Built in LiPos

[Tony K]

On BEB's "Tiffie" thread Steve Hargreaves wrote, "...why not "build in" your Lipos & charge them in the model......?"

Is this worthy of more discussion?

BEB wrote, "I know that traditional wisdom says "don't charge lipos in-situ" - but with modern "smart" chargers that know if you set them up wrong (and then refuse to work!) I too think the danger involved in this has become very small indeed."

Is there a real danger or risk?

As a relative newcomer and after reading some of the dire warnings, I was a bit worried about charging these things indoors but it is really a non event.

Danny Fenton made the point that LiPos are not as reliable as 123s, which may be true, but does that mean that they are more dangerous or more risky to charge in situ?

[Tony Bennett]

i have often wondered about this.

it would make life so much easier if you built in the lipo, save on hatches and wing removal.

plus if it is a fully scale model, it will not be flown all day every day, so having it on charge for an hour while you fly some thing else would not be a problem.

i suppose you could line the battery box with fire proof material of some sort.

[Biggles' Elder Brother - Moderator]

I think its a "non-event" if you do it right! Otherwise it can become a very big event!

Thinking about this I still believe its possible to do it safely - but I'm thinking that you would need a charger and balance connector all keyed in such a way that it was impossible to do it wrongly. Also, as I said a charger that would detect if the wrong setting is selected and refuse to proceed.

But with that - and maybe Tony's idea of lining the comparment with the stuff from a Lipo charging bag just so if it did all "go to hell in a handacart" then at least the whole model won't end up ablaze from end to end - then I'm coming round to the idea that this might well be possible in a safe manner.

BEB

[Tony Bennett]

i would have thought so.

line the battery box. fit the charger points to the side of the fuselage under a panel.

then plug in the charger and balance plug and charge away.

in suppose the only problem would be if you ever need to remove the battery at some point.

but if you use a new battery i would expect a good years worth of flights before you might have to think about changing it.

[Martin Harris - Moderator]

Didn't Boeing build their LiPos into the Dreamliner?

[Biggles' Elder Brother - Moderator]

A valid point Martin. <- On Boeing's behalf!

Picking up Tony's point, the Lipo doesn't need to be so built in that you'd never get it out without taking the model apart. You could install it with a view to being able to replace it without too much trouble if you had to, but equally you wouldn't have to worry about it being accessable on a "minute by minute" basis.

BEB

[Tom Sharp]

Posted by Martin Harris on 08/08/2013 23:54:12:

Didn't Boeing build their LiPos into the Dreamliner?

[Tony Bennett]

a screw on cover to the battey box.

hide the screws in a panel line or some other feature.

then there would be minimum damage if you ever had to take it out.

but you would not have the huge gaps that a removable hatch normaly creates.

[Martin Harris - Moderator]

In case Boeing's lawyers are watching this thread, I would like to point out that I thoroughly enjoyed flying my splendid Boeings this afternoon - PT17 Stearman and Blue Angels F18 Hornet - and although the Stearman uses old technology internal combustion (safely contained within its cylinder wall) the Hornet managed not to ignite its LiPo at any point!

[Phil 9]

if you build in the lipos compleatley you have an in built limit to the life of the model. If you have a screw on cover you are limiting your number of flights when at the field. I would not like to make the effort to build a model only to have it at the field on charge for most of the time. IMHO you either need to be able to change the batteries after each flight or top it up with liquid fuel and if you cant you might as well build a static model

[Frank Skilbeck]

One other point, is that if you have a short in the aircraft, you'll need to be able to unplug the battery quickly. So it's not just charging you need to be concerned with.

But having said that one of our club members brought in a Lipo which I think he charged on Nimh setting, it was a 3s blown up like a football, it measured 14v on the battery monitor, we hooked it up to the motor and ran it up, the power output was rubbish. But even with this amount of abuse it hadn't exploded or caught fire, but there will beinstances where it could happen. Remember the chargers are only smart if you have them set to Lipo, if you've set it to Nicd or Nimh it won't recognise that you have a Lipo fitted and will try and charge is a one of those which uses a completely different "full" measurment.

Edited By Frank Skilbeck on 09/08/2013 07:43:25

[GrahamC]

I'm not so sure that this is a good idea at all.

