LM317: 12v to 7.4v DC + Rebel power data + Antarctican bonus
I'm sure this has been done by many here, in many different ways, but since I had the photos ... It's simply a standard LM317 voltage regulation circuit (http://diyaudioprojects.com/Technical/V ... Regulator/
) placed inside a BP511 case.
I dismantled an old BP511 battery - very interesting it was too - and simply fitted in the circuit. The output wires are soldered directly to the BP511 +/- tabs. The incoming 12v power line (with JST connector) comes in via a hole, and a zip-tie is used as a strain relief. The hole is cunningly positioned to mimic the cable routing from Canon's own DC adapter.
The large capacitor is simply a charge reservoir that supplements the current draw when the LM317 by itself (max 1.5Amps) is incapable of sating the camera's thirst. Simply using an LM338 instead (which I didn't have) would obviate the need for the capacitor, as it can pass 5Amps. I must say that the capacitor fits the battery case beautifully.
The obvious concern is the power dissipated (as heat) by the LM317 (P = 5volt drop * current <= 1.5Watts) which now occurs inside the battery compartment. If you're in Antarctica this may be a good thing ... I find that the heat generated isn't a problem provided the camera isn't constantly working hard.Digital Rebel, basic time-averaged current draw:
Idle: 100mA (if you use power-down feature it will eventually drop to <<1mA)
Pretrigger (half-press): ~200mA (+ ~50mA for AF). Lasts for 10seconds before returning to Idle mode.
Trigger (full-press): ~200mA
Using menu: 200mA
Preview: 200mA, 300mA while reading CF card.
There are of course momentary current spikes, reputed to be >1.5amps, which is why the LM317 is not an ideal choice. Nevertheless these ICs are excellent, and a must-have for even the beginner. They also function as current regulators (see link above), which I have used in some special dimmable-LED time-lapse lighting I built recently, and will describe in a post at some point in the near future.
I know this will make most of you wince, but I recently read that a chap had bravely run his dSLR directly from 12v, without any conversion, and without any trouble. The camera's built-in voltage regulation seemed to be able to take the load, although I'm pretty sure he was just taking occasional photos, not time-lapses.