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Topic: BatLev -- LiFePo4 Cell Balancer (Read 3416 times) previous topic - next topic

BatLev -- LiFePo4 Cell Balancer

Lithium Feric Phosphate cells are a lower engergy density variety of lithium-ion cells that don't have the fire hazard and short life problems of the more common li-ion cells.  They are popular for electric vehicles and are gradually making their way into marine and RV applications.  When used in series (for higher than 3.2 volts), they need protection circiutry to avoid over-charging a cell.

This project is a cell balancer, that acts about like a zener diode.  Over the set voltage, (variable over a small range) it acts as a load on the cell, turns on a red LED, and has a opto-isolated indicator for turning off the charger.  The TL431A is followed by a two-transistor amplifier for the 3.3 ohm 5 watt load.

This is the first project I did using kicad, and I had some problems including the to220 outlines from one of the part libraries I used had the pins numbered strangly, fortunatly I noticed this and switched to a different outline before I ordered the boards.[attachment=0]

Re: BatLev -- LiFePo4 Cell Balancer

Reply #1
Can you upload the KiCad project? The image is not really readable :(

Re: BatLev -- LiFePo4 Cell Balancer

Reply #2
Now I'm interested in these batteries. How much do they cost?

Re: BatLev -- LiFePo4 Cell Balancer

Reply #3
I purchased the cells from, $286 for a 260 Ah cell, plus shipping.  They also have hardware for them available, but not on their web page.  Note that a set of four 260Ah  3.2v cells has about as much usable power as a set of four 220Ah 6.3v AGM batteries, and weight about 1/3 and has about 1/3 the volume, should have four times the life, and costs about the same.  (Non-sealed lead-acid batteries are about 1/2 the cost of AGM, but require more maintanence.)


Re: BatLev -- LiFePo4 Cell Balancer

Reply #4
As some of you may have noticed, I'm not as quick on my projects as some other people. 
I've got the parts (mostly from ebay) and the PC boards (with errors and quirks, so I won't share) and should be assembling soon.
Not shown in the schematic is the fuse, I'm using inline fuse holders.  URL below is for the kikad schematic.