What's a DIY method to check Li-Ion batteries ?- Mtbr.com
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  1. #1
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    What's a DIY method to check Li-Ion batteries ?

    What's a DIY method to check Li-Ion batteries ? Last year my son & I DIY'ed a couple of LED lights setups. They look and work great (iBlaast equiv great, see http://forums.mtbr.com/showthread.php?p=5517151) but from new my battery pack has always been a little down on duration compared to the other. Recently it's deteriorated really quickly, now less than 1/2hr with driver set to 700mA :-(
    I'm thinking one cell has died….but which one. Thought I ask the 'how' question before cutting into the sealed battery pack.

    Battery pack is a
    Li-Ion 18650 14.8V 2200 mAh Rechargeable Battery Pack with PCB Protection
    http://www.all-battery.com/li-ion186...rotection.aspx
    It's not a driver or charger problem causing battery failure as using nightlinghtning bflex
    http://www.nightlightning.co.nz/diy%20details.htm
    And a smart charger
    http://www.all-battery.com/universal...v1-4cells.aspx

  2. #2
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    Exile, I had a bad cell in a battery pack. Check the voltage of each cell and they should be above 3 volts (more like about 3.6 ish).

  3. #3
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    Charged ? Uncharged ?

    Pack says 14.8V so divide by 4 = 3.7V each.
    Charger info says cuts out when full or cells reach 4.2V peak.

    I thought I would need to do something like testing while under load.

  4. #4
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    I'm pretty new to this battery stuff, so someone with more experience may correct me but:

    Testing each cell whilst the pack is under load, especially towards the middle or end of it's overall charge, should give you an idea if a single cell is bad. There should be a marked voltage difference with the bad cell. I've been testing a new 4 cell pack, and the voltage readings that I'm getting across cells are very constant (off memory, within .05V but I'd have to check again to be sure).

    You're running Li-ion cells with nominal voltages of 3.7. The *initial* unloaded voltage should be 4.2 per cell, then they drop rapidly towards nominal under load. The PCB probably cuts out the pack when one cell hits 2.4 or 2.5V, which not healthy in the long term for Li-ion.


    This is a good resource on batteries and charging: http://www.buchmann.ca/Chap5-page3.asp

    If you've just got one bad cell and can identify it, I'm not sure whether simply replacing it is a good option. When building a simple pack that doesn't allow for balance charging (such as the all-batteries one), you're supposed use matched cells charged to identical voltages. The cells are supposed to stay balanced throughout the life of the pack by virtue of being matched in the first place, so just throwing a new cell in there is going to throw this off. This is especially important as that 'smart charger' is actually pretty dumb as it doesn't monitor and adjust the state of individual cells. Again, I'm fairly new at batteries myself, but I've read enough about the potential dangers of Li-ion to convince me to be fairly cautious when messing about with packs.

  5. #5
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    The nightlinghtning bflex does it's series of warning battery level flashes before turning off so I doubt the batteries own PCB is doing anything.
    Seems what we thought was 'smart' charger 12 months ago is no longer smart !

  6. #6
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    This is another site full of information: http://www.batteryuniversity.com/index.htm

  7. #7
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    Based on comment so far my plan right now is to cut open the wrapping and check voltages across each cell with the lights on. I'm hoping one is way lower and I can replace just that cell.

  8. #8
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    you should not just replace one cell. All cells muct match within at least 0.05V.
    The individual cell capacity will be different and then you risk overcharging that one new cell which will be dangerous.
    However, if you have a decent charger and balance plugs on the cells you may be able to get away with it.

  9. #9
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    My experience with Li-ion packs is they don't last for the exact reason the OP has stated.

    I've ended up rewiring the packs to accept a balance charger and had better results. It costs more in the short run for the balance charger, but over the longer haul, the packs last longer.

    The problem I ran into though is that I had to discard the PCB in order to have the balance charger work correctly. A component on the pcb becomes hot enough to burn my hand during charging.

    Now I occasionally kill cells by over-discharge. I tried wiring the pcb as a plug-in module for the battery pack, but it requires a bias(?) voltage to be applied to the output terminals each time it's disconnected or it won't work.

    I'm really not happy with the pack+pcb+smart charger setup, or my own.

    Walt

  10. #10
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    Am I correct in saying that you pretty much have to choose between running balanced charger leads or a protection PCB and that most PCBs provide over charge protection but do not actually balance your cells? Am I missing somthing?

    Some one has to manufacture a do it all battery management board that is simpe-ish and does not cost the earth. Something that connects to the cells individually and provides all the protection features of a traditional PCB, fuel gauging, and balanced charging. Just connect a load to one set of pin headers and another set of pin headers for charging that accept a 12 or 24v Dc source. Oh and something like this built into a turbo ferret style holder would really be a hit. Then I could permanently attach my pack to the light head with no connectors and just a plug on the pack for charging by connecting a basic wall wart.

