"Sticks 'o dynamite" battery pack.

Quick 18650 battery pack to power a canon P&S camera for CHDK

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Taking the mystery out of LiPo batteries, and hopefully not making them in to "Sticks of dynamite" . See here ( ) for the original remark that spurred me in to starting this build log.

I recently built a couple of battery packs out of recovered laptop 18650 LiPos.

While this has no doubt been done a thousand times before, I thought it worth a quick write up here. The hard work is being done by one of these modules, take care when looking for these to ensure you get the protected version.

The objective is to build a safe 3.6 V approx. supply out of unprotected 18650 cells. In theory we can parallel up as many as we like, but in practice probably 4 or 6 cells would be about as far as we can push the little charger board we are going to use, without modification. More cells would give us a longer running time, but would also proportionally increase the charge time.

I'm using my packs to power a Canon P&S camera running CHDK, but you can obviously use the method to power anything that will operate on 3.6V. Long timelapses and long duration motion detection are two of my goals. So far I have managed to power the camera for more than 24 hours at a stretch.

We also need to be careful with recovered cells, often one or two of them may be unwise to re-use, if they have been allowed to discharge below the safe limit. Discard anything which reads less than 1.5V, it is almost certainly not worth the risk of recharging, cells left at or below this threshold for prolonged periods can fail dramatically when you attempt to recharge them.

Of the two dozen or so cells I have recovered recently, only one was unserviceable. It had failed open circuit, and this failure may well have been the reason the entire pack no longer took a charge. It is probable that single cell failure is one of the conditions that the inbuilt charge protection controller in laptop packs can sense. It is therefore entirely plausible that the charge controller in the pack deemed the pack unsafe to recharge as a result of this condition.

You could of course use new 18650 cells, as they are available reasonably cheaply from all of the usual sources (often with wildly exaggerated capacities, and potentially of dubious quality). I would suggest however that recovered cells, make for a more interesting build, and are usually high quality cells.

Recovering them involves quite a bit of genuine "hackery", while extracting them from the failed laptop battery. Watch your fingers while you attempt this, the tabs on the cells (which you need to carefully detach and remove with a pair of pliers) are razor sharp.

There are several youtube videos showing what is involved, so I wont go over that here. Use suitable gloves to protect you from the sharp edges, and take care not to short out anything. Work in a location where you will not be too worried about throwing the hot, hissing firecracher that is an errant lipo out of harms way. Take care with sharp knifes and conductive screwdrivers, a stabbed or shorted LiPo is a dangerous one.

Everything described here, you do it *entirely* at your own risk. Don't forget your safety neck tie .

Laptop battery packs are "intelligent" in the sense that they contain a charge monitoring circuit, which will kill the battery (usually permanently) if it detects any problem. Often a single cell failure is all it takes for the charge monitoring circuit to deem the battery beyond its serviceable life, and under these circumstances, all of the remaining cells are usually perfectly usable (assuming they have not been allowed to discharge below 1.5 V).

Unprotected LiPo cells are also slightly more dangerous than some other battery technologies, in that if we short them out, things can quickly get out of hand. Melted wires, smoke, flames, potentially even an explosion can result, so care must be taken when constructing this build. Having said all that, lead acid, Nicad, NiMh .. in fact pretty much any battery technology can set things on fire, so LiPo's are not unique in this resepect.

If you would like to learn a bit more about cell and battery technology, one of the best battery related resources on the web can be found at

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  • 4 × 18650 LiPo batteries .. or more, depending on your needs. Cost - nill
  • 4 × 18650 battery holders. Search ebay for Single Slot 18650 Mobile Battery Clip Case Holder with Wire Leads Expect to pay about £1.50 for a pack of 5
  • 1 × Micro USB LiPo Charger board. Search ebay for Micro USB1A 5V Lithium Battery Charging Board Charger Module 18650+Protection ET - expect to pay about £0.90p
  • 1 × Roll of electrical tape I'll leave the choice of colour up to you.
  • 1 × Micro USB USB Wall wart charger.

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  • 1
    Step 1

    Follow the example in the pictures.

    Make sure the B+ and B- go to the LiPos obviously and the Out+ and Out- go ... well out to the equipment obviously. The Out wires in my photos are the fatter brown (B+) and blue (B-) wires, which I soldered to the reds (+) and blacks (-) of the battery holders respecively.

    Parallel up all of your battery holders, connect them to B+ (all the red wires from the battery holders) and B- (all the black wires from the battery holders).

    Use tape, hot snot (aka hot glue) and heatshrink tubing to keep it all neat and tidy, and minimise the risk of shorting things out. Add an inline fuse and a switch if you want to be a little more sensible. I didn't bother, relying instead on the protection offered by the charging board. I like to live life on the edge... although I must admit I charge the things on the tiles in my fire hearth just in case of unexpected smoke.

    Just to confuse you I also have red and black wires going out to the equipment connectors. Just dont get them mixed up or something will go fazoosh!!

    Once you have double checked everything, plug in the USB connector and your cells will begin to charge. Keep an eye on them watch out for smoke, flames, singularity events or other dangerous problems.

    Once charged, disconnect from the USB cable and plug in to your camera or whatever. Be aware that some of these usb charger boards have a nasty habit of deliverying the full +5V to the equipment when the batteries are fully charged, so i would suggest charging with the equipment disconnected if you are at all uncertain how well behaved your board is. Some 3.6V items might not appreciate +5V.

    One final warning. When fitting the cells prior to charging for the first time, ensure all of your cells are within a few tens of milivolts of each other. Parallelling up an unprotected fully charged and fully discharged Lipo can be a *very* bad experience. Things get hot, fast.. very fast... things go pop... don't say I didn't warn you.

    Also take care not to fit any cells the wrong way round, this will also make for an interesting time and lots of strong language when previosuly cool safe looking cylinders weld themselves instantly in to place and start to hiss like a bunch of hot demented vipers.

    There is a reason why LiPos use charge protection circuits.

    On a more positive note (pun intended), once you have charged up a bunch of cells in parallel for the first time, they will always stay at the same voltage as each other, so you shouldn't experience any major issues after the first charging cycle.

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