Portable DC power for a Nikon D40

I shoot long exposures with my Nikon D40 for astronomy. That means I have to leave the shutter open for long periods of time for most of the night. One battery will not last the whole night. You can get spare batteries but the Nikon batteries are expensive and the generic batteries don’t last as long and eventually fail.

My solution at the time was to buy an AC power supply for the D40 (EH-5A and EP-5) but that setup still required me to use an AC inverter to change 12 volts to 110 volts. Using an inverter on 12 volts wastes a lot of energy from my precious deep cycle marine battery. I need to conserve this battery to run my laptop and the rest of my remote astrophotography equipment. Who wants to spend over  $100.00 on an AC power adapter and plug?

I needed a DC power source for my camera that could run off of a deep cycle marine battery (12 volt battery) without having to use an inverter. My total setup minus a battery cost about $20.00. It’s lighter, smaller, and way more efficient. This should work for a Nikon D40, D40X, D60, D5000, and D3000. Check  your battery and adapter voltage specs for other camera applications. The process will be similar, but the parts will vary. As a word of caution, even though the cameras listed above should work, still test the voltages and look up the specs. And make sure you test everything several times before you use it.

Here’s the part list:

• DC12V to 9V 3A Power Adapter (buck) -ebay $6.00 free shipping
• Nikon EP-5 Replacement Power Supply connector for D40 -Amazon $13.00 shipped
• 12 Volt DC cigarette light plug –used free
• Wire -used free

Total $19.00

Tools needed:
Soldering gun
Heat shrink tube
Wire cutters
Digital multi meter

Step 1: Testing

First I tested the Nikon battery to see what voltage it put out. The battery says it’s 7.4 volts. It tested at 7.61 volts from the positive terminal to the negative terminal. I also checked the voltage between positive terminal and the “S” terminal. Here it was 7.54 volts. On the AC adapter for this camera at the battery adapter, the voltage was 9.38 volts between positive and negative, and 9.29 volts between positive and “S.” That showed me that the camera accepts between 7.4-9.29 volts. As far as how much current is needed I guessed around 3 amps max for this camera. This is based on some tests I’ve seen posted online. The actual draw is probably half that, but to be safe I used a 3 amp power source.
<p>This didn't work for me. I'm using Anderson PowerPoles and a Paradan Power Strip. When I plugged the dummy battery into the power strip, the battery stopped outputting and, unless I was hearing things, started emitting a dim whirring noise. I immediately unplugged everything and disconnected the power strip from the battery. Looks like I'll go back to using a regular battery until I ditch my DSLR for a designated astro camera.</p>

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