One of my other hobbies is photography, and whilst I don’t spend as much time with the camera as I would like  I still like to have plenty of power. I shoot with a 30D and/or 40D, which uses the old style BP-511/A Canon battery.  The dilemna I had is that I would like to power my camera from a 12-14V source (such as a SLA battery) to get plenty of juice, but I need to provide the requisite 7.4V expected from the battery. There are two aspects to this – electronic compatibility and mechanical compatibility.  Luckily the electronic compatability is easy (at least on the older models – I can’t speak for the new ones) as you just need to provide the expected 7.4V.  Mechanically I looked at a few options such as custom fabrications, but in the end I just settled for the tried and true “crack open a battery that no longer works”.

BP-511A Casing after removing cells and control board.

Daniel McCauley of http://www.easternvoltageresearch.com/ used to have a wonderful document that listed the current draw of a 300D when operating in different conditions.  Whilst the document has long gone online, I recall that the peak current was in the range of about 1A, albeit for very short periods.  It does however provide a rough estimate of the currents involved.  I credit him with the original idea behind doing this as well!

Whilst the original design Daniel provided used a standard linear regulator, I figured that the size of switch mode supplies had decreased enough such that it should be possible to mount an entire DC/DC converter inside the battery compartment.  This way I can feed in any (reasonable) voltage and the camera will operate happily.  Being a touch lazy (and enjoying other things then power supply design) I just grabbed a module off the shelf that was small, and had what I thought would be acceptable specifications (lowish ripple, high efficiency).  I settled on the TI PTN78000W module (in the surface mount variety).  It was then just a matter of designing a rudimentary board around it that contained a protection diode as well as some input and output filtering. If you would like a copy of the schematic feel free to contact me!

Testing the new DC/DC converter board for fit - and it does!

I opted to get this board professionally made as I wanted a nice reliable final product that worked in some pretty horrid conditions (cold, dampy, hot, dusty – all the usual suspects!).  It was then time to get the hot plate out and do some soldering:

The board is assembled except for 3x 2.2uF 0805 caps (and the cable connectors!).

And that is where this first post ends – I need to order some caps that I apparently don’t have in my junk box.  I’ll post again once it is assembled and tested.

Note: I did contemplate purchasing a non genuine one from eBay, but I liked the idea of having something that I knew was a bit more reliable. Ironically enough I trust my own fabrications more when connected to expensive equipment then the really cheap knockoffs.

 

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