So as I bet we all have noticed internal Battery on the Cinema Cameras isn’t very good, especially over time.
BMD states 90 mins, I can best around a little over an hour almost 3 years after. Which of course is not bad. The camera was designed to be powered off external batteries after all.
However it made me wonder If I could change or swap out the internal Battery for another pack of similar electrical characteristics.
My findings were quite revealing.
1st off the Cinema Camera uses a MinMax LP904086 Lipo Battery. It’s a 7.4v 3800mah Battery in a 2s1p configuration.
http://www.minmaxenergy.com/newproductShow.asp?id=11The battery uses a standard charging voltage of 8.4v (4.2v per cell) and cuts out at 6v (3v per cell)
This is great because it essentially uses a very standard voltage commonly associated with a 2 Series Battery Pack.
So with this I plan to upgrade the internal Battery to a custom made 7.4v 6800mah battery using 18650 Cells. Specifically the Panasonic NCR18650B, which is among the highest capacity 18650 you can buy at 3400mah per cell.
http://industrial.panasonic.com/lecs/ww ... 0CE417.pdfNext was determining the internal power consumption of the Cinema Camera. So I hooked up the internal battery connector to my bench power supply and this is what it looked like. ( pardon the crappy iPhone quality )
As you can see the power consumption steadily hovers at around ~15-16 watts. And what’s interesting is power usage actually slightly drops when recording as opposed to being idle. Not alot, but contrary to what one might believe.
The other thing I later tested is what happens to power usage with regards to the display backlight. From 100%-0% you see a drop of about 100ma. It’s not significant. So it will save you battery but not much.
The most intriguing part of this test was the fact the camera drops out at around 7.30v. Anything below that and the camera will just shut off when you try to record.
This is an issue because the internal battery and most batteries of that configuration have remaining power down to 5-6v (3-2.5v x2 )
So when the Cam battery is “dead” it in fact still has capacity and from my calculations this remaining capacity can be as high as 40%-50% of the batteries total capacity.
This is mind boggling to me and very much a Blackmagic design flaw.
So if we do the math here’s the theoretical run times of the camera with the internal and my proposed battery.
BMD Internal Battery
7.4v x 3800mah = 28.12wh
28.12wh / 16w = 1.76hr or 1h46m
Proposed Battery
7.4v x 6800mah = 50.32wh
50.32wh / 16w = 3.145hr or ~3h9m
The real world performance is obviously less and degrades from several factors including time, temperature and environment.
I put together a crude test battery pack that is 7.4v and 4800mah and it ran the camera for 2 1/2 hours.
So there’s a look into how the Camera breathes. It’s less than perfect I’d say from these tests, but It works great as its designed for external batteries.
However It can be modified and used more practically in some situations with any external power.
More to come on that as await my shipment of new batteries.