External Lithium Polymer Battery for Canon 400D, anyone tried?

[Astroman]

Hi all,

I am thinking aloud here so any comments you have would be appreciated, especially from those that have done it or know a bit about the electrics in cameras...

I am contemplating using a Lithium Polymer battery the same as they use on RC Model Aircraft to power my Canon 400D. The Batteries that are used on my Canon are 7.4v, the AC adapter I have is also rated at 7.4v. The lithium Polymer Batteries I use in my RC aircraft are also 7.4v being 2cell LiPo I can get these reasonably cheap off the net, and I have the LiPo charger etc... The good thing about the RC batteries is instead of the usual 1200mAh per battery I can get a 5000mAh LiPo and run 4 times as long or more if I put these batteries in parrallel.

The idea I have is to use the existing AC adapter dummy battery thing, and the wire that comes from it, cut that into two and add a plug to it then I can plug the Battery straight into the Dummy Battery, or if I want to use the AC adapter, I just plug that into the dummy battery.

The idea came from this website: http://www.tellurian.ca/newastro/eosbatterypg.html I have tried getting in touch with the owner without success...

The only issue I may have is the full charge voltages of the LiPo compared to those standard batteries. Unless these is something else someone can think of...

Does this sound like it could be done? Has anyone attempted something like this? Am I crazy for thinking such a thing?

The idea of using the larger batteries is so I can do a full nights continuous shooting using the batteries, the Battery grip and two batteries I use still have to change them before the full session is over, which is a pain, and where I usually shoot AC power is not an option.

[Bennymiata]

I would imagine that it would work.
There must be some tolerance in the camera's power supply to allow for variable voltages, at least to some extent.
Maybe the trick would be to put the Li-Po batteries into the grip rather than breaking up your AC power supply, or just buy the correct plug to go into your camera and wire that up to the batteries.
You could even buy a cheap, aftermarket grip and use that.
You will need a little skill in soldering and knowing which wire to connect to which terminal, but if you have been playing with electric RC models for a while, you should have learned these skills already.

[jjphoto]

I have used various batteries to power 20/40D which also use a 7.4 battery but in a different rating (BP-511). The exact voltage is not that critical, IMHO, but I don't know what the limits really are and when you'll get into trouble (ie fry something).

I use a normal (cheap) Sealed Lead Acid battery (12V) with a cheap voltage regulater set to 7.5v. Works fine.

JJ

[Astroman]

Okay, thanks for your replies. So I would need to sit down and do some voltage tests first to determine the highest voltages that the cameras Batteries and AC adapter use, then see if the LiPo Batteries are the same or lower. A case of suck it up and try I think. I'll get another plug to go into the dummy battery first, so I don't have to cut any wires.

I had though of using the SLA batteries which I still might use since I use 3 of them in Parrallel to power dew heaters a computerised alt/Azimuth head, and eventually a photography Dolly also with them. So running the camera from the same pack might have it's advantages also.

Do you have a circuit for the 7.5v regulator?

[jjphoto]

If you are already using SLA's then you'd be nuts to complicate things further and use another battery. You might ultimately have to use a larger SLA, depending on current draw, but you'll have to judge that for yourself.


...
Do you have a circuit for the 7.5v regulator?

Although you could make one, it's actually cheaper, quicker and easier to just buy one. If you needed a much higher current supply, ie if you wanted to power several cameras from the same adapter, then you'd probably have to make one or buy a seperate adapter for each camera.

http://www.johnjovic.com/temp/BP511/DS_0728.jpg

If you want to make your own then you could use an LM338 based circuit, which is a 5A variable voltage regulator. Circuits are available all over the InterWeb, Google is your friend. I have an electronics background and have everything I need to make this kind of thing and still think it's easier to just buy one, unless you specifically needed higher current.

JJ

[Astroman]

And for only about $30 from DSE, seems like a cheaper option also, thanks for that, really helpful.

[Astroman]

I just checked the voltages from the AC adapter and also a fully charged Battery, and a Battery that has just been used up in the camera.

AC Adapter - 7.7v
Full Battery - 8.33v
Used Battery - 7.1v

So it seems there is a little amount of voltage variation I could use, so that not that critical, as long as I keep it around 7.5-8v I should be fine.