lusifur

I get that 40C puts out more power than 22C, but at what point is it too much and a waste of power/money? How much does capacity matter (mah)?

Currently setup on MMM w/ 2650 (1/8) on 3S 22C 8000mah which is working great.

Basically, how do you determine how high a discharge rate your setup requires?

If I go with 4S (for large tracks), would I be better off with a 40C 5000 mah battery or a 25C 5400 mah battery?

Other suggestions? Advice?

Davidka

iTrader: (86)

C rating relates directly to capacity. The monkey wrench is when you increase voltage, amp draw drops at a given wattage output. 40C is probably not necessary with a 4s setup, the fact that you're having good results with a 3s/22c/8000mah setup means you're probably fine with the same C rating. You may want a lower kv motor though, 2560kv on 14.8v might be a little much.

jaymaxx

well i ran a 2500mh 2cell 20c in my slash and it runs grate !! but then i ran it with a 5000mh 2 cell 40c and it was night and day , the 40c had more punch !

malik

iTrader: (19)

If I am right I belive that large mah packs you can get away with lower C ratings because the high mah acts like more C for some reason. This is what I was told a while back when I was considering an 8000 mah set up. Someone correct me if I am wrong. Now for your question no you with the 2650 do not need 40C, I run the CC/2200 w/Hyperion G3 4S 5000 25C and couldnt ask for more.

lookieaefanboi

iTrader: (39)

Yes but you will find that the higher mah pack will account for some of that. It is a trade off as higher mah packs will give you better average voltage over a run but they do weigh more. The C rating refers to discharge the higher the C rating the more power can be drawn from the battery. That being said most setups will not see much difference between a 30c and a 40c of the same mah. Paying the premiums you do for 40c batteries is really not worth it as you can pick up a good 30-35c pack for a lot less and the performance will be very similar to a 40c pack.

malik

iTrader: (19)

I agree but I did find the ProMatch hard case 5100 mah 40C 4S pack thats only $160, $90 less than any other 40C 4S 5000 pack and with an extra hundred mah. Its tempting not so much the 40C its the hardcase and which car I want it for. My Ve8 has a restricted battery tray size.

jaymaxx

the promatch is a beast ! thats all you will ever need

wayboarder

iTrader: (14)

ok, enough of this battery nuthugger(brand A is better than brand B) session. I made a post about this not long ago in the B4T4 thread. Heres some information that will help you make a decision on what battery to buy (mah vs C rating)

http://www.rctech.net/forum/6351478-post9525.html

"also most people forget that maximum current output is a product of both the c rating and capacity of the battery.

heres some small info on this found at http://www.airthunder.com/lipoabc.aspx
Li-poly cells are also commonly given a C or current rating that specifies how much current it is capable of supplying. The charge and discharge current of a battery is measured in C-rate. This is also the maximum average recommended discharge current for the cell. For example, the AirThunder 2200mAh packs have a 25C rating. To determine the maximum recommended discharge rate, multiply the capacity times the C rating, i.e. 2200mAh x 25C = 55,000. The maximum recommended discharge rate would be 55,000mA or 55 amps.

To calculate of load current value with charge/discharge rate, it can be done by:

C-rate( C )= Charge or Discharge Current ( A) /Rated Capacity of Battery

for them math types:
Ok so what that means is..
the maximum current the battery is capable of discharging can be viewed as
MAX discharge current = (C-rate)x(rated capacity of battery)
so in the case of the orion lipos
The 30c/3800 orions will do
3800mAH(30C)= 114000mA or 114 amps
the 20c/4800 orions will do
4800mAH(20C) = 96000mA or 96 Amps

Your stock brushless motors wont pull that kind of amperage, now this is where everything gets thrown for a loop. In talking to the great Jeremy felles, he had said (and im just quoting him) that through onroad testing that he had heard(hahaha) the lower C rating cells will perform better in stock racing when you bring temperature into play. The higher the temperature of lipos, the higher the voltage will get, hence the lipo warmers by trinity. the lower C rating packs will create heat because they will operate closer to the max efficiency of the battery and will therefore increase temperature throughout the run and by doing so increase the voltage of the pack and give you a higher average voltage throughout the race. The bad mamajamma packs not operating at near their max discharge will cool down and will drop voltage as the temperature decreases as well therefore having a lower average voltage throughout the race. So in all this the lower C batteries will result in more consistent power output throughout the race."

Have fun!

ses601

iTrader: (29)

another thing to think about is charging. i use two-2S reedy 35C 5000 packs to get my 14.8V

it only takes me about 20 min to top off both batteries between heats....a 4S can take up to 40-45 min to top off

just throwing this out there in case charging time is limited....

y2kgtp

iTrader: (35)

This sounds like a limitation of your charger, not because it's a 4S

ses601

iTrader: (29)

my chargers each charge a 2S pack, i don't run a 4S single pack

i could be wrong but it seems like any charger charging/balancing twice the cells would be less efficient than two separate chargers charging/balancing half the cells.

i just haven't seen otherwise from those who run the single 4S setups at all the tracks i've been to - they all seem to take at least 40-50 min to top off between heats regardless of battery and charger brands

y2kgtp

iTrader: (35)

Do you know the charger brand and type? I am guessing they are
50w max as most are unless you get a slightly pricier one.

You won't get 5A into a 14.8v pack if you have a 50A limit
on the charger.

50 / 14.8 is only 3.3A charge rate at best....well under the
1C charge rate.

ses601

iTrader: (29)

i remember a couple that they were using - the blue losi multipro w/the standard four round buttons on it, and a triton. oh, the one i now have someone was using for 4S too - the venom pro

y2kgtp

iTrader: (35)

These are all basicly the same charger guts inside, just re-branded by different companies. All 50W chargers. The triton2 can charge up to 90W at 1C rating so it will be a bit better then the ones below. Triton2 EQ is even better up to 8A 120W.

(I have 2 of the 37$ Turnigy's myself)