I want to power my Canon T3 from the car. That means getting a 12VDC output to a 7.4VDC. Easy, right?

First, deciding between a custom solution (pcb) and an off-the-shelf solution. Off-the-shelf solutions exist to convert 12VDC to various ranges - among them, 7.5VDC. Perfect.

But then comes a wrinkle: What size plug? I simply cannot find a plug for the DRE-10 battery eliminator. Or, rather, I can't figure out which plug it needs, since nothing will say. Okay, so here's a simpler solution: I can simply disassemble the battery eliminator a bit, and wire/solder to the appropriate terminals directly. That'll do the job, as it's unlikely that any plug - except one made specifically for it - will have the profile to fit inside the camera.

Then a thought: Not only do I want to power my camera, but also my external hard drive. I am getting large SD cards, but not large enough; I need to get two. While one fills up, I'd like to copy data from the other one. My hard drive takes a 12VDC 1.5A line. The aforementioned adapter offers a 12VDC 1.2A output. Good enough? Probably.

 

It doesn't help that along with never mentioning plug sizes, chargers seem to never mention whether they're center-tip positive or negative (their polarity). My ACW018A3-12U charger is center-tip positive, like most chargers. Thankfully I have a nice multimeter to tell me. If I end up getting a cord with the wrong polarity, wire cutters, solder, and electrical tape will fix the problem, but it won't be pretty.

I'd love to make a custom solution, and update with pictures and part numbers. So far a decent plan is: one converter with multiple plugs, and some hacked wiring to do the rest.

 

I don't own solder nor electrical tape, at the moment. I do have a soldering gun. In light of that, the costs for an off-the-shelf solution are:

• $10 - GE 94360/23600 Universal DC Adapter
• $6 - Roll of 60/40 flux-core solder, 1/4 lb
• $3 - Electrical tape
• $10 - DC coupler (battery replacement; power pass-through device)

Downside to all that: Chance of melting, burning, and otherwise destroying expensive electronics. Also a chance of not supplying enough power, and several subsequent purchases. Given the general "bad luck" tax, the subtotal of $29 would be doubled to $58.

 

A from-scratch solution would mean creating my own board, with a 12VDC-7.4VDC buck converter and power regulator, and a 12VDC-12VDC direct line (with the appropriate plug on the end.) Approximate costs:

• $15 - Circuit board from Seeeedstudio Fusion, 5 boards at 5x5cm
• $15 - PCB components in singles
• $6 - Roll of 60/40 flux-core solder, 1/4 lb
• $3 - Electrical tape
• $10 - DC coupler (battery replacement; power pass-through device)

Downside to all that: Chance of melting, burning, and otherwise destroying expensive electronics. On one hand, I can guarantee the device will be designed to supply the right power and voltages. On the other hand, I can't guarantee that it actually will. I love to spend money on my engineering education, but I'm not a fan of sticking the results of that into where they can destroy $500 worth of electronics. The subtotal works out to about $49, and with the "bad luck" tax, a 50% adder brings that to $75 or so. The components are very cheap unless you buy them in singles like I would be doing.

 

The dumb solution:

• $27 - 12VDC to 110VAC inverter, dual channel
• $10 - DC coupler (battery replacement; power pass-through device)
• $5 - Extra gas burned due to inefficiency of solution

Downside: Incredibly inefficient to convert 12VDC to 110VAC, back down to 7.4VDC and 12VDC. It'll probably burn about $5 worth of gas money. Upside: My devices won't burn, and I'll be able to do this in a non-destructive manner. Subtotal: $43.

I think the dumb solution wins.