Batteries and chargers

[Oscar Spier]

Originally the Elphel has 48v POE (power over ethernet), but it is possible ( Modifying the camera for 12-36v mobile applications - ElphelWiki )with a modified Elphel to use a power source within the 12v (9v-36v) range.
An important post on this by Sebastian:

Careful with the amps!

5W power consumption does not equal 5 Amps.

P (Watt) = U (Volts) * I (Ampere)
so I = P / U

Using a 12V battery as example:
I = 5W / 12V
I = 0.417A or 417mA

Battery capacity is rated in mAh (milli ampere hours).

So if in our example we have a fully charged 12V battery pack with
4000mAh we can estimate the camera (assuming 5W power consumption) to
last for around 9.5 hours.

This is a theoretical maximum value as you would have to consider DC-DC
losses, degree of efficiency, etc. as well.

Maybe the battery pack would last for 8 hours or less.

Regards Sebastian

5 Watt power consumption is not much at all. My EeePC draws around 15W
in idle mode and most laptops use up to 50 W.

5 W at say a battery

Right now, I've tested a 11.1v LiPo battery. It works well and they are extremely lightweight, but they are difficult to charge because they also need to be balanced so they require an expensive charger. Another issue is that you have to make your own housing with a small project box for example.

Alexandre from Elphel is testing this product which looks most promising so far: http://www.digipowersolutions.com/st...929b7124103a4d Here is an image with the camera: Hardware | Apertus Open Source Cinema It can be charged and used at the same time, has status LEDs on the side and also provides a 5v USB power.

[Andrey Filippov]

I would recommend to use 18-19V (as in most laptops), not the 12V. There are diode bridges (as required for PoE in IEEE802.3af) in the camera that waste around 1V or so. It is possible to bypass them but - but that requires soldering and makes camera vulnerable to wrong polarity.

Additionally - I'm working now on next model 373 camera (Elphel Development Blog Circuit design - 10373 ) - it uses TI DaVinci CPU that is more power hungry, some with GigE, faster FPGA and memory. 373 will have flexible power supply voltage (CPU core) and frequency tuning to balance performance/consumption, but still it would be nice to avoid additional limitations on the power cased by low voltage/high current input.

[Sebastian Pichelhofer]

More universal battery packs:

Portable lithium ion battery pack Battery Power Station weighs only 1 pound

http://www.bixnet.com/exnobapo80.html