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  1. #1
    pedalphile
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    Gutting a laptop battery to make a light pack?

    I have a high capacity laptop battery I bought for an HP laptop that has since gone to laptop heaven.

    It worked well when the laptop decided to no longer work well, so I believe the cells are good.

    This battery is twice the size of the OEM battery. It is labeled as 10.8V, 8800mAh. Judging by the shape of it, I believe it consists on 12 18650 cells, there are four rows of three.

    I was thinking of cracking it open and reconfiguring it as 3 parallel rows of 4. This would result in a 14.4V, 6600mAh pack, if my math is right.

    I would like to use this pack as a replacement for my 7Ah SLA boat anchor to power my nightsun halogens. This headlight consists of 2 lights, a 35W and a 10W (I think). I generally run just the 35, keeping the 10 as a spare to get me home if the other blows.

    I have a few questions. Is 14.4V too much of an overvolting? I have read some about how overvolting works pretty well. My 35W nightsun does pretty well already, overvolting it ought to make it quite the flamethrower.

    How much will this increase current flow? Is it just simple ohms law, meaning about a 20% increase? if so, I can live with it, as my 7A SLA gets me through 2 round trips with ease. It would probably mean having to recharge each trip.

    And how much will a charger set me back?

    It probably makes more financial sense to just sell it as is on fleabay and buy a new magicshine, but where's the fun in that? My inner geek tells me to give this a shot.

    I guess another option would be to make it into a lower voltage pack for an LED light or better yet, a pair of them. And buy an LED light and charger.

  2. #2
    I am a caffine girl colleen c's Avatar
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    Based on the 10.8v 8800mah description, it seems like they are using 3.6v 2200mah battery hooked with three in series and 4 rows in parrallel. Although these battery are rated 3.6v nominal volt instead of the typical 3.7v 18650, the problem is that the final SOC at full charge will still be 4.2v pet cell. If you hook 4 in series you will get a SOC volt of 16.8v. This volt will be present until after a certain amount of time depending on your load before dropping to the nominal 3.6v per cell yeilding the 14.4v you require. The final volt after fully charge will be much to high for halogen bulbs. You can try making a high amperage voltage regulator, however after cost of that plus charger and some kind of protection PCB, you probably better off buying a new LED light set.
    "Difference between a well dressed cyclist riding a two wheeled bicycle and a badly dressed cyclist riding a Recumbent is only a-tire"
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  3. #3
    pedalphile
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    thanks for the response, colleen. that is exactly what i have, 4 parallel banks of 3 in series.

    looks like i will do the smart thing rather than the fun geek thing, unless someone can provide me with a schematic for a cheap, easy to build regulator.

    anybody wanna buy a nice battery pack for their hp laptop?

  4. #4
    Certified Bike Brat Burton's Avatar
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    Nothing wrong with that light actually. The battery technology is a little dated but something like this would solve that issue by giving more run time and less weight.
    http://www.batteryspace.com/Polymer-...ch-female.aspx

    Over opting a halogen will result in greatly reduced run times do I wouldn't suggest it. But there might be a few other items on that site that might interest you.

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