  11. #11
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    Quote Originally Posted by Walt Dizzy
    The problem I ran into though is that I had to discard the PCB in order to have the balance charger work correctly. A component on the pcb becomes hot enough to burn my hand during charging.
    When you wired up the PCB were you charging through the board? Did you try bypassing the board (balance taps, positive and negative leads) completely? I'm wondering as I'm running the same non-PCB setup and was about to add a PCB.

    Another option would be to use a balancing PCB, which as far as I can tell, slowly balances the cells after the pack has been charged. The only downside of this is that you can't use the pack immediately post-charge, and balancing PCBs are pretty sizable- certainly too large to fit neatly against a 4 x 18650 cell pack.

  12. #12
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    Quote Originally Posted by bikerjay

    Some one has to manufacture a do it all battery management board that is simpe-ish and does not cost the earth. Something that connects to the cells individually and provides all the protection features of a traditional PCB, fuel gauging, and balanced charging.

    I think you mean


    http://www.batteryspace.com/index.as...OD&ProdID=4343

    plus

    http://www.batteryspace.com/index.as...OD&ProdID=4479

  13. #13
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    Quote Originally Posted by bikerjay
    Am I correct in saying that you pretty much have to choose between running balanced charger leads or a protection PCB and that most PCBs provide over charge protection but do not actually balance your cells? Am I missing somthing?

    Some one has to manufacture a do it all battery management board that is simpe-ish and does not cost the earth. Something that connects to the cells individually and provides all the protection features of a traditional PCB, fuel gauging, and balanced charging. Just connect a load to one set of pin headers and another set of pin headers for charging that accept a 12 or 24v Dc source. Oh and something like this built into a turbo ferret style holder would really be a hit. Then I could permanently attach my pack to the light head with no connectors and just a plug on the pack for charging by connecting a basic wall wart.
    You can get PCB's that also balance as well as protect from over/under charge from battery space and I think allbattery sell them too.

    But they are expensive especially if you want to make a few packs.

    I have put balance plugs on all my packs and then the cost of a good balance charger is paying for it's self.

    Nothing is perfect though and you have to use a driver with low voltage cutoff To prevent over discharge or there are all sorts of things in the RC world that plug into the balance lead that will do the job.

  14. #14
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    I charged the pack Wednesday evening & today (Friday) cut it open to do some tests.
    Nominal pack voltage is 14.8V, each cell 3.7V and peak charge of 16.8V (4.2V/cell)

    Cell 1 2 3 4 Total voltage
    Unloaded
    4.18 3.77 3.70 4.18 15.82

    Loaded via nightlighning bflex driver set to 700mA
    4.08 3.68 3.62 4.05
    And falling over time (random checking intervals)
    4.06 3.67 3.61 4.04
    4.05 3.65 3.61 4.02
    4.05 3.65 3.60 4.01 15.31
    3.97 3.59 3.00 3.96 15.25
    Then the bflex flashed it's first battery level flashes and voltage fell very rapidly over just a few seconds
    ? ? ? ? 14.67
    ? ? ? ? 13.9
    Before the batteries PCB cut off and total went to zero.
    So my light was going off because of battery cell cut off , not via the bflex cut off activating.
    I then measured individual cells when cut off and got
    4.08 3.70 3.02 4.09
    My guess is under load cell 3 dipped to the battery PCB cut off of 2.4V

    Conclusion of all this ?
    Cells 1 & 4 are probably ok but cells 2 & 3 are dead with 3 being the worst. The batteries PCB would have prevented individuals cells ever being above 4.35V or below 2.4V hence why 1 & 4 are still ok (?). Maybe I could replace 2 & 3 but am concenred about risk soldering cells.
    While it seems a good idea to buy a new individual monitoring charger and compatible battery pack, I'm just going to buy a similar pack again. I've just been unlucky this time to get dud cells.
    Can't justify a $250+ charger for the amount it's used. At US$40 for a battery pack I could replace packs several times before a new charger could be justifed.
    Perhaps in couple of years the individual monitoring chargers and packs will cost less. I'll upgrade then.

  15. #15
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    It looks to me like 2 & 3 were never fully charged and the PCB stopped the charging as soon as one of the cells reached 4.2v, that's the problem with a non balancing PCB.

    something that could be worth a try is to drain cells 1 & 4 so that they are the same voltage as 2 & 3 (balancing them), then when you charge the pack they are all starting from the same place and should all reach full charge at the same time.

    I don't know about where you live but I am sure that you can pick up a balance charger for less than you think. I only paid £35 GBP for a 6 cell one.

  16. #16
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    What sort of chargers have you been looking at for $250? Reasonable hobby chargers can be had for around $50 including shipping (Turnigy Accucell 6 is probably the cheapest one with good reviews).

    Anyway, yeah, just replacing the pack would probably be a good option.

