Rx-seperate battery ?

[Geoffrey Harris]

Whilst charging a battery one of the supply leads parted company with a connector and it struck me that had this happened during a flight not only would I have lost power to the motor but also to the Rx and therefore all the controls. So,as a safeguard would it be sensible to fit a seperate battery and if so does one leave the battery lead from the esc/Rx unconnected as the power would now be supplied by the dedicated battery, or should it still be connected.

[Peter Beeney]

Geoff, you’ve hit bullseye! Right in the middle! Something that I’ve advocated for years! And it’s not always due to a connector parting company that you can lose the main battery, either.
If your BEC supply is 5 volts and you use a 4 cell rx battery then just pugging them together won’t notice although there is a massive aeromodelling consensus of opinion that says they must not be connected in parallel. So it doesn’t really matter much either way. If you use a 5 cell battery leaving them together will always keep the BEC regular shut down anyway, again it’s not obvious, but there’s little point in this so you can disconnect just the red wire from the ESC. Leave the black and signal wires in place.

If you want a more in-depth description of the situation when batts and regs are connected together it’s been described in previous threads, but we can cover it again if you wish.

This is something that personally I would do on any thing but the smallest and lightweight of models.

Good Luck!

PB

[Peter Beeney]

Silly forum, it can’t count! It doesn’t know the difference between single and double posts!

PB      
 

Edited By Peter Beeney on 04/03/2012 15:51:36

[Daithi O Buitigh]

As far as I know, disconnecting the centre red lead will do it (Pete Lowe covered a two battery setup, albeit for retracts back in the May 2011 issue)

However, while I won't dispute that a failed connection will result in loss of control, have you considered what would happen if the Rx battery failed in that way - the motor would keep running and you would still have no control which would be a tad worse than no control and a dead motor

[Tim Hooper]

Posted by Daithi O Buitigh on 04/03/2012 16:00:24: - the motor would keep running and you would still have no control which would be a tad worse than no control and a dead motor

I'm not sure about that, but I expect somebody will be along soon who can tell us for certain!

Geoffrey, I see your point about the seperate rx battery, but there's a school of thought that contends that every addtional connection/switch is just another potential point of failure.

I think the lesson here is to make sure that every battery connection is securely soldered to its cabling.

tim

[Peter Beeney]

I have a funny feeling that if the rx battery failed there would now no longer be any signal to the ESC which would now (hopefully) cause it to shut down. Were this not the case then it’s wide open to the same situation on say a loss of signal etc. Certainly this has been the case on the ESC’s that I’ve owned, the first thing that I would try. If an ESC did not shut down on loss of signal I personally would not be using it, and I would consider it a serious safety issue, too.

I’ve lost the main battery twice, admittedly on a hotliner where I was seriously caning the flight pack, which I fully accepted. I was able to land quite safely both times. This was using nicads, the overload burnt through the connection inside the cell, which needless to say went instantly open circuit, one of which I cut open and repaired. It ran as a glow driver for a while.
My view is that if a rx battery is treated correctly, with occasional capacity checks etc., then it is relatively unlikely to suffer from any sudden failures anyway. They only appear to fail suddenly because the owner has probably totally disregard them; and have most likely been sailing very close to the wind for a long time. Compared with the flight pack, the rx pack has the Life of Old Riley, really.

For a number of reasons, I will always consider a separate rx to be the safest option.

But, as with everything aeromodelling, it's all down to an individual choice.

PB

[PatMc]

I completely disagree with your conclusions, Peter. BEC has been around long enough now to have shown it's reliability in practice.

IMO a flight pack with BEC is inherently more reliable & less likely to result in a loss of control than a discreet Rx battery even when the latter is in a pure glider or ic model.

I'd be more concerned to find out why the OPs battery connector joint failed in the first place.

[Alan Cantwell]

never had a joint fail yet, as Pat says, investigate, and rectify, i would be interested in what make the lead was though, and if it had been strained, modified, or just of poor quality, thinking of all the connections in any model, it would not be possible to 2nd guess every connection

[crispin church]

if the model needs extra weight for the cg then why not use a battery for rx i use A123 and last for ages when making joints in your leads use a good solder and clean all and tinned the wires and conectors and dont use low rated switches

[PatMc]

Crispin, are you referring to ic/gliders or e-power with the potential to use a BEC ?

If the former - fair enough but if the latter it's just an unecessary complication.

