# Charging and monitoring of low-voltage LiFePO4 systems



## CroDriver (Jan 8, 2009)

I have build a small battery prototype for a company that will test it. If they like it they will order a lot of them.

Voltages:

100% SOC = 16V 

90% SOC = 15V 

50% SOC = 13V 

10% SOC = 12V 

5% SOC = 10,5 V 

They have used lead batteries before so they asked me if they could use the lead chargers to charge this LiFePO4 batteries. Has anyone tried to charge Li batteries with a lead 12V charger?

And are there some cheap BMS systems for only four cells in series?

The prototype looks like this now:











I will add a fancy plexiglass sheet with LEDs and engraved technical specs on the top of the pack


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## dimitri (May 16, 2008)

Yes, 12V nominal LA charger can be used for 4 cell pack of LFP cells. Typical 12v charger will produce about 14.5-15V , which means 3.75V per LFP cell in a 4 cell pack, which is perfect for risk free full charge.

You may just add VoltBlochers to each cell to keep them balanced or any other simple 4 channel LFP BMS.


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## major (Apr 4, 2008)

CroDriver said:


> I have build a small battery prototype for a company that will test it. If they like it they will order a lot of them.
> 
> 
> The prototype looks like this now:
> ...


Hi Cro,

Don't you have to have solid ends on the box to prevent cell swelling? Also, you have the series connectors same size as the parallel jumpers. Those will have up to 3 times the current. It depends on the intended application, but might be trouble for high amp discharge.

Regards,

major


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## CroDriver (Jan 8, 2009)

major said:


> Hi Cro,
> 
> Don't you have to have solid ends on the box to prevent cell swelling? Also, you have the series connectors same size as the parallel jumpers. Those will have up to 3 times the current. It depends on the intended application, but might be trouble for high amp discharge.
> 
> ...


Hi Major

The customer needs high energy, not high power. He'll pull only 30Amp max.

The cells shouldn't swell at this power demands and the connections are even oversized for 30Amps.

Anyway, thanks for your advice


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## MN Driver (Sep 29, 2009)

Is there a reason why you went with 12 cells and put them in parallel sets instead of 4 larger cells? or was this what was the most readily available?


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## CroDriver (Jan 8, 2009)

MN Driver said:


> Is there a reason why you went with 12 cells and put them in parallel sets instead of 4 larger cells? or was this what was the most readily available?


This where cells I already had in my garage. If I had 400Ah cells I would just connect four of them in series


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## JRP3 (Mar 7, 2008)

CroDriver said:


> The cells shouldn't swell at this power demands and the connections are even oversized for 30Amps.


I thought swelling could occur when charging so it still might be a concern.


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## CroDriver (Jan 8, 2009)

JRP3 said:


> I thought swelling could occur when charging so it still might be a concern.


Hmm, I don't really know...

I thought they swell only at high discharge rates


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## adamj12b (May 4, 2009)

What size cells are those? I love the casing you built. I hope do something like that for my conversion so that I can easily remove the batteries. 

-Adam


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## JRP3 (Mar 7, 2008)

Wouldn't be that hard to ad an end plate or cross bar in the middle to your design just to be safe.


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## CroDriver (Jan 8, 2009)

JRP3 said:


> Wouldn't be that hard to ad an end plate or cross bar in the middle to your design just to be safe.


Good idea... I'll do that.

I guess that the sides don't need to be compressed too?



adamj12b said:


> What size cells are those? I love the casing you built. I hope do something like that for my conversion so that I can easily remove the batteries.
> 
> -Adam


This are 100Ah cells.

Wait to see some other batteries we're building 

Looks like I will take the battery pack of my car apart before it's even completed


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## JRP3 (Mar 7, 2008)

CroDriver said:


> I guess that the sides don't need to be compressed too?


I believe you are correct. For one the sides of the cells are narrow so are more resistant to flex than the wide ends and the way the cells are built inside the layers would more likely swell towards the ends not the sides.


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