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Thread: NiMH cells at 0V, won't charge? ... Tip to Charge them

  1. #1

    Default NiMH cells at 0V, won't charge? ... Tip to Charge them

    Last year I decided to go all "Rechargeable" for flashlights and other devices that use AAA thru D cells.

    My main use is for an 8 cell flourescent lantern and 4 cell Maglite (all D size).
    They both get used quite often in the Winter season.

    I purchased the Accumanager20 and CTA 12000mAh D cells and like both.
    This was quite an investment, but well worth it as long as I get plenty of use out of them.

    Unfortunately, I didn't use the lantern for a couple of months and 8 D cells went to 0V. I put them in the Accumanager20 and as you can imagine they would not charge due to being at 0V (initially, I was worried and bummed that I had ruined the cells and wasted my investment.

    Determined to do what I could to get the cells recharged, I put the cells into the Accumanager20 and used a charged AA size and wire in parallel with each D cell, letting the LED blink around 10 times, then removed the parallel AA cell and wire and moved on the the next D cell.

    Once I had all the LEDs blinking, I let the D cells charge for about 5 minutes before removing them from the charger.
    I unplugged the charger (making sure that it was reset), plugged it back in and placed the D cells in the charger for a normal charge cycle.

    The CTA 12000mAh D cells came up to full charge and work as great as ever.

    Whew!

    Just wanted to share how I did this, I couldn't find much information on how to revive a NiMH cell when it has been sitting too long and lost all of it's charge (to 0V).

    I do like the Accumanager20, it takes a while to charge NiMH cell of this capacity (12000mAh), but it does so topping them off nicely.

  2. #2
    Flashaholic*
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    The old "battery jump start" trick. I have an Accumanager20 and sometimes it refuses to charge the cells if I drained them. The jump start trick works well and never failed to give it enough static voltage for the Accumanager20 to take over.
    Peak Pacific AAA UP brass (EDC) E01 (keys), Peaks, Arcs, Fenix, Q5 Aspheric HA-III Mag etc.

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    Flashaholic* Sub_Umbra's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    There is a very similar 'jump start trick' I used successfully some years ago: just hold a second (charged) cell of the same size right next to it in your hand. Hold both cells and two paperclips to act as jumpers across the contacts for a few seconds. That will often give the 0V cell just enough of a charge to be recognized by the smart charger.

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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    I was using that "jump start trick" on some neglected AA cells. I happened to my low current clamp meter right there and measured the draw. Most of them were around 300ma or so but a few were over 3A! Those cells didn't gain anything by jump starting and I tossed them.

    Watch the paper clip, it may get a bit hot!! I used some clamps that I have made up with leads for charging.
    Bill

    I'm a retired mechanic not a electronic/electrical engineer!

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    Flashaholic MikeHunt79's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Hmm, I wonder if there's anything similar that would work for 0v Li-ion cells?
    Fenix L1T - 7W golston modded with Prolight 5w star - HY SWAT modded 2 stage - Nuwai TM-800X3 - currently getting parts for a modded mag 3D

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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Quote Originally Posted by MikeHunt79
    Hmm, I wonder if there's anything similar that would work for 0v Li-ion cells?
    If the Li-Ion is protected it may have triggered the circuit and as soon as a it's put on a charger it'll RESET! Now, if it's truely zero, it's suggested to charge at about 50ma till the cell's voltage reaches around 3V and then use standard charging methods.
    Bill

    I'm a retired mechanic not a electronic/electrical engineer!

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    Flashaholic* MrAl's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Hi there,

    In the past i have used the jump start trick using a DC wall wart that has a capacitor
    inside. Plugging the wall wart in, the cap charges up to maybe 9vdc. Then,
    connecting the 0v cell to the wall wart (polarity observered) for one second.
    The extra current pulse from the cap usually gets the cell voltage up to maybe
    0.5v or so, or else do it again.

    I like the cell to cell idea too, but i would be worried that the current from the
    good cell would be too high and might cause a problem.
    Take care,
    Al
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    MrAl, have you ever had a problem charging a flat NiMH with your CCrane? I think those chargers could put a charge into a dummy cell. I guess it's the "soft start" that does it.

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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    This is a bit OT but the 50ma charge till 3V per cell I mentioned above. Well, I happen to run one of my brand new Ipower Li-Poly 9V cells down to 3.2V! I have a variable voltage/current supply which I've used on single cells.

    I set it up for around 50ma at just over 6V for the two cell battery. I get zero current. I tried it on a single cell and it charges, of course it's one that's not been driven into deep discharge too. What's up with this???
    Bill

    I'm a retired mechanic not a electronic/electrical engineer!

  10. #10

    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    For 8 cells, the easy trick is to connect them all in series, then charge it with a 12v auto-charger with a brake lamp in series (change between low, high or both filaments to change current) to limit current. Charge like this for an hour to get things started.

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    Flashaholic* Ty_Bower's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    I've used a 9 volt battery (like the kind you used to find inside AM radios, or smoke detectors) to jump start a 12 volt lead-acid motorcycle battery. I had to leave the 9 volt connected for the first half hour or so of charging. If I disconnected it, the smart charger would once again decide the motorcycle battery was dead, and it would stop charging.

