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  1. #1
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    Laptop charger for 4 18650s?

    The chargers i got from DX are horrid. Takes 9 hours to charge 2 of them.

    I have an old laptop charger with a wrecked end. Is it possible to use it to charge my 4 18650s wired to 14.8v?

    It is a 19v 6.3a It powered 8 18650 in series/parallel.

    Im guessing the amprage is a bit high, but I thought I would ask.

  2. #2
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    Your laptop unit is not a charger, it is just a power supply. The charger circuit is in the laptop itself.

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    Ditto what Vanc said that cord didn't charge the battery, it ran the laptop. The charger is usally in the laptop's battery pack itself. That much voltage and amperage would destroy your battery pack. You need a 14.8-16.8v output, probably 1.8 to 2.2A charger to get a safe quick charge. You never want to charge a lithium battery at more than 1C to be safe. (1C is 1xCapacity of your pack - so for a 14.8v, 2200mah pack - 2.2A charge rate would be 1C. for a 3000mah capacity pack, it would be 3A rate for 1C.)

    The prob with your DX chargers is that they were probably designed to be safe slow chargers. That's why they charge at a low amperage rate.

    For less than about $30 shipped you can get a nice charger that will charge about any battery you throw at it.: Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories

    Needs a 12V powersource though - car battery, or a regulated powersupply with 11-17V DC output.

  4. #4
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    Makes sence. I figured it was to high an output.

  5. #5
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    Your lap top power supply can probably be used to power a nice charger the turnigy linked above. Hobbyking is a good place to look for cheap chargers and battery's.

  6. #6
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    Quote Originally Posted by adrenalnjunky View Post
    Ditto what Vanc said that cord didn't charge the battery, it ran the laptop. The charger is usally in the laptop's battery pack itself. That much voltage and amperage would destroy your battery pack. You need a 14.8-16.8v output, probably 1.8 to 2.2A charger to get a safe quick charge. You never want to charge a lithium battery at more than 1C to be safe. (1C is 1xCapacity of your pack - so for a 14.8v, 2200mah pack - 2.2A charge rate would be 1C. for a 3000mah capacity pack, it would be 3A rate for 1C.)

    The prob with your DX chargers is that they were probably designed to be safe slow chargers. That's why they charge at a low amperage rate.

    For less than about $30 shipped you can get a nice charger that will charge about any battery you throw at it.: Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories

    Needs a 12V powersource though - car battery, or a regulated powersupply with 11-17V DC output.
    Can someone remind me what a safe max charge rate is for, say, a 1s2p (3.7v 5400 mAh) battery pack?

  7. #7
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    Quote Originally Posted by Ofroad'bent View Post
    Can someone remind me what a safe max charge rate is for, say, a 1s2p (3.7v 5400 mAh) battery pack?
    I generally charge all my batteries at 1C. So for that 2p pack I would run my charger at 5.5A

  8. #8
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    Quote Originally Posted by irv_usc View Post
    I generally charge all my batteries at 1C. So for that 2p pack I would run my charger at 5.5A
    Seriously? 5.5A for a 2cell parallel pack? I'd been nervous about using 3A.

  9. #9
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    Quote Originally Posted by irv_usc View Post
    I generally charge all my batteries at 1C. So for that 2p pack I would run my charger at 5.5A
    Almost correct. Here is more of the whole story.

    Parallel cells are kind of a special case. If the resistance of each cell is exactly the same you could charge at 1 times the combine capacity. I.E. 2 2200mah cells would charge at 4.4A. However they may have some difference in resistance so one cell may get 2.3 and the other 2.1 causing some degradation.

    1C means 1 times the capacity. In the example above the capacity is 5400mah. A 1 C charge rate is thus 5.4 amps.

    In reality 5.5 would probably be fine but generally the lower the charge current the more cycles the pack will last.

    Some times you can actually determine the make and model number of a cell and find a data sheet. Often the average number of cycles until the pack only has half its original capacity will be listed at different discharge levels and different charge currents. A pack may last 500 cycles at 1C and 800 at .5C.

    Also lithium ion or lithium polymer batteries do not charge at constant current through out the charge. Toward the end of the charge cycle it will be far less.

    I have a lithium polymer pack that is rated to charge at 5C. The capacity is 2.65 amp hours so 2.65 x 5 = 13.25A. My charger will only put out 10A! However I charge at 5A because its still very quick and I want my pack to last a lot of cycles.

    Another example is some 18650 lithium ion cells I had long time ago were 2400mah but only at .8C so 2.4 x .9 = 2.16 at 1C they were 2200mah.

    How conservative or aggressive to charge your pack is a personal decision and should be made based on the trade off of charge time vs number of cycles the pack will last. Some times if I forget to charge until just before a ride I will throw my 2.65Ah 5C charge pack on at 10A and let it fast charge.

    Its still better to fast charge with in the spec and have it run from full to half charge than to go out partially charged and run from half to empty. Running to empty puts a lot of ware on a pack.
    Last edited by bikerjay; 11-05-2012 at 10:30 AM. Reason: added more details

  10. #10
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    Thanks, best explanation I've heard so far. I might even remember this one.

    To get back on topic, you can see there's a lot more to charging than just hooking the pack up to voltage. I have a versatile hobby charger, but for lights I make for friends I just sell them a cheap simple charger.

    Quote Originally Posted by bikerjay View Post
    Almost correct. Here is more of the whole story.

    Parallel cells are kind of a special case. If the resistance of each cell is exactly the same you could charge at 1 times the combine capacity. I.E. 2 2200mah cells would charge at 4.4A. However they may have some difference in resistance so one cell may get 2.3 and the other 2.1 causing some degradation.

    1C means 1 times the capacity. In the example above the capacity is 5400mah. A 1 C charge rate is thus 5.4 amps.

    In reality 5.5 would probably be fine but generally the lower the charge current the more cycles the pack will last.


    Its still better to fast charge with in the spec and have it run from full to half charge than to go out partially charged and run from half to empty. Running to empty puts a lot of ware on a pack.

  11. #11
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    Quote Originally Posted by Ofroad'bent View Post
    Thanks, best explanation I've heard so far. I might even remember this one.

    To get back on topic, you can see there's a lot more to charging than just hooking the pack up to voltage. I have a versatile hobby charger, but for lights I make for friends I just sell them a cheap simple charger.
    What charger are you selling? I have a couple of friends that I'm selling lights to that I'd like to have an inexpensive charger that is worth selling.

  12. #12
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    Quote Originally Posted by adrenalnjunky View Post
    What charger are you selling? I have a couple of friends that I'm selling lights to that I'd like to have an inexpensive charger that is worth selling.
    This is the cheapo one. I just order it for them.
    DC4 2V 1A Intelligent Smart Charger for 3 6V 3 7V LiIon LiPo Battery Pack USS | eBay

    If they want a decent one I get them a Turnigy from Hobby King.
    Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories

  13. #13
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    I gotcha. 1A charge rates not too bad. Unfortunately I've been using buck drivers and 2 LED's in my recent lights - i'd need at least a 3S capable charger.

    The really sick thing is that I can't build a XM-L based light for anywhere close to where you can get a MS clone XM-L setup, complete with battery and charger these days ~$44 shipped from a US warehouse? Even if the quality is not that great, it's hard to beat that. Heck buy 2 for less than $90.

  14. #14
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    I got one of these from a friend and bought another from DX. Sku#1251

    it's sold out right now. But check to see if a newer model came out. It charges the batteries in about 4-5hrs.

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