mah,C rating and current draw question

[flynow1]

Amp hour ratings various C ratings. I thought I had a basic understanding of the following; however some recent discussions have me wondering so here’s the question.
The motor in question would be a 3665, 2200, max amps are 72 and max watts 1065.
Batteries 2 ea. 2S batteries in parallel.
First scenario, 2S, 3300mah, 65-130C x 2
Second scenario, 2S, 5000mah, 40-50C x 2
Required run time at full throttle is 1.5 minutes.
What would be the best performer?
Thx

[Chilli]

If that's a 2200kv motor, are you sure you won't be running in series meaning 4S power? RPM would be way low for that KV on 2S.

FYI-Max amps ratings don't mean much in boating. We are capable of push the motors way harder.

Wish we knew more about the boat set up. But assuming batteries are of equal quality, they're rated output in amps is relatively close. 214 amps for the 65C versus 200 for the 40C. If the set up was 4S, I would be concerned about running down the batteries too much with the 3300's. This can overheat the packs shortening their life and putting stress on your speed controller.

[flynow1]

I already had the 5k packs, the 3.3's are new. I have run the 5k (4S) for the last year. Our club has come out with a ruling limiting to 3.3 (don't ask). I tried the 3.3 for about a minute (no heat or functionally issues) but the boat was simply not as fast. I had assumed that I would see little difference for the first minute or so but that's not the case. I will probably do 2 things for the future, change clubs for coming out with something this stupid and continue to use my 5k packs.
thx

[Peter A]

To be fair, depending on the make of packs, I would think that the 5000's would perform better.

Our club has come out with a ruling limiting to 3.3 (don't ask).

That'd be a handbrake! Why are there so many stupid people!

[lenny]

Hi,
When you say best performer.
Are you talking about speed or run time ?
Because sometimes the added weight from the packs help with CG and then you get better speeds and also handling to.
I have not tested yet if just adding the weight makes the difference in the speeds,
And handling.
It may just be a better AOA or helping with the strut adjustment setting + a little.

[flynow1]

The 5K packs are better! Considerable better even in the first minute. I would not have thought that. After the first minute I could better understand it but that's not the case. I had downloaded a formula for calculating run time, current draw, # of cells etc. and it shows the first minute to have the same available current but that's not the result. I guess it's one of those experience things
Thx

[flynow1]

Actually just the current draw was the question but I totally agree with the other factors you stated.
Thx

[TheShaughnessy]

I wouldn't even run 3300 batts. My spec boat averages 55 amps around the oval. That's roughly 1000 Mah per minute,a two minute race plus a 30 sec mill(not full power but still eats battery) and your close to 2500 Mah add a penalty lap and you burn 3000. Leaves you with only ~ 10 % left in the tanks. That's a good way to ruin lipos, or drastically reduce the lifespan. I would protest the rule. Bad all the way around from an electronics standpoint.

[kevinpratt823]

Keep in mind that many "ratings", but especially the C ratings, are really just implied ratings. A 45C Hyperion is right on par with a 65C Thunder Power, Dinogy, or Max Amps in performance. At 65C/5000mah that is 325 amps continuous, and I have yet to see a 5000mah pack that is actually capable of putting that out(continuously). On top of that, the C rating is based on what you could (hypothetically) draw without damaging the cells, it does not take into account how well the pack will maintain it's voltage. Of two similarly "rated" packs, both drawing say 200 amps, the better one could easily be holding .5v per cell higher than the other, and with a 4s/2200 kv setup, that translates to potentially 4400 rpm's more............

[flynow1]

I’ve talked myself blue in the face trying to get help with the new rule. Actually I can't seem to get a good reason why anyone even thought it up. Your data is great. Don't know if it will help get any support or not but great data never the less. I'm not running the 3.3, period. I'm not going to burn expensive stuff up because someone wants to be an idiot. Thx for the reply