    The 9 volt got sacrificed in this experiment. It was a messy, oozing pile of goo by the time all was said and done. I guess I'm lucky it didn't pop, burn, or explode. The 12 volt was successfully resuscitated, and went on to live a useful life.

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    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Yello'

    I recently purchased six NiMH 4/5 Sub-C GP2200's, and the speedy box charger (I believe its made by Vantec) for my ROP. The batteries arrived before the charger did, and though it wasn't reccomended, I let my patience (or lack of) get the best of me and I put them in my ROP.

    I completely drained the batteries and now they won't charge. I know the charger works, so I am thinking that I just need to jump the GP2200's.

    Has anyone jumped Sub-C's before? If so could you give me some tips to get started.

    Can I just use any old battery, or must I match the voltages of the jumper battery to that of the jumpee? Must I match the mAh?

    could I use a NiMH rechargable AA to jump the GP2200's?

    Thanks in advance
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  13. #13

    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Should work fine as long as it's the same voltage and also a NiMh.
    Once it starts to take a charge remove all cells from the charger, unplug it to reset it then place the cells back in for a normal charge cycle.
    I let mine charge for around one minute before resetting the charger.
    I used an AA size to jump a D size.

  14. #14
    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    The AA and the Sub-C won't fit in my charger together...

    If I hold the batteries in series outside of the charger, could i use copper wire to make the connection to the charger terminals?

    Can I hold the whole assembly with my fingers (do i have to worry about electricution)
    or should I make the connection another way?

    If I cannot just hold the wires in place... any suggestions as to what to do?
    EDC: HDS Ra Clicky T SN7156 (100L WWGD) or Lunasol 20 (I can't choose between the two)
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  15. #15

    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Never thought about the jumpstart trick. I'll have to consider that the next time my AccuManager20 gets stubborn with the low voltage. Usually if I power cycle it enough times, it will work. Or I put the battery in my VERY SLOW mattery manager charger (from Real Goods) for a half hour or so, and that takes care of the voltage.

    -Mike

  16. #16

    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    I did the jump start trick with a bad cell that wouldn't charge and was at 0.03V. It charged but about 10 days later reverted back to 0.03V.

    This was a CTA 12,000 MaH cell, but the distributor replaced it promptly.

  17. #17
    Flashaholic*
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Aepoc, at less than 40 - 50 volts and dry hands, you don't have to worry about a shock. I'm not sure about NiMH cells but NiCds sometimes fail from internal shorts - essentially they become a wire. In this case you might be dumping 5 - 12 amps into the dead cell from the good one and the connecting wires will get HOT.
    I'm absolutely certain that I need another flashlight.

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    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    thanks jayflash
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    Flashaholic* AndyTiedye's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    I thought this "jumping" procedure was to try to BURN OUT the short-circuit in the cell.

  20. #20
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    Quote Originally Posted by wptski
    This is a bit OT but the 50ma charge till 3V per cell I mentioned above. Well, I happen to run one of my brand new Ipower Li-Poly 9V cells down to 3.2V! I have a variable voltage/current supply which I've used on single cells.

    I set it up for around 50ma at just over 6V for the two cell battery. I get zero current. I tried it on a single cell and it charges, of course it's one that's not been driven into deep discharge too. What's up with this???
    if a li-ion is deep discharged, its junk. if it was down to 0 for any time it not only will be junk, but its dangerous (gets hot) to charge it.
    something about the plates not having enough metal left to "seed" the existance of an anode, or cathode or something?

    thats weird because the 9V li-ions i got (cheap unmarked china) had a Single protection curcuit in it. it doesnt balance, but it would keep the batts from a deep discharge for a while. BUT also remember if it got discharged complely AND was not re-charged quickly after that, it would self discharge itself to death. so even with discharge protection, there was no Balance, and over time a fully discharged part of it, would ruin the battery.
    SO
    IMO they aint ready for smoke alarms yet. and they really aint safe yet, but still a good battery vrses replacing one all the time.
    use it or lose it.
    Last edited by VidPro; 11-30-2006 at 04:59 AM.

  21. #21
    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    I think somebody here might enjoy these pics:

    [img]file:///D:/Documents%20and%20Settings/Zachary/Desktop/Phone%20Stuff/Pics/Flashlights%20and%20Beamshots/1207061554.jpg[/img][img]file:///D:/Documents%20and%20Settings/Zachary/Desktop/Phone%20Stuff/Pics/Flashlights%20and%20Beamshots/1207061554.jpg[/img]
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  22. #22
    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    sorry... I guess i don't know how to post a pic. Anyways, they were of a jumper I made with some paper clips, a 1.2v AA NiMH, one nut, a solder iron and some electrical solder.
    EDC: HDS Ra Clicky T SN7156 (100L WWGD) or Lunasol 20 (I can't choose between the two)
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  23. #23
    Flashaholic Aepoc's Avatar
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    Default Re: NiMH cells at 0V, won't charge? ... Tip to Charge them

    There... one of the pics is my avitar
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