I got another Mah ?

[tiqueman]

So it seems everyone likes mah.. the more the better.. but, when is it too much? For example, lets take a common set up like the SV27. Lets go lipo, 2s in series for 4S, and most will say, "5000mah or more." BUT, what about small scale stuff. For instance, a 30A esc, 3650 KV outrunner on 2S. How do you figure out what a good mah would be? Ive heard some on here say mah only provides longer run times. I call BS on that. When I used to race cars, there was significant speed differences when we went from 2000mah packs to 2500 or 3k. Yeah I know, it was a loong time ago. I ran my Hammer EP for quite some time on 2500mah Nimh packs. When I ran a 3500mah, I smoked the stock esc. AND, it ran much faster until it let out the magic.

Anyway, 30A esc, 2s, 3650kv OUTRUNNER.... What mah should I be looking for. ESC says its rated to 18V, motor to 18V...

heres what Im refering to

http://cgi.ebay.com/RC-Model-3650-Outrunner-Brushless-Motor-30A-ESC-CA029-/270591202379?pt=RC_Modellbau

Thanks,
Scott

[Simon.O.]

I think I can see where you are at.
I have a similar issue with some of my smaller hulls. mAh times C equals Amps and thus power available. If I have written that equation poorly then sing out.

I have some on water experience that will show how all the calculations can go a bit misty.

So..back to your original question
I work on a projected Amps pull from a motor. I use FECalc as a guide and water time as a prover ( I am not sure that is a real word)

A 5000mAh 20C pack will give the same as a 2500mAh 40C pack on paper, that is 100A.
I have yet to prove it all but I suspect that the "bigger" pack will be the winner on the day.
I want it to be equal (as is the paper version) so that I can feed some of my hulls some serious volts to keep the Amps down as I do some nasty things to these hulls.

Now I guess it is all a bit cloudy ?? I hope not.

For my little hulls I like wicked rpm on small props as that ssems to work for me.
3500kv+ OR motors to a 427prop with a 40 to 60A esc on 3S ranging from 1300mAh to 1800mAh all at 30C+

I like rpm and high volts. Gives me wicked sounds, low amps and good speed.

[Fluid]

When I used to race cars...

Completely different. As nickel chemistry cells evolved their internal resistance decreased as their mAh capacity increased. The reason 3300 cells kicked butt over 2400 cells was the reduced internal resistance, not the capacity.

With LiPo cells two things effect performance. One is capacity indirectly, but when combined with the internal resistance - called "C" rating - watt delivery is determined. A 5000 mAh pack with a 15C rating can safely deliver 75 amps continuously. A 5000 mAh pack with a 40C rating can deliver 200 amps - in theory at least. You cannot go by capacity alone to predict performance.

How to determine the cells to use in your low amp application? First off - the motor is not really suitable for more than 7.4 volts so you are limited to 2S. Tiny props are inefficient and excessive rpm just increases wear. With the 30 amp ESC you should not exceed 80% of the rating, that leaves you with 24 amps maximum draw. No need for 45C cells here. In this application 2500 mAh 20C cells will deliver plenty of power, with run times around 5 minutes at WOT, longer with less throttle.





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[RandyatBBY]

I also look at the amount of capacity in relation to the weight to power ratio. To maximize this sometimes you will not need 2P, ie it is too heavy to attain the speed you want like in Spec setups.

[tiqueman]

2P. I can barely fit 1P. This is all great info. And thanks Fluid for the "schooling" as to why Mimh showed differences in mah. I have been wanting to do a test with lipos mah to mah but havent got to it.

Anyway, right now Im running some 1500mah flight power (or something) batteries. They are the red ones that I think you can get from Tower. I was given them to try out. They are 15C, which come in stressed after short runs, showing a little bit of puffing. They do go back to the norm though. Id like to go to a 16 or even 1800 if I can get it to fit, and 20C or maybe even 25? Again, its all about the fit though?

Heres a pic of what Im dealing with