# Cheap & Easy DIY 18650 battery pack



## [email protected] (Mar 28, 2007)

Not to take anything away from all of you who have been busy fabricating your own 18650 holders, but there are some nice ones made by MPD and available from DigiKey: https://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=393250&k=18650.

My lights, based on my own custom driver, run on anything from 9.6 to 25 volts. I came up with a way to use one of the standard MPD holders and a camera bag (https://www.dealextreme.com/details.dx/sku.15290) to make a reasonably rugged battery pack based on cheap protected cells from China: https://www.dealextreme.com/details.dx/sku.19624

Here's a shot of the completed pack, note the odd orientation of the batteries.










Here's a shot of how I wired it up. Note the + and - markings were photoshopped in. One of these days I'll probably print up some stickers to put inside the holder indicating the right polarity for each cell. I did the odd arrangement I used here so the positive and negative leads for the power cord would both wind up on the same end of the holder.










Here's the pack with some sticky back foam stuck on the back to keep solder points from shorting against anything, some foam on the front to hold everything tight, and a zippy-tie used as a strain relief for the power cord (pointed at by blue arrow). The red arrow points at one of the corners I notched to make inserting the whole thing in my camera bag easier. The plastic seems to handle high temperatures pretty well. I just soldered wires to the pins coming out the back of the holder and didn't seem to melt any of the plastic. It trims pretty well with a pair of diagonal cutters.
I'm sure somebody can come up with something more elegant than sticky back foam on the back of the pack to insulate solder points, but it seems to work and takes no time to do (if you happen to have the foam lying around).










I ran this pack with one of my 20 watt dual MCE lights just to test it out and it ran for 1.25 hours, about what I'd expect from cheap DX batteries. This will make a great spare pack to take along on longer or cold weather rides. It isn't terribly waterproof, but I guess I could just shove the holder in a plastic bag before putting it in the camera bag.

Mark

PS Sorry for the delay with the photos, the photo gallery was slooooooow.


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## HuffyPuffy (Jun 9, 2008)

Your pics are missing (EDIT: see em now thx), but the MPD holders look excellent and cheap too!


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## Vancbiker (May 25, 2005)

+1 for the Digikey 18650 holders.

I have made a few holders of 2 different designs using the single cell MPD holders from Digikey. I prefer the single cell holders as they have curved "lips" that hold the cell really tightly. I have a 3 cell that I use on my microlight.

http://forums.mtbr.com/showthread.php?t=574292

and an 8 cell for my dual MC-E light.

http://forums.mtbr.com/showthread.php?t=578463

The 8 cell holder is wired 2P4S so it can be loaded with 4 cells for shorter rides or 8 for the epics. Both designs use a piece of 6mm Lexan with holes drilled and tapped to screw the holders to. This also provides space for wiring and in the case of the microlight, a place hold the buckpuck.

These save loads of time when building battery holders. My first 18650 holder....

http://forums.mtbr.com/showthread.php?t=501179

had so many parts that had to be made that it probably took 3 evenings at the shop.

The 8 cell holder can be done in an hour or so.


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## mattthemuppet (Jul 16, 2004)

that's a really neat tip, thanks!


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## [email protected] (Mar 28, 2007)

Yeah, the single cell holders probably hold the cells better than the multi cell holder. I'm getting over a cold, so haven't tried bouncing my 15 minute wonder holder over rocks and logs yet. I'm pretty sure that some extra foam and a good velcro cinch strap will hold things together pretty well.

I had a couple of problems with the single cell holders and so never got around to building a pack with them.

1 - the plastic seemed kind of soft, which I associate with easy to melt while soldering. Never tried soldering the single cell holders, so I could be way wrong on that.

2 - I never found a way to mount them that didn't involve using really tiny, hard to find, machine screws. And there was some amount of drilling and machining involved.Your finished holders look good, but I doubt if I'd used the single cell holders my results would have been very nice looking (not that what I posted looks great, but hey it was quick, if you can solder, you can probably get it to work).

Mark


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## Vancbiker (May 25, 2005)

[email protected] said:


> I'm pretty sure that some extra foam and a good velcro cinch strap will hold things together pretty well.


I am sure you won't have any problems with the cells coming loose with them cinched like your picture.



[email protected] said:


> I had a couple of problems with the single cell holders and so never got around to building a pack with them.
> 
> 1 - the plastic seemed kind of soft, which I associate with easy to melt while soldering. Never tried soldering the single cell holders, so I could be way wrong on that.
> 
> 2 - I never found a way to mount them that didn't involve using really tiny, hard to find, machine screws. And there was some amount of drilling and machining involved.


Soldering is no problem. The tab is tinned and small. I just re-tinned the tab and pre-tinned the wire, then hold them together and a couple seconds touch with the iron joins them. A kludgy hand at soldering could certainly cause problems

Yes the screws are pretty small. I used 4-40 button head screws. To do something similar to the way I used them would require a saw and a drill at the minimum. I have the use of a milling machine so am somewhat spoiled.


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## mattthemuppet (Jul 16, 2004)

forgot to ask a silly question - where did you get the velcro cinch strap from?


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## [email protected] (Mar 28, 2007)

I got a bunch of 5/8 inch by 12 inch velcro straps at McMaster-Carr. Probably not a cheap way to buy just one  

You might look in hardware stores or camping stores.

The closed cell foam was from them as well. That will be a little harder to find a local source of.

Mark


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## mattthemuppet (Jul 16, 2004)

thanks for the tips. I'm toying with either going the strap route and remove the cells for charging, or have a small plug for each cell to plug into a dummy cell in a cheap DX charger (or fancier balance charger when I have the cash) then plastidip the whole pack..


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## [email protected] (Mar 28, 2007)

Cheap balance charger: http://www.dealextreme.com/details.dx/sku.20025

Source for connector parts that mate with above charger: http://www.digikey.com

Connector for battery pack: search digikey for part # 455-2267-ND

Pins for connector: search digikey for part # 455-1135-1-ND

If you poke around on DX you can find a 12V 1 amp power supply for a few bucks.

Including postage, you can put together a balance charger setup for a 3 cell battery for less than $20.


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## mattthemuppet (Jul 16, 2004)

[email protected] said:


> Cheap balance charger: http://www.dealextreme.com/details.dx/sku.20025
> 
> Source for connector parts that mate with above charger: http://www.digikey.com
> 
> ...


wow, thanks for the info, that's awesome stuff  Just ordered a charger and brick, and the digikey bits will wait for me to figure out all the other bits I need for a couple more lights (switches etc). :thumbsup:


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