18650 gurus - want to upgrade cell

Discussion in 'Electronics & Electrics' started by trackhappy, Jul 12, 2016.

  1. trackhappy

    trackhappy Member

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    Hey guys. I'm kinda new to Li-Ion batteries, or at least new to actually tinkering with them.

    I bought this work light and being the person I am, the first thing I did was crack it open and have a look inside. I was surprised to find a general lack of circuitry, and a seemingly no-name battery. While I'm happy with the quality of the worklight, and the light output, I would like to get a bit extra runtime. I tested the light and it seems to get just a bit over 4 hours on full power, which is about right.

    Plugging these values into a calculator,

    2100mAh, 500mA discharge (tested with multimeter) = 4.2 hours runtime.

    If I swap this battery for a Panasonic NCR18650, I should get between 6 and 7 hours runtime, which would be awesome. I've had a play around with the case and I can only really fit the one 18650 in it. But that's ok.

    So, some details which might help, along with photos.

    Both the wall and car charger output 4.2v. Wall charger 600mA, car charger can't be bothered to check. I'd also like an opinion as to whether the wall charger is decent quality or not (is it safe?).

    There is no apparent charging circuitry, apart from the PCB on the battery. I can't read all of the part number but I THINK it is an FS8205A. Someone will have to confirm.

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    Note that I peeled the outer plastic off the battery before taking this photo. There were no identifying marks on the plastic.

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    Sorry for all the pics! I just want to make sure I'm doing this mod right. I'm assuming all I need to do is transplant that PCB on the old cell to the new one, and I'm good to go? Or is there more to it?

    Cheers guys.
     
    Last edited: Jul 12, 2016
  2. dakiller

    dakiller (Oscillating & Impeding)

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  3. OP
    OP
    trackhappy

    trackhappy Member

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    Not even these? Or are they like memory cards in that they're nearly always fake?
     
  4. OP
    OP
    trackhappy

    trackhappy Member

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    Sorry to bump so soon, but would those cells on eBay be any good? I gotta do some stuff in that area today so thinking about swinging by to pick them up.

    Cheers.
     
  5. SLATYE

    SLATYE SLATYE, not SLAYTE

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    I've used some that looked just like that and were branded as 3200mAh Panasonic 18650Bs. Actual capacity was around 2600mAh, which isn't hopeless but is definitely not what was advertised.
     
  6. reflex898

    reflex898 Member

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    Got any dead laptop batteries? how about looting the good cells from them. I've done it a lot. It's cheap and generally only 1 or 2 dead cells I've come across.
     
  7. RobRoySyd

    RobRoySyd Member

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    I've had packs made up by Battery Space. They do sell a range of 18650 cells, they will not sell unprotected cells. They've been in business for years and claim to have a certified testing facility which is good because shipping these things by air can be a challenge without certification.
    Currently they have the LG 18650 3500mAh cell for USD 8.95. Last time I bought off them shipping charges to Au were reasonable.
     
  8. Thrawn

    Thrawn Member

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    Fasttech, gearbest has cheap and genuine cells.

    Also, the charge and discharge circuitry may affect the cutoffs. Presumably it was designed for the original battery characteristic and may not be ideal for another model cell (with an unprotected cell it may even get dangerous)
     
  9. RobRoySyd

    RobRoySyd Member

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    No.
    Any new cell that you're likely able to buy will come with that PCB already fitted. That PCB is there to protect the cell from getting into a state where lots of magic smoke and flame is likely.

    Possible causes of a Li-Ion cell having a catastrophe include too much current flowing in / out of the cell and discharging the cell below a certain voltage. I'm not 100% certain of this but it'd be safe to assume the parameters are cell design specific i.e. even if you could transplant a protection PCB to another cell it might not be set to the correct values for the other cell.

    Another concern is how is the existing cell connected?
    Not clear from the photos if it's in a battery holder or if the wires are directly connected. Soldering wires to a Li-Ion cell is a bit of an art, generally connection is made by spot welding solder tabs to the cell. The supplier I posted a link to above will fit solder tabs to a cell for 25c per tab.
     
  10. wpra3

    wpra3 Member

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    My trick to solder on these battery is to sand the surface a little bit with high grit sand paper. If the solder doesn't stick, sand it again, it should work.

    Try to salvage the battery from some powerbank or laptop, that is way better than the 'brand new' from ebay.
     
  11. miicah

    miicah Member

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    Do you have a guide on this? Good chance I could have access to around 100+ laptop batteries in the near future.
     
  12. MacroP

    MacroP Member

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    In my experience, the slender PCB the OP shows is a proper charging circuit which will also protects the cell. Looks like a mosfet and change controller on the one small PCB. And it can be safely transferred IMO in most cases unless the original cell is a LIFE or something which it is not anyway. I've found most 3.6 and 3.7 rated cells charge to 4.0-4.2volts and discharge safely to 2.8 to 3.0V. Some may go a little lower but there's not much gain anyway - the voltage drops off very fast. 95% of the discharge capacity is somewhere between 3.0 and 4.0 volts. There are some cells that charge to 4.35v but these are much rarer and charging them to just 4.2v will still give you 95%+ of full charge anyway.

    A simple 'protected' cell has a button on the tip which adds a couple of mm to the overall length. The is for simple overvolt and undervolt protection but is does not regulate and certainly does not do CC/CV charging. I use these in things like cheap head torches which don't come with any protection circuitry.

    You can buy genuine Panasonic B cells with no protection (button), protected, and also with solder tabs (unprotected) that are pre-spot welded on. Makes it very easy to attach/solder a charge PCB to it, like the OP has. I'd recommend these for the OP.

    I buy mostly from Fasttech but I have bought from an Aussie seller on eBay a few times who stocks these variants of the Pana B cell.
     
    Last edited: Aug 22, 2016

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