A Hot-Swappable Battery Grip Keeps The Camera Rolling

There’s nothing worse than being in the middle of an important shot, only to have the camera’s batteries die on you. The losses can be very real, so it’s best to avoid them entirely. In an effort to do so, [funkster] built himself a battery grip for his Canon EOS M.

The hack is based around the venerable 18650 battery, packing 3.6V of lithium-ion goodness into a compact metal can. [funkster]’s build has slots for two of these cells, powering the camera off of one and keeping the other in reserve. The cells are monitored by a STM32 microcontroller, which switches from one battery to another as they run out or are removed. This allows batteries to be swapped while the camera is on – a highly useful feature. There’s even an OLED display to keep an eye on the state of charge of each cell.

The manner in which power is connected to the camera is rather amusing. An original Canon battery that slides inside the camera was gutted and turned into a simple adapter for the battery port. The battery grip, which wraps around the camera body, connects to this via pin headers that pass through a hole drilled in the camera’s case. It’s a permanent mod, but one [funkster] is happy with for the added usability – especially as doing it this way still provides easy access to the SD card slot.

Keeping a camera juiced on the go can be a headache without the right gear. [funkster] demonstrates that if you can’t buy it, you can always build it yourself. If your problem isn’t battery power, but your camera is overheating, you can of course fix that too. Video after the break.

14 thoughts on “A Hot-Swappable Battery Grip Keeps The Camera Rolling

  1. I like this! I’m going to have to do something similar for my Samsung NX500. It’s getting a little long in the tooth but still works great, but the batteries are losing capacity.

    Where do you get quality 18650 cells that are anywhere close to their advertised capacity?

    1. I think best bet at this point, would be find a company that is buying them in bulk for a product and ask if you can purchase from them. To many fakes out there these days, or refurbished ones out there being sold as new by questionable sellers.

    2. For one off projects I would pay the tax and purchase big name cells (I’m out of the game, not sure who’s the leader right now) from a reputable vape equipment distributor.

    3. If you are only using one cell, or one at a time, it matters little just how good the cell is – it will hold some charge and do something useful with reasonable expectation of safety, multi cell and big power draws are where you really need to worry about it.

      I’d still suggest inspecting and testing the cells, and picking the best ones of course. But unless you really must have maximum the power stored (where just pony up the cash and buy new from a reputable retailer) you are probably better off asking to pick out some from a battery recycling bin, that will probably cost you nothing but a little time…

      If you think about it for something like a DSLR the added 18650 cell is probably double its stock battery in capacity when both are new, so even a half knackered one will keep it running for a pretty long time (Of course variation in camera and cell capacity could make it much closer).

    4. There are a few suppliers around the world with good reputations for supplying 18650s – hang out in 18650masterrace on reddit, or ask in your local vape shop. Current capability is just as important as capacity – in this rig the cells regularly see bursts of over 5A which a rubbish cell will just not cope with.

    5. For that i normally scavenge Notebook-Battery-Packs. If from a notable brand like HP, Dell, Acer and so on you can be quite sure they are the real deal…

      But honestly, for hot-swap only, you really need no big capacity… I made such a contraption once for another completely different project at home with an old LiPo-Cell (Those aluminium-Foil-Packs) which had about 100mAh capacity. Was anough for a load of average 500mA to hotswap…

  2. Could also do the switching with a couple of schottky diodes. The switching over is very fast.
    If you want much lower drops, there are active Or-ing (aka Ideal diode) controllers that can be used with MOSFET. This also allows for power sharing when both batteries are in.

      1. You’ll get *twice as long* usage out of the batteries. Current sharing means that the cells see 1/2 of the current each and in some case it would mean a slightly more efficient discharge curve.

        You can still swap out the old batteries for a new set one battery at a time.

    1. TI: TPS2412,2413 works down to 3V and the drop is 10mV limited by Ron of external N-MOSFET.

      RPi schematics (RPi B+ page 1.pdf) in the USB power section (upper left corner) shows a discrete version of OR-ing diode with P-MOSFET and a pair of matched PNP. I have simulated the circuit in LTSpice with discrete transistors (different part numbers to simulate non-matched PNP) and it seems to work. The drop is around 0.2V because of linear feedback. They also do current sharing if you use multiple power sources.

  3. Why is there a hole drilled in the camera’s case? The EOS M battery door has a built in hole under the rubber grip panel, I think meant for this kind of use case. Is it just to not screw up tripod mounting?

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