Lipo batteries die and come to life

Discussion in 'Electronics' started by Shawnee, Jul 11, 2009.

  1. Shawnee

    Shawnee Rookie

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    So this is what happen to me I grab a pack of batteries that where not charged and was working on my heli placed hem in to check the servos and stuff. notice that the receiver light was blinking Oh Shoes! Battery is real low BAD THING! charger will not charge even when pressing the INC button. So I grab a pack that was fully charge and place a dean plug on the end of and plug it in to the other pack. positive to positive negative to negative for a minute and then tried the charger again. IT Works!

    To Dave and Val please pass this on it will save some one money.


    Shawnee
     
  2. Loopy-de-loop

    Loopy-de-loop Rookie

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    Do you think its safe?:zap:
     
  3. Jbirky

    Jbirky Ace Pilot

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    It is not safe mainly because the charge current is as high as the other battery can push. This is a major danger. If you are going to do this, an it is dangerous, select Lead-Acid charge because at least the charger uses a similar algoritm.

    NiCD and NiMH use a DeltaV or Peak, which detects an exponential peaking of voltage to indicate the battery is charged, where the other batteries do NOT. This means, a LiPo will NOT peak, so it will keep charging and charging until it explodes.

    My recomendation is to set 6V Lead Acid for a 7.2v LiPo, set 10V Lead Acid for an 11.1v LiPo, and choose a charge rate like .1 AMP or 1/20 C until you get some voltage on the battery at which point, you may charge at about 1/5 C.

    Once you get over 3 Volts per cell, switch to a LiPo Charge at about 1/5C with a balancer. Once you reach about 3.2 volts per cell & the pack is in balance, you can charge at 1/2 or even 1 C.

    Do this at your own risk. The idea is to have a shut-off point on the charger below the nominal voltage of the cells, and to charge very slow. When you get in the ballpark to the voltage of a properly dead LiPo 3v/cell, balance it out proceeding carfully with a LiPo charge. Once all checks out, just charge it normally.
     
  4. Shawnee

    Shawnee Rookie

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    Lipo back from the dead

    I had watched the charger when I charge the battery back up. The charger kept saying low voltage and would not even try to fix them. so I thought that people will hook up two three cells to get a six s pack. I have seen!

    So I know what you are saying, So what is the best way to leave a pack setting around. how many volts 3.7 or above and thank you for your concentration. I just needed to get them up a little so that the charger would see it. also I went to THUNDER Charger web site and it say to push the INC button but to no avail. Thanks again...
     
  5. Skyblue

    Skyblue Rookie

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    Similar solution

    I have one lipo doing the same thing frequently. My balancer didn't 'see' the battery, so I disconnected the balancer and charged the battery for about 1 minute without the balancer. Reconnected the balancer and voila! It charged no probelm, balancing and everything.
    Safe :confused: No clue! But I know a lot of guys only use their balancer every now and then, so in that case they wouldn'y know the difference.

    Cheers!
     
  6. MoTheG

    MoTheG Airman

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    that is save. just don't give it a full charge that way, because if one of the cells is dead the others might get overcharged.
    I think Shawnee's method is ok too, if you do it only for 30 seconds or less and then connect it quickly to the charger. every battery has a capacity like a capacitor that can store some electricity on the short term that will be charged and show some voltage to the charger.
    that is something that would get me thinking.
    after some discharge and letting is lay around for two days, you should check the voltage of the individual cells and replace the one with the lowest voltage.
     
  7. liquid_tr

    liquid_tr Rookie

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    you can save any "low voltage" pack, that the lipo charger doesnt see by charging the pack in NiCd or NimH mode without balancer for 20-30 seconds. this will punch up the voltage in the lipo just enough for the lipo charger to see. then continue on with the proper LiPo charger.. This is by no means "unsafe" - presuming you know about basic electricity and battery chemistry. This has no risk if the LiPo pack is not damaged in anyway physically. But still do it on your own risk.. Treat these Lipo packs as basic capacitors..
     
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  8. ShadowRyder

    ShadowRyder Cadet

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    I left one of my 1000 mah batteries in the truck for about 2 days when the weather was the coldest around here. I know that it was low enough that the esc was cutting the motor off.

    when I went to charge it tuesday it was so low that the charger wouldnt read it. so I did like Shawnee did and took another 1000mah battery and hooked them together ( red to red, black to black) and counted to 5 and unhooked them. I took the dead battery and hooked it to the charger and it charged like there was never a problem. Had me worried that I would have to buy another battery. But it works fine now.
     
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  9. JettaManDan

    JettaManDan Administrator

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    what i've done, and mentioned before, was setting my charger to NiMh mode at .5 amp and hit the pack for about 30 seconds with a charge..and then shut it off...then do it again till you see 3v per cell in each pack..then hit it with a low amp lipo balance charge..i've rescued like 10 packs this way after they have been down near zero...is it safe? hell no...

    but it has worked...

    do this at your own risk..

    the OP's method of pack to pack is not a safe one...i wouldn't do it that way...

    Dan
     
  10. That's the way I would do it. I'm not risking a good lipo just to try to save another
     
  11. all4smallrc

    all4smallrc Airman

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    Yep. I've used the same method a couple times Shawnee. It's completely safe as long as you are careful not to short the lipos in the process. Sorry Jbirky, but you are way off on this one. DO NOT use a lead acid battery! This is potentially dangerous. Hooking two lipos together, positive to positive, negative to negative is essentially just putting them in series. They will naturally balance each other out partially, and the charger will do the rest once the voltage has come up enough. It's completely safe as long as you are careful and watch the voltage and temp. Actually, this is even safer than using a NiMh charger as long as it is done right. :)
     
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  12. blaumph2cool

    blaumph2cool Ace Pilot

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    Thanks Dan!! you saved my bacon...I thought my 3S Lipo was toast (down to 1.8v in one cell). Did just like you said and its now on balance charge.

    Thanks,
    -Chris
     
  13. LukeWarm

    LukeWarm Top Gun

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    It is safe, monitor the heat. If you have to do this, the battery is not as good as it was before the problem. Take extra precautions in the future when charging that battery.
     
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  14. john bero

    john bero Rookie

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  15. john bero

    john bero Rookie

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    I agree fully with what is said here. If you are going to try any of the saves mentioned in this thread, consider a couple of safety measures. 1.) Use a safety bag, or at least mount the battery pack in a glass or ceramic jar packed with sand, wires up. Have a quart of water handy to flood the battery and sand if necessary (you will know when it is necessary). 2.) Consider doing this outside or at least in a place where smoke and fumes are not an issue. (Exploding lipo’s are very gaseous and noxious) The term explosive, though correct, is a little misleading. The event starts slowly and ramps up quickly causing a lot of fire and smoke. If you are lucky, it will only smoke. Also, consider charging only the affected cell either through the balance port or by clipping the charger to the individual cell with alligator clips. Start the charge at very low amp settings and keep checking progress with a VOM, never exceeding the 4.18-4.20 volt max. This will require some expertise and skill. (Do not attempt unless proficient @ working with live circuits.) An alternative, is to un-pack the cells and discard the bad one, it can be replaced if you are able to find an exact replacement. Or, you can make a small pack out of the remaining cells erg: going from a 4S to a 3S. Only experienced technicians should attempt this.
     
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