Hi guys

Any suggestions please on a good on-board battery backup system for jets.

Current jets are a Strikemaster(TJT3000) and MB339 (PST600) using JR 10X radio. I shudder to think about my single Sanyo 1500 mah Rx pack failing and wondered what people are using??

Cheers.....Rene
New Zealand.......Home of the America's cup (but I feel not for long)

Read latest "JetPpower" mag. for a product review on a battery backup system, regards Fank.

Thanks Fank.........have you actually used this system? or are you qouting a review?

Cheers

I have converted many jet jocks to this....

two 1650 NiMH packs.. all wrapped as one pack with
two 18" leads

These cells are reg AA sanyo cells and with over 3000 mah
you will not need to charge all day... (we still do)

I will have a few at FL Jets to show.

Eddie Weeks

I'm using a system similar to that described in RCJI, but plan to purchase the unit in the review. Reagards Frank

Thanks Eddie, that sounds like a plan! I presume these packs go thru independant switch harnesses into 2 Rx positions ie: battery and a spare channel??

Thanks again.........Rene

I use two independant Nicad or NiMh (like Eddie is saying) packs into two good switch harnesses into the Multiplex 12 ch receiver. That RX has a built in isolation circuit and always draws from the strong pack. If your receiver does not have this built in, you can use the Electrodynamics Battery Back R, or some similar product. In addition, I have an Electrodynamics voltage display unit. When I am ready to fly, I power up one pack, wiggle the servos and check voltage, turn #2 on and #1 off, do the check again, then turn #1 back on and fly. Works great!

Hi Rene

Have you checked this link: http://www.fly-giantrc.org/technical/parallelbatt.html

Two battery pack in parallel while connected to the rx, but with seperate charge jacks.., interesting reading.

I've installed this in my Starfighter (JR rx) and have had some flights with no problem.

Regards
Gordon.

Isolation circuits (back up) to draw off the strong pack is not a very good concept. As the pack under load is always going to be weaker than the pack not under load. Thus constant switching is done back and forth between the two packs. Sometimes with dire consequences, especially if the timing threshold is slightly too long, and some of your electronics (ecu, gyro, etc...) may have to re-initialize.

I've seen this to cause engines to flame out. The ecu didn't like it.

I am not certain, but I think that the MPX receiver does it with a simple Zener diode circuit. However it works, it works very well with never an issue. Same with the Electrodynamics thingy, when I used that.

The Multiplex RX switches off or isolates the battery pack that is deemed unusable and switches onto the back-up battery pack? Is the ill battery pack completely disconnected internally from the power buss? If so WOW...

Why not just use two batteries and switches as others have mentioned. Cheap, simple, perceived failures are the lowest of any other system... AND it works flawlessly... The perceived drawbacks are negligible. The only decent argument against this method is a shorted cell which subsequently takes out the battery pack and eventually the back-up battery pack. But this isn't what happens, the cell simply becomes an OPEN conductor and passes energy as if it was't even there.

I have numerous GS Aerobatic models rigged this way, in fact I believe that more than 90% of the GS models out there use the dual battery/switch system for redundancy.

As I stated above, I think it is a simple Zener diode circuit and it too works flawlessly, is integrated into the receiver, and I don't have to worry about whether or not cross charging really happens. Of course, in 30 years of flying R/C I have only had one cell ever go bad.

Thanks for all your suggestions guys.......big help!!

Looks like I'll go for the twin battery packs and harnesses, thanks for that link Gordon it certainly is well worth a read!!

I have also done the twin batteries and harnesses in the past with good results. In fact, I have never had a battery problem at all except for that series 1973 Kraft Sport Series in my 40 Kaos circa 1975, and that was no doubt my fault as I did not know diddly about NiCad care. Off to Florida!!!