ORIGINAL: stratosn
I want to hook up a second battery in a large plane I am building. Some say plug the 2nd. battery in a spare channel of the receiver. Use a 2nd. switch. Then they tell me if one shorts out it will short out the other one, so what's the use. How can I do it right? Thanks, Nick
A short is about the only situation that a dual battery setup won't cover. But also consider what happens with a short occurs in a single battery situation. Same thing.
But what other things could happen, which a dual battery setup would come in handy. Such as a battery goes weak and doesn't hold its charge, the switch goes bad and opens, the battery becomes unplugged from the receiver due to a loose connector, one of the wires goes open, one of the battery cells fail, you connected your charger but it didn't fully charge your pack, etc... In all these cases, having the dual batteries will make a difference. And these are the usual failure modes of batteries, where a short is rare.
To setup a dual battery system, just plug a second battery and switch to your receiver like you did with the first one, but use any unused port in the receiver. The positive and negative pins on all the ports are connected together in a bus arrangement. There is really no significance to the battery port other than it doesn't have a signal lead to it. If you are not using the signal for a channel anyway, its basically becomes just another battery port
Use the same number of cells and capacity as the first battery. Charge them separately (one after the other with one charger, or use two chargers and do them simultaneously), but if you charge one, charge the other one also. Don't charge one battery,
and not do the other.
Also, before each flight, test each battery separately. Use an ESV meter and check the voltage for each battery. They will be very close to each other. Mine are usually within a few 10th of each other after charge, and typically the same or within 1/10 after a flight since they equalize each other. To test the switches and wiring to the receiver, just before your flight turn on one battery and make sure everything looks ok. Then turn on the second one and immediately turn off the first one, and again make sure everything looks good. If everything is fine, both batteries are connected and working fine as independent batteries. Now turn them both on and go fly.