Lucky LiPo Lesson
erco
Posts: 20,261
I was charging 3 Lipos today (inside, I know...), two went quick but the third one was taking forever, the small balance charger making a louder & longer squeal than normal. This battery was buried inside a robot, not in plain view. Before we left for lunch, I glanced through the PCBs and nest of wiring and caught the LiPo bulging badly, it might have made a mess of things had it caught fire inside the robot. Lesson learned: Keep your Lipos in view while charging, do it in a safe place, and check on them regularly. Pics show swelled battery next to a normal one. And yes, Gordon, these are are all "non-prime" batteries from Ebay China. Barely used, it's a shame...
Should I even bother putting the errant LiPo on the "freebie" table next Expo?
Should I even bother putting the errant LiPo on the "freebie" table next Expo?
Comments
-Phil
Browser..a little bad humor moderation pleaz.
They may still be fine.
I have a couple of pregnant Thunder Power LiPo's that still work fine.
Of course they are charged under watch in a Pyrex baking dish with cover.
@erco, If you give them away and someone gets hurt you are liable. I say keep them for yourself or just toss them. Better safe than sorry or sued!!!
In case you hadn't seen this post from JimInCA...
http://www.ebay.com/itm/7-4V-900mAh-LiPo-Battery-For-RC-Helicopter-ESKY-LAMA-V3-15C-AKKU-Rechargeable-/110904138540?pt=US_Rechargeable_Batteries&hash=item19d266db2c
This is the balance charger I was using: http://www.ebay.com/itm/7-4v-11-1v-LiPo-RC-Battery-Balance-Charger-2s-3s-3-Cell-/320819145906?pt=Radio_Control_Vehicles&hash=item4ab24facb2
-Phil
Was that battery being charged by a generator driven from a conveyor under a jet?
Two things that need to be done.
1. If the battery has an interface for a 'balance charger' (usually a smaller 3 wire connection, not the huge wire pair that are intended to drive a motor), USE a good balance charger.
"IN Theory", you might charge via the two big wires, but it won't be balanced and it won't be very safe.
2. After having another battery self-destruct (a Gel cell Lead Acid), I build a simple thermal sensor and connected to a solid-state relay that can shut off the charger if and when the battery is getting too hot. While there are all sorts of documents that mention various temperatures, I simply will shut out at about 35 degrees centigrade.
We all know that you start out watching the battery charge and then forget to stick with it. Something comes up and your attention is diverted.
Use this >>>> http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol1/col/nv2.pdf
3. Get a good quality charger. Episode number Three was using a cheap Taiwanese gel cell charger and that went up in flames. Not only that, it was transformer-less and gave nice big shocks if you used it carelessly with bare feet.
What may have happened? Well, LiPo batteries that fall below their minimum discharge can actually become a short. The batteries may have been used without first charging or their may be no protective circuitry limiting their discharge (to something between 3.0 and 3.2 volts, depending on chemistry).
In other words, lots of people are thinking about 'good charging' practices, but one bad discharge and the best of cells are trash. I recently loaned a robot to a kid with two new LiPo cells fully charged, he forgot to turn it off, then he accidentally shorted the battery when trying to make it work. End result, two new brand-name 18650 cells that are now useless. I need to get a protective circuit designed an built for these.
Any other choice? Use Parallax's LiPo board that has both charge AND discharge protection built in. Just using 18650 in a battery holder may be a big disappointment.