Help calculating battery charging rate off Solar

[fridgerova]

Hi there,

Can you please confirm/correct my calculation?
I have a battery bank/charger with 4x 18650 Lithium batteries (3400mAh, 3.7V)
I am looking at possibly getting a 20W Solar pannel charger

I am trying to understand How fast I'll be able to charge that battery bank using that solar panel in ideal sunny conditions.

Power stored in 4 above mentioned batteries:
4(batteries) * 3.4A * 3.7V * 3600s (hour) = 181152J

Solar panel generation:
20W = 20J per s

181152J / 20J / 60s = 150 minutes

It will take 2.5 hours to charge the 4 batteries in ideal conditions? Am I correct or totally off?
Sorry, haven't done these type of calucations in some time heh.

 

[Arouse1973]

Yes you are correct. I did it this way and got the same answer. 4*3.4*3.7 = 50.32 Wh. 50.32 Wh / 20 W = 2.516 hours. Remember nothing is 100% efficient so this would be for a perfect system. You do understand that you will need a certain charger also for those cells?
Adam

 

[fridgerova]

Thanks for your clarification!
I believe the bank battery/charger i linked above IS the charger. It says it takes 5V in though.

 

[BobK]

Yes, the solar charger seems to put out 5V for USB connector charging and the battery bank accepts this voltage so you have everything you need to charge the batteries. I would expect 3H to be the typical charge time.

Bob

 

[fridgerova]

Excellent, thank you! Exciting camping times ahead.