


Joined Feb 2013
15 Posts

Question
Understanding battery ...
Hi
Dont worry i will not ask you to explain all. I have made my own researches on websites and forums I gathered infos and I think I understood but I have some doubts Can u confirm or correct the facts ? Example : 3S 2100mAh 25C 2C So what does this say ?: 1) How many amps maximum can be drawn : Amp*C*P Amp = Capacity A (2,1A) C = Discharge Rate (25) P = number of parallele block ( 3S1P = 3S ) 2.1*25*1 = 52.5 A 52.5 Amp maximum can be produced by the battery Why is it useful? We can check if the motors can be well supplied ex : motor drawing 5A For a quadricopter : 5*4 = 20 A The battery can deliver 52.5 A, which is enough ( 52.5A > 20A) 2) The flying time when the battery discharges max 1 hour = 2.1A we need 20A to supply 4 motors (5*4) 20/2.1 = 9.5 times more than the capacity per hour meaning it consumes 9.5 times faster 60/(rmotors Amp / battery Ah) = 60/(20/2.1) = 6.30 min the batttery will be empty after 6.30 min is it correct ?? coz I have read another method which gives a different result mAh : 2100 / 60 = 35mA per minute 35mA*C = 35*25 = 875 2100/875 = 2.4 min the battery will be empty after 2.4 min this is the original text : Quote:
3) we have not to empty the battery at 100%, it would damage it 100% = 2100mAh , 80% = 1680mAh Question bonus : if we have a battery : 3S2P 2100mAh 25C 2C 2P means parallele connexion = double capacity so it means we multiplicate mAh by 2 ?? (4200mAh) thanks for your help 





"52.5 Amp maximum can be produced by the battery "
The manufacturer/supplier claims that up to 52.5 amps can be delivered, not produced by the battery. Manufacturer and supplier claims are not to be trusted. 25C is 2.4 minutes, which you figured out but simpler formula is 60 minutes / 25C = 2.4 minutes 


Joined Feb 2013
15 Posts

Quote:
well, i am french, maybe i used the wrong english word I understand what u mean. About flight time, my method which for me was logic is not good then it's the other formula that I have read which is the right one. thanks 



Staffs, UK
Joined Nov 2003
12,001 Posts

The first method you used for flight time is correct. When you say 20/2.1 is 9.5 times that's the same as saying the actual discharge rate you're using is 9.5C (not the full 25C that the battery COULD do).
The second one is working out the time if you discharge at the full 25C. If you notice, the real current you are using (20A) doesn't appear anywhere in the calculation which can't possibly make sense . Steve 


Joined Feb 2013
15 Posts

Quote:
I guess it's not very smart actually to calculate with these formulas . As Ken said, if we can't trust the manufacturers about the discharge rate and that the autonomy of the drone depends how we use it I have not a quadricopter yet, so i can't really realize with real experience but it seems it's often less then 15 min 

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