Modifying a quality battery- Mtbr.com
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  1. #1
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    Modifying a quality battery

    Hi guys.

    I've been following Ledomain's thread about the Panasonic cell'd battery packs from Kaidomain, but I had the thought that they will still suffer with the balancing problem that the cheap Chinese packs have issue with.

    Has anyone replaced the PCM on a cheap pack with something like this from Hunk_Lee?
    7.4V 2S Li-ion Li-Po Battery Protection Balance BMS PCM Current 7A 2S7AW006 | eBay

    It looks like it would be straight forward enough to change.

    Am I putting too much stock in having balanced cells?
    It seems to be a big deal in the RC community.

  2. #2
    RAKC
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    It is for lipo batteries and performance there. Panasonic cells are the best there is really. All I ever do is balance the cells (open the pack up) the first time and go. As long as you dont run down fill discharge all the time, will take a good while before they fall out of balance and need it again. Part of the thing with constant balancing these cells is they have a cycle life. So balancing constantly cycles the battery multiple times each charge. Each time you charge and discharge even a few % of capacity its a cycle. Each time a a pack is balanced it charges all cells the discharges the cells with higher voltage till they even out, then charges more. Some good chargers (rc chargers) charge via the balance port instead which helps that's with lipo packs.

    Can or can't, up to you, just overrated with good cells. Only need a Balance a few times throughout life of the pack.

  3. #3
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    Quote Originally Posted by tigris99 View Post
    Part of the thing with constant balancing these cells is they have a cycle life. So balancing constantly cycles the battery multiple times each charge. Each time you charge and discharge even a few % of capacity its a cycle.
    Everything I've read says that lightly discharging and then charging a lithium Ion battery does not qualify as a cycle. A "cycle" in battery terms is a complete discharge and recharge, anything less is some percentage of a cycle. But still even a small amount of discharge and charge adds up over time, so you're absolutely correct in saying that balance charging contributes to wear on the cells.

    I also agree that for bike light use, a pack made with good quality cells shouldn't require balance charging as long as all the cells start of at the same voltage for the initial charge.

    LiPo cells used in RC applications are a different story because of the way they are typically used with extremely high discharge currents, followed by fast recharging. This can really stresses the cells and amplify small differences in cell resistance leading to out of balance conditions. This can be quite dangerous due to the high currents involved which is why balance charging is the norm in the RC world and even then many folks charge LiPo cells in fireproof containers due to the risks.

  4. #4
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    I'm in the balancing is good camp. I've got some Chinese 18650s that are ~7 years old and though they are down on capacity some, still very usable at ~1600mAh capacity. Since I use them in holders and charge individually, they are "balanced" each charging. Seems like most folks using packs with no balancing ability get 4-5 years before they are way down on capacity or dead.
    GoPro adapters for bike lights http://www.pacifier.com/~kevinb/index.html

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    I was under the impression that in this configuration, balancing was important as the Chargers don't know what's actually going on with the battery other than it was reaching the desired voltage. It could be one cell is developing higher internal resistance and charging slower than the rest. The charger would over charge the other cells to compensate.

  6. #6
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    Quote Originally Posted by soopahfly View Post
    I was under the impression that in this configuration, balancing was important as the Chargers don't know what's actually going on with the battery other than it was reaching the desired voltage. It could be one cell is developing higher internal resistance and charging slower than the rest. The charger would over charge the other cells to compensate.
    That's pretty much true, hence the comment that balancing generally isn't required *if* you use quality matched cells. Panasonic NCR18650s from the same batch would fill the requirement in my experience.

    There certainly is no harm in balance charging them if it makes you feel more comfortable but in that case I'd be inclined to say just get one of the battery cases that allow you to easily remove the batteries and charge them individually.

  7. #7
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    Vancikers way is how I charge my loose cells, I have a set of holders (holds up to 4 cells) attached in parallel. So cells self balance by the time I pull them off. Cells in cases I charge on that first then install, dont mess with for a while, just charge on wallwort. Packs I open up and use clips to hook up via balance port on my charger, double check via dmm before replacing shrink wrap. Then dont worry about it beyond that (for quality cells). Chinese cells I gut the pack, use as loose cells.

    Honestly wouldn't be bad for cheap packs to have a balance circuit.

    As for "overcharging" any of the cells, that's why a protection circuit. CAN'T overcharge, except in the case of cheap Chinese crap that fails to function correctly. The protection cuts off power going to the cells once they hit max voltage. That when you end up with noticeable run time loss. Because protection again cuts off when one side gets to low, the side that isn't fully charged.

  8. #8
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    Quote Originally Posted by tigris99 View Post
    Vancikers way is how I charge my loose cells, I have a set of holders (holds up to 4 cells) attached in parallel. So cells self balance by the time I pull them off. Cells in cases I charge on that first then install, dont mess with for a while, just charge on wallwort. Packs I open up and use clips to hook up via balance port on my charger, double check via dmm before replacing shrink wrap. Then dont worry about it beyond that (for quality cells). Chinese cells I gut the pack, use as loose cells.

    Honestly wouldn't be bad for cheap packs to have a balance circuit.

    As for "overcharging" any of the cells, that's why a protection circuit. CAN'T overcharge, except in the case of cheap Chinese crap that fails to function correctly. The protection cuts off power going to the cells once they hit max voltage. That when you end up with noticeable run time loss. Because protection again cuts off when one side gets to low, the side that isn't fully charged.
    Do we know if those packs have a good protection circuit though?

  9. #9
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    Ledoman has tested some (assuming he checked his). No complaint I know of. I just received my 6 cell version to check (though it is pre-update to 20awg). I'll check protection on it as I have one of the infamous wall wort chargers that charges at 10.3v, the ones that if protection circuit fails is what caused the posts if houses and garages being gutted. I keep it around cause itll charge my Samsung 4.35v cells. I just watch closely with a voltage monitor and disconnect when 2s pack hits 8.7V.

    The failing protection circuit issue is what you find on the cheap stuff where you get some "crazy" light, battery and such for $25. Same place u find these "detonator class" charges.

  10. #10
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    Did not followed this thread before. My opinions goes in two directions. I assume we are talking about quality cells like Kaidoman pack with Panasonic NCR18650B (or essentialy any other good brand).

    1. For average user who don't want to deal with his pack balancing circuit would be nice but it would add to the cost and average user won't bother to replace it anyway so it has to be done in the factory. Average user won't worn out the pack in a 5 years so he might be happy with it just like it is even if little unbalanced. Probably won't notice anyway.

    2. For more demanding and skilled users there are recomended methods to either modify pack with balancing plug (and use hobby charger) or regulary check the voltage (of the pack and/or cells). Tipical indication when the pack is unbalanced happen when pack won't charge fully - ie. to the end voltage as before. Skilled users would tear down the pack, balance the cells and seal it back. Heavy users might check it very often. So those won't need balancing PCM.

    There might be cases when balancing feature has it's use. This is when we have pack we can't or to lazy to tear down and check situation. Ok, no one wants to tear down his packs. Specialy if the pack is hardshell and glued. In this case I would say balancing PCM would be very nice and valuable on long term use even with the best cells used.

    Tig, on 4cell pack from Kaidomain I've tested the current it supports but not limits for evercharge/discharge. The PCM was welded not soldered so I didn't want to ruin it. Based on chip inspection I would say it should work, just the exact limits are unknown.
    I might try to get plain PCM to test and yes I would use 4.35V cells too. Yesterday I've done it on a PCM from KD 2S1P pack the same way.

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