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Old May 17, 2008, 12:15 AM
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Conroe, TX
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I think once you reach that temp, it's too late. I had an idea for a puff sensor once. It would gently clamp the battery. Movement in the thing would flip a switch, and cut power to the charger. Probably would also be too late, but maybe not, I don't know. any thoughts?
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Old May 17, 2008, 04:45 AM
like a rock!
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Finland
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Bantam BC-6 for example supports a temperature probe. You can set up a cutoff temperature.
Just don't rely on it. It may reduce the likelyhood of a fire. But you must be able to deal with a fire in any case.
Mr Murphy will find ways to outsmart your clever ideas. Or, in clear words: Anybody who relies on those ideas to protect him from a fire is a fool.
(yes, I have seen chargers failing, short-circuiting the LiPo).
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Old May 17, 2008, 06:57 AM
I'll frame U!
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A good indicator of any problem is the cell temperature. So the best thing to do there would be to use some kind of non-touching, heat sensing sensor, such as a pyrosensor. Like the kind that is used in in-ear fever thermometers. That, hooked up to a small circuit that talks to the charger, would switch off the charger whenever the temperature rises above a set threshhold. But it would "watch" the whole pack, not just touch one cell in a tiny spot.

The pack could then charge in a steel ammo-box half full of dry sand, and you would basically be safe to walk away.

OK, you still shouldn't place it in the garage next to the canister with the lawn mower fuel...
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Old May 17, 2008, 12:53 PM
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The Hyperion chargers (I've reviewed the Duo here on Ezone) has a temperature-probe hookup, and it lets you set a temperature alarm. If it goes above whatever you've set it to, it will shut off.
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Old May 17, 2008, 01:39 PM
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Quote:
Originally Posted by Bogomir67
...and you would basically be safe to walk away.
believe what you like, it's your responsibility.But unless your ammo box is safe by itself, it will not prevent setting your house on fire. It just makes it less likely.
You're making assumptions that I wouldn't bet any money on, much less the safety of my neighbors:

- you assume that overtemperature shows at the outside soon enough
- you assume that turning off the charger will prevent an overheated cell from burning up

Now I'm no expert on LiPo safety besides using them on a daily basis, but I know that there is one scenario called "thermal runaway" - once a spot inside the cell reaches a critical temperature, it generates more heat than the package can dissipate, and it will burn after a short while no matter whether you keep charging or not.

There is a simple rule printed on every LiPo: Don't charge without supervision. Simple as that. Everything else (besides the obvious "charge-in-the-middle-of-the-desert-where-it-can-do-no-harm") is just wishful thinking.

PS: http://www.rcgroups.com/forums/showp...2&postcount=77
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Old May 18, 2008, 02:19 AM
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the idea would be to stop charging well before it got anywhere near thermal runaway, i really like the idea of a pyrosensor to watch the whole pack for hot spots.
an amo container or lipo sack is still not unwarranted.

i think i'd trust a balancing charger with a temp probe (thats really sensitive) inside a fire proof container with my house, but i still dint like the thought of smoke damage
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Old May 19, 2008, 06:38 AM
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Pineville, LA
Joined Dec 2006
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Are Micro RTF lipos much of a danger?

I'm fairly new to RC. I have quite a few of the AA planes and one Parkzone Citabria. Do I need to be very concerned with a fire hazard when charging the AA's or the Citabria battieries?

Thanks,
Robert
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Old May 19, 2008, 01:12 PM
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Quote:
Originally Posted by gravityKills
1- you assume that overtemperature shows at the outside soon enough
2- you assume that turning off the charger will prevent an overheated cell from burning up
1- well, it does. We frequently light up used (bloated, dented, "mushy") lipos for demonstration purposes. You can see the heat build up pretty well for quite a while. I'd be more concearned with a stick-on heat probe falling off from a cell bloating (and thus physically changeing position of the sensor).
2- it does, unless the heat came frome something else, such as a short. Also in multiple-p pack there might still be enough charge in a good cell to get the bad cell up in flames.

Yes, I am assuming a number ogf things here. But the world isn't black and white only. Lipo cells are neither perfectly safe, nor are they a bottle of overheated nitroglycerin approaching the kitchen floor at 50mph.
Otherwise, driving a car on public streets should be considered atempted suicide.

One of my favourite examples:
Over here in Germany, we get about 2 homes blown up from a leaky gas line per year. Always - meaning 100% of the cases - it turns out that somebody messed with the system, either trying to bypass the meter, or running an extra line to the other apartment, or such. So - is a gas heater a safety problem? No! Is it 100% safe to use? No!

But using a charger that has a good safety reputation, along with some care around the cells, checking up on what you are doing without 100 different things on your mind at the time, and maybe a thought or two about the placement of the pack while charging it will put you definitely much nearer the safe end of the spectrum.

That's all I am saying.

"...safely walk away..." was just a quote from that Cellpro ad. Which I think is quite an irresponsible statement. If I was responsible for that product - no matter how bad I wanted to sell it, I would still never stick my neck out that far!


Now you are the one
- assuming that this fellow was using the right charger set to the right number of cells and current
- assuming that the inside of the car was not at 150F, but much lower
- assuming that he was charging a practically new, never bloated, never dented pack...
- asuming, that he did everythig else right.
Indeed, hey may have done all of that wrong (I am not suggesting that he did, I know as litte about the incident as you do)

Assumptions cut both ways!

