[RE-wrenches] Lithium Iron Phosphate

Peter Parrish peter.parrish at calsolareng.com
Tue Aug 18 07:31:35 PDT 2015


I too am interested in LiFeP batteries. I think we need some more
information on charge/discharge cycles. I've bits and pieces, but there must
be some solid data from Panasonic or one of the other LiFeP manufacturers.
Such as, 

 

Recommended charge cycle

Maximum discharge rate

Low voltage disconnect

 

Also I expect all of the CC manufacturers are thinking about LiFeP or
similar Li technology. Maybe if one of us has a friend at Outback Power,
Morningstar, Midnite Solar, we could find out more.

 

-          Peter

 

Peter T. Parrish, Ph.D.

President, SolarGnosis

1107 Fair Oaks Ave.

Suite 351

South Pasadena, CA 91030

(323) 839-6108

petertor at pobox.com

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Daniel Young
Sent: Monday, August 17, 2015 2:29 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Lithium Iron Phosphate

 

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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