Yet another attempt at charging with server PSU

[circuit]

Hey guys. I, like most of you, struggle with finding a good (cheap, small and powerful) charger. I am writing now to express my happiness that, looks like it for now, I have managed to solve this.
So I got a couple of Cherokee CAR1248FP power supplies of off ebay. These are used in servers, give out 48V 1200W and, very important, have current limiting. In other words, they work in CCCV mode, used to charge lithium batteries.

I did some mods: changed some output caps, diodes, transistors, modded feedback circuitry, rewound a couple of transformers... And here it is:

I still had no time to do any serious measurements (such as ripple, efficiency comparisons, temperatures, etc), but was really happy at this "working and not exploding in my face" point, so I took a picture to share it with you.

I am going to use a couple of these PSUs paralleled as an onboard charger for my 22s 20Ah A123 pack.

I have wrote a couple of articles on the topic on my blog:
http://tinyurl.com/7nqmmsa
http://tinyurl.com/8aaqwnt
These are auto-translated links from Lithuanian.

I will post further 'development news' here and on the blog.

 

[heathyoung]

Very interesting - I have been considering this as well, been looking at the massive box of 12V server PSU's with active PFC wondering if they could be modified to do the same thing - Mine would have to be closer to 160V hot though...

More details would be good (ie. rewind details, voltage divider details etc.)

 

[andreym]

I did some mods: changed some output caps, diodes, transistors, modded feedback circuitry, rewound a couple of transformers...

Could you please post the details?
I use these PSU for more than a year now and I`m happy with it power to weight ratio. But the higher voltage mod would be the best option here
thanks in advance!

 

[auraslip]

I did a more complete write up on my site here: https://sites.google.com/site/shelbyelectro/batteries/batteries/server-psu-charger

 

[circuit]

I did a more complete write up on my site here: https://sites.google.com/site/shelbyelectro/batteries/batteries/server-psu-charger

I confess I have not read it, pictures were enough. It looks like your and mine work is completely different: you have connected a few wires and mine involves electronics design.


I will post more info when the solution is confirmed as stable and ready to use.

 

[Stielz]

Hey Circuit, how did this charger turn out in the end? I wanting to make one myself using these current limited supplies

 

[circuit]

Hi Stielz. I have managed to charge my battery pack a few times without a glitch, but, unfortunately, my project plans went sideways and I have dismantled and sold out my whole bike... Custom frame, battery, motor... The only thing I still have is this charger. I consider it a "prototype" and "not safe for general public's use", so did not sell it. Will be lying around until next project comes.