Rx with BEC and extra 4.8V NiCd Battery?

[X34]

Attached is a diagram of bec with battery backup. THis system would not charge each other.

[Babylon5]

links at http://www.rcbatteryclinic.com/ Look under parallel operation. With diagram and text.

No regulator here, just normal switch. I fly cheap cheap. Everything I use is budget de.

Hi Baby_zyklon, went to the website and here is my comment and analysis.

The writter mention no diode is required but this is my concern as follows:-

Scenario1
1) Due to a failure , say one of the cells is shorted(zero voltage) The faulty pack average voltage would drop to 3.6V. The good pack at 4.8V would discharge into the faulty pack. It will not maintain 4.8V anymore and will drop to below 4V.
The receiver may not function at 4V .

Scenario2
Assuming the Rx can still function at just 4V
The good packs would continues to bleed current at very high rate into the faulty packs until it runs out of juice.
It may also damage the other 3 good cells of the faulty packs. If the packs run out of juice while in flight then you can expect the worst .

From the electrical point of view, I think the two diode(rectifiers) acting as a one way blocking, with 5 cells is safer.
If one cells is faulty the good pack will not discharge or bleed current into the faulty packs.

Nowadays AAA size NIMH has 900maH capacity putting 10 cells with 2 diodes will not increase the weight significantly for large model compare to 8 cells in parallel with two switches.



Cheers and good luck.

[baby_zyklon]

It is not so much about weight increase, it is the inclusion of more items in the circuit and more things to fail. Try a redundent setup with double switch and our standard electronic today cram into a r50 and you will understand what I am trying to say.

While I think it is possible, I do not think the voltage will drop to 4.0v that fast, at least not within the 1-2mins before I detect voltage drop through on board volt led.

To each his own, you might think the safest circuit is with a diode, for me it is the simplest setup of all and requires no effort. If you think its dangerous, stay away from me when I fly

[Babylon5]

Hi Baby_Zyklon, I always put safety first especially when modifying the circuit in an RC plane. Nicad or NIMH cell fails usually with a short or exhibit very low cells voltages, but occasionally it opens. Cell failure usually fails not in the first flight but subsequent flight.

Do you know why because usually one of the cells becomes weak that is it no longer retain 1.35V when fully charge but drops to somewhere below 1.3V.

When this happen, this weakest cells will experience a reverse voltage during operation (that is when your plane is in the air) by the other three healthy cells(assuming are balance ) .The weaker cell will not damaged immediately but as you operate longer the weaker cells will eventually bleed dry and goes into reverse chemincal reaction and usually resulted in a short or substantial drop in voltages.

If you measure on the voltage on the ground one may l not detect this problem immediately .

I think so far you are lucky but if I were you I would not want to take this chance.

Cheers and good luck

[Ghostfit]

To each his own, you might think the safest circuit is with a diode, for me it is the simplest setup of all and requires no effort. If you think its dangerous, stay away from me when I fly

Not saying if you're right or wrong Bro ! ....but with an attitude like that, all those who are serious about the hobby here will be concerned !

Remember, if you screw up and something happens .....you are screwing the other bros here too ...especially if the GOV acts and put a nationwide ban on RC flying !

You may think your nitro heli is a toy ! but let me assure you that you wun look at it the same way after you lose control of it and it goes off into a crowd of spectators.

Dun mean to flame you or anything ! ......but that last comment kinda sparked off something inside my head

Incidentally, where do you fly ?

[baby_zyklon]

Ghostfit...eh u really like to start flaming ppl....
can u see the at the end of the senstence....it wasn't intended to be serious....

n btw, though I can't deny the possibility of lvc even with another pack after prolong period, I believe running two packs without a diode don't put me any less safe than any tom dick or harry who runs only 1 PACK AND 1 SWITCH. At least I can confidently say that my heli will still function good and well even if one of my switches die in flight , even if one of my batter connection/wire break in flight, can you, can everyone else??

Babylon5, actually I had a cell failure in rx pack before. Not in flight though, the pack fully charged voltage just got lower and lower and then it just died, 0v. Suprisingly, my 4 standard 1 digital servos were still working with only that spoilt battery pack on the bench, just that my voltwatch was showing red. So I would assume with full digitals n load, the servos will just quit working, but if there is another rx pack supplying power, it will continue to work even with load.

Its actually very easy to detact packs with faulty cells. The voltage will drop a lot to as low as 4.2v just by cycling the sticks and no matter how you slow charge fast charge charge and charge also same problem. IMHO, cells don't go from very healthy to dead within 1second that often, they usually show ample warning signs. Do also take note that some digital servos can draw more amp on ground than in flight just by cycling them violently on the bench and I am not talking about hover, but light 3d. Why? I also don't know.

