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Originally Posted by Ron101
(Post 11770842)
Internal resistance will vary, good packs will be much lower and more uniform from cell to cell
I have been keeping an eye on I.R. for several years on my packs. I use FMA (cellpro and power lab) balance chargers they will tell you the I.R, while charging. The other variable you will come across is the mah of the pack. What may be considered low I.R for a 2300mah pack would be high for a 8000 mah pack. My thunder power 6s 65c 5000 mah packs started there life in the 1.2 mohm to 1.4 mohm range after about two years and many flights later they are pushing 1.7 to 1.9 These have been very good packs. They stay in very good balance before and after a flight I've had a hyperion 6s 35c 6500 that was not staying in balance, the I.R. of a few cells was all over the place... might look like this ( 2.3, 4.5, 6.4, 2.4, 3, 2, 4.6) I would question whats going on with this pack along with the fact it's not staying balance... you may also notice the charger starting to stay in balance mode much longer at the end of a charge. Could indicate this pack is going bad.. I got rid of it The best I.R. I have seen came for a recent batch of 6s 25c 8000 mah Nano Tech packs..... these are cheap packs from hobby king. I'm seeing cells in the (.08 to 1.1) range they stay in perfect balance, very cool and come out of balance charge fast..... tells me there good cells Now a smaller 3s 2300 mah pack may be considered good at 3 to 4 mohm .... if you see a cell hitting 7 mohm but the rest are down at 5 mohm and it's not staying in balance I would start to question that pack. If it was old I would get rid of it at that point. I also mark the date on my packs if there getting to be 4 years old I'm about done with them... time to move them out. I used to mark cycles on the side of my packs but other than seeing how many cycles I got it really didn't help. I'm more interested in the balance and I.R., I like to look at the balance before and after every flight with my tester. Check my I.R. every charge, just take a mental note and watch for something out of the ordinary. I find it kind of fun in some sick way...lol For the record I buy expensive, cheap, and middle of the road packs mostly based on testing others have done. I've found bad cells in expensive brands and seen some of my best cells in very cheap packs. It's really hard to gauge... I will say the big name expensive brand packs seem to have better matching and consistency. I bough a batch of cheap 6s 40c 5000 mah packs one was crap right out of the box, but the others were perfect and turned out to be some of the best cells I've owned I take my old packs to our local household waste recycle center, they take them for free no matter what shape they are in Watch those out of balance packs, any puffing or swelling and balance charge everytime |
Since no one else said anything. Couple of pages ago someone mentioned salt water to dispose of lipo batteries. Don't do it. All it does is corrode the aluminum battery tabs off making the battery appear at zero voltage but it may still have most of a full charge. Hook the battery to a couple of car brake light bulbs and let it discharge fully. Then throw it in the trash.
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This Info always has me thinking. Why are there no sensors in a charger that can detect when there is a LIPO malfunction. My Dewalt charger will not charge unless all the conditions are right. It will not try to charge a bad battery. Although they are Li-Ion isn't that similar technology. |
How likely do you think it is for a Lipo just on the shelf would flame up? I understand just after use or charge is more volatile.
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Dave, Sorry for your loss and thanks for posting.
There is a tendancy to ignore the risks because these type of things happen infrequently. We need to be reminded. I know I have charged mine recently without adequate protection. The safe report is interesting. A fire safe is supposed to protect the inside contents from an outside fire not the other way around. BBQ pit is probably better. |
Be glad it was just your tv and not your house. Another reason I don't use lipos.
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I ment rv not TV. Damn spell check
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Thx for the warning, next shop project...
Isolated battery charging area |
I use those big fire safes too. Mine have ceramic tiles laid down on the base. It has never been tested but it should buy me enough time to get the conflagration outside. The solid, locking lid has a gasket and a pressure relief valve so there is some hope of containment. Not perfect and certainly not as expensive as that $500 Graupner safe listed above.
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Originally Posted by David Searles
(Post 11769978)
For not trying, you've done an excellent job. Must come naturally to you!
#1 I unplugged the battery just prior to leaving for the store, so they weren't left unattended while charging. Your ASSumption is incorrect. The failure had apparently already started prior to me unplugging it and continued to conclusion in my absence. #2 I never claimed it was anything else other than my fault. But thanks for your statement of blame, we can all rest easy now. Scotty, I assume the battery was bad, as I had unplugged the final battery from the charger before leaving. It apparently went nova at some point after I left. Raptureboy, Yes I admitted my mistake in public, now comes my public flogging by those who love restating the obvious. Thanks for your concern. If there is anything to be learned here, IMO, it is that there is apparently a period after charging that these things can still explode. When I unplugged the final battery I assumed I was safe. NOT SO! David S You are the one after all who said "I had a couple batteries on charge, so I'd be all charged up & ready to fly upon arrival. Left to go to the store..." I am no professional hieroglyphics deciphering expert, but those words you chose sure sounds alot like you "had a couple batteries on charge" and you "Left to go to the store"... Either way, it's a damn shame, but you really shouldn't pounce on the guy who was dead on right.... based on the info you provided. Clarify a little more next time. (Obviously I hope there is no next time, fire -wise of course) |
"Yes I admitted my mistake in public, now comes my public flogging by those who love restating the obvious."
