Problem with charging lifepo4 with server psu

bike4life

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Apr 10, 2020
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I have 4 server psu that i arranged in series and combined the outputs. They each make 12v x 4 = 48v total. I took a kiln wire and clamped the 48v + and - and the kiln wire had 5 amps running through them (DC clamp meter). The psu have a indicator light at the end and it was green.

Now when i combine the 4 psu and put the leads against my lifepo4 battery which is like medium charge. It is 13s lifepo4 and measures 39v total. Basically the indicator lights go yellow and my clamp meter shows a current draw of 1/2 an amp... This is a problem!!!!

What is going on here.... I dont understand. Why cant i charge my batteries with the psu... The psu was fine putting out 250watts for the kiln wire at 48v, (48 x 5), yet it doesnt charge the battery and goes into shutdown mode!!!!
 
Depends on the PSU design. In this case, it may not see the battery as the same kind of load as the wire; the wire is purely resistive and does not have a voltage across it except for what the resistance vs current generates.

The battery already has a voltage across it, and when current is applied to it's internal resistance that voltage increases further. The PSU may not be able to deal with this, because there are four in series, and one or more of them may not react the same as the others. If any of their error trip points or other characteristics are not exactly the same as all the others', perhaps one of the PSUs is tripping and then causing the rest to do so.

If you can, try using just one PSU connected across just enough of the cells for it to charge normally, rather than the series set of PSUs across teh whole battery. See if it works then.

If so, you may simply have to connect them that way--one PSU across just that much of the pack, but all four at the same time that way.

If not, then you may not be able to use those specific PSUs.
 
..it's designed to do that.

A server PSU is not a properly current controlled device in the way that a battery charger is.. it will trip at certain currents and voltages to protect what is connected to it. You'll need some electrical expertise to convince it to act another way.
 
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