[Geoffrey Harris]

Thanks for your responses which are appreciated Being fairly new to electrics I find it to be something of a black art as I also do with soldering. I would point out that it was not the actual battery lead that failed but the connecting lead which I think failed due to flexing at the point where it was soldered, sadly all my own work. There is a possibility that the wire was not ideal but I have now purchased some silcon wire which should be more pliable. I am aware of dry joints etc. so must keep practising.

However the incident highlights a" possible" future weakness and having seen both sides of the argument I am somewhat in limbo until I perfect my soldering techniques, so I might adopt the belt and braces approach.

Any other thoughts will be appreciated as it becomes obvious that it is quite a large learning curve.

Geoff.

[Peter Beeney]

PatMc, Yes, I’m very sorry, perhaps I didn’t make make my reasoning quite clear enough. I have no qualms at all about about using a regulator, as I’ve said many times before, to destroy such a device, and indeed most solid state contraptions you probably have to give it a clout with a small hammer. Or perhaps with a severe overdose of voltage perhaps. However, I firmly believe that if you ain’t not got nothin’ going in, you won’t be getting now’t coming out. And that can easily become painfully obvious! Quite rapidly.
So whilst I personally would totally accept the reliability of the BEC, it’s the whole system I’m not so happy with. One argument might be that the rx battery is a dedicated one job unit, the flight pack is doing two jobs. But I’d consider that a rx battery, in known good condition, i.e. one that has regular checks and is in a reasonably sound installation such as secure locked plugs and sockets, plus very importantly a modern voltage monitor is just about as reliable as it gets. I’ll agree that the same could be said about the flight pack, but if it becomes overworked for whatever reason anything can happen.
Certainly I’d also be very concerned about Geoff’s dodgy connector. However, I think it might well be the case that a brand new ESC could be assembled with just the wire end pushed into the bullet solder buckets, no solder, just heatshrink. That might work ok a couple of times, so how would you know, short of cutting the heatshrink off and inspecting? How many modellers do that? I have seen almost that, a perfectly dry soldered joint that pulled apart after many flights.
Also soldering can sometimes require a second look. I’ve seen one or two suspect areas so I ask if I can do it properly. Or at least, what I think is correct. I’ve found that adults and youngsters alike as beginners are always keen to learn, so I try and help when I can.

I think it’s a bit like the seatbelt syndrome, many drivers will never need the seatbelt in anger, but for those that do, if they are not wearing one it’s far too late.

Also I’ve always thought the BEC to be something of a cobble up anyway. A regulator installed in say a piece of high quality hi-fi equipment will most likely be mounted on a sophisticated piece of heatsink and the input and output will be in well defined limits. A regulator on a ESC is out of anyone’s control, anything can be connected to the input and output. Also living on an ESC, which is maybe also getting hot, and little or no heatsinking. So a little bit evidence of it’s resilience, perhaps. However, I’ve related the story before of the model that crashed because the pilot had not connected the battery in parallel with the BEC on one occasion. Unfortunately not everyone is totally aware of volts, amps and watts sufficiently to be able to get it right all the time.

I’m sure that people often completely disagree with my conclusions, I don’t have a problem with that at all, as long as my own models are within my own spec. But I’m always concerned when there is a crash due to a failure that can easily be avoided.

Anyway, each to his own, all good discussion, plenty of yet more confusion for the beginner…

PB

Edited By Peter Beeney on 04/03/2012 21:36:33

[Chris Bott - Moderator]

Personally I'd rather use a BEC than a Rx battery. Then I get a fresh Rx supply every time I change the flight battery. I use the BEC in an ESC for small models, and a separate Switching BEC in larger models.

This way I don't have to use any of those horrid NiMhs, I don't have to charge them, and I don't have the extra failure points of more servo plugs sockets and a switch.

As Peter says, it's a personal choice.

[Trevor Crook]

Geoffrey

I couldn't see in your posts whether you had used heatshrink over your joint. If you don't, even silicone wire will fail as it will flex at the end of the solder and fatigue. If you cover the joint with heatshrink, the flexing will occur at the end of the heatshrink, away from the solder, and should be fine.

[Vecchio Austriaco]

I suppose it is also a question of voltage - with a conventional (analog) BEC I would not go to 6 cells - use it rather only for 3 of 4 cell models. With an S-Bec it should be ok. In any case I prefer a sepaerate battery on larger model having larger and higher voltage batteries. There will be also no weight issue for a seperate RX battery. Example: Sebart Angel 50 - 6 cells - seperate RX battery. Yak 54 - 1100mm - 3 cells - BEC

Regards VA