Bill Schlatterer
Joined: 09 Jan 2006
Posts: 195
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 Posted: Sat Jan 05, 2008 12:17 pm Post subject: Aux Bat Charging Circuit - Small battery limited to 3 amp c |
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Wondering how this works ? Help appreciated!
I have a 7ah battery on a separate bus for EFIS(alternate power) that is not directly connected to the main bus during starting or normal operations. However, I do have a charging circuit off the main bus through a D25 diode which should put 14.4 - .6 or 13.8 volts to the small battery during normal operations to keep it charged. It is a fused circuit and intended to be hot anytime the main bus is on. That way the Aux Bat should be always charged, available to run the EFIS before and during starting with no draw on it, and not drain back if the main bus is off. And no switching required during normal ops.
The Z35 Light Aux Bat figure http://www.aeroelectric.com/PPS/DCPwr/Z35K_Light_Aux_Battery.pdf is similar except that I think it is intended to be turned on after starting and not be available from before to after starting.
My question: It was just pointed out to me that the 7ah battery has a 3 amp charging limit (per B&C spec sheet) and I am wondering if there should be a resistor in this circuit to limit the charging current? I see that the full size batteries do not have a charging limit. Is there any danger if the smaller 7ah is fully discharged that it could draw enough charging current to damage it without a limiting resistor.
If it does require a resistor for the small battery, wouldn't the same thing apply to the Z35 figure since you could easily have a fully discharged aux bat, start the airplane, and then hit the switch putting full current to the fully discharged battery?
All comments appreciated.
Bill S
7a 80/80
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