The main components of a V-Mount system are listed below. For a great little overview of affordable batteries, check out this DSLR Video Shooter blog post by Caleb Pike. I will compare semi-professional solutions as found on Amazon or B&H with the parts that I used for my build:
- The battery pack: should use good, branded Li-Ion cells for obvious safety and performance reasons. There can be pretty dramatic differences even between branded off-the-shelf V-Mount battery packs as seen in this (highly entertaining, like the whole channel) video (these guys deserve more views!) I don't expect to compete with high-end V-Mount batteries but the recycled pack I'm using still contains genuine Panasonic 18650 cells. We managed to find a pack for, I would say, 1/10th of the price of a good V-Mount battery but because it was quite a lucky find and specific to our local area I won't post details or exact costs. Individual 18650 cells go for around $11 a pair so you could still build your own 90 Wh pack for about $66. The configuration is 3 batteries in parallel and 4 in series. Make sure your pack has over-current and over-temperature protection! So let's say total cost so far: $70.
- The battery pack mount: This keeps the battery securely attached to the mounting system. In V-Mount batteries it is part of the battery pack mould and there shouldn't be any way it could fall apart under normal usage. My recycled pack didn't have much in the way of strong attachment points and I didn't want to rely on glue but luckily some bolts through the plastic tabs on the side worked great. There is no way the battery is falling off and the mounting plate can hardly move despite my mediocre machining skills. Purchased from Aliexpress this was the most expensive part at $33. This brings the total cost to a nice round $100.
- The camera rig mount: Most packs mount directly to the back of a camera or a 15 mm rails rig. Besides strong rail mounts, the mounting plate usually also provides outputs at varying voltages to power different devices such as camera, monitor, audio equipment, etc. Decent plates, e.g. from Lanparte or more professional brands, can easily cost $250 or more. Buying the parts separately, it really comes down to a cheap $9 plate, a $1 voltage converter, and a $18 rail rod clamp from SmallRig. This only bumps the total cost up slightly to about $130.
- Now all that's left are some cables to connect the battery plate to your camera, your monitor, and other equipment. Since we're already building this ourselves, absolutely avoid regulator cables like the ones listed in the DSLR Video Shooter blog post above: they are horrendously over-priced for what they do. A standard low-power step-down voltage regulator (this means it's efficient and won't produce much heat) only costs $1. For my camera I got a D-Tap to BMPCC cable for $3.50 feeding the 14-15V from the battery directly into the DC input, and for the monitor a dummy LP-E6 for $4 which has to be regulated down to 7.2V to match the LP-E6 batteries.
So there you have it: a fairly sturdy DIY V-Mount system for just $150, maybe less if you can find some cheap recycled batteries. Obviously, cost is the main reason why an enthusiast would go through the trouble of building something like this from scratch, spending 1-2 days getting everything figured out and assembled, instead of dropping $300-$500 and just getting something off the shelf. Time will tell if it is sturdy enough to hold up to regular hobby usage (to be perfectly honest, I wouldn't recommend it for daily and professional use). Hopefully my instructions and photos are useful and will save others a lot of time.
So here is how it was put together. First, I had to drill several holes in the metal bottom plate of the V-Mount adapter that will be screwed onto the battery. These holes are for the five wires that are connected to the battery pack. Two are positive and negative (make sure the insulation is sturdy since the plate is made of metal) and the three others get soldered onto the control pins of the battery pack to put it into discharge or charge mode.
The receiving plate already has a D-Tap socket built in so I only had to add the 7.2V output for the dummy battery for my monitor. The regulator has a little screw that needs to be calibrated using a multimeter to output exactly 7.2V (input voltage can vary as long as it's over ~10 and below the regulator's maximum of 23V). It is so small that it easily fits inside the housing.
I then bolted the SmallRig rail clamp into the bottom (two would be better but I don't see a need at the moment) to mount the whole system onto my camera. With the cables I've linked to earlier, I can then connect my camera and monitor to whooping 90 Wh, compared to the next-to-nothing mAh of the BMPCC batteries and the 1800mAh of genuine LP-E6s.
To charge the pack you'll need a dedicated Li-Ion charger or a good programmable power supply. However, this is the case for any battery system and there are of course proper V-Mount chargers out there. Because the receiving plate was so cheap, it would be easy to use one as a dedicated charger port.
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