Solar powered raspberry Pi servers
 

After my EV Motorcycle conversion I'll have a row of little 12v 3 amp hour batteries (I think 12 batteries total). I want to make a server farm out of raspberry Pis. Don't let this post scare you off immediately, it's a pretty basic question.

The pi runs on 5v and 1.2 amp.

(keep in mind I'm new to solar stuff and the math behind it all).

If I run the batteries in parallel, how do I do the math to figure out how long the raspberry Pi will last on the batteries?

After this math is figured out, next I want to figure out what solar panel(s) I could use to charge the batteries. I live in the desert, so it'd be cool if I could use the panel to run the pi during the day and at night have it run off the battery pack. The solar panel during the day could also charge the battery pack.

In parallel add the amps up for the bats. Then divide the draw into the total for run time assuming room temp as extreme temps reduce battery capacity.

12 x 12 volt 3 amp bats in parallel = 12 volts 36 amps.

Lets assume you use a 12 volt usb power supply. 12 volts half an amp 72 hours for one pi.

I see how you calculated draw. Amps times volts of the Pi. 1.5 amps x 5 volts = 6 watts

So 6 watts

As far as the batteries go, 36 amps.

But how did you get 72 hours out of that calculation? Was it (12v * 3amp) * 12 and that divided by the 6 watts from the Pi?

Well, you can multiple amps x volts to get watts and then math that way. In a real world there is always losses as to why I guestimated the run time.

So you could say 1 bat is 36 watts, 12 bats is 12 x 36 is 432 watts

Raspberry pi is 5 volts x 1.2 amps or 6 watts

432 / 6 is 72 hours, assuming no losses and all bats are fully charged and have full capacity.

There are a few different raspberry pis out there and some use less power than others. Then you got the accessories and such. A NAS drive you got to take into account what the drives use too or if you use it to mine bit coins need to take into account the dongles power consumption.

Just a note, the Pi will probably use less power than that unless you're really pushing it, so 72 hours would likely be the minimum. Also, the batteries would be 12v and 3Ah, so the total capacity of the 12 batteries would be 432wh. Ah and wh are the capacity, like a water tank, A and w are the flow rates, like gallons/hour. Amps need to be listed with the voltage to be useful in most cases, watts are universal. You need to use watts in your case because of the batteries being 12v and the Pi using 5v.

For the solar panels, 20-30w would probably be enough for one Pi running 24/7.

Ok, I learned something. Calculations are only good for estimates. You guys are right, I'd need to gather more numbers by testing a setup and documenting everything.

Or, just trial and error, which is more fun.

Id like to know more about the decision to go from an EV motorcycle to a solar powered raspberry pi. :confused:

It's a future project. I'm looking for things to do in the future to build up my energy efficient tech arsenal. I want to learn about solar power, wind power, and efficiency because I've got plans in my future to move and setup some land and build a self-sustaining house.