All I am saying is this: If you are sure about what you are doing, and keep double checking anyway - the residual risk is low - but not zero, of course.
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Old May 19, 2008, 02:44 PM
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Finland
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Quote:
Originally Posted by Bogomir67
Now you are the one
...
Assumptions cut both ways!
huh? It's solely an example where the temperature sensor didn't prevent the fire.
Sorry, but I don't see the connection between your comment and what I wrote. But then I didn't see that "you're safe to walk away" was a quote, either.
I guess you're just more clever than I am, and I am too dumb even to outsmart a burning LiPo.

I'm not really keen to continue this discussion. Let someone else uphold the unpopular arguments, for a change.
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Old Jun 25, 2008, 12:06 PM
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Quote:
Originally Posted by Spackles94
The Hyperion chargers (I've reviewed the Duo here on Ezone) has a temperature-probe hookup, and it lets you set a temperature alarm. If it goes above whatever you've set it to, it will shut off.
This is what I'm using. I felt a lot better having it on. My workshop is in the basement, so even though I'm always home and don't recharge at night, I think it was a smart investment. I wonder if it's the kind of equipment that keeps improving and offering better versions of itself.
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Old Jun 25, 2008, 04:25 PM
From a Different Planet!
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Lagrange, Ohio
Joined Jun 2005
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Thats probably a good idea.

Just to let everyone know another horror story of LiPo batteries! Last week my brothers house burnt down due to LiPo being charged in the garage. He was checking on them every so often but it only took a few minutes to cause the fire, It went from no puff, no heat to flames in under 10 minutes. A 5000 mah 3 cell battery exploded and lit the house on fire, They lost EVERYTHING! His 2 girls, wife + him made it out OK. This woke me up, I will nopt quit using LiPo's, but I treat them with more respect now. This battery has been charged before (not new), He was using a good charger, and he was charging it at a safe rate. This proves to me a MUST for a fire proof container to charge them inside of!!!!!!!!
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Old Jun 25, 2008, 11:55 PM
like a rock!
gravityKills's Avatar
Finland
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Quote:
Originally Posted by edge_pilot
Thats probably a good idea.

Just to let everyone know another horror story of LiPo batteries! Last week my brothers house burnt down due to LiPo being charged in the garage. He was checking on them every so often but it only took a few minutes to cause the fire, It went from no puff, no heat to flames in under 10 minutes. A 5000 mah 3 cell battery exploded and lit the house on fire, They lost EVERYTHING! His 2 girls, wife + him made it out OK. This woke me up, I will nopt quit using LiPo's, but I treat them with more respect now. This battery has been charged before (not new), He was using a good charger, and he was charging it at a safe rate. This proves to me a MUST for a fire proof container to charge them inside of!!!!!!!!
Jeez glad to hear no one got injured.

>>This proves to me a MUST for a fire proof container to charge them inside of!!!!!!!

well, yes and no. KEEP THEM UNDER SUPERVISION WHILE CHARGING, that's the point, period. That's what would have prevented most (all?) reported fires. That's what every LiPo manual tells us.
Those who still do, may want to stop dreaming about temperature sensors, automatic fans etc or whatever to PREVENT a fire with CERTAINTY. There's just a certain chance that they will burn, violently, like fireworks, and you have to be around to deal with it while the fire is still small.
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Old Jun 26, 2008, 02:38 AM
Always fly HIGH!
Manito Illinois
Joined Jun 2008
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I happen to disagree with this entire thread. I believe li-po fires under normal use are UNREAL. Been around too many people useing too many li-pos to go along with the paranoia I read here. BTW. I was the guy who predicted the demise of the old adage "never charge above 1C" a year or so ago. HUUU,AAA. But I have a brother in law that is an engineer with GM working in the battery technology department. (They are very busy these days pushing the envelope on lithium battery technology like never before. For a change maybe we will see some trickle down technology instead of the way li-po tech. has evolved. (r/c community being the only major comsumer, Dont misunderstand me,Im talking li-po,not li-on The auto makers are very interested in this technology.
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Old Jun 26, 2008, 04:03 AM
like a rock!
gravityKills's Avatar
Finland
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Quote:
Originally Posted by maxim1100
...to go along with the paranoia I read here...
"paranoia" is maybe the wrong word... The cost pressure on manufacturers is immense, and you may get a sample from a bad batch that burns even though you did everything right. That alone should suffice.

Given that two posts ago, somebody reported an incident with considerable material damage, I am really scratching my head and wondering what you are intending with your post. Not that I care much, everybody is entitled to his opinion.
Please, if you act according to your beliefs, think twice whether you are endangering other people.
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Old Jun 26, 2008, 08:36 AM
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Dickinson, Tx.
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Quote:
Originally Posted by maxim1100
I happen to disagree with this entire thread. I believe li-po fires under normal use are UNREAL
All you have to do is: read the stories from regular people just like you.

I use to charge them in the garage in a fire proof bowl, but had a cell puff on a 4S1P 2100 back in '05. If I hadn't checked on the pack when I did, I would have had a fire. It scared me bad, as I have a boat, lawn mower, cans of gasoline, etc. in there....and it is an attached garage.

I don't want to get complacent when I charge Lipo packs.

Challenger413
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