<font size=2 face="sans-serif">Hi:</font>
<br>
<br><font size=2 face="sans-serif">I understand from your e-mail that the
EV DIY industry has been successfully using a Lion pack with minimal monitoring/battery
management and perhaps the packs will continue to work out. However,
a relatively small number of systems do not validate the safety and reliability
of a solution.</font>
<br>
<br><font size=2 face="sans-serif">Over the last decade or so, the biggest
application of series connected Lion cells has been in laptops. From
that it has been learned that battery management is needed for reliable,
long life and safe operation. Indeed, to meet that need all the major
semiconductor manufacturers have designed a multitude of dedicated battery
management chips. Here for example are links to some of the Texas
Instruments offer and its easy to find much more from any number of manufacturers.</font>
<br>
<br><a href="http://focus.ti.com/download/trng/docs/seminar/Topic%202%20-%20Battery%20Cell%20Balancing%20-%20What%20to%20Balance%20and%20How.pdf"><font size=2 color=blue face="sans-serif"><u>http://focus.ti.com/download/trng/docs/seminar/Topic%202%20-%20Battery%20Cell%20Balancing%20-%20What%20to%20Balance%20and%20How.pdf</u></font></a>
<br>
<br><a href=http://www.ti.com/lit/an/slaa478/slaa478.pdf><font size=2 color=blue face="sans-serif"><u>http://www.ti.com/lit/an/slaa478/slaa478.pdf</u></font></a>
<br><a href=http://www.ti.com/lit/an/slyt322/slyt322.pdf><font size=2 color=blue face="sans-serif"><u>http://www.ti.com/lit/an/slyt322/slyt322.pdf</u></font></a>
<br><a href=http://www.ti.com/lit/an/slua463/slua463.pdf><font size=2 color=blue face="sans-serif"><u>http://www.ti.com/lit/an/slua463/slua463.pdf</u></font></a>
<br>
<br><a href=http://liionbms.com/php/about_us.php><font size=2 color=blue face="sans-serif"><u>http://liionbms.com/php/about_us.php</u></font></a>
<br>
<br>
<br><font size=2 face="sans-serif">The specifics of how much and how complex
the monitoring should be could be debated, but as rule the key elements
are precise voltage monitoring and regulation, cell balancing, temperature
sensing and for large banks over current protection. Indeed, we have
found these functions in all the Lion battery packs which we have so far
evaluated.</font>
<br>
<br><font size=2 face="sans-serif">JARMO</font>
<br><font size=2 face="sans-serif"><br>
</font><font size=3 color=#008000>_____________________________________________________________________________________</font><font size=3>
<br>
</font><font size=1 face="Arial"><b><br>
Jarmo Venalainen</b> | </font><font size=1 color=#008000 face="Arial"><b>
Schneider Electric </b></font><font size=1 face="Arial"><b> | Solar
Business</b> | <b>CANADA</b> | <b>Training &
Development Specialist - Senior</b> <b><br>
Phone:</b> +604-422-2528 | <b>Fax:</b> +604-420-1591 |
<b>Mobile:</b> +604-505-0291 <b><br>
Email:</b> </font><a href="mailto:jarmo.venalainen@schneider-electric.com"><font size=1 color=blue face="Arial"><u>jarmo.venalainen@schneider-electric.com</u></font></a><font size=1 face="Arial">
| <b>Site:</b></font><a href=http://www.sesolar.com/ target=_blank><font size=1 color=blue face="Arial"><u>
www.SEsolar.com</u></font></a><font size=1 face="Arial"> |
<b>Address:</b> 3700 Gilmore Way, Burnaby, BC V5G4M1 <br>
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<br>
</font>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">From:</font>
<td><font size=1 face="sans-serif">Starlight Solar Power Systems <larry@starlightsolar.com></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">To:</font>
<td><font size=1 face="sans-serif">RE-wrenches <re-wrenches@lists.re-wrenches.org>,
</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Date:</font>
<td><font size=1 face="sans-serif">09/16/2014 10:14 AM</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Subject:</font>
<td><font size=1 face="sans-serif">Re: [RE-wrenches] LiFePo4</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Sent by:</font>
<td><font size=1 face="sans-serif">"RE-wrenches" <re-wrenches-bounces@lists.re-wrenches.org></font></table>
<br>
<hr noshade>
<br>
<br>
<br><font size=3>Jarmo,</font>
<br>
<br><font size=3>I must say I disagree with most of what you have said.
In the EV DIY industry, there are a growing number of conversions using
LFP battery banks without any BMS or EMS at all. These pioneers are risking
there multi-thousand banks because they have learned something about these
cells. They will stay in balance and perform perfectly as long as they
prevent over and under voltage or charging a frozen battery with high current.