Well Dave, have you had enough flogging yet.:rolleyes: |
Originally Posted by retransit
(Post 11770901)
I think what is needed is one of these aimed at an open window:
A self-triggering auto-launch system.http://www.rcuniverse.com/forum/atta...mentid=1982350 Great invention! I like it. |
I was a lot more fortunate. About 2 years ago, I started charging one of my lipo's and my wife and I decided to go for a 1 mile walk around the local track...20 minutes later and to the sound of smoke alarms going off and white smoke billowing out through the front doorway, this was the end results, after I put out the small fire...
https://www.youtube.com/watch?v=i0EBjGh9A3c |
WOW David that is one heck of a scare.....sure delighted you did not have any of your outstanding planes in the fire!
Hope your insurance will make you whole....... Roger |
https://www.youtube.com/watch?feature=player_detailpage&v=k9mcNvOGKtI
this was passed around awhile back
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I've used metal ammo boxes, I line them with thin ply. I have tested the things by lighting off some old packs inside and they don't breach. I have tried them with and without venting with no noticeable difference in safety. There is still a lot of smoke and the box is trash afterwards. I have even left two packs inside with the third that I set off and the other two packs were charred but had not seemed too add to the fire.
Dennis |
Wow just read what happen. Dave Sorry for the loss. This is a eye opener. I use fire safe. Looks like a ammo can is the way to go. Dan
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Just picked up two more ammo cans today from my local Army/Navy store.
Even so, I am also wondering how I can find a way to store these lipos away from my house, as the garage and workshop are both part of the house, not stand-alone structures. I'm thinking about getting an outdoor weather resistant storage unit, but as has been mentioned in an earlier post, that brings the swings in outside temperature and moisture in to play. As far as the smoke damage from a lipo cook-off, I saw the result of it in a bud's trailer. It, too, burned itself out, and was not discovered until the next morning. Pretty much anything metal in the trailer ended up corroded. The door hinges looked like they had been soaked in salt water. There was also some corrosion damage to metal components in the jets that were stored in the trailer...not good. The smoke is bad juju. |
my plan is a small fridge in my shed .... with an inline thermostat to keep the temp around 60... keep them the same temp year round
but I'm in california and dont have to worry about super cold temps, we get some good heat in the summer 90-110 so want to keep them cool |
I have often wondered about these packs and fluctuating temps. I have old thunderpower packs first generation I have been using for over at least 8-9 years now and they still work like they always have. Even most of my less expensive packs show no signs of any problems. I live in Canada the temp in my garage in the summer is a steady 78 degrees F with AC and in the winter with heat and a programmable thermostat goes from 42 for 14 hrs. to 70 for 8 hrs. every day. Any failures I have had can be attributed to operator error (expecting too much from something like a 25C pack) or having a battery lead or balance lead breaking or coming unsoldered. I have flown them in freezing temps after being in the back of the van for hours. A few times I may have thought they had a reduced efficiency because of the cold outside temps but once in use they quickly heat up to at least hand temperature which is well within the recommended operating range and seem to run just as long as on summer days. On the other hand I have noticed all batteries used under low draw operations were they don’t heat up, like transmitter batteries do suffer some reduced efficiency but if you’re on top of things you notice before any problems arise. Once temps return to the warmer norms of summer I have notices no lingering affects from the usage during cold times.
Dennis |
Sorry for your loss Dave. That RV looks like it came out of a scene from Breaking Bad. I fly mostly glow but have a few electric airplanes. I plan on putting all my Lipos in a small metal tool box now.
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I've wondered the same thing to Dennis, mine are always on the shop floor in the ammo cans. I've hit them with the temp gun and they will be about 55 in the winter, 65 to 70 most of the year I've checked them when it's 110 outside and the hottest I've seen them was 85 on the shop floor. So I think my cement and insulated garage helps keep them at a constant temp. Now my outdoor shed is a different story it's going to get really hot in that thing and fairly cold. That's why I want the mini fridge to keep them constant, I would think even in the winter when we get a freezing night if the fridge was off they would stay at a good temp like maybe 50? I'm going to give it a try in the coming weeks to get the packs out of my shop and away from the house
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Maybe a little overkill here but been thinking about using an ammo can or a large steel container lined with some castable refactory cement ( https://www.rutland.com/p/13/castable-refractory-cement ). Then throw the can or box inside of an old ten gallon or larger fish tank(that can be lined with ply or some of the cement) and find a way to seal the top of the tank and use a thermal switch to turn on an exhaust fan that's mounted to the tank with flex hose that exits the house/garage/basement. This should get a lot of the smoke and gas out of the house which in some cases seems to do more damage than the fire.
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3 Attachment(s)
http://www.rcuniverse.com/forum/atta...mentid=1982759http://www.rcuniverse.com/forum/atta...mentid=1982760http://www.rcuniverse.com/forum/atta...mentid=1982761Below is a description and pictures of a recent fire while charging in a Lipo bag.
"It was a 2650 Mah 4 s 50c Flight Power Pro50 being charged by a Thunder Power Dual AC 680 in a Nitroplanes lipo -safe bag. Fully charged battery discharged in flight about a minute and a half earlier than normal and was puffed up and hot. After battery cooled ,I was charging it for about 12 minutes when standing in room next to laundry room which is where I did my charging, it blew up with a big flash of light . Upon running into room I found soccer ball size flame engulfing the lipo safe bag. I knocked bag to the concrete floor and quickly removed it to front yard with a dust pan. Here's the pics. Eric S." |
Unfortunately the litmus test for testing which system would work the best is an unplanned lipo fire. i'm going to try my darnedest to avoid that at all costs. From what I have observed the ammo boxes kept away from any flammables seems to be the best for me at the moment. I had not thought of the reaction of the stuff in close proximity to the smoke from these things. I have lots of machinery in my garage and I am to understand the gasses from a lipo fire are very corrosive. This needs some investigating on my part.
Dennis |
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