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Old 03-04-2017, 09:28 PM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 9,803

Originally Posted by Larry DeCamp View Post
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 was poking around on the EarthX website last night. Turns out they recommend using a diode between the main battery and a small backup battery, to drop some voltage on purpose, and thus limit charge current. The graphs don't make much sense to me, but here, read for yourself:

Originally Posted by Alan Carroll View Post
Presumably you also have a way to check the backup battery voltage during preflight to make sure it actually has a charge? (the fusible link won't let you know when its blown)
Previously mentioned I was looking at some very inexpensive voltage monitor boards. Ordered two kinds, and I've been playing a bit on the bench tonight. This one seems to be the ticket:

Costs a whopping $4.59. Voltage readout matches my trusty Fluke. Easy to set upper and lower limits in 0.1V increments. Closes an on-the-board relay if voltage reaches either limit, and sets off a buzzer. It will watch voltage on the #2 ignition's battery bus all the time.
Dan Horton
Barrett IO-390

Last edited by DanH : 11-15-2018 at 08:07 AM.
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