Accumulative power for an electromangetic induction generator

[tkelly-lord]

Hi all,

i'm test rigging a generator I am designing. Based on theories of electromagnetic induction and harvests small amounts of energy over a long period to hopefully charge your phone (fingers crossed).

I've worked out that I gain approximatley 22mA every second with an average voltage of 1.5v. The device will charge for approx 6 hours.

I wanted to find roughly how much i could charge my phone. I've tried to work it out but not 100% this is write. If you have a second could you please check over this...



coulombs = amps X time(seconds)

And 1 ampere hour = 3600 coulombs

A phone battery that is 1400 mAh or 1.4A/h equates to 5040 coulombs. so in total it needs 5040 coulombs of electricty passing into the battery in order to charge it. That means for a 6 hour charge we need to have 5040 coulombs of electricity delivered in a 6 hour period, therefore we need 5040coulombs/the number of seconds in 6 hours

5040/(6 x 60 x 60) = 0.233 amps second.

so if the average current was to be 22mA or 0.022A then we could accumulate 0.022 x 6 x 60 x 60 coulombs = 475.2. Using the 1400mAh phone battery as a reference the the phone could operate at this capacity for 5.657 minutes.( 5040/60 = 84 coulombs/minute).

If the phone uses 5Watts of power at 3.7 volts, that gives 1.35 amps.................5.86 minutes of full use. ((3600 x 1.35)/60) = 81 and 475.2/81 = 5.86 minutes


thanks if you could check

Tom

 

[Diver300]

You Coulomb / Ah calculations look about right, but there is not much point in bothering with Coulombs. You could just work in Ah.

Your phase "22mA every second" is a bit meaningless. If you are getting 22 mA, then that doesn't depend on the how long it has been running for.

Also, if you are getting 22 mA at 1.5 V, you can't charge a 3.7 V battery at 22 mA with that. You would need a boost regulator or charge pump or something to bump the voltage up to more than 3.7 V, and that will cut the current down to less than about 7 mA.

Also, Lithium batteries have a maximum voltage of 4.2 V, so you have to allow for that.