voltage down to a little below 40 V that would be better (42 V is on the bleeding edge for most chipamps), but if you don't know how, it's probably better not to guess.

Since these rectify and filter the AC mains directly, you must be careful poking around inside. Those big capacitors can have over 170 VDC on them (350 V in 240 VAC countries!). There is sometimes a 'bleeder' resistor across those to drain the charge, but it can take at least several minutes to drain it after pulling the plug. Even still, you should must drain those high voltage capacitors with a large 100 ohm or so resistor across the terminals for several seconds. Don't touch anything until you know the high voltages are drained.
I do have a few, and yea I was gonna use 2 for +/- 42 - no problem. The adjustment - I doubt I got the knowledge to do that. However the chipamp I am building is an L20. Easy 42v capable.

I am trying to get it into a slightly better chassis, the ground isn't the negative, I'd be OK I think.
Thanks.
Srinath.
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Old 11th May 2012, 06:26 PM   #8
srinath is offline srinath  United States
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Yikes, 420vdc is the output from that 2 pin plug, OK I better get this guy back together asap, I am messing with things way more powerful than I can imagine.
Cool.
Srinath.
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Old 14th May 2012, 02:46 AM   #9
srinath is offline srinath  United States
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Default Back together

OK its all back together and nothing caught on fire ... always good that.

So now the pic below - I have a couple questions about that.

The red wire in the fore ground - bottom left of the attached pic is 42v, the black wire next to it is 12v. The red wire toward the center left of the pic is also 42v dc. The black wire just before it is the negative - its not referenced to ground/body.

The 2 42v red wires are not even from the same location in the power supply, and they obviously dont show continuity to each other.
Now can I use this 1 supply to supply the -42 0 and +42 volt DC needed by the l20 amp ?

Thanks guys.
Cool.
Srinath.
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Old 14th May 2012, 06:58 AM   #10
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"Cisco Systems" tells me it's probably a big supply for a rack of networking equipment. Is there any type of model # identifier on the case or pcb? You might get lucky and find some docs online.
Quote:
The 2 42v red wires are not even from the same location in the power supply, and they obviously dont show continuity to each other.
Now can I use this 1 supply to supply the -42 0 and +42 volt DC needed by the l20 amp ?
Is there 2 grounds, or do they share just 1?
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