Originally Posted by Larry DeCamp
I purchased duel ignition units for SDS CPI system. Ross sent me a schematic for a 7AH battery to power the second unit as backup. My question is, can I use the main buss alternator voltage to charge TWO Earthex batteries. The second to power one ignition as backup if needed.
I asked Kathy at EarthX about this and she pointed out that their batteries are limited in maximum allowable charging current. For the ETX12A for example this limit is 20 amps. I noted that in a backup capacity the battery would normally be at full charge and thus would likely never pull anywhere close to 20 amps. Kathy nonetheless felt that the backup battery should have a charging current capacity equal to or greater than output capacity of alternator that was charging it. So, the backup battery would either need to be relatively large (and expensive), or else it would need to be charged on the ground rather than via the main aircraft bus. The latter is probably not a bad solution since these batteries are supposed to hold their charge well?