Balancing the Magicshine MJ-836 Bike Light Battery

There are many reports about unbalanced Li-Ion cells in Magicshine Bike lights. This can lead into overcharged cells, which is dangerous, or at least will damage the cells. The charger which comes with the light does not have any balancing capabilities, the battery itself only has some very limited under/over voltage protection.

To solve this problem, you’ll need to modify the battery (add a balancing connector), and use a different charger, or external balancer. I’ll use my hobby charger, which has an integrated balancer.

This is no complete guide, it needs common sense, and some knowledge about electronics. You should also know, that working with Li-XX cells is dangerous.

If you don’t know how Li-XX balancing works, please read:
http://scriptasylum.com/rc_speed/lipo.html
http://www.rcgroups.com/forums/showthread.php?t=599316
before starting to modify your battery pack.

Adding the balancing connector:

Open up the pack:

The interesting part is the four 18650 cells, remove the top of the pack (shown on the left):

Add a new wire which will end as your balancing connector, this is connected to the “middle” of the pack, the pack is 2S2P.

Your Magicshine Pack should now look like that:

The next Step is to put back the isolation, and bring the balancer wire out of the case. this can be done through the original cable exit:

I’ve added a 2mm banana connector, some heat shrink tube, and a cable tie:

Finished Pack, charging:

test

As you can see, the connections were made as follows:

- from the battery goes to – of the charger, and pin1 of the balancer.
newly made balancing wire goes to pin2 of the charger
+ goes to + of the charger, and pin3 of the balancer.

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5 Comments

  1. User says:

    Hi,

    could you please take same better pictures so that we can actually see what you are doing?
    What does this magic balancing connector do?

  2. Nico says:

    Hi,

    I’m not willing to take it apart again, but if you really need further explanation, why didn’t you post your e-mail address? It won’t be published to the public.

  3. I got a Gens Ace LiPo, ran it for 2 races and the stupid thing puffed! Look at this thing! http://www.flickr.com/photos/74798847@N06/6730741877/in/photostream

  4. 123 says:

    Hello, I opened up my light, and it appears to have a balancing wire connection already(running from the protection PCB mounted on top of the battery pack. You can just see one end of it in your photograph above (the red wire connected at the same point as your balancing wire).
    Does this do the same thing as your external balancing wire, i.e. does the battery pack actually have a build in balancing function?

  5. Nico says:

    Hi Ken
    No it doesn’t that’s just to let the protection PCB know the voltage of each individual cell. There are protection PCB’s with integrated balancers (search ebay), but I’ve never tested one of these.

    happy riding
    Nico

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