Taking a lipo and embeding it in a model where it cannot be inspected and surround it with a selection of tinder (balsa, light ply etc) ....

The risk of lipo ignition is not entirely limited to times when they are being charged. I know of one that went off after use on the way home from the model field, and there are a disturbing number of accounts of lipos igniting while being stored....

So.... No I think it's a bonkers idea!

On the other hand.... Inserting a lipo when a model is assembled, and then charging it in situ at the field.... I might well consider that.... I m planning to convert my spitfire, and that would make the conversion easier.

[Bob Cotsford]

Would I charge a LiPo in situ ? Yes, I have a couple of models with LiPo rx packs that I charge in place, but I would only do so outdoors or with the model in sight at all times ready to lob it out of the door or window if it starts smoking. It really does take just one moments distraction to set the charger off on the wong settings. OK, it will only happen in exceptional circumstances that you get a dangerous condition with modern chargers but it can happen.

I doubt a LiPo sack built in would contain the rather vigorous fire (think blowlamp) that you get so the balsa structure would be alight in, oooh - 5 seconds?

We have always had the possibility to overcharge and detonate ni* chemistry cells but they are not as impressive when they go, most likely a bit of heat and a big bang which is cool in itself but not in the same league as a lithium battery fire.

So would I build in a flight pack? Having seen 3 and 5 cell flight packs ignite, not a chance!

[GrahamC]

Posted by Bob Cotsford on 09/08/2013 07:58:11:

Would I charge a LiPo in situ ? Yes, I have a couple of models with LiPo rx packs that I charge in place, but I would only do so outdoors or with the model in sight at all times ready to lob it out of the door or window if it starts smoking. It really does take just one moments distraction to set the charger off on the wong settings. OK, it will only happen in exceptional circumstances that you get a dangerous condition with modern chargers but it can happen.

I doubt a LiPo sack built in would contain the rather vigorous fire (think blowlamp) that you get so the balsa structure would be alight in, oooh - 5 seconds?

We have always had the possibility to overcharge and detonate ni* chemistry cells but they are not as impressive when they go, most likely a bit of heat and a big bang which is cool in itself but not in the same league as a lithium battery fire.

So would I build in a flight pack? Having seen 3 and 5 cell flight packs ignite, not a chance!

I think my point exactly.. If a model ignites at the field while a lipo is being charged in situ its unfortunate, and might mean the loss of a model.... If it were to ignite while the model is in storage in a shed or garrage storage the consequences are potentially horrendous.

Here is an example on youtube of what happens when a larger cell blows... If you read the description, it was being charged in situ. 

Edited By GrahamC on 09/08/2013 08:21:06

[Devcon1]

I can see a time in the future ( as electronics become smaller and more integrated and capacities continue to increase whilst weight and size further reduce) when we won't need to be taking handfulls of batteries to the field.

All we'd need to do would be to plug in a 12V source to our model and a single charge would see us through the day

We already have the high end Spektrum and other brand transmitters with built in LiPo balance chargers, why couldn't models be the same with a balance charging circuit built into the flight pack?

Regards

John

[Martyn Johnston]

This question must have been asked before, but why are 'our' batteries so different from the millions and millions of Li-Pos sold in other devices every year?

I have a phone with a Li-Po in it; I never take the battery out to charge it.

I have an iPad; you can't even take the battery out of that.

[simon burch]

I'd have concerns about charging in the model. My PL8 which i consider a very smart charger went bang last week for no reason. It managed to weld one of the lipo connectors together and blow 3 of the 80amp FETs (so I'm told by the chap who is trying to repair it). The lipo is not always the weak point in the chain, and it's made me far more aware over my charging. This is the first incident I've had since flying electric models, I always thought it would be a bad lipo which would cause the issues !!

Cheers,

Simon

[Martin Harris - Moderator]

Posted by Martyn Johnston on 09/08/2013 10:22:44:

This question must have been asked before, but why are 'our' batteries so different from the millions and millions of Li-Pos sold in other devices every year?

I have a phone with a Li-Po in it; I never take the battery out to charge it.

I have an iPad; you can't even take the battery out of that.

