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Old 01-16-2018, 05:01 PM   #1
spleenharvester
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Default Turning laptop PSU into a bench supply

Hi all,

Though I have a bench supply at my university I could do with one for my home uses.

Use: I need the supply to be able to find shorted components on a laptop motherboard via heat generation/freeze spray method.

I have a spare Dell PA-10 (which I can't use on its own as the overcurrent will trip it), I was thinking maybe attach it to a DC-DC buck converter like an LM2596:

http://www.ebay.co.uk/itm/LM2596-DC-...0AAMXQeKNTOq~W

This site seems to suggest it can handle a short across the output, but is this likely to be feasible for generating heat through a short for a brief period of time?

Thanks!
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Old 01-16-2018, 07:54 PM   #2
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Default Re: Turning laptop PSU into a bench supply

This might work better for what you want to do I have use this power a laptop at one time
It was a module very similar

https://www.ebay.com/itm/26084610301...84.m1436.l2649

I have not used this type of module but I have used host converters before

https://www.ebay.com/itm/LM2587-over....c100752.m1982
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Old 01-17-2018, 09:41 AM   #3
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Default Re: Turning laptop PSU into a bench supply

Quote:
Originally Posted by sam_sam_sam View Post
This might work better for what you want to do I have use this power a laptop at one time
It was a module very similar

https://www.ebay.com/itm/26084610301...84.m1436.l2649

I have not used this type of module but I have used host converters before

https://www.ebay.com/itm/LM2587-over....c100752.m1982
Thank you - I ended up ordering an LM2596S as it was the only one I could order with fast delivery, but I'll try those if I get no luck. Hopefully this strategy works as it is a lot cheaper and smaller than a benchtop supply. Will report back!
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Old 01-20-2018, 02:02 PM   #4
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Default Re: Turning laptop PSU into a bench supply

So this is what I ended up ordering: https://www.ebay.co.uk/itm/LM2596-St...53.m2749.l2649

I attached a Vostro 3560 DC jack to the input screw terminals, and a Dell PA-10 to that. I then attached some multimeter leads to the output terminal.

The supply seems to be good enough to power up a Vostro 3560 stably. When placed across the short, the voltage obviously drops heavily and a current of about 3.5 amps is pulled through the short. The board emits a bit of an unpleasant squealing sound when this occurs, but I've tested it with an output short for 20 seconds and the LM2596 survives and gets hot - most importantly, the PA-10 overcurrent does not kick in

How useful this will be in an actual short finding context I haven't yet tested, but it appears to work well.
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Old 01-20-2018, 02:54 PM   #5
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Default Re: Turning laptop PSU into a bench supply

Quote:
Originally Posted by spleenharvester View Post
When placed across the short, the voltage obviously drops heavily and a current of about 3.5 amps is pulled through the short. The board emits a bit of an unpleasant squealing sound when this occurs, but I've tested it with an output short for 20 seconds and the LM2596 survives and gets hot - most importantly, the PA-10 overcurrent does not kick in

How useful this will be in an actual short finding context I haven't yet tested, but it appears to work well.
The “over current not kicking in “
Is not a good thing

If I were you I would put a resettable fuse in it at a little bit more than the amperage I am going to use all the time and a regulator fuse for what the device can handle

They do make units where you can also adjust the voltage and amperage which I am surprised that you did not buy that one instead of the one you bought

Or

Just the regulator fuse rated for the amperage of the device not your load now if you want to a fuse for the load that would not be a bad idea either

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Old 01-20-2018, 08:14 PM   #6
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Default Re: Turning laptop PSU into a bench supply

Quote:
Originally Posted by sam_sam_sam View Post
The “over current not kicking in “
Is not a good thing

If I were you I would put a resettable fuse in it at a little bit more than the amperage I am going to use all the time and a regulator fuse for what the device can handle

They do make units where you can also adjust the voltage and amperage which I am surprised that you did not buy that one instead of the one you bought

Or

Just the regulator fuse rated for the amperage of the device not your load now if you want to a fuse for the load that would not be a bad idea either
I considered it to be a good thing because the input voltage remains stable (which was the problem originally as just applying power straight to the board would short the actual PSU itself and thus kill the power - this scenario does not). I haven't done anything to 'override' the PSU's own overcurrent protection - it could still kick in if something happened. Also I believe the board itself has overcurrent protection on the output.

I do see your point though, I might throw a fuse in line just in case.

Last edited by spleenharvester; 01-20-2018 at 08:22 PM..
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Old 02-01-2018, 11:17 AM   #7
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Default Re: Turning laptop PSU into a bench supply

Why not use desktop power supply? I can commiserate with the safety trip on these sort of things. Tried to use a xbox 360 supply once for a cordless drill. I got it wired but the PS tripped whenever I pulled the trigger down fully on the drill.
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