# charger from PC power supplies/laptop chargers



## bgoner (Feb 16, 2011)

Can I build a charger from laptop chargers or PC power supplies?
PC power supply - 12v 300W 25A. I will need 10 of those to get 120v and 25A to charge my batts. Would this be doable?

I'd need about 35 laptop chargers to do it...


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## icec0o1 (Sep 3, 2009)

bgoner said:


> Can I build a charger from laptop chargers or PC power supplies?
> PC power supply - 12v 300W 25A. I will need 10 of those to get 120v and 25A to charge my batts. Would this be doable?
> 
> I'd need about 35 laptop chargers to do it...


1.) The charger would have 10 to 35 times more points of failure. 
2.) PC power supplies are CV and limit current by just cutting out at a certain max. If you use a 12v supply to charge a battery at 11V, it'll try to put out 100's of amps and just cut out.


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## bgoner (Feb 16, 2011)

I'll do the limiting of voltage and current myself, just using the transformators. 

Yeah lot's of points to break but it won't cost $2k...


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## icec0o1 (Sep 3, 2009)

bgoner said:


> I'll* do the limiting of voltage and current myself*, just using the transformators.
> 
> Yeah lot's of points to break but it won't cost $2k...


That's what a charger is... why need/use power supplies in the first place then?


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## JRoque (Mar 9, 2010)

Hi. My 2 cents on this is that you will go nuts trying to mod so many power supplies, deal with all of those fans and their boxy bulk. But your point about not having to spend >$2K is well taken. Look on this forum for a thread called "$200 charger" or something like that where folks are building lower cost chargers that perform well. 

Done right, your idea has merit. I picked up a box of 20 DC/DC converters from eBay for $200 that I might use for something like that. Those DC/DC can take a rectified 120V AC input and output the ~13VDC you need to charge each of your batteries. Search for "VICOR DC-DC Converter, VI-251-09" being sold by Azure Dynamics on eBay. It's a great deal even if you don't plan to use them on a charger.

BTW, what in the world is a "transformator"? Something like a transformer inside a gator? sorry...

JR


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## nimblemotors (Oct 1, 2010)

I built a battery charger for my 144v lead acid pack using 12v power supplies connected in series. This was just because I had about 50 of them that I used for my 9v R/C battery chargers product, so they were free. Of course I created a controller for the actual charging.

If I didn't have them free, I would not suggest this approach, at least not 12v power supplies. I'd use 48v ones instead, less to go wrong, as I did kill a few of the 12v units, but heck I just replaced them when they died, and in fact, the charger still worked with dead ones, the voltage was just lower.

But really creating a custom power supply is best. I think $2k for a simple charger is rather expensive. 



JRoque said:


> Hi. My 2 cents on this is that you will go nuts trying to mod so many power supplies, deal with all of those fans and their boxy bulk. But your point about not having to spend >$2K is well taken. Look on this forum for a thread called "$200 charger" or something like that where folks are building lower cost chargers that perform well.
> 
> Done right, your idea has merit. I picked up a box of 20 DC/DC converters from eBay for $200 that I might use for something like that. Those DC/DC can take a rectified 120V AC input and output the ~13VDC you need to charge each of your batteries. Search for "VICOR DC-DC Converter, VI-251-09" being sold by Azure Dynamics on eBay. It's a great deal even if you don't plan to use them on a charger.
> 
> ...


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## icec0o1 (Sep 3, 2009)

nimblemotors said:


> But really creating a custom power supply is best. I think $2k for a simple charger is rather expensive.


It really isn't simple though, is it? That's why there aren't even any good ones you can buy for $2k. You can get an even better idea by the length of the "DIY $200 home made charger" thread. And the components are quite expensive if you need 5kw+ charger.


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## ngrimm (Oct 19, 2007)

This is the option I am taking but it has it's risks. I was a timber faller at one time so that doesn't bother me  http://www.diyelectriccar.com/forums/showthread.php?t=48691&highlight=capacitor+charger


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## nimblemotors (Oct 1, 2010)

I dunno, seems fairly simple, but it does takes time to test one and get it working properly. If you don't have the time and interest $2k isn't out of line for a high-powered charger.

What I'm likely to do is use multiple 48vdc power supplies and charge 48v sub-packs. So a 144v pack can be done using just 3 48v chargers.
This gives some minimal "pack balancing" as well. 
Something like three of these, http://www.mpja.com/prodinfo.asp?number=16505+PS at $200 each, so $600 gets you 1.5kw, about as much as you can draw from a 120v house circuit.
For more power, you could go 24v sub-packs, $1200 for 3kw, and use two 120v (240v)
The microcontrollers for each are cheap for me, might not be for someone else.



icec0o1 said:


> It really isn't simple though, is it? That's why there aren't even any good ones you can buy for $2k. You can get an even better idea by the length of the "DIY $200 home made charger" thread. And the components are quite expensive if you need 5kw+ charger.


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## icec0o1 (Sep 3, 2009)

Be careful, because if you don't let the chargers finish every time, your pack will be unbalanced for that ride because it's unlikely the three chargers put out the exact amount of amps.


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## nimblemotors (Oct 1, 2010)

If one failed to work properly it could be a disaster, so clearly they must be coordinated and failsafe. yes let's be careful 


icec0o1 said:


> Be careful, because if you don't let the chargers finish every time, your pack will be unbalanced for that ride because it's unlikely the three chargers put out the exact amount of amps.


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