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Hydra question running on battery?


Has anyone run the Hydra on a battery? I need it to run for 1 week without a change…


A hydra certainly will run on a battery. I’ve used a 2 cell lipo (~7.4V) with a barrel jack to the DP module just fine. How long depends on what you have plugged in. You’ll have to measure current draw and extrapolate based on mAH rating of your battery.


The current requirements for the Hydra have not been posted yet.

But, lets do some rough order estimates:

Assuming the drain is around 150ma, for a week you would need .150 * 24 * 7 amp/hour capacity. That is 25.2 amp/hours. The 150ma estimate may be low. This assumes that the device is running all the time.

25 amp hours is not a small battery! I believe that is in the realm of automobile batteries.

I believe that larger capacity AA rechargeable batteries are in the range of 3.0 amp hours.

If the device does not need to be active all the time, there might be a low drain sleep mode for the chip, as there is on other FEZs.

72MHZ+ devices do eat up batteries. :slight_smile:


It will be running two analog acceleration sensors and the sd card. Dangit…

That is a big battery indeed. 150 mA draw is more than I thought.

So if I can get 1.5 Volts times 5 = 7.5 V = 1 battery at 3 amp hours…

25/3=approximately 8 * 5= 40 AA batteries…

I can live with that…



first, rechargeable batteries are more like 1.25 volts, but are enough.

I don’t think you can just connect eight sets of five rechargeable batteries in parallel. you might need a controller. not my area.



Pretty sure that is how it works. I have used it before on other boards it is in parallel or rows. Either way it never fails me.

I think I can use two lantern batteries that I found for very cheap although I am not sure about the 6 volts. I may need to figure this out some other way. D batteries might work as well.

A lot of batteries nonetheless!


Yep, you can serial-connect a number of batteries to change the voltage (individual voltage * number of batteries = total voltage) and the AH capacity does not change. You can then parallel-connect multiple of those “units” to increase the AH capacity (AH rating * #units = total AH rating).

The real problem you get in the scenario with a lot of individual cells is failing cells - one bad cell in the “pack” can play havoc with everything. And certainly you wouldn’t want to try to charge them in-situ in that configuration, you’d end up with unbalanced cells that would cause all sorts of cell damage.


Have you thought of using a rechargeable battery pack then add a solar panel charging station?