Since it seems like we are going into a unresolvable debate, why not lets find a pack with 1 dead cell and do the experiment. That will thoroughly resolve any myth about dead battery packs.

[Ghostfit]

Ghostfit...eh u really like to start flaming ppl....
can u see the at the end of the senstence....it wasn't intended to be serious....

I guess you didn't read until the end of my post ....let me repeat it here :
"
Dun mean to flame you or anything ! ......but that last comment kinda sparked off something inside my head"

I dun go around flaming 'pple for fun and can understand if you meant it as a joke, but it gave me the impression that you dun care about safety.
I am sorry ! ....but when I percieve a threat to the future of this hobby, I will get vocal about it even to the extend of being labeled the "pai nan" ....I may also make a few enemies .....but at least, I've done my part to inform and possible help avert an accident.

You are flying a nitro heli and any mishap would be quite hard to ignore ....I give you an example: ....the Gov is trying to open up Singapore's water ways for recreational activities .....everybody wants to get in on it .....just need an accident .....like the recent drowning at Seletar ! ....that puts a damper on the activities ....now the authorities are using a magifiying glass to look at the safety aspect of those clubs making use of the bodies of water.

I do not know and have not meet Babylon5, but it appears that he is trying to advise and warn you of a possible danger and your reply is that so far you have no mishaps and so he is wrong .......thats like telling someone who informs you that you should charge lipos on a non-flamable surface that he is bullshitting as you never had any lipo fires before !

Anyway, as I've said .....I'm not flameing you, just trying to let you know the impression you're creating.... ......and now thats done, I will not continue any further.

Cheers !

[baby_zyklon]

1. I DO NOT think babylon is wrong. Nobody is wrong here. It is just wheather is it applicable to that particular flyer or not. My setup only allows for a full 7.5mins of flying before my tank is empty. I top up both my batteries after every flight, which is why I said that I do not need a diode because in a short flight time like that, it is almost impossible for one pack to get pulled down by another if one fails. If I am flying a 30mins/flight gasser running two small packs, that probably will apply to me, but I am not.

2. PLS think before suggesting that I am doing things in the dangerous way and that I hack care safety and advice from fellow forumers. If in the event of a mishaps, one of my packs fail. I DO NOT see how a normal flyer running only 1 pack will be more safe or stand a better chance than me.

Your lipo analogy about me isn't very correct either. I believe my situation is more like I acknowledge the possibility of a lipo fire and I charge my lipo in the flower pot, whereas the typical flyers running only 1 rx packs can be said as charging their lipo w/o a sack or a pot. And babylon is trying to suggest to me to try using a lipo sack and I am telling him a pot is enough for me.

Lastly, I have had RX pack fail in flight before, it wasn't total failure, but intermittent disconnection because the battery stripes(those metal pieces that connect between batteries) wasn't holding well and no it wasn't some diy pack, but a original futaba pack. It was scary. In my 15years with nitro including runaway heli and runaway car also, I believe I have been through enough incidents to be not labelled as "aiya you don't bullshit me lah, I never had that happen, you don't come here bluff people lah".

[Babylon5]

Hi Baby_zyklon, I think this topic is getting more interesting but let us not get to heated up but look at the analysis and topic of discussion objectively.

Speaking for myself, I would usually look at the circuit and analyse and explore its strength and weakness before I make a decision.

Likewise when you gave us the link the the website , I look at the circuit and analyse and gave you the analysis . I also pointed out the weakness of the systems and two batteries(two switches packs in parallel)so that reader can decide and make informed choices.


It is really up to you.

As far as I am concern I would not want to try the two switches and two batteries packs in parallel as it does not look quite right and fool proof.

I would like to use the two packs & 2 power rectifiers diode method because I think it is simpler and no switches is required and "no worry" systems. If one of packs fails it will not effect the good packs in anyway.
The only weakness is this setup is voltage is on the high side when the NIMH or NICAD is fully charge ,so need to check that the Rx and servo can operate up to 6.5 to 7V.

cheers

[Ghostfit]

In my 15years with nitro including runaway heli and runaway car also, I believe I have been through enough incidents to be not labelled as "aiya you don't bullshit me lah, I never had that happen, you don't come here bluff people lah".

Okay, .....No hard feelings Bro ! .....sometimes on the road, you see these chiong cars with a sticker that says "If you dun like the way I drive, get the heck outta my way !" ....I know it's a joke but the impression it give you is that the driver doesn't give a hoot .... ....and sometime these drivers drives like what the sticker says !

I guess with 15 years in this hobby, .......you should know what you're doing !

....cheers and stay safe !