charging lithium batteries with an alternator
charging lithium batteries with an alternator:
While an alternator looks like a foolproof way to charge a 12v battery, there's an unobvious hazard when it
comes to charging a lithium battery.
In a nutshell, lead-acid batteries have a much higher ISR (internal series resistance) when charging, while a
lithium battery can present a very low ISR when charging. This means charge current on lead-acid batteries
tend to be self-limiting and alternators will tend to have their max current ratings at an appropriate level
to prevent damage, so most alternators don't have current limiters because they're unnecessary.
Lithium batteries, with their low charge ISR, can present much higher charge currents, running an alternator
near or over its rated current. This alone can damage an alternator. This problem is magnified when running
the alternator at a lower speed, because the cooling provided by the alternator's internal fins drops much
faster than the charge current. So a combination of current at or over rated capacity and cooling far below the
normal level can smoke the windings on an alternator.
