Calculate mAh Needed for Load @ 1.5V, 57mA 4min

[dnyberg2]

If I have a load that needs 57 milliamps for 4 minutes @ 1.5V, how do I calculate the mAh rating needed to satisfy that load?

 

[anorlunda]

57 milliamps * 4 minutes = 57 milliamps * 0.066 hours = 3.8 mAh.

The voltage plays no role.

Of course, that is an ideal number assuming 100% efficiency. In real life, figure double that amount.

If you give us more details, we might be able to give a more specific answer.

 

[Windadct]

Technically ... it is straightforward if you do the math, and include the units:

57ma * 4 min = 228 mA*min ... now you need Unit Conversion 60 min = 1 H, so 1 H/ 60 Min = 1

228 mA * Min * ( 1 H / 60 Min) = 228/60 mA * H = 3.8 mAh... very small amount.

I say technically because battery selection also should involve a number of other factors, number of cycles(lifetime), how deeply the discharge cycle is relative to the capacity of the battery and -- the RATE of discharge dramatically affects the real capacity of the battery. For example, if you had a 4 mAh rated battery, it meets the 3.8 mAh requirment, but would probably die at a discharge rate of 57mA very quickly.

 

[Borek]

Looks homeworkish to me. Basically a dimensional analysis problem, with several conversion factors.

 

[dnyberg2]

Ha! I wish it was homework but at 54 years of age, I'm outta school now but thanks for the flattering thought!

 

[dnyberg2]

Not to mention, my "Some timers" is kicking in pretty good these days...