BG-E2 Battery grip and NiMH AA batteries

[finn]

First some facts:

- The BG-E2 with 2x Canon BP511 Li-Ion batteries lasts for 4 hours continuous shooting. Power indicator showed full.

- The BG-E2 with 6x 2500mAh NiMH batteries lasts for 3.25 hours continuous shooting. Power indicator showed half-full.


I was expecting a longer shooting time with the AA batteries, however I have found the problem of this being 1.2v rechargable AA batteries instead of the 1.5v disposable AA batteries which it was designed for.

Now, the Canon BP511 battery has a voltage of 7.2v, and the 6x AA NiMH also have 7.2v, so in theory, the AA batteries should last longer as they have more capacity. But they do not - which leads me to think that the wiring of the Canon batteries versus the AA batteries is different.

If this is true, can the BG-E2 be re-wired for AA batteries to *trick* the camera into thinking that a BP511 is attached ? It seems that the low-power cut off kicks in sooner for AA batteries than the Canon batteries.


Regards,

[Clubmanmc]

with the capacity of a battery, you have to look at both the voltage and the Amps...

the AA rechargables will be possibly 2200mA or up to 2700mA compared to the BP511 which is "just" 1100mA but the rate at which they discharge is also a factor in the amount of shots they will be able to take...

the camera does nothing of the sort in "knowing" which battery is connected, it is the drain on the batteries that is reducing the number of shots that you can take.

if the battery supplier lets you know the rate of discharge of the AA batteries, then you may be able to work out the rest

to put it in other ways,

the AA batteries will be able to pump out qalmost twice as much, but for not as long..

imagine them being both runners, the AA's are 100m sprinters, the BP511's being 1500m runners... the 100m sprinter will burst out and run fast but be exhausted quickly, the BP511 will run slower, but will do more distance.

the reason for this is that the camera has many different battery needs, charging the flash, driving the Focus motor, doings its calculations, priming the shutter magnet, showing you the result on the screen, running the LCD screens, each one of those uses power differently, and hence the best battery to do that is a long running BP511...

hope i aint ranted...

M

[MarkChap]

hours of shooting is not a good comparison either.

How many shots did you get with the BP-511 compared to the AA's ??

What did you do different each time - more or less flash, more or less reviewing images, lens with or with out IS,
There are a lot of variables to take into account.

[MarkChap]

Well that was a waste of time, just spent 20 minutes and still can't find anything on the Canon site ??

I am sure I read in the enclosed instructions that with the AA's not to expect the same battery life as from the BP-511's

Will check the paper work from my BG-E7 when I get home

[finn]

To help clarify things:

1) When I had 2x BP511 batteries fully charged, the camera battery indicator also showed fully charged.

2) When I had 6x AA 2500mAh NiMH batteries fully charged, the camera battery indicator showed half-full.

3) I measured both set ups and both were 7.2 volts - which tells me the reading for AA batteries is different some how.

4) The reason for continuous shooting is I am aiming to make a star trail image from numerous individual images taken at 5 minutes exposure each.

5) No zooming, no auto focus, nor image playback was done during my tests, no flash. Just set it and forget it until the batteries run out.

6) During my tests, the 2x BP511 produced about 47 images (5 minutes exposure each). The 6x AA's produced about 38 images (5 minutes exposure each).

I hope this extra info helps.

[MarkChap]

ah ha, okie dokie.

The battery meter on the camera would not be measure of voltage, but rather the battery capacity, I would think.

As to why it would show full with BP-511's and half with AA's has me beat.
As I said before, I do recall reading somewhere that battery life is reduced greatly when using AA's, and I think you will find it is, as Michael pointed out, the way the different batteries deliver their power to the system.

The BP-511's are not chipped, so I don't think it will be anything like the camera knowing which batteries are there.

[finn]

On the weekend I did some tests and can now manage to get more than 12 hours of shooting with some modifications. Here is what I have found:

a) the BP-511A batteries show low capacity when they are approx 7.4v

b) the 6x AA NiMH batteries were running around 7.4v to 7.2v - hence them showing low capacity even though they were fully charged

c) 6x AA alkaline batteries (which the battery grip is designed for) run at 9v and show full capacity.

That proves that the camera battery capacity meter is measuring voltage to show you if the battery full or not.

The underside of the 5D has a label showing the camera operates at 8.1v, indeed 9v does not do it any harm (using 6x AA alkaline). So I thought of making a custom 8.1v power supply from a 12v lead-acid battery. I was really nervous about hooking my expensive camera up to my custom power supply, but it worked like a charm.

It showed full capacity and I set it running over night (about 12 hours before I turned it off), yielding about 140 images at 5 minutes exposure each. The lead acid battery still had enough power to go for longer, however I was just aiming to get a full 12 hours done (in order to capture the movement of stars during the night).

I hope to show some images of my little unit in the future. Anyone with a soldering iron and some electronic know-how can build one.

This would be especially great for astro-photographers - which is what this is all about. Of course you will need to lug an extra 2-3kg of lead acid battery into the field, but once its set, it stays put, so should be of minimal extra burden to allow you to capture images the whole night through.

Now I just need to wait for this rainy weather to vanish so I can try it out.

One happy snapper :)

[MarkChap]

Good to see you have found a solution.

I don't know that I will be trying that one though, just in case :)

[darylcheshire]

Be careful with those extra Amps

Daryl

[finn]

I have finally managed to get some time together to take photos of my project and also update my website.

For those vaguely interested, here is a link to my website (still being updated):

http://manga0.freewebsites.com/photo/powersupply/powersupply.html

I will update this at a later date once time becomes available again.

Enjoy.