[RE-wrenches] Lithium Iron Phosphate

[Daniel Young]

Hello Wrenches,

 

I've been trying to think through how I can mate some lower cost charge
controllers (prostar 15A 24v PWM units, or the new 30A Midnite solar Brat)
to some 8s LiFePo battery banks.

 

As I understand it, lithium batteries meant to be charged to around 3.65V
per cell (29.2V for the 8 cell bank) and then the charge is terminated, not
put into a float mode.

 

Assuming I use a PCM to protect the batteries, so that each cell has a
balancing function and also over/under voltage protection. Would the battery
bank accept a simple charge controller that in essence, charged to
3.65V/cell, then backed down to a float voltage that was lower than it's
resting voltage, say 3.3V/cell. In theory at that voltage, there would be
little/no charge current going to the batteries. Or would the cells still
take in a small amount of power at these voltages and start to
overcharge/degrade?

 

Again, I'd plan to have a full PCM circuit protecting cells and balancing
them, but I'd like to have a good way to charge the batteries with solar
(right now I'm shooting for using a 72cell module and 24V nominal LiFePo
battery stack, so maybe there is another way that I can use, but I've not
decided to buy any batteries I am ok with accidently blowing up if I'm
wrongJ).

 

With Regards,

 

Daniel Young, 

NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90

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