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  1. #1
    mtbr member
    Reputation: ironbrewer's Avatar
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    Oct 2012

    Newby to DIY wants to make a couple 2S2P batteries

    I just want to keep them simple.

    Will be using these batteries

    Thinking about using this battery holder for my helmet light. I'll be carrying it in a pack anyway.

    Want to use 2 of these glued back to back in parallel for my bar light, so I have a cube form factor. I'll pick up a couple magic shine extender cable for connectors.

    This whole electrical thing is foreign to me. I was a commercial brewer for 12 years and now I treat water for a living. Electricity doesn't mix with water, so I try to stay away from it. I have a solder iron and can solder to wires together, but don't know the proper wiring to make them be parallel. Also will the PCM's still work if I hook them together??

    Any advice would be greatly appreciated, and treat me like I know nothing. I've tried to research it, but there is way too much information and I am very confused by it.

    Would I be better off getting a 4 cell charger or just plugging in to a 7.4 volt charger I got with some of my lights?? It seems to me like a 4 cell charger will be more of a pain to use, but would keep the batteries healthier.

  2. #2
    mtbr member
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    May 2011
    You will find most people are hesitant to give advice on building your own battery packs - the results can be spectacular if you get it wrong.

    For me, the fact that you are hesitant is a good sign

    First the good news, what you are proposing for your helmet light should work. My preference would be to use a hobby charger, but with Panasonic batteries, a 7.4 v charger should be fine. I wouldn't take the cells out to charge them.

    Sadly it is a bad idea to try connecting 2 2s1p packs together in the way you are considering. (1) you want to wire both pairs of parallel batteries together - see this thread. (2) the protection circuits will not work wired together like it appears you are thinking of. If you read MtbMcgyvers's post, you should start to understand why.

    If I was in your situation I would seriously consider getting a pre-built pack for your bar light - something like the Gloworm 5800mAh 4-cell Battery Pack would be a good option using the Panasonic cells.

  3. #3
    mtbr member
    Reputation: Wombat's Avatar
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    Jan 2004
    I'm not answering you question, but you could also consider a battery case like this: for $17.

    It comes with (poor quality) batteries. Some discussion about the case and batteries here: The Battery Thread: 2013 from post 133 onwards.

    The other alternative is a magicshine battery pack, which now use much better quality batteries for $35 from here: Action-LED-Lights ? MJ-6002 4400mAh Waterproof Battery

    You'd also need a charger. There may be other sites that sell the magicshine pack for less, but action led provides good service and is a regular poster here.


  4. #4
    mtbr member
    Reputation: mattthemuppet's Avatar
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    Jul 2004
    I dunno Bruce, I've never had any problems building batteries, other than the time I spot welded my craft knife to a terminal

    ironbrewer - what's the impetus behind making your own packs? Do you want to be able to remove the cells for charging? Or will they be sealed up and charged via the power cable? I'd second the suggestion of an MS pack as you won't be able to build your own for less.
    If you want to remove the cells for charging, which is not a bad idea as you can then use them in other things and they'll never go out of balance, then some protected cells and the appropriate cell holders from Digikey/ eBay/ Batteryspace would work fine.
    If you want a sealed pack, I would very strongly recommend getting a hobby charger (very useful thing) for $40 or so and solder the cells directly, with an appropriate PCB from eBay/ Batteryspace/ Fasttech and a balance tap. Seal with marine silicone tape and heatshrink.

    There's no real mystery to it. Solder + bits to + bits and - bits to - bits and don't stick your fingers in between the + and - wires. I'm an electrical idiot and I've been doing it fine for years without killing myself.

  5. #5
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    Join Date
    Apr 2008
    Cell holders are OK, but I'm a fan of packs myself. Holders can intermittently disconnect if they are hit by a sharp jolt.

    If this is your first time building your own packs, then I highly advise not soldering directly to cells. It can be done, but it requires some skill to perform without causing heat damage to the cells. The solution is to get yourself some pre-tabbed cells and solder to the tabs instead. Batteryspace charges an extra $0.25 per cell to add tabs, which is not very much, and worth the peace of mind if you're not so confident in your soldering ability.

    Before you start soldering, you'll need to glue the cells together. CA glue (aka superglue) works for me. Use some "kicker" or sprinkle some baking soda on it if you're impatient and want it to dry immediately.

    You'll also need to add a protection PCB to protect the pack from overcharge and overdischarge. You'll need a "2-cell" PCB even though it's really 4 cells, because it's the number of series cells that counts. Likewise you'll need to add a "2-cell" balance cable for use with a balance charger.

    For charging, a multi-cell, multi-chemistry hobby charger, as mattthemuppet suggested, is the best. Examples include the Turnigy Accucel 6 and
    Imax B6. These mini marvels track the charge and discharge capacity, voltage, and can perform discharge tests, cycling tests, datalogging, and perform a storage (dis)charge. But if you don't want to spend much and you don't want all these features, a ~$10 2 or 3 cell balance charger is good enough.

    Once everything is glued and soldered together, you'll need to wrap everything up. Tape or heat shrink will work. But lately I've been using Plasti-Dip, or tape/heatshrink followed by Plasti-Dip. Plasti-Dip will make the pack waterproof, which is a big bonus for me since I ride year round and sometimes the pack gets wet. A few of my buddies fried their PCBs on their Magicshine packs due to water spray, so it's a real issue.

  6. #6
    mtbr member
    Reputation: ironbrewer's Avatar
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    Oct 2012
    The impetus is to know that I have the best cell I can get. I like the idea of having the Pani 3400 mah cells.

    Prebuilt packs with these batteries seem to be very expensive.

    If I can take the batteries out I can have the cells stay in balance, plus I can just carry an extra 4 cells just in case. I also like that idea.

    I always ride with 2 lights and like the idea of having backup power. I don't really have a problem with just going the battery pack instead. It would be ok to carry 2 of them, but also like the flexibility of having the batteries not tied together. Using a multi emitter light might use up more than 4400 Mahs if I keep them on high for most of my ride.

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