12 fridge power supply

Submitted: Tuesday, Feb 08, 2005 at 15:24
ThreadID: 20242 Views:4156 Replies:3 FollowUps:2
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Hi all
On the weekend I modified a power supply from an old PC I found on the side of the road during council cleanup.

I use the power supply to run my fridge and it works great. It hardly gets warm and the 12volt rail is rated at 8 amps. I have had the fridge running on it since sunday so far and all is well.

I used information from This Site text but mounted a cigarette lighter socket in the power supply case instead of the binding posts show in the site.

Its not a very difficult modification at all and works very well.
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Reply By: Groove - Tuesday, Feb 08, 2005 at 15:29

Tuesday, Feb 08, 2005 at 15:29
PS The instruction mentions that you might have to use a load resistor on the 5 volt rail. I didnt do this and it still works fine.
AnswerID: 97255

Reply By: Member - Jeff M (WA) - Tuesday, Feb 08, 2005 at 16:19

Tuesday, Feb 08, 2005 at 16:19
We have used these for running cameras. Not ideal as they are switchmode and have some high end interference (very minute). But for the fridge will work well. The only problem is they are not exactly small. ie you can't fit them in the compartment the factory ones slip into to take with you.

For round the house though, would be perfect. Should be able to buy cheap ones from any computer store for about $40 brand new.
AnswerID: 97263

Reply By: joc45 - Wednesday, Feb 09, 2005 at 12:51

Wednesday, Feb 09, 2005 at 12:51
Agreed, they work well.
I am currently using a 200 watt one, albeit modified. In its original form, the overall voltage regulation is on the +5v rail, leaving the +12v unregulated. I have modified it so that the regulation is now on the +12v rail (and cranked it up a bit). Also swapped the 5v shottky diodes with the 12v diodes (5v diodes are bigger) to give higher current out at 12v. I can get about 14A out of mine now.
Some power supplies do like a small load (say 0.5A) on the +5v rail, but mine works fine without a load.
Also, it is not recommended that you put one of these across a battery; an earlier one of mine died a serious death, tho I've modded the current one to work ok - too much to describe here.
Another suggestion is to connect the fan via a thermal switch (avail from Jaycar), so the fan cuts in when the heatsink gets to about 60deg. This means it rarely cuts in, and therefore little noise.
And remember that there are some serious AC and DC high voltages present, where quite often the construction of the power supply doesn't do much to separate the high voltage from the low voltage, so when modiying it, try not to disturb anything which could later affect the high voltage side.
Cheeers, Gerry
AnswerID: 97435

Follow Up By: Groove - Wednesday, Feb 09, 2005 at 17:25

Wednesday, Feb 09, 2005 at 17:25
Actually I considered a thermal switch and then decided to run the power supply without a fan to see how it performed. The housing is very well vented and given its not mounted in a PC case I figured it would not run hot. I have much larger power supplies that run without a fan.

Anyway it goes great without a fan. As for regulating the 12 volt output, in a car the fridge runs over a range of voltages from 11 to nearly 14 so I didnt bother. The output from the power supply is 11.8 volts under load and all is good
FollowupID: 356073

Follow Up By: joc45 - Thursday, Feb 10, 2005 at 19:24

Thursday, Feb 10, 2005 at 19:24
I found in Broome last year, the fan did cut in from time to time in 35deg heat, but I reckon without the fan, the temp rise would not be enough to hurt the psu.
You're right about the fridge coping with a range of voltages, therefore not requiring good regulation. Mine was also charging the battery, so I was regularly drawing over 10A with the fridge running, and it had to maintain 14v, which it did admirably.
FollowupID: 356269

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