This is a follow-up to my prior post about a DIY DC to DC power supply for my FujiFilm S100fs camera. I recently purchased a Pentax K-5 which I hope to use for time lapse work. After doing some testing I found that the internal battery in the K-5 will power the camera for 3 hours and was capable of taking more than 10,000 6MP stills in continuous shooting mode. However for longer term shooting, a DC power source is necessary.
The K-5 provides a strange DC-IN port labeled 8.3vdc. This is the same port used on several of the K-series cameras and would normally be connected to Pentax’s D-AC50 AC power adapter. But this would require me having an DC to AC inverter to power the AC to DC adapter. This DC to AC to DC conversion would be very inefficient, requiring 5x the battery capacity. So I built a similar DC to DC converter based on Dimension Engineering’s SWADJ-3 and D-SWADJ switching regulators.
The complete wiring harness can be powered by any DC source from 9-30 vdc including these 8 cell battery packs from RadioShack, a sealed lead acid battery, or solar panel. The Nice thing about the K-5 is that when the DC-IN power fails, it falls back to the internal battery, which we had seen can keep the camera power for about 3 hours. This is typically enough to swap out a battery or ride out a short brown out in solar arrays.
Based on the K-5′s power consumption teasting, it uses about 6 watts maximum ( including the overhead of the SWADJ regulator ) so you could use the smaller, 10 watt, D-SWADJ. But for a safety margin, I used the SWADJ-3 which is capable of 25 watts. Both are about the same efficiency.
When you get one of these components, you need to use a digital volt meter to dial in the output voltage to the desired 8.4 vdc. This is accomplished via the small multi-turn pot. The SWADJ is very stable and will stay adjusted for long periods. I would re-test it annually to make sure.
OK, so up to this point, its same-old, same-old. However where do you get that funky DC-IN connector for the Pentax camera? I figured it out quite accidentally when paging through the Digikey catalog. Its a HiRose low profile 3-pin connector. It is keyed, and can only be inserted into the camera one way.
The connector is inserted into the camera with the metal portion of the connector facing the front of the camera, the exposed plastic towards the back of the camera, and the key way at the bottom of the connector. With the camera off, insert the middle ( plug ) component into the DC-IN port to properly orient the connector. The top most pin will be Ground ( – ), the bottom most pin will be 8.3vdc ( + ), the middle pin is not connected ( NC ). Because the connector is so small, I sheared off the middle, unused pin to make soldering easier.
The DC to DC switching power supply is more efficient than many voltage regulators, and had built in capacitors to decouple the output, I have not found it necessary to add capacitors. I used some mylar insulated, shielded 3-conductor, cable. This is very stuff, durable stuff. You may want to use something more supple. I like stiff cable as it will not move around in the wind, and the mylar is very durable and will not rub through. It will also handle high heat. But obviously whatever is convenient will work fine.