[RE-wrenches] LiFePo4

Mon Sep 15 19:08:33 PDT 2014

Hi:

We've done some testing and operation of Lion battery banks in the 10 kWh 
range with our inverter chargers and so far the most important findings 
are:

1. The battery pack must have its own battery management system to:
a. regulate the individual cell voltages during charge and discharge
b. balance the cell voltages during charge and discharge
c. adjust cell charging voltages due to temperature variations
d. not provide a continuous float voltage to the battery bank
d. provide a built in safety cutoff disconnect, which turns off the 
current if for any reason either the charge or discharge current is too 
high.

A series string of Lion cells, without the battery management system 
functions above is very likely to result in damaged cells or worse.  The 
most likely mechanism which ultimately causes damage is individual cell 
temperature or cell to cell voltage imbalance. 

2. The inverter system must be designed so that the inverter never draws 
so much current that the current limit circuit in the battery bank is 
triggered. 

3. It may be necessary to adjust the current limit circuit as they 
typically respond within milli-seconds and may be triggered on simple 
power up as the inverter cap bank charges up.

4. When working with Lion, the inverter/charger should be configured so 
that it is a simple current limited voltage source when in charge mode. 
The built in battery management system should take care of the required 
charge cycle operation.

5. Whether the pack is LiFePO4, Lion polymer or other does not appear to 
be as important as a having a reputable brand and more importantly a well 
designed built in battery management system.

The short version is that lead acid cells are amazingly forgiving with 
regards charging and discharging voltages, currents and temperatures. Lion 
cells on the other hand are amazingly sensitive and going out of bounds on 
any of these can and will cause irreparable damage. 

Given the sensitivity, it doesn't make sense to take on responsibility for 
Lion battery management.

Management of that sensitivity and responsibility is best left to the 
battery bank manufacturer. 

JARMO
_____________________________________________________________________________________ 

Jarmo Venalainen  |   Schneider Electric   |  Solar Business  |   CANADA | 
  Training & Development Specialist - Senior 
Phone: +604-422-2528  |   Fax: +604-420-1591  |   Mobile: +604-505-0291 
Email: jarmo.venalainen at schneider-electric.com  |   Site: www.SEsolar.com 
|   Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 

*** Please consider the environment before printing this e-mail 

From:
"William Miller" <william at millersolar.com>
To:
"RE-wrenches" <re-wrenches at lists.re-wrenches.org>, 
Date:
09/15/2014 04:27 PM
Subject:
[RE-wrenches] LiFePo4
Sent by:
"RE-wrenches" <re-wrenches-bounces at lists.re-wrenches.org>

Wrenches:

Does anyone have any experience with Lithium Ferrous Phosphate cells? What 
are your experiences?  I am looking at an installation tomorrow and would 
like some input.

Thanks in advance.

William Miller

Lic 773985
millersolar.com
805-438-5600

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