Bring the power pack

Years ago, I standardized on the DeWalt 20v MAX system for work and the battery packs have become ubiquitous around home and the office. I’ve been thinking about how I can use the packs to power a remote time-lapse system for taking long exposure shots, in remote areas, over long intervals. This is something I haven’t been able to do with the stock Nikon EN-EL 15 packs, even with a grip holding a second one. So, for about $50, I built my own solution (copy at your own risk).

Parts

Although it’s generally good practice to buy genuine parts from the original manufacturer, I consider parts for hack jobs an exception. Partly, it’s about saving money during the experimental phase, but OEM parts also tend to be “smarter”. The last thing you want is to blow out a power conditioning circuit, or interfere with some kind of communications protocol used to identify genuine accessories. I trust the reviews (and Amazon’s return policy) will lead my to 3rd party accessories that work, and that those accessories will be simple enough that I can hack them easily.

At a minimum, the following parts are needed

DC Coupler (Amazon) – this is simply a battery-shaped connector with a set of wires leading out of the camera body. If you provide a source of power to the wires, they’ll be transmitted to the camera as though they have come from a genuine battery. Careful, though, there are no protections here. Provide the wrong voltage to the camera and unpredictable (or expensive) issues can result.

Battery-USB Charger (Amazon) – I went with the name brand version to protect my batteries. In this case, the DeWalt DCB090, comes with LEDs to indicate the available charge, USB ports to power accessories (like an intervalometer), and intelligent features to ensure the battery isn’t damaged by drawing too many electrons out of the cells.

Voltage Regulator (Amazon) – The DeWalt packs provide approximately about 20v by default, and the USB outputs are regulated to provide 5v. Because the DSLR needs about 8v, we need to separately regulate the power provided to the camera. I bought adjustable regulators so that I could fine-tune, but you could alternatively design a fixed circuit to do the same thing.

Other optional items

I had these on hand already, but you may need them:

  • Batteries (Amazon) – I actually used the 60v FLEXVOLT version, though I haven’t done any analysis to determine the most size/weight efficient combination
  • 3rd Party Battery Grip (Amazon links for: D800, D810, D500) – in theory, this will allow you to hot swap batteries for super-extended shooting.

Tools

These tools are already part of my collection.

  • Security bit set (Amazon – just get one of everything) – it’s a security Torx of some kind to get into the DeWalt charger. I just drilled out the screw
  • Multimeter (Amazon – get a decent one) – I’m not
  • Soldering Iron (Amazon – with temperature control)
  • Hot glue gun (Amazon)
  • Utility knife (Amazon) and small file (Amazon) to clean things up

Assembly

  1. Crack into the USB adapter – I drilled out the security screw, then found a large metal clip covered by a sticker on the underside of the pack.
  2. Cut into the battery pack leads – Easiest to just cut off the cable near the power brick. That way you get
  3. Solder the leads – To the “out” side of the regulator.
  4. Find the supply of 20v on the DeWalt board – Make sure you find a ground (I grabbed a big resistor somewhere) and a source of 20v after the power control IC (so you don’t bypass the low voltage cutout features – I used one of the leads from the big capacitor). I don’t know what I’m doing, so there are probably better choices.
  5. Solder the regulator to the DeWalt board – you need your own wires for this. Long enough that you can get the regulator board neatly outside the case
  6. Glue it together – Neaten everything up and hold in place with hot glue.
  7. Set the output voltage to about 8v – Plug everything into a battery and measure the output voltage as you adjust the potentiometer. About 8v should be right (worked for me)
  8. Insert into the camera and power up – Check that the battery reads as full on the camera’s LCD. If not, you could try turning the voltage up a little.

Tuning and testing

I carried this rig with me when I visited the mountains of Wyoming for the 2017 Solar Eclipse (more on that trip here, and the resulting time-lapse here). My plan was to shoot a day-night-day-eclipse-day time-lapse over about 18 hours, but I didn’t end up with enough time to learn how to use the new exposure ramping intervalometer.  In the end, I shot about 8 multi-hour time-lapse sessions, including 3 overnight sessions with 30s exposures, and the first battery still reads full.

General observations for next time:

  • I’m not sure whether I like, or dislike the red LED on this regulator. It’s a little annoying, but it sure helps when looking for a camera left in a mountain meadow on a moonless night.
  • Overall, this could use some waterproofing. I didn’t have any issues although I did cover the exposed electronics with large leaves to keep the dew off.
  • I can’t decide whether I like the plug in the middle of the line or not. If I ever used AC power, I would certainly appreciate being able to swap power sources, but I don’t.
  • The voltage seems to drop in the cold. I didn’t measure it, but the camera reported lower power (just reduced by one bar) on cold mornings.
  • I had weird camera behavior where it wouldn’t let me set a 30s exposure consistently using the built in intervalometer. I think this was due to some other camera setting that I couldn’t figure out in the dark. Better to use an external, smarter trigger anyway.

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