Battery Management
AGM / Lithium Battery Monitoring
Updated 9/07/09
The BATMON Battery Management Interface is a small but powerful tool in managing the battery state
during charging and EV operation. The BATMON is fully optoisolated and communicates between the
PFC Charger and Power Center systems during Charge and Run states to alleviate many of the pitfalls of
building your own Electric Vehicle. Since the battery pack is now under constant observation, reversing
cells within a battery are a thing of the past.
So what batteries can I use with this EV Kit? 12V AGM batteries from Hawker Genesis, NPX,
Marathon, Optima, Deka AGM, Deka Gel, Trojan Gel, LifeLine, Universal Battery and Werker. Other
battery mfg’s may be similar and require verification of charging temperature compensation. 6V AGM's
can likely be done as well. And the newest below, ThunderSky's 3.2V LiFePO4 for use with the LionMon
battery monitor. More to be added moving forward. An interesting note is most AGM's 20 hour ratings
can be multiplied by 0.6 to get a realistic 1hr rating. Unfortunately I haven't found the factor for a 30 minute
rating just yet, where most EV's batteries will be used. Its possible the Ah rating could fall under 0.5, or
half of the 20 hour rating

Some of the BATMON features are:
The LVP threshold is 10.7V
The OVP threshold is dependent on battery temperature
Very low standby current ~ 1mA.

The BATMON is calibrated for either AGM or AGM/GEL type temperature compensation profiles at the
factory. The BATMON has an onboard diverter circuit which turns on an external load resistor to keep a
battery from being overcharged in a series string. It has a 5A capability, which allows faster charging and
safer operation against overcharging.
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Just a note, if the clamp circuit does not have enough capability, you can still overcharge a battery with a
battery management device. With only a 1-2A clamping capability, batteries can still be overcharged in a
series string if a few batteries are weaker than the rest of the pack. Careful management and interaction
with the charger is needed to ensure safe charging.
Now available (with system purchase) is a Lithium Ion Cell Monitor for LiFePo4 cells, with a high limit of
3.85V (China High Power) or 4.25V (ThunderSky) and low limit of 2.1V for (CHP) or 2.85V(TS)
threshold levels. Other threshold voltage levels available upon request. Additional system cost due to high
number of cells monitored (up to 44). Note that other voltage trip levels can be accommodated!
Photo of China High Power 100Ah cell
with LionMon attached. CHP cells use a
lower charge voltage (3.85V) and cutoff
(2.1V) levels that can be used on the
LionMon board.
Low volume pricing on the CHP cells is
currently $1.4/Ah. Larger volume
purchase can lower this number.
Here is a pic of the CHP cell installed in
series with the Lead Acid pack for
testing purposes. Read more