10/18/2015 - How many of you parallel charge your lipo batteries? Quite a few I imagine. The upside is if you have enough power capacity you can charge a bunch of batteries in the time it takes to do one. The downside? If you have one battery with a shorted cell, a leaking cell or very low cell you may be setting yourself up for a large fire. Take a good look at the picture above. What would you do if one of those packs started torching flames?

The charger does not know one cell from another when parallel charging. Since all the battteries are wired together one shorted cell could take down all of the cells in the same position. If that one cell does not take a charge heat will cause it to expand and rupture. The resulting fire will cause the other cells to go up and very likey all the nearby batteries that are on the parallel.

Another issue is mixing batteries with different charges remaining. Plug an almost dead battery or one with an almost dead cell into a parallel grouping of batteries with much higher remaining voltage and the higher charge will try to even out the low voltage on the one low battery or cell. Resulting in a obscenely high recharge rate for the low battery which can result in a meltdown and fire.

Things to look for? 

  • Check the voltage of every cell for every battery BEFORE charging. If you have a low cell, charge that battery by itself. 
  • Check that the voltage of the packs you are paralleling are within a tenth of a volt of each other.
  • Be on the look out for odd smells in your battery storage box. You may have a leaking cell if you smell electrolyte. When a cell starts leaking a low voltage and the smell are telltales. Safely dispose of that pack.

Some general safety tips for LiPo charging:

  • Do not mix batteries of different cell counts when parallel charging! Only charge 3s with 3s and 4s with 4s, etc. 
  • NEVER leave charging batteries unattended. Always be within reach of them.
  • NEVER charge on a flammable surface!
  • NEVER charge the batteries on your car or under its hood.
  • DO have an emergency plan in case one of batteries catches fire. Think about what you need to have in position to get a burning battery to a safe location for it to burn out.

If you don’t know what is safe, get with the club safety officer.

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