Charging EI backup battery ?

[Carl Froehlich]

Colin,

What battery are you planning to charge with this?

I’m confused, why not just charge the batteries using the alternator? For that matter why a “resistor trickle charge”?

Carl

[WingsOnWheels]

Originally Posted by Carl Froehlich

Colin,

What battery are you planning to charge with this?

I?m confused, why not just charge the batteries using the alternator? For that matter why a ?resistor trickle charge??

Carl

Not using a full-size battery for backup. It would be a small 4ah AGM or similar. Connecting directly into the system with the PC680 would result in overcharging that little battery.

[Carl Froehlich]

Originally Posted by WingsOnWheels

Not using a full-size battery for backup. It would be a small 4ah AGM or similar. Connecting directly into the system with the PC680 would result in overcharging that little battery.

Sorry, no. Healthy batteries in parallel do not act that way. There is no issue with having different size batteries (assuming same chemistry) in parallel on an alternator. Each battery only cares about terminal voltage. From that it will draw whatever charging current it gets based on battery internal resistance.

I also suggest that a 4ah battery is far too small for an electrically dependent engine backup battery.

PM me if you want details.
Carl

[WingsOnWheels]

Originally Posted by Carl Froehlich

Sorry, no. Healthy batteries in parallel do not act that way. There is no issue with having different size batteries (assuming same chemistry) in parallel on an alternator. Each battery only cares about terminal voltage. From that it will draw whatever charging current it gets based on battery internal resistance.

I also suggest that a 4ah battery is far too small for an electrically dependent engine backup battery.

PM me if you want details.
Carl

I'm no battery expert, that is just based off what I have read here. If that is the case, why do TWC and companies like that get such a premium for their backup batteries?

If I can get away with just the diodes, that is one less component to fail, so sounds good to me.

The backup is only for the ignition. Average current draw per side should be less than 1.5amps. So the 4ah battery should give me up to an hour assuming a total electrical failure. SDS backup uses a 2.9ah battery, but I'm not sure if that is for a single or dual system.

[RVDan]

If you use AGM battery, which is a lead/ acid chemistry, internal resistance is high enough to self limit charge current to an acceptable level. You can connect directly to the bus for charging.

If you are talking about the TCW battery, the cells are LiFeO2, which have very low internal resistance, and will not self limit without a control circuit.

[WingsOnWheels]

Originally Posted by RVDan

If you use AGM battery, which is a lead/ acid chemistry, internal resistance is high enough to self limit charge current to an acceptable level. You can connect directly to the bus for charging.

If you are talking about the TCW battery, the cells are LiFeO2, which have very low internal resistance, and will not self limit without a control circuit.

Ok, that makes sense. This is why the forum is so great, get to learn something new every day.