PSU as battery charger?

[reboot]

Would an older 230w power supply make a 12v battery charger for a car battery?
Somewhat akin to a trickle charger?
It could be put on a timer to shut down after x hours...
Any thoughts?

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Who needs a life?, I have internet!
Cheers, Jim
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[M. A. Dockter]

Would that supply enough power to charge the battery faster than a retail charger?

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M. A. Dockter
Forum Administrator
mdockter@pcmech.com
http://www.pcmech.com/dockter.htm

[reboot]

Doesn't matter.
What I'm getting at is...I have lots of old PSU's, and no "retail" charger.
Why not make use of a few of them?
They're all AT, and kinda obsolete.
Chop off all the extra leads, stick a couple of heavy duty alligator clips on the ends of the +12v and gnd....
I'd give them away to friends if they'd work.



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Who needs a life?, I have internet!
Cheers, Jim
Jim & Sue's Free Files (http://members.cnx.net/reboot) | Jims Modems (http://members.cnx.net/reboot/modems.htm)

[bob]

It would not stop when the battery was charged. Over charging will ruin the battery.

[Larry E.]

To charge a 12 volt battery you would need more than 12 volts. A fully charged battery is 12.6 volts. The minimum voltage required would be 13.8 Vehicle alternators charge at between 14.2 and 14.8 If you could set the voltage to those specs it would work just fine. A battery charged at 13.6 to 13.8 can be charged indefinitly any higher and you would overheat the battery once it is fully charged.

[reboot]

Alright, let's rephrase it a bit.
If a guys battery were dead, and he had a couple of hours to kill, COULD he use one of these to, at least, get the car started?
I'm aware that overcharging would be a no-no, that's not an issue here.
In an emergency, could this work?

------------------
Who needs a life?, I have internet!
Cheers, Jim
Jim & Sue's Free Files (http://members.cnx.net/reboot) | Jims Modems (http://members.cnx.net/reboot/modems.htm)

[Toaster]

Larry hit the nail on the head.
You need at least 1 volt above "full charge voltage" to effectively charge a wet cell.
That is: 12.6 volts nominal charge + 1 volt= a minimum charge voltage of 13.6 volts.
This is well in excess of the nominal 12 volts (+/- 5%) that a P/S would deliver.
Aside from this, the supply has inadaquate "reverse voltage protection" because it is a "switching" power supply instead of a conventional "linear" power supply. (transformer and diode(s))
I can fully invision the supply "failing" under such a load request. AKA, poof.

[M. A. Dockter]

If you can kick up that 12V to about 14V, it might. But then again, it would be just as easy to find someone to jump you as to find an A/C outlet in an emergency...

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M. A. Dockter
Forum Administrator
mdockter@pcmech.com
http://www.pcmech.com/dockter.htm

[theENiGMA]

Hey Dok, you're from WIsconsin (moo!) too? I never realized that. Which part?
-KEiTH


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Well, I'm off to go look for myself. If I should get back before I return, tell myself to wait for me.

[Larry E.]

Charging a 12 volt battery with 12 volts will not work. I don't know the inner workings of a power supply but if you could put the +12 and the +5 volts together to make 15 it would probably work. If you wire the 12 positive to the 5 negative then use 12neg. and 5 pos. for the battery connections it would in theory work. I've never had a power supply apart or seen a wiring diagram so I don't know how it would react being connected in this manner. But to answer reboots question a 12 volt battery with 12 volts in it is considered dead.

[Toaster]

Boot,
You will just have to try it.
I think the supply will either fail or "fold up" to proctect itself.
Another matter would be if the battery attempted to draw in excess of the supplies output, the supply would fold-up (shut down).
Try it boot, worst thing is a toasted P/S and wounded pride.

