Oh Darn … again I find myself saying something that conflicts with an expert except this expert I have great respect for. The following is a few clips from his document.
On the other hand, Red Scholefield (who is often credited as being the Battery Guru in the R/C hobby) has his http://www.rcbatteryclinic.com
website, and openly recommends plugging two packs, each with its own switch, into two channels of a receiver. He even says that the packs don't have to be the same current rating... just the same voltage.
I know you all have made up your own minds but let me give you a couple of things to think about.
The use of redundant parallel fight packs is an excellent way to increase the available flight time and significantly improve the reliability of the on power system.
The dual redundancy concept is to protect against the failure having the highest probability - that being the circuit path from the battery to the power buss in the receiver.
These concerns show a lack in the understanding of the charge and discharge potentials involved in Ni-Cd cells.
Parallel charging of Ni-Cds is not recommended
1. I think the highest probability of a power failure is flying with a dead battery. I have seen it a hundred times, you’ve seen it a hundred time. People take off thinking they have enough left in the pack and it doesn’t make it. THIS WOULD NEVER HAPPEN TO RED SCHOLEFIELD.
What happens if one battery is not up to snuff? True the good battery won’t charge it but the weak battery will put a load on the good battery so the system goes dead even sooner! With a nitro you stand a better chance of getting away with it because of the shorter flights. Not so with a gasser. We set our timers on the transmitter thinking we can make it to the end.
2. If I take a single pack that has the same capacity as the two he suggest and put two switches and two inputs to the receiver then I have accomplished the same thing (failure of the circuit path from the battery to the power buss in the receiver).
But I have also decreased the probability of failure because I only have one battery that can short, go dead or be at low capacity. Simple mathematics…
If you subscribe to the thought that eliminating the switch all together is a good practice you may or may not lower the risk of failure. At least a switch is designed to be connected and opened frequently. RC connectors are definitely not designed for that so you need a regimented policy for replacement to be safe.
3. Red has always been a proponent of Ni-Cd cells. So am I. But do all of you strictly use Ni-Cds? It would be a wrong assumption to take Red’s words on Ni-Cds and directly apply what he says to all the other battery technologies in use today.
4. I don’t think Red emphasizes the charging requirements of using two packs enough. You must not charge them is parallel and you must fully charge both packs if you use two or else the highest probability (power failure) will get you. You become accustomed to getting a certain amount of time out of your batteries. When a source becomes a sink you are in a world of hurt.
The last thing I would like to say is Red’s site is a great place to get a good understanding of battery knowledge. It surely has helped many a newbies, me included. Most of his information is for newbies getting into RC airplanes that typically start with the standard .40 glow. It would be great to get his opinion on the best battery circuit for a gasoline helicopter rather than extrapolate what he has said for other hobbies. I am thinking he would lean for the use of a generator. But maybe I am wrong. Anybody know him personally?
What could be more fun?