LiFePO4 Batteries for aircraft
(Click on images for larger view.)
I decided to try the new LiFePO4 Ballistic EVO2 batteries to replace the SQ2000 rear PC680 cranking battery.
A single 12 cell Ballistic with 410CCA did not have enough cranking power for the TCM IO-360.
The PC-680 is rated at 210CCA but it has 680CCA for the first 5 seconds which is enough
to crank the Franklin and the TCM IO-360.
Adding a second Ballistic 12 cell and connecting them in parallel gave plenty of cranking power.
The parallel combo still weighs only 5 lbs with 14AH charge capacity compared to the PC-680 14 lbs with 10AH.
Note: PC680 specifies 16AH but that is at 20 hour discharge rate (0.8A). At a realistic 15A current the
rating is about 10AH - after which voltage drops below 10.5V and current draw is near useless.
Will do more testing and report flight performance later.
Connect the dual, parallel batteries with short equal cables or connection straps
- at least 4 gauge. To prevent possible unequal charging and unequal high current discharging,
stagger the starter/ground cable and other cable connections - one battery to have
all ground connections and the other battery to have all power connections.
Ballistic EVO2 have a 20A charging limitation. Two batteries in parallel
should then have a 40A charging limit - more in line with typical alternator
output. Ballistic specifies batteries be charged
13.8-14.4 volts. They can be maintained at 13.6 V.
A heavy current diode from alternator to the battery will reduce the
typical alternator 14.5V voltage to a suitable 13.8V.
However from available literature on LiFePO4's elsewhere
it seems 14.5V will not hurt the battery.
Occasional cell balance charging will
lengthen LiFePO4 battery life. When balancing parallel batteries,
disconnect one strap (as shown - or install
a quick battery disconnect switch.) and
balance each battery individually.
Ballistic sells their own ballance charger. Best price I have seen
Battery discharge limits:
It is advised to not let the battery get below 9V.
And if it gets below 6V the battery is a goner - bye, bye $300+.
Make sure not to leave anything on that might drain the battery after shutdown.
Other LiFePO4 Batteries:
You can get individual battery cells and build your own battery. The unit on left
is a four cell (prismatic = flat), 40AH battery from all-battery.com. They kindly
included the connecting straps. The battery is about the
size of a PC925 lead-acid but half the weight and twice the charge capacity.
Got it after deciding to replace my front battery too. This should give over two
hours current in case of alternator failure. Home made adapter for hookup to
Ballistic balance charger is shown.