LiPoly fire

Overheating in the sun, or previously overcharged/overheated. Once the pack swells up, it can get progressively likely to short internally. Some newer packs seem more prone to this.

Undoubtedly it would be nice to have a power supply that didn't do this.

Do you leave glo fuel canisters in the sun too?

Not usually. However, the jug just swells a little. No fires.

John VB

another possibility is a bad solder joint in the battery pack. I've read some reports of extremely poor solder jobs on ready-made packs, waiting for the short to happen. I cannot tell if this is the case, but that is one possibility.

It might be a good idea to make the lithium packs yourself, that way you could wire them for "serial use, parallel charge" (bring each termina of each cell to the connector, and have special connectors foo flight and charge that re-organize the pack. Parallel charging of a lithium pack is a good idea, as it automatically balances the back, which should be done after every 3rd to 5th charge anyway.

-Tapio-

Yes, I have left glow fuel canisters in the sun on many occasions. No one I have known or flown with has ever experienced a fire because of it. And, the heat in Arizona is FAR higher than in the UK. If LiPos will melt my electrics merely by sitting in the sun, then I will look elsewhere.

What brand of batteries?

BobbyG

Would like to see a diagram of this "serial use- parallel charge" wiring.!!!

waiting for

termina of

They are Kokam USA, marketed/distributed by FMA Direct.

Bobby Galvez wrote

:> Would like to see a diagram of this "serial use- parallel charge" :> wiring.!!! :>

: Its possible. You need twice as many connector pins as there are serial : cells.

Precisely.

: One harness wires the cells in parallel for charging, the other in the : plane in series.

: Its not a perfect solution, because shorting cells at potentially : slightly different levels of discharge can overheat them as well...

But if you parallel-charge them every time they are darn likely to be on the same level of discharge every time you start charging...

-Tapio-

No. That would imply that they are all *exactly* equal capacity. No two cells are exactly alike.

One could equally well argue that, if you make up your pack with exactly equally charged cells (but of slightly different capacities) to start with, then after discharging, no matter what their end point voltages individually are, once charged up in series with exactly the same amount going into each as has been taken out, they will all end up at the same voltage fully charged.

Which is, in fact, more ore less why series charging does not blow every pack up every time its used.

The devil is, as always, in the detail.

Parallel charging SOUNDS like a good idea to the simple minded. Investigation of it shows it has as many flaws as series charging.

Ultimately cell voltage clamps and series charging is the way to go, or INDIVIDUAL charging of cells one by ne to restore balance - but if balance has been badly lost in a series pack, one should probably investigate why. It may well be the first sign the pack is on its last legs.

Many of the problems being experienced are actually problems of MARKETING. Packs are sold as '1000mA/h 10C discharge' but in reality, whilst they may do that under carefully controlled tests, once, they are liable to fail dramatically if exposed to it on a regular basis.

I use half the current draw and half the capacity that the marketing alleges is safe. I haven't had any problems so far. LIPOS have so much more power to weight and duration that I actually need, that there seems no point in pushing them to the limits.

| Parallel charging SOUNDS like a good idea to the simple minded.

It sounds like a fine idea to those not so simple minded too ...

| Investigation of it shows it has as many flaws as series charging.

Really? I only see one big flaw -- when you hook the batteries up in parallel, if there is any signifigant voltage difference between the cells a possibly large current will flow until the voltages match. As long as the cells are fairly close in charge level this shouldn't be a big problem. You could also put some

I have 10 Li Poly 1500 ma packs that are going in a pattern plane. Five are 7.4 volts , 5 are 11.1 volts. I plan on wiring one 7.4 and one 11.1 in series to attain 18.5 volts ,make 5 packs this way and then wire the five in parallel to get 7500 ma. These will be hard wired together terminating into one Deans ultra connector. I have an Astro Flight 109 D and that will charge everything at once. Have any of you wired this many this way ? Have you encountered any problems charging ?

Thanks

Ken Day

Ken: take that question over to the ezone -

It sound's to me that you haven't been there. Trust me, and go.

There is no quick answer, except to say that you are playing with fire, literally, and although at a glance I think it should work,at least for a while, I would much rather you were TOTALLY aware of the potential problems and how to anticipate them.

: Have any of you wired this many this way ? Have you encountered any : problems charging ?

Have not wired anything more than 3 series 1 parallel myself, but I've seen how some big boys do their stuff, and they seem to have all the cells parallel while charging. The reason is that every time you have cells in series while charging (and you plan to have 5, right), you run into risk of unbalance, overheating and fire. So if you plan to charge the pack in it's flight configuration be prepared too check the balance of each (sub)pack before each charge, and balance them anyway every third charge or so (by individually/parallel charging). HAving said that, ezone would indeed be a good place to discuss there matters, with people with first-hand experience.

-Tapio-

Thanks. I appreciate your help.

Ken

Can someone please tell me why we never have a problem with cell phon

batteries that are lipos or liions but there is such a problem with th use of those batteries in our planes?? IE, why do they never explode i cell phones or in the charging process but we lose so many batterie due to fires while charging them for r/c aplications??

Thanks!

-- WingsofEagle

----------------------------------------------------------------------- WingsofEagles's Profile:

there are a couple of possible explanations, One of which is that most cell phones etc operate on ONE cell LiPo or Li-Ion batteries. If there is only one cell, there is no chance of imbalance between cells causing problems. In addition, Most of these devices use a relatively gentle charge and discharge curve where we DO tend to push the batteries in our planes to and beyond the limits of the technology.

The more likely explanation is that LiPo fires relative to RC equipment tend to be over-reported, and other types of incidents involving the batteries tend to be ignored.

There HAVE been occasional reports of cell phone batteries having problems

Largely because the charge/discharge is electronically controlled to stay within limits which are far more conservative than those used flying a plane.

Those of us whop never use LIPOS at more than about 65% of ratings are rewarded with long service life and zero fires.

A F1 engine lasts about 800 miles before its toast, too..their tyres do at best about 100 miles.

I have 53000 miles on a Diesel Landrover..the engine is barely run in and I have just put new tyres on the front wheels..the first ever.

Go figure.

Simply because of all the protective circuitry built into those units. An example of just how much was shown in Model Aviation a few months ago.

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at