DIY AC Adapter for The Pentax K10D and K20D

Milapse pointed me out to this image showing the part # from digikey that works perfectly as a male cable end for the K10D’s 8.3V DC input. So, a few parts later, and a couple of hours of soldering and testing, and I now have a power supply for the K10D that lets me hook up to:

• 12V Cigarette Lighter Plug
• 12V AC->DC adapter
• Any one of my 12V SLA batteries

Note: The K10D and K20D share the same AC adapter (D-AC50), so this design will work for both cameras.

All can be done for less than the price of the standard Pentax D-AC50 AC adapter, and a few hours of sweating over a hot iron =) Namely, I can now run the camera from the same 8Ah battery I run the TLA from, meaning I only have to charge one battery out in the field! (Try getting enough engine time to charge the big SLA, three NiMH’s, a laptop, etc..) And, you know, I can run it on AC inside of the studio!

So, here’s my DIY guide for building the adapter based around an LM338 adjustable voltage regulator.

Circuit: (adapted from the LM317 Application guide)

• D1 prevents shorting in case of failure condition in the LM338
• D2 prevents damage if the power is hooked up backwards.
• Ci = 0.1 uF disc capacitor
• Co = 1 uF electrolytic capacitor
• R1 = 390 Ohm
• R2 = 2.2 kOhm

Actual voltage is around 8.4V, but works perfectly with my K10D.

The following parts are needed:

• Electronics:
• 1x LM338T-ND voltage regulator
• 1x TO-220 heat sink (required for the voltage regulator)
• 2x SB540-E3 5A/40V schottky diode
• 1x 0.1 uF disc capacitor
• 1x 1 uF electrolytic capacitor
• 1x 390 ohm resistor
• 1x 2.2 k ohm resistor

• Hardware:
• 1x approximately 3.5x2x1.5 project box
• 1x 2.5×5.5mm DC power jack (panel mount)
• 1x 3.5mm mono audio jack (panel mount) (use different mounts for camera out and input to prevent confusion)
• 1x Hirose H10485-ND 3 Pos Connector Plug (K10D male power plug)
  
• 1x MPD APP-002-ND cigarette lighter plug
  
• 1x AC->DC 12V 3A power inverter
• 1x 3.5mm mono cable with soldered tails
• 2x 2.5×5.5mm male DC power cable with soldered tails (one is used to hook up to the lighter plug, the other you can use to hook up to any 12V DC source)

• Step 0: Breadboard the circuit and make sure everything works fine =)
• Step 1: cut perf board to size for project box, and drill mounting holes
• Step 2: place and solder all components, take care to check all bridges and connections
• Step 2.1: Test, test, and test again
• Step 3: Drill holes in either side of project box for panel-mount jacks (size depends on type you get)
• Step 4: Attach input and output leads from circuit to panel-mount jacks. (preference for DC jacks is center pin is +V and shield is GND, preference for mono jack is tip is +V and ring is GND)
• Step 5: wire lighter cable. The center pin (fused) on the cigarette plug is +V. Be cautious as there is a spring and a few other small parts when disassembling the plug.
• Step 6: Wire Hirose connector. Note that the GND is the top-most pin when the plug is inserted into the camera, the +8.3V is the bottom most pin when plugged in. Center pin is unused. Use extreme caution, these plugs are easy to damage when soldering. You may have to strip part of the cable’s coating and replace it with heat-shrink to fit into the stress-relief end of the housing.

That’s it! You now have an adapter for the K10D that runs off a cigarette lighter plug, a 12V AC->DC adapter, and any old 12V battery!

Here’re some photos of the finished product:

circuit, top (LM338 on bottom)

detail of camera output jack

detail of DC input jack

the box and all connectors

Note: the original design used an LM317, the K10D requires more power than the LM317 can support in a simple configuration, so the design has been updated to utilize the LM338 which can handle up to 5A of current draw.

~ by c.a. church on September 26, 2008.