Opinions please?

[BrianG]

The only reason to race with larger cap batteries that I can think of is to get the most out of the batteries. When you discharge close to the max continuous rating of the batteries, you don't get the full capacity, Ah-wise, that you would if the batteries were discharged at, say, half their max C discharge.

For instance, if you have some 4Ah batts rated at 15C (60A) and you discharged close to 60A, you probably won't get 4Ah out. Whereas if you had 4Ah batts rated for for 30C (120A) and you still discharged at 60A, then you'd get closer to 4Ah out of the batteries, which would translate as extra runtime.

Either way, we're only talking about a couple minutes extra at most in the example above.

In your case, since you are racing times so close to the runtime of the battery, it could mean the difference between finishing first or last if they die 1/2 lap left to go. Differences in ambient temps and slight changes in how much you gun the throttle can change the runtime too. Personally, if I was running that close, I'd go with 6Ah to be safe, but that's just me.

[starscream]

Originally Posted by BrianG

The only reason to race with larger cap batteries that I can think of is to get the most out of the batteries. When you discharge close to the max continuous rating of the batteries, you don't get the full capacity, Ah-wise, that you would if the batteries were discharged at, say, half their max C discharge.

For instance, if you have some 4Ah batts rated at 15C (60A) and you discharged close to 60A, you probably won't get 4Ah out. Whereas if you had 4Ah batts rated for for 30C (120A) and you still discharged at 60A, then you'd get closer to 4Ah out of the batteries, which would translate as extra runtime.

Either way, we're only talking about a couple minutes extra at most in the example above.

In your case, since you are racing times so close to the runtime of the battery, it could mean the difference between finishing first or last if they die 1/2 lap left to go. Differences in ambient temps and slight changes in how much you gun the throttle can change the runtime too. Personally, if I was running that close, I'd go with 6Ah to be safe, but that's just me.

The run times I quoted are actual run times not estimated from mAh. But, you are absolutly right, you need to run the appropriate mAh for you race duration or you could end up going from 1st to worst :027:
I know from experience what mAh I need for my system for a particular race duration at my local track. The reason I run 6S is so that I do not have such a dependancy on current thus I am not as concerned with the need for excess mAh. I said I needed 60AMPS but its probably closer to 50AMPS. In any case, thats just another reason to run higher voltage so that you don't have to run excess mAh to provide the current as you mentioned above.

[squeeforever]

I need at least 8000mah....Thats why I said that. Our mains at your big races (points races; the ones that matter) are 30 minutes and some of the really big nitro races run 45 minutes....Thats why I said I will probably go for 8ah, but maybe 12 or 16,000mah... I think 12,000mah would get me 45 minutes...I guess I will find out soon enough...Anybody wanna buy a 9920 :p.

[neweuser]

Originally Posted by squeeforever

I need at least 8000mah....Thats why I said that. Our mains at your big races (points races; the ones that matter) are 30 minutes and some of the really big nitro races run 45 minutes....Thats why I said I will probably go for 8ah, but maybe 12 or 16,000mah... I think 12,000mah would get me 45 minutes...I guess I will find out soon enough...Anybody wanna buy a 9920 :p.

Is the 9920 in good condition?

[squeeforever]

Yea. Just needs to be reshrunk with some heatshrink tubing....It was smooth as butter last time I used it...

[starscream]

Originally Posted by squeeforever

I need at least 8000mah....Thats why I said that. Our mains at your big races (points races; the ones that matter) are 30 minutes and some of the really big nitro races run 45 minutes....Thats why I said I will probably go for 8ah, but maybe 12 or 16,000mah... I think 12,000mah would get me 45 minutes...I guess I will find out soon enough...Anybody wanna buy a 9920 :p.

Yikes, thats a lot of weight to run for 30-45 minutes.
A quick pit solution would make life a lot easier and give your truck much better performance.

[squeeforever]

Yea. I have thought about that as well...Only thing is I need more than 40 amps continous and 60 amps burst...To be honest, my 3S2P 8000mah pack isn't really that heavy. I can't imagine 2 extra cells making alot worse...

[MetalMan]

The only problem is, you would need 3 more cells instead of 2 ;).

[squeeforever]

How so? 3S2P is 6 cells and 4S2P is 8 cells...

[MetalMan]

Oh, woops. I misread your post. I thought you were referring to making the 3s2p pack into 3s3p for more runtime, in response to starscream's post. Sorry 'bout that!

[squeeforever]

It's cool....I might go with a 3P setup if I need the extra runtime.