  17. #17
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    Don't know what charger it was. It was just one I noticed on advert area at bottom of all-battery page when I was checking my battery, charger & PCB specs

  18. #18
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    Yetibetty, where can you get balancing plugs from, are they a standard size?

  19. #19
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    Balance leads are available from RC stores. Try some of these:

    http://www.liposack.com/Dealers/Dealers.htm

    Balance leads vary according to how many cells you need to balance (e.g. 2 serial, 3 serial, etc) and by the shape of the plug (determined by your brand of charger).

  20. #20
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    Quote Originally Posted by G_Mozz
    Yetibetty, where can you get balancing plugs from, are they a standard size?
    As Womble said you can get balance plugs from RC shops.

    However, they haven't standardised them and there are a few different types about. Best thing to do is to take your balance charger to an RC shop and they will have the suitable plugs for your charger.

  21. #21
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    Thanks!

  22. #22
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    Ok next problem, replacement battery pack from all-battery.com is US$37.99 but shipping to New Zealand is US$69.59 !!!!! It's a little light weight pack, not a big heavy box !!!!!
    No way I'm paying that rip off shipping price. Where else can battery packs is brought online from ? Dealextreme only seems to have individual cells. But they do have free shipping :-) Should I just buy a few extra cells and have a go soldering them ?

  23. #23
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    Try asking if they will ship via USPS air. Batteryspace will do so if asked.

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    They won't. I asked.

    But I just stumbled across these 18650 holders
    http://www.turboferret.co.uk/Index.htm
    So new plan is to use that holder and from dealextreme get 4 individual protected cells with free shipping :-)

  25. #25
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    Quote Originally Posted by uk_exile
    Ok next problem, replacement battery pack from all-battery.com is US$37.99 but shipping to New Zealand is US$69.59 !!!!! It's a little light weight pack, not a big heavy box !!!!!
    No way I'm paying that rip off shipping price. Where else can battery packs is brought online from ? Dealextreme only seems to have individual cells. But they do have free shipping :-) Should I just buy a few extra cells and have a go soldering them ?
    Your lucky, they want $87 to ship to the UK.(hence my home made packs)
    all-battery do have an ebay shop and for some reason, probably because ebay won't allow exessive postage charges the postage is quite a bit less.

    Type Tenergy into the ebay search and it should find it.

  26. #26
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    Quote Originally Posted by uk_exile
    They won't. I asked.

    But I just stumbled across these 18650 holders
    http://www.turboferret.co.uk/Index.htm
    So new plan is to use that holder and from dealextreme get 4 individual protected cells with free shipping :-)
    If you do go the Turboferret route then don't forget to get one of these: http://www.dealextreme.com/details.dx/sku.6105

    BTW I bought a Turboferret holder they are very nice and well made.

  27. #27
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    yeti, how do you make your homemade packs ? Do you use a holder ? Or solder ?

  28. #28
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    I'll just continue to use existing charger. It cuts off on cell voltage so basically same as the sku.6105 you listed. Just it's doing 4 at once rather than 2.

  29. #29
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    I did use a holder but as I required lots of packs with different voltages I now do this madness in post 46 http://forums.mtbr.com/showthread.php?t=494261

  30. #30
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    You can get batteries made up by Siomar in Perth, WA. They make batteries for Nighlightning and a few other down under bike light builders. I'd imagine their postage to NZ would be reasonable.

    I had them make me a couple of batteries over 5 years ago. Recently I sent one back as it stopped working. They tested it and found at least one cell was dead so I'm getting a new one made up as we speak.

  31. #31
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    Thanks, I've emailed them. I did think about a pack from nightlightning as they're based in my city but cost approx double a holder from UK and cells from DX

  32. #32
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    FWIW, I've compared some of those cheapie Chinese-made 18650s (2400 Ultrafires) with a set of Sanyos 2500s. The Ultrafires have been quite random- I've gotten capacities between 1500-1900 (and one dud at 300). A set of 4 Sanyos all gave me 2400 +/- 30mA.

    The folks here and over on CPF seem to like the DX cells as a cheap and cheerful option, but using stuff that is so obviously poorly made just bugs me so I won't buy them again. Admittedly, the Sanyos are unprotected and cost 60% more, but I can mitigate the former and the latter is worth it to me in runtime.

  33. #33
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    That decides it. I'm getting the better option just offfered by Siomar.
    They quoted
    Using 2200mAh Chinese cells AU$50.00
    Using 2400mAh Taiwanese or Japanese cells AU$80.00
    Post AU$12.50
    Express Post AU$37.00
    That's for packaged in heatshrink with leads and inbuilt protection circuit. Siomar pricing for the chinese cells is similar to buying holder from UK and cells from DX. Its more for the 2400mAh japanese cells but if DX cells vary as much as you say it will be worth it spend more now.
    Thanks everyone for your help.

  34. #34
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    I can't read the text but the graph says it all http://www.messerforum.net/showpost....5&postcount=37

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