KC
Elite Veteran
Location: WA
| Think of C like MPG ratings on a new car....
if a pack is 25C and 4000mA (4A), it can be pushed to 4x25 = 100A for a period of time that is determined in controlled testing as its sustainable max current draw.
in the real world, your current draw will not be a continuous even number, but you can determine an average number by noting how much juice the charger put back into a battery after flying it for a set amount of time...
for example: I take each new battery and fly it for 4 minutes for a few charges, I note how many A were put back into it, lets say its usually 2A, now I know that my heli used an average of (4/60)x2, or 30A, throughout the flight.
Here's what I do,
I aim for an average current draw of 1/3 max C-rating over the course of the flight and take out no more than 75% of the charge,
i.e. I have a heli with a 4A pack that is 25C, 1/3 of (25x4) is 33A
If I draw an average of 33A from the pack and not exceed using more than 75% of the charge, I must aim to fly no longer than,
0.75 x((4/33)x 60), or 5.5 minutes
so now I know I can do whatever I want to that heli in the first 5.5 minutes without a worry at all about the pack...if I want to fly a little longer, I have to be careful, but usually I stop at that time and recharge.
why 1/3 max C? I chose this number because I aimed for 6C discharge on older 10C packs (2/3 max) and that was about the max they could sustain for my flying style...8C from a 25C pack is really conservative, but my goal is to get atleast 25 hours of flying from each pack.
regarding spikes, spikes that reach max current are not going to hurt a good pack...'good' meaning, if they say its 17C, its 17C.
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is higher C better? this question has a kinda loaded answer that depends on the voltage you use...in simple terms, V x C = power, the more volts you have, the less current you need to match the power necessary to fly. If you fix the volts, its always better to have as much C as you can get! |
