calculation for power usage ?

[Midnitewarrior4]

is there a calculation to see how long i could run something off a battery ? say it uses 5 watts and i have a 22,000 Mah battery how long could it run ?

trying to build a portable raspberry pi system and trying to figure out how long it could run off the battery bank i chose

[Mattyp92]

2 minutes ago, Midnitewarrior4 said:

is there a calculation to see how long i could run something off a battery ? say it uses 5 watts and i have a 22,000 Mah battery how long could it run ?

trying to build a portable raspberry pi system and trying to figure out how long it could run off the battery bank i chose

Amphours*volts = watthours, or (mAh*V)/(W*1000) = hours

 

So for you, let's say it is 5 volts and 5 watts, it would be 22 hours.

[Midnitewarrior4]

2 minutes ago, Mattyp92 said:

Amphours*volts = watthours, or (mAh*V)/(W*1000) = hours

 

So for you, let's say it is 5 volts and 5 watts, it would be 22 hours.

sorry you may have answered this but im tired and not thinking right but al i can find is that it will need about a 2 amp supply would i just do 22,000 mah divide by 2000 ma ?

[Mattyp92]

5 minutes ago, Midnitewarrior4 said:

sorry you may have answered this but im tired and not thinking right but al i can find is that it will need about a 2 amp supply would i just do 22,000 mah divide by 2000 ma ?

22,000mAh = 22 Ah.  If it runs on 2 amps, you will get 11 hours out of the pack. 

[Midnitewarrior4]

2 minutes ago, Mattyp92 said:

22,000mAh = 22 Ah.  If it runs on 2 amps, you will get 11 hours out of the pack. 

ok thank you, and wow 11 hours on constant use isnt bad.... and the case i want to use has enough room for about 4 of them... would be good for about 2 days of constant full load use

[Mattyp92]

4 minutes ago, Midnitewarrior4 said:

ok thank you, and wow 11 hours on constant use isnt bad.... and the case i want to use has enough room for about 4 of them... would be good for about 2 days of constant full load use

Make sure the batteries are in parallel not series but that may require some rewiring there and at that point it would get tricky.  You could go from one to another to another but you will lose power while you swap the batteries.

[byalexandr]

29 minutes ago, Midnitewarrior4 said:

is there a calculation to see how long i could run something off a battery ? say it uses 5 watts and i have a 22,000 Mah battery how long could it run ?

trying to build a portable raspberry pi system and trying to figure out how long it could run off the battery bank i chose

What is the input voltage? Divide the 5W by the voltage to get the amperage, and then divide 22 by the amperage you got to get the hours it will run.

[Midnitewarrior4]

3 minutes ago, Mattyp92 said:

Make sure the batteries are in parallel not series but that may require some rewiring there and at that point it would get tricky.  You could go from one to another to another but you will lose power while you swap the batteries.

i think il start with one and go from there