Modifying old AT-powersupply

[Snatten]

I need to modify an old AT-power to supply a peltier element with 15V, so I would like to change the +5V output to +15V. I'v been trying to look for a regulator like 7805, but no such thing to be found. Anyone who has an idea on how to find the regulator component (I guess it is a zener-diode)? Has anyone done something similar? The power is a "Super Power Computer CO.LTD Model SP-230W!

Thanks for any tips.

 

[Rolf]

No way......

I need to modify an old AT-power to supply a peltier element with 15V, so I would like to change the +5V output to +15V. I'v been trying to look for a regulator like 7805, but no such thing to be found. Anyone who has an idea on how to find the regulator component (I guess it is a zener-diode)? Has anyone done something similar? The power is a "Super Power Computer CO.LTD Model SP-230W!

Thanks for any tips.

If I understand you correctly, then there is no practical way to change the +5v to +15v. You could take the +12v, if it has enough current for you purpose and maybe put it in series with the 5v. I am not completely sure this would work, you might get smoke but if it works then you will have 17v that you could bring down to about 15v with a couple of diodes in series.

 

[Nigel Goodwin]

To change the 5V output to 15V would require rewinding the 5V winding(s) on the transformer - you're not going to be able to get a 300% increase just by altering the feedback regulation - plus all the secondary components probably aren't of high enough voltage ratings.

 

[Stellarcore]

There should also be a +12V and -12V source in the PSU. Couldn't you just call the -12V ground and the +12V would become 24V for you to play with? Then you can stick in some diodes or variable regulator to clamp it to 15V.

The only thing I'm not sure about with this setup is that the -12 may be meant only as a reference voltage and it may not be able to safely sink much current, so it would be good to experiment by slowly increasing your current and checking for excess heat/smoke/fire. Let me know how this works out for you, I was thinking of doing something like this myself.

 

[Snatten]

There should also be a +12V and -12V source in the PSU. Couldn't you just call the -12V ground and the +12V would become 24V for you to play with? Then you can stick in some diodes or variable regulator to clamp it to 15V.

The only thing I'm not sure about with this setup is that the -12 may be meant only as a reference voltage and it may not be able to safely sink much current, so it would be good to experiment by slowly increasing your current and checking for excess heat/smoke/fire. Let me know how this works out for you, I was thinking of doing something like this myself.

You'r right, the -12V can give only 0.5A, the +12V 9A and I need 12 - 16 A for the peltier element. So, as I understand the +5V is set by the number of windings on the ocillating transformer, so it is not possible to do what I first thougt of. But it should be possible to link 3 AT-supplys in series (I have stacks of them ). Or?

 

[mneary]

You'll have to do some modification to put three AT style supplies in series.

All AT supplies I've seen have their 0V connected to case Ground. And Ground on the supply is connected to the safety ground (green in US) on the power cord. Which would connect the 0V on all supplies together.

Breaking the 0V - GND connection is a possibility, but you'll have to do it carefully to avoid creating a safety hazard.

 

[Nigel Goodwin]

A fairly recent EPE had a project for converting a PC PSU to a 12V PSU, by replaing the 5V winding, presumably it would be easy to extend this to 15V?.

EDIT:

Quick update, I've checked EPE, it was the July 2006 issue, and converted a PC supply to 13.8V at 17A.

 

[Snatten]

A fairly recent EPE had a project for converting a PC PSU to a 12V PSU, by replaing the 5V winding, presumably it would be easy to extend this to 15V?.

EDIT:

Quick update, I've checked EPE, it was the July 2006 issue, and converted a PC supply to 13.8V at 17A.

Thanks a lot Nigel! Pretty sure this article will help me solve the issue, so I'v ordered it. BTW, suprises me that no one has asked me what the project is all about . If it successfull, I'll come back with a full description, so wish me luck

 

[Sceadwian]

What's wrong with just using the 12 volt supply?? 3 volts isn't going to end the world on efficiency. You didn't mention the current it requires though. If you can't use the 12 volt rail nativly then adjusting it to 15 volts isn't going to help with current and adjust a 5 volt supply to 12 volts is not going to be as simple as replacing the coil. The EPE project is only 12 to 13.8volts 5 to 15 is likley going to require replacing a signifcant number of other components,

 

[things]

peltiers prefer current over voltage for efficiancy. so 12 volts at a couple of amps should be fine, peltiers work at voltages as low as 1.5 volts

 

[Snatten]

peltiers prefer current over voltage for efficiancy. so 12 volts at a couple of amps should be fine, peltiers work at voltages as low as 1.5 volts

Well, the datasheet for my element states that it har an operating voltage of +15V and a current of 16.3A. Yes, that IS 245W!

 

[Nigel Goodwin]

BTW, suprises me that no one has asked me what the project is all about

You said it was to feed a peltier, so no need to say anything more - I think we've all got bored with people trying to do silly things with peltiers!

 

[things]

yeah there has been a few weird peltier ideas on here, just like the usb drink cooler\warmer, theres no way a usb port can supply a peltier with enough current to work properly, let alone cool a whole can of drink sitting ontop of it without insulation. i haven't even managed to cool a can with a peltier running 12volts at about 10 amps. i think the max amount of power a usb port can supply is about 5 volts at about 100ma?

 

[Snatten]

yeah there has been a few weird peltier ideas on here, just like the usb drink cooler\warmer, theres no way a usb port can supply a peltier with enough current to work properly, let alone cool a whole can of drink sitting ontop of it without insulation. i haven't even managed to cool a can with a peltier running 12volts at about 10 amps. i think the max amount of power a usb port can supply is about 5 volts at about 100ma?

Relax guys, nothing stupid like that, but if it works I think some people might find it useful.

 

[Sceadwian]

Snaten, I have a PSU I converted for a benchtop supply. It's a 200 watt supply and the output on the 12 volt rail is limited to 6 amps. You're going to need a pretty beefy power supply to provide the kinds of current you're looking for, simple quick and dirty modification of a 12 volt supplies coil isn't going to cut it. Have you looked around mpja.com? They have a monstrous assortment of power supplies, at least one of which should work for your usage. Based on the 6amps available on my 200watt supply you're going to need a 500-700 watt supply to get 13 amps efficiency is going to change with the current but a peltier device is not usually more than 5-10% efficient so it can basically be considered a resistor. That's something to keep in mind when you state that massive 250watt power requirement =) as it deliver only about 25 watts of actual cooling ability. They're pretty horrible.

 

[things]

keep in mind that the peltier has to dissipate 245W of heat, so you are going to need a massive heatsink!