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Canon 350d battery mod


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Having done a lot of research before I even thought about attempting this, I have decided to butcher a dead 350d battery so that I can power up the camera without the need for batteries. This should mean longer imaging runs and less fumbling about in the dark trying to swap batteries about without disturbing the set up.

At this point I should make it clear that I have done lots of research and have not yet finished nor tried the dummy battery set up, so if you choose to go ahead and do this yourself before I have finished, on your head be it :blush:

First of all I opened up the dead battery pack. This wasn't too difficult, I just used a very sharp craft knife to carefully slice through the very thin plastic around 1 side and an end of the pack where the little line is. Then carefully prised it open using a small screw driver. The case will break, but this will be glued back later.

Inside there are 2 x cells joined together at one end by a metal strip which also goes to a point on the printed circuit board marked BC. The other ends were attatched to the opposite end of the board, the positive to B+, the negative to B-. I carefully removed the two cells and most of the metal strips except a small amount at B+ and B-, these will be used later for somewhere to solder the power cable to.

The middle of the battery pack comes out, bringing with it the 3 metal terminals. I removed this carefully to enable the two cells to be removed from the assy more easily.

The Three Terminals.

Research showed that the three terminals are +, - and "T". The "T" serves as a thermal cut out both for the charging process, and the fact there is a third contact in the camera body would indicate that it may also do the same in use. The "T" and - are connected via the ciruit board via a Thermister. In one article I read it suggested placing a 10K resistor in it's place if you are removing the board all together, which I have decided not to do. Instead I am using the original board. The "T" terminal is the part that regulates the overheat protection when charging etc, it shouldn't have anything to do with the power side of things as such.

I next will connect the positive from my PSU to the B+ and the negative to B- this should in theory be all I need to do, other than glue it all back together with a small hole in the battery case to let the wire out. This will be best done by dropping a std battery in, opening up the small cover for the cable and marking where it meets the battery, this can then be passed accross to the case I'm playing with.

From research power needs to be between 7.2 and 8.0v, the battery states 7.4v, I have a regulated power supply from Maplins that works on mains which I shall first try. This has a 7.5v setting which should be fine I hope.

But What About "BC"?

Having tested the circuit, it appears to be a secondary connection to the "T" circuit, this was originally at the join between the two cells, so I am assuming it was so if one cell got too hot or became faulty it would trip the circuitry into action to avoid damage. From that viewpoint I am leaving that disconnected. There is no mention in any of the articles I have read of this connection, so assume it is not important in what I am trying to do.

I'll add some pictures later and if I get it all sorted will report back if it goes well or not.

If anybody knows of anything I have overlooked, or has a bad experience of trying this in the past, please post up now before I blow the camera apart ;)

Edited by Perkil8r
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Before I got a factory built unit I looked into this conversion myself.

The only problem I found was if you stick your multimeter across a charged battery the center pin is also part of a circuit,

Unable to discover what this did inside the camera I decided to play safe and get a 'proper' one so to speak.

The one I am using at the moment will not run the camera on 7.5 volts but needs to be on the 9 volt setting.

I wish you all the best with this but after blowing up one 350 D I decided discression was the better part of valour where this project was concerned.

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The centre pin is there for the overload detection which shuts off the charger and presumably the camera in the event of over voltage. Which unit did you end up going for graham? I can't find my soldering iron for love nor money, so I might end up cheaper buying a ready built unit rather than buying a new soldering iron etc etc....

One page I got info from is: http://www.togastro.com/ozzzy/batt_elim.html

Edited by Perkil8r
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