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What to do with a 37V 12.5A switch mode power supply.

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Chris Cristini

Thu Apr 09 2009, 05:19PM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

I was in the chat room and asked about it and came up with some ideas it does not have protection for output it does not shut down under short circuit conditions can I get some ideas about filtering and short circuit protection don't want to burn it out when using it for ZVS drivers and heavy loads. Or mod it for manually charging batteries I don't know where to start.

GeordieBoy

Thu Apr 09 2009, 07:41PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

It is odd that the SMPS does not include short-circuit protection? Can you give us any more info about how you acquired this supply? Who it is made by? What was it's intended application?

EEYORE

Thu Apr 09 2009, 07:57PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

How did you figure out that it isnt short-circuit protected? Seems all SMPS would have that in them seeing as they can deliver alot of power!
You could build something to short circuit protect it if your that concerned. Something along the lines of a zener diode and SCR/fuse combo seems to be in order for short circuit protection.
Matt

Chris Cristini

Fri Apr 10 2009, 01:19AM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

It came out of a large home theater system 12" subwoofer the amp was on a separate circuit board with a huge heatsink there were six of these under it

I found out about no protection by shorting it out the wire turn cherry red while the lights were getting dim as i pulled it apart there was a huge spark but the psu was still on so i asume there is no protection here are some pics. Oh the PSU is made by AVIS it came out of a Philips sub.

I put it all on a nice piece of wood and added thick wire and gator clips for the output it was only shorted for less than a second alot of current for a mid size smps the ferrite transformer is twice the size of one in a 300W PC PSU could i mod it for more power or voltage or build a nice plexiglass or metal case for it. It may just be a cheap power supply but could be a nice little project right?

Chris Cristini

Fri Apr 10 2009, 10:27PM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

mattrg2 wrote ...

How did you figure out that it isnt short-circuit protected? Seems all SMPS would have that in them seeing as they can deliver alot of power!
You could build something to short circuit protect it if your that concerned. Something along the lines of a zener diode and SCR/fuse combo seems to be in order for short circuit protection.
Matt

What about this instead of a SCR

for protection?

Marko

Sat Apr 11 2009, 08:43AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well, if the supply neither turns off or instantly explodes when shorted, It must have built-in current mode control (which is the case with most modern SMPS's anyway). If I wanted the output disengaged under short circuit I'd just use a fuse or a circuit breaker on the output.

Marko

Chris Cristini

Tue Apr 14 2009, 03:01AM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

It does I think here are a few I.C's that are on the SMPS.

and this one

Steve Conner

Tue Apr 14 2009, 10:47AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

KA7500 is just an alternate part number for the TL494. This IC doesn't have peak current mode control, but it can be set up for average current limiting.

It would make sense for a SMPS in a subwoofer to have a current limit instead of shutdown. That way they can undersize it a bit, without having it turn itself off every time Godzilla tramples on a car.

Bear in mind that the current limit might not be good enough to withstand a dead short for a long time.

Chris Cristini

Tue Apr 14 2009, 02:36PM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

Thank you Steve McConner now I don't have to worry about it that much but still what would I have to do in order to keep spikes away from vital electrical components. And I was trying to figure out how to regulate the voltage from 1.5 to 36 at its same current output? It has me scratching my head I just need to learn more about SMPS's huh.

EEYORE

Tue Apr 14 2009, 03:21PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

I dont think you could trim the voltage down very much on that thing. Youll basically have to use a couple high current voltage regulators to have a low voltage and be able to go to a high voltage. For spikes, youll need to build a filter. What kind of spikes are you worried about here? Does this thing misbehave or something? Or do you mean spikes from something else hurting the SMPS?
Matt

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