I'd guess it's due to the abuse that we subject our packs to (laptops typically don't exceed 1/5 C average discharge compared with probably 30 times that rate for the mildest of our typical models), few charge at anywhere near 1C  and the lack of limiting/protection circuitry as fitted to "normal" packs. Most devices these days use Lithium Ion technology anyway.

Having said that, there have been massive recall programmes by a couple of laptop manufacturers after a few laptop batteries did self-ignite.

Edited By Martin Harris on 09/08/2013 10:58:36

[Vecchio Austriaco]

I think ignition while charging can only happen if the user made an error. As long as the charger is up to date and from a reliable source and it is connected the right way I see little problems. The bigger problem is the lifetime - my experience with LiPos is rather mixed, I was just flying yesterday and had gas build up in the lipos even they are the right size and C - this is after 40 charges. (loong max tipple 4 cells 4000mAh 20C - motor takes 55A max) Same happened to my son, here the batteries are even younger.

If the LiPo is for the board circuits (receiver and servos) and not a power source this problem may not be relevant and it may be possible to leave them in the model.

VA

[Biggles' Elder Brother - Moderator]

I agree on the lifetime issue - which is why I suggested engineering it in such a way that could be removed - it just wouldn'y be trival. As Tony suggests maybe a screw on hatch or paerhaps requiring the removal of the cowl or such like. So we've not talking about sealing it away "forever" or having it in such an arrangement that basically you'd have to cut the model apart to get to it. And likewise periodic inspection would be a sensible precaution, as would the ability to check individual cell voltages whilst the battery was installed - a good early indicator of potential problems and/or end of useful life.

BEB

[Mowerman]

I always hate having to remove wings to take battery packs out for recharging.So far I have managed to avoid this by modifing models to have a suitable hatch,however if this is not easily done then I would take a (very small)chance and charge in situ at the field but remove the pack for transport/charging/storage at the end of the session.

[Chris Bott - Moderator]

The difference between our LiPos and those in phones and laptops, is that we are dealing with the raw battery. Phones and laptops have very specific chargers built in, and built into the batteries. No amount of finger trouble can set those incorrectly.

The difference between charging A123s and LiPos (either in or out of our models) is that the A123s are inherently safe. On the other hand, LiPos can easily be provoked into a very unstable state.

We are advised to be present when we are charging lipos, and I think that charging them in a model removes us from being able to observe them. Once we notice something is wrong, the chain reaction will be well under way. Once on fire they produce their own oxygen and will not be extinguished by any means, and it's pretty violent to boot.

The most important thing to mitigate this is balance chargeing. This can of course be arranged with an "in model" LiPo, and in my experience, if you balance at every charge, then balance charges take no longer than non balance charges.

On the other hand, A123s just won't burst into flames, the chemistry makes sure of that. So I'm happy to charge my A123s inside the model, at high rates, and I generally have them charged in 15 minutes. Not a great wait at the flying field.

I'm still undecided about charging LiPos in the model. It should be OK if balancing, but you can't actually see if they've started swelling. If you take them out every flight, then a quick cursory check is possible. Are all the connections tight? is all the insulation intact, including between balance wires? is there any sign of swelling? etc etc.

Maybe a compromise is a system where they can be charged in the model at the field, but they can also be taken out after every flying session without too much bother?

[Biggles' Elder Brother - Moderator]

I've looked at A123's Chris and they look very interesting. But could you go through a few things for us?

1. Where can you get them?

2. What sort of set up with them would broadly speaking equate to say 6s 5000mAh Lipo?

3. Do you need a special charger to charge them?

Thanks

BEB

[Chris Bott - Moderator]

Good questions BEB.

I'll just put one thing out there - I'm staring to fall out with A123s to some extent these days (there I said it). LiPos have developed so much now, and the cost has gone down and down, such that the only real downsides with them are the safety issue and in my experience so far they don't tend to last more than a season or two, no matter how carefully you treat them.

The A123s that I'm flying with, including those in the 10.5lb Sea Fury, mostly started life around 2008/9.

OK, I think this needs a longer reply than I have time for at this moment. So, I'll just promise to answer the questions a little later in the evening.

[Concorde Speedbird]

Hmm, post disappeared. If a moderator deleted it please could I have an explanation?

CS