RunRyder - Redundancy mixing BEC and NiCad?

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e-Electric Batteries & Chargers > Redundancy mixing BEC and NiCad?

Cpig
Heliman
Location: Colorado Springs

Questions:
1. Can I power my Rx with a LiPo fed 5v UBEC in conjunction with a 4.8v NiCad for a redundant system?

2. If this won't work what do I need for a redundant setup?

Situation:
I have an electric heli and I use a 5v Koolflight UBEC to power my Rx.
I want to add redundancy in case of BEC or battery failure.
I have read the article at Red's Clinic and some posts here on the forum about redundant systems and they say use like batteries. However, I only found one post about someone who used a BEC in conjunction with a NiCad (and he may have fried his UBEC because of it?).

04-17-2008 01:24 AM

MrMel
Elite Veteran
Location: Lidingo, Sweden

1. no, paralelling need to be same voltage,bec dont like higher voltage being pushed in reverse..

2. Either 2 bec or 2 batteries

im not 100% sure ubec work in paralell, but ive run western robotics becs myself in paralell.

04-17-2008 05:17 AM

Cpig
Heliman
Location: Colorado Springs

Thanks Mel

04-17-2008 10:26 PM

pgoelz
Senior Heliman
Location: Rochester MI

With a battery and BEC output in parallel....

If the battery voltage is LOWER than the BEC output, the BEC will try to charge the battery to the BEC voltage at a current limited only by the output capacity of the BEC. Depending on the BEC and battery voltages, this could overload the BEC output and/or damage the battery.

If the battery voltage is HIGHER than the BEC output, the battery will pull the BEC output above its normal output voltage. Depending on the BEC design, this may be harmless.... or it may damage the BEC. You will also rapidly discharge the battery to the BEC voltage level, possibly reducing the battery capacity if it is needed.

In any event, unless you have a way of monitoring the BEC and battery voltages before (during?) and after each flight, I don't see the advantage. Yes, you might prevent a crash in the event of a failure of one or the other power source. But unless you know it has failed, you can be flying without the redundant power sources you are counting on.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com

04-22-2008 06:15 PM

HOMEPAGE

Cpig
Heliman
Location: Colorado Springs

I ended up going with two UBECs from different LiPos. One from a dedicated 2S 800Mah battery and one from the main 10S 4270 battery.
My question now is if these batteries are draining at seperate rates, will one backflow into/through the other BEC in an attempt to charge the other batt?

Paul,
I don't understand how you cannot see the advantage of a redundant system? You state yourself that it "might prevent a crash in the event of a failure of one or the other power sources" - well that is plain and simple the advantage right there. Regardless if you know whether or not one of your power sources failed - it still prevented a crash that otherwise would have happened.
Am I missing something or did I just misunderstand you?

04-23-2008 02:39 AM

pgoelz
Senior Heliman
Location: Rochester MI

What I am getting at is that any dual setup isn't much better than a single setup unless you have a way of knowing that one of the power sources has failed. If one source has failed and you are not aware of it, you are back to a single source..... but you think you have two.

And additionally, unless carefully designed, a dual setup can add complexity and actually decrease reliability. Personally, I would go with a single reliable battery of adequate capacity. Unless a wire breaks, a failure is very unlikely.

Just me though.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com

04-23-2008 03:07 AM

HOMEPAGE

Cpig
Heliman
Location: Colorado Springs

Thanks Paul,
I'll just add both power systems to my preflight checks. I'll just switch the order that I power up my receiver at every flight. That way I can check each system independently every other time I power up. (If I turn on my dedicated Rx power and nothing happens, I know it has failed, or if I plug in my Main Power Batt first..... same thing).

04-23-2008 01:26 PM

Rob_T
Elite Veteran
Location: Tualatin, OR - USA

Just a thought , I've not actually tried this...

The large scale plank guys use a battery backup system that automatically switches between 2 batteries. You might be able to use one of those to switch between BECs or BEC and battery...

Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift

04-23-2008 05:44 PM

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e-Electric Batteries & Chargers > Redundancy mixing BEC and NiCad?

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