[Junkman]

I have been thinking on ideas for older psu's and such also. A battery charger sounded good at first but from these responses maybe not a good use.
Here's another possibility I was thinking of, why not use the lower watt supply and other misc parts to make a breadboard/testboard kit for electronics projects. I picture young electronic learners hooking up jumpers to IC chips and LEDS ect..
A thought....

[Toaster]

Junkman,
Your thoughts are valid, however, most older supplies produce several voltages and require that you draw about 10% of the total capacity for EACH voltage. Many older supplies can produce 20 amps and greater on the 5volt line and 10 amps and greater on the 12 volt line.
If one could provide the minimum current draw, then your idea is sound because of the close tolerances of the supplies voltage(s).
A typical 200 watt supply will deliver about 18 amps of 5volt and 8 amps of 12volt power. This is grossly in excess of needs for most "experimenters" but still quite usable.
On the above mentioned supply, a minimum load of 2amps/1 amp is required to "load" the supply. A benifit is the additional voltages from the supply in the -12 and -5 volt voltages. Each of these voltages provide very limited currents (0.5 amp typical) but are great for "split voltage circuits".

[This message has been edited by Toaster (edited 07-29-2000).]

[Spiffman]

I picture young electronic learners "folding up" or failing when they touch a few pieces of metal together. Maybe they best be stayin' away from that. Nice Ideas though guys. I have an old 230 AT power supply and a battery that needs a little juice although I don't really need the battery either. Its just taking up space where my little sister's bike might go. Even if I fry it I can still make it hard for her to get into the garage with a bad battery sitting there. I would try it but I don't have the know-how. My dad is a physics major and I think I'll consult him on this topic. Lots of electronic know how inside his brain. Keep posting! POST ON POSTERS!!! w00t... err... no more pepsi tonight... no more.

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Spiƒƒ
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[Tuf]

Reboot: I'm not sure if a power supply would work in this application or not. But its worth a shot if you have the stuff to gamble with. I think its true that you can charge more rapidly with additional voltage over 12. But I freqently boost batteries on oilfield equipment by hooking another 12 volt battery to them for a little while. My good battery might start out at 11.8 volts and my "bad" battery is usually under 9. Usually this will bring the "bad" one up to 10.5 or 11 volts. And this is generally enough to get our equipment started and let the equipment's alternator or generator fully charge the battery. So I think several people here have posted valid answers. Maybe you can't really charge a 12 volt battery to its capacity, but if the power supply is regulated and doesn't burn up I think it would likely get you out of a jam.
Let us know if you try it.

Tuf

[Joe Auman]

Guys, your forgetting about amps, the real work horses. The only reason a car battery is so large is because of amps. A starter requires a lot of amperage, and using one PS would simply not be able to supply that much amperage (would most likely fry instantly). Just a though, but why would they have 200 amp chargers and starters? Houshold wiring should only handle, at max, 15 amps where the breakers can only handle 20 amps. I'm unsure of exactly how much amperage a starter will pull, but I'll find out.

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FATAL ERROR!!

Non-System brain or brain error!!
Replace and strike any key when ready.

[glc]

I don't think he wants to actually try to start the car with the PSU - so amperage isn't really the issue here. I have a 10 amp battery charger that will recharge an average car battery from stone cold dead in about 12 hours.

[Joe Auman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by reboot:
Alright, let's rephrase it a bit.
If a guys battery were dead, and he had a couple of hours to kill, COULD he use one of these to, at least, get the car started?
I'm aware that overcharging would be a no-no, that's not an issue here.
In an emergency, could this work?

<HR></BLOCKQUOTE>

I agree glc. It would work great as a charger if you could jump up the voltage a volt. As a starter, no.



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FATAL ERROR!!

Non-System brain or brain error!!
Replace and strike any key when ready.

[Tuf]

ok guys , Yes it will work. I took an old Sparkle 250 watt power supply that I had and charged the battery for my riding mower. I also charged a rather large battery that I had removed from pickup. It did get pretty warm, so It might not ultimately be as durable as a battery charger but it worked.