I wanna run a backup rx battery in case my rx battery fails. I got a couple questions though. I'll have to use 2 different batteries,but all are nimh's. 1) Can I use one 6v battery and one 4.8v battery(yeah I doubt it). 2) Can I use 2 different nimh 6v batteries,but with different mah's?

Thanks.....

Different voltages: No

Different capacities: Yes. I've done this on a couple planes and found each battery was drained proportionally. For example, each battery would be drained by say 40% of it's capacity at the end of the day. (not exact numbers, just an example)

I'd also use a separate switch for each battery to add redundancy there too.

Chuck

Hit the Nail on the Head.


Bob

Dang Chuck, I was always told to run the same size battery and always wondered about that draw question, thanks. Always the two switches!! I have had several switches go out but only one battery.

Hi Jester,

http://www.precisionaerobatics.com/p...ls.php?pid=272

This device is solid state with no moving parts to wear, vibrate and fail, it turns on and off with a magnet, takes all types of batteries and monitors battery condition as well as drawing equally from each battery. I use these in my more "precious" models. No I don't work for the company.

Cheers,

Colin

Hi Crash,
What device? At least on their US website, they don't seem to have anything like you describe. What is the name of the device? What category is it under?

Sorry if it was obvious, but it's not idiot-proof obvious.......... Thanks

Gray Beard,
Remember, voltage is the pressure that delivers the mAh, the amount of energy stored.
Think of two buckets of water (mAh) with pumps (volts) on each one.
The voltage or pressure needs to be the same or all kinds of problems happen.
The higher voltage will be trying to push its current into the lower voltage battery.
However, the receiver will take the amount of energy it needs to run.
Therefore, the difference in the capacity doesn't matter.
It doesn't care who gives it to him, if it is available he'll take it.
If one runs out he'll take it from the other.
If the second one runs out.... we all know what happens then.
Hope this helps,
KW_Counter

I was always told it would deplete the smaller battery first then the bigger battery. I didn't buy this so I tested it for myself. They always were drained proportionally. If a 1000mAh battery was drained by 200mAh, a 2000mAh battery in parallel would be drained 400mAh or both by 20%. Now I will say that I do always use packs from the same manufacturer, same brand of cells, etc. That might make a difference, not sure.

Hi,

It is on the Australian web site under large model accessories, click on the Australian flag. It is a german Emcotec switch that allows you to use two batteries of any type. I have been using two for over three years since I nearly lost a model when a mechanical switch self destructed.

Cheers,

Colin

I dont like adding complication to simple electronics myself I like the KISS method Keep It Simple Stupid.

although 5V relay circuit might work for whatever pack mah or voltage would have to sit down draw it out and find the relay (digikey is a good source), switching between batteries using a normally open contact on one pack and normally closed on the other. One pack would power the circuit closing the relay and sending its power to the switch and all the radio components when this battery failed or dropped too low the relay would open up and switch to the other pack.

That's what I was told so I have always just bought the same size batteries for a plane. Because I often have packs of different mAh sitting in my shop it's a good thing to know.
Crash, way cool device/switch. A bit out of my price range at the moment but I have a couple of planes I would like to have it on!! They just keep coming up with better and better equipment every time I look. Sure beats the days of going into radio shack to buy my electronics!!

Hi Gray Beard,

Yeah they arn't cheap but neither are some of my models. Don't forget that if you looked at the Australian site one Oz dollar is currently about 84 cents US, so the prices arn't quite so scary for those in the USA.

Cheers,

Colin