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Lorn writes: <<<<
As I look for a replacement for my
battery, I ran across (suggested by Wolfgang) the following batteries.
At only 2.5 lbs (compared to 25 lbs) and a reasonable $181 price
these batteries appear to be a real breakthrough.
<>Does anyone have any practical experience with the lithium
batteries? >>>>
Your airplane battery has two uses, cranking the engine and
powering your avionics in the event of an alternator failure. The
battery in the above link has a specific energy of 40 watt hours per
pound (12V, 6AH, 2.12Lb). Lead Acid (PbSO4) runs 18 watt hours per
pound (12V, 20AH, 13.5Lb) so the Lithium batteries have about 2.2 times
better specific energy, NOT 10 times. The manufacturer claims the
battery has 18 amp hour PbSO4 equivalent rating, in
truth it has a 6 amp hour actual rating (see their FAQs),
so it will power your avionics for 1/3 the amount of time. In order to
have the equivalent energy storage, you would need three of
these LiFePO batteries (6.2 Lbs & $550).
LiFePO (Lithium Iron Phosphate) is the third(ish) generation of Lithium
battery and the least likely to catch fire. It is the preferred
chemistry for electric vehicles, including electric aircraft. Older
Lithium Polymer are the most dangerous and frequently featured on
YouTube videos for their pyrotechnic characteristics. They have a
higher specific energy and are frequently used in electric RC models.
All Lithium batteries require careful attention and precise charging
with a constant current, constant voltage charger, cell temperature
monitoring and cell balancing. That said, Space Ship Two uses a Valence
LiFePO battery http://www.valence.com/ .
My .02, wait for the cost to come down and reliability to go up.
Regards
Brent Regan
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