</font>
<br>
<br><font size=3>My reply numbers correlate to yours:</font>
<br><font size=2 face="sans-serif">1. </font><font size=3>I
agree for most customers a BMS is necessary.</font>
<ul>
<li><font size=3>Disagree: The battery systems (with BMS) that I sell do
not regulate cell voltages during charge or discharge. They only adjust
voltage after the cells reach 3.55 Vpc. However, at that 3.55 Vpc, I have
terminated charge and entered a float/maintenance charge. On my personal
battery bank, 24 cells, I have charged and discharged daily since May.
My cell voltages still only vary by 0.02 volts per cell.</font>
<li><font size=3>Disagree: There is no temperature adjustment for voltage
during charge or discharge. All temperature compensation circuits are removed
from the RE equipment per manufacturers specifications.</font>
<li><font size=3>Disagree: We provide a continuous float voltage per manufacturer
specifications. A float voltage can keep the battery at any SoC. I program
for 90%.</font>
<li><font size=3>Our CPU provides protection for over current BUT that
will likely never happen because the cells can be charged and discharged
up to 10C and continuously at 3C!</font></ul><font size=2 face="sans-serif">2.
</font><font size=3>Disagree: No need
to limit inverter current as the battery can produce 10C.</font>
<br><font size=2 face="sans-serif">3. </font><font size=3>Disagree:
Ditto above.</font>
<br><font size=2 face="sans-serif">4. </font><font size=3>Disagree:
No need to limit inverter charge current because of the 10C capability.</font>
<br><font size=2 face="sans-serif">5. </font><font size=3>I
agree that for most consumers a BMS is required. So far we install the
BMS provided by the manufacturer on every system. I will be installing
systems without BMS in the future but openly for select customers.</font>
<br>
<br><font size=3>I have not found that LFP batteries are “amazingly sensitive”.
I have discharged cells past 100% DoD, in fact as low as 0.35 Vpc, and
recharged without any harm. I have started very complex loads like air
conditioners with repeatable success from small battery banks. While I
do not recommend this, I believe there is a robustness with modern LFP
cells. </font>
<br>
<br><font size=3>The benefits of LFP batteries are many. Each year I recycle
between 30,000 and 40,000 pounds of lead acid batteries. MOST of them are
damaged by the consumer deficit charging them. I consider this to be a
very unfavorable aspect of lead acid when compared to LFP batteries that
never need to be fully charged or equalized or watered.</font>
<br>
<br><font size=3>One thing that will damage LFP batteries is if a cell
in a series string is ever discharged below 0 volts, it will take on reverse
polarity and is usually not recoverable. But, you can simple replace it
and balance it with the other cells. </font>
<br>
<br><font size=3>I welcome your comments.</font>
<br>
<br><font size=3>Respectfully yours,</font>
<br>
<br><font size=3>Larry Crutcher</font>
<br>
<br>
<br><font size=3>On Sep 15, 2014, at 8:08 PM, </font><a href="mailto:Jarmo.Venalainen@schneider-electric.com"><font size=3 color=blue><u>Jarmo.Venalainen@schneider-electric.com</u></font></a><font size=3>
wrote:</font>
<br>
<br><font size=2 face="sans-serif">Hi:</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
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:</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
1. The battery pack must have its own battery management system to:</font><font size=3>
</font><font size=2 face="sans-serif"><br>
a. regulate the individual cell voltages during charge and discharge</font><font size=3>
</font><font size=2 face="sans-serif"><br>
b. balance the cell voltages during charge and discharge</font><font size=3>
</font><font size=2 face="sans-serif"><br>
c. adjust cell charging voltages due to temperature variations</font><font size=3>
</font><font size=2 face="sans-serif"><br>
d. not provide a continuous float voltage to the battery bank</font><font size=3>
</font><font size=2 face="sans-serif"><br>
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.</font><font size=3>
<br>
</font><font size=2 face="sans-serif"><br>
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. </font><font size=3><br>
</font><font size=2 face="sans-serif"><br>
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.
</font><font size=3><br>
</font><font size=2 face="sans-serif"><br>
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.</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
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.</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
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.</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
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. </font><font size=3>
<br>
</font><font size=2 face="sans-serif"><br>
Given the sensitivity, it doesn't make sense to take on responsibility
for Lion battery management.</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
Management of that sensitivity and responsibility is best left to the battery
bank manufacturer. </font><font size=3><br>
</font><font size=2 face="sans-serif"><br>
JARMO</font>
<br><font size=3><br>
<br>
<br>
<br>
<br>
</font>
<br><font size=3><br>
<br>
<br>
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