discharge C or mAh size

[kenghock]

Had a question for the electric experts.

If cost per mAh is the same, then what should I be considering if deciding between discharge C rate or battery size? ie
A is 3000mAh at 25-50C
B is 2650mAh at 3570C
I am guessing its flying time versus flying style.

What kind of flying do you need 70C peak discharge. Or is 50c good enough.

Thanks
Ken

[Pang]

Hi,

yap you are right, flying time vs flying style.

if you are learing/sports flying/mild 3d , most likely the burst rate wont be high, A will be more suitable and you get longer flight time.

if you do hard 3D, you will need the high C burst to sustain those moves., then B will be more suitable.

[edmond22]

Had a question for the electric experts.

If cost per mAh is the same, then what should I be considering if deciding between discharge C rate or battery size? ie
A is 3000mAh at 25-50C
B is 2650mAh at 3570C
I am guessing its flying time versus flying style.

What kind of flying do you need 70C peak discharge. Or is 50c good enough.

Thanks
Ken

Hi Ken,

Maybe the question can be asked differently. Normally, for me in considering my needs, I look at my application first.

For example, I need to power a 5kg plane for 3D flying. I calculated that I need about near 3kw to get decent performance (on par with gaso or nitro for example), I decided on 10s 37volt x 80 amp draw = 2960 watts. I could go other config like 8s or even 6s or extreme 14s for example but the deciding factor will be on its practicality. For 10s config at 80 amp draw, the plane in question could afford 5000mah comfortably and that works out to a very nice 20c battery - 20c x (5000mah/1000)= 100 amp constant discharge. For 6s, I can save weight but to arrive at 3kw, I will need 135 amp capable batts, meaning 30c ratings and also more capable electronics like ESC (80 vs 135 amp) and motor KV suitable to take such a draw. The motor for the 10s application is 220KV rated for 70 amp continuous, to find a motor for 6s driving a 20x10 prop for a 5kg plane capable of 3kw will be quite tough.

So in this case, I think it is probably easier to drill down from a application point of view in terms of watt power needed (google watt per pound rule). With that, you can then find the best mix of voltage, battery and electronics choice that makes the most sense for best money vs performance mix.

So for a 5KG 3D plane unlimited performance, arriving at 80amp esc, 20c battery and about 9-10 mins of all out 3D flight is considered imho practical and reasonable to the pocket.

In short:
- Watt per pound needed
- Mah of battery - usually related to flight duration and C ratings (C can be low but offset by large mah capacity or higher cell count)
- Voltage - impacts your electronic choices (poor setup will need crazy numbers)


OK, NOW FOR the other side (food for thought)

I also happen to dabble in f5B hotliners. Now with a Neu motor 16x17 carbon setup and just 4s 4000mah for example, you need incredible electronics to support the 280 amp draw, the Neu motor is no exception that is capable of incredible power and RPM. Even the flying style is different ( I found out the hard way in CD field keke, smoke effect). For this kind of application, you knowingly needed the C ratings to get the maximum performance. But as another bro like SniperWJ pointed out, this 4-6s setup is because of the stupid F5B rules, we can always go higher s and lower mah to make up the same watt power and stay more sane in terms of electronics needed.

Hope this helps.

[kenghock]

Thanks Edmund
It helps tremendously!

Actually gives a good overview an earlier question of mine. getting an overview of the dynamics /tradeoffs for electric power systems in RC applications.

Maybe the moderator could make your response a sticky. I'll be saving it to provide pointers to learn more. Not an engineer by training, hence all the electric stuff was voodoo to me.