Elu SAB75K Batteries

Discussion in 'Tool Talk' started by doobleshaft, Sep 8, 2013.

  1. big all

    big all Screwfix Select

    if you reform batteries you must match the cells as in type[lion/nicad/nmh]
    and the capacity with the same amp hour as in 1.5 1.7 2ah ect
    the reformed batteries will have limited life off a few months
    shapping batteries will be at best a short term solution
    in other words 90%  off short term fixes  do not help to any extent a battery that is failing will have virtually no extra use on average with "zapping" or simmilar treatment
  2. doobleshaft

    doobleshaft New Member

    By reform do you mean replace cells?

    I've never had a shortage of life when replacing cells but then I check every cell to make sure that at the start of the procedure it holds minimum 1v and after charging it holds 1.2 or 1.3v minimum.

    By doing this I've had battery packs last a year and more still giving good service.

    Zapping the pack seems to have little success. Sometimes zapping cells does but rarely. If you can't open the pack then there's nothing to lose from zapping the pack. Sometimes I find if there is little voltage in a pack and you zap it the pack will take a charge. Most though are no better at holding a charge after thoug

    The best way to do this if you really want them to last is to buy new cells and change them all. This is tricky though and best done with a spare for reference. Spot welding the tabs on is by far the best way of reconnecting tabs as there is less heat and less chance of damage to the cells.

    I have a Panasonic 12v pack that just dies within minutes of a full charge but the cells are easy to change in a small pack so going to see what happens. May be selling this one as I have too many with dead or dying packs around.
  3. Ray Retired

    Ray Retired Active Member

    Hi big all... Cheers for that reminder, but kinda figured replacement battery cells will have to be compatible in terms of amp hours & chemistry.

    Not sure I understand what you mean when you say... "the reformed batteries will have limited life of a few months".

    Surely if ALL the Sub-C cells are replaced with compatible branded cells then the battery pack will be as good as new... No??
  4. doobleshaft

    doobleshaft New Member

    Yes Ray Retired. If you replace all the cells there's no reason why they won't last years especially if you select NiMH cells.

    The only limitation will be the life of any electronics in the pack. There's usually something in there even for the cheapest packs which I can't remember the name of at the mo.

    Personally I go for testing the cells and if they have a voltage of 1v+ they should be ok but if 1.2v or 1.3v should perform normally. There is frequent mention of balancing the packs to preserve life which means ensuring that all cells have the same voltage. The only safe way I know of to do this is to completely drain the pack so all cells show as close to zero as possible.

    Otherwise you can zap the cells and try to make sure they all show the same voltage but this isn't so safe (though I've not had any problems) and it's very hard to ensure the same voltage is retained in each cell. The brand is pretty much irrelevant to be honest as trial and error is the only way to identify which cells are the best. Despite brand image many are just a brand sleeve put on a cheap battery from China but I do understand the point.

    I have heard of hospital staff zapping batteries (lead acid ones even) with a defibrilator. Personally I don't think this is a good idea...
  5. Sean_ork

    Sean_ork Screwfix Select

    if you drag a cells voltage down to near zero you've quite effectively killed that cell, you might have some joy bringing it's voltage back up to it's 1.2v (for a nicad) norm, but it will plummet under load - the only way to properly balance nicads is to individually charge them using a constant voltage source, the end point is deemed be when the charge current has dropped to a negligible level (less than a millamp)

    SLA batteries are more forgiving in terms of their ability to withstand large currents in order to cleanse the plates, BUT you have to be very sure of the batteries chemistry before you try using any C+ (rather than C/) methods of waking them up, C+ chargeing at the rates mentioned is a great way of making to very hot, and often they will explode - so be careful folks
  6. doobleshaft

    doobleshaft New Member

    SLA? Do you mean sealed lead acid? Not sure I agree there (gel lead acid batteries do tend to be better at this) but to be honest there are mixed reports of whether there is a need to completely drain NiCd cells or not (definitely not needed for NiMh). Some dispute the memory effect and others insist that it exists giving ways to allegedly fix the cells. I'm not convinced either way personally but only when a cell shows absolutely zero have I found that they can't be recovered.

    No idea what you mean by C+ or C/.

    Constant voltage charging by individual cells is going to be difficult in a pack, but would be ideal. A means of clamping to each cell is going to be awkward at best or impossible on some packs e.g. Hitachi 18v NiCD/NiMH which hve two cells in one tube. I do have a constant voltage supply that can provide 1.2v but it is at 8A which I'd be concerned about using. I'd have to have a way of monitoring the current taken by the cell which I don't have short of using a separate meter.

    Anyone know of such a charger that can clamp a cell in a battery pack?? If so and price is right I'd be happy to have one but still impossible to get them all spot on the same, just getting them close would be a good start though.

    Yes I've noticed the heat does rise somewhat if you use a higher current or higher voltage than would be expected so agree be careful. If you decide to zap with a high voltage do it briefly (a fraction of a second then remove) and repeat but keep checking the temperature at least to touch, stopping if you detect it getting warmer than normal charging. Wise also if you do this to have at least goggles on or a welding mask. Ideal is one that goes dark automatically when it detects a spark as I have.

    I have packs which I could show photos of that are warped due to the heat when being charged making them unusable. Sadly these were being charged on their charger and also killed the charger. A sign that I need to modify the replacement with a fan to blow the air through to help cool it.
  7. big all

    big all Screwfix Select

    yes ment odd cell replacing by canabalising 1 pack to fix several
  8. doobleshaft

    doobleshaft New Member

    That's what I've been doing so far but also bought new cells for some. Hitachi 18v take 4/5 sub c while most take sub c. So I had to purchase new cells for this pack. If someone asks for me to revive their dying pack I recycle known good cells rather than buy new unless they want to provide them...

    I've noticed that compatible packs are larger probably because they use the larger sub c instead.
  9. Sean_ork

    Sean_ork Screwfix Select

    cells usually have a max recommended chare rate loosely based on their Ah capacity - so a C10 rate of charge (of the Ah rating) - would be 100 milliamps for a 1Ah battery - these figures are just for example btw

    so C+ charge rates would be charging at anything above their specified C rating - putting 10 amps at 52v would be fine for my 1100Ah Rolls array, but putting that through a C sized nicads might be an exciting and interesting experience
  10. Jcacob

    Jcacob New Member

    Well I have some or so old 9v BearWalts, that either refuse to charge or hold a poor charge been significance to recycle 'em but will be looking into the chance, of changing cells.

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