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New to fast electric, but not boat racing. What's capacity does a P mono need for a full IMPBA race? Will 5000 do it?
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It wont. I carry 8000. My son usually runs 10,000mah. He doesn't dump all of that but it makes the boat stay on the water a little better.Noisy person -
glad I asked. thanksComment
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In fairness, you could run it on 5000 if your C rating was high enough. You would just have to go slow enough to not run out of mah before you finished. In other words.....you'd get killed speed wise in a race.Noisy personComment
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Fred
Here is something to remember about Batteries and racing.
This is also the reason that I run 4S2P - 5000 packs (10,000mAh total) in my 33" Delta Force for "P" mono
The higher the mAh total, and the higher the "C" rating = higher Voltage under load
Seeing that the RPM our motors are rated by KV (rpm per volt)
A higher voltage under load = more RPM under load.
LarryPast NAMBA- P Mono -1 Mile Race Record holder
Past NAMBA- P Sport -1 Mile Race Record holder
Bump & Grind Racing Props -We Like Em Smooth & WetComment
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Excellent tip on battery capacity. Another thing to keep in mind, the battery’s resistance. There are many low cost, high capacity batteries that may have higher resistance under race conditions. Chargers won’t read the “true” resistance, that while delivering high current to the load and elevated temps. We, as a group, need to keep each other informed on the best deals. A battery with high capacity and high resistance is not much better than a low capacity battery...Comment
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Craig
Your statement above is why these are my go-to packs for racing.
LarryPast NAMBA- P Mono -1 Mile Race Record holder
Past NAMBA- P Sport -1 Mile Race Record holder
Bump & Grind Racing Props -We Like Em Smooth & WetComment
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Nice lead... Thanks!Comment
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Giant Power are all I own these days. I am totally biased and totally admit it. Bob from Mojo helps Ty and I out a lot.
Another interesting brain up (pushups with yer brain).......haha Amperage. A cell deliver a different voltage at different amps. The more amps the lower the voltage. The C rating tells us at what amperage the cell is supposed to be able to deliver that 3.7 volts per cell. Static voltage is higher. Max static off the charger is 4.2v. Usually 4.189 or so by the time you get them plugged in. Our motors are volts times rpm per volt (kv). Our inclination is to throw more prop at a boat, more prop, more prop. Doesn't always translate to more speed though. My boat might turn a x447 prop but be no faster than the x445 because the rpm turned out a tic lower with the 447 than the 445 due to reduced voltage available at the higher amp draw. You can do the same mental exercise with pitch. 1.4 vs 1.5.
Carrying more mah than you actually need like Larry and I do ensures that you maintain higher voltage even when you get into stupid amp draws. We never get anywhere near the actual C rating this way. Higher voltage...more rpm. Cells hold up longer too. In theory.
Then each motor has it's happy place where it is most efficient. It might be capable of 200 amps but is more efficient at 160 amps for example. This is where testing is so fun. You have the boats which are beautiful, throw in some physics, some educated guessing, and a sprinkle of crazy............mwahhhhh. Glorious!Noisy personComment
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I didn’t know that about C-Rate Terry, thanks, a valuable piece of info! I don’t run the amperage even close to the C-Rate, I like to leave a little in the Bank. No battery likes being used at its stated specs. Those are the max-max specs, but they won’t live there long if you use them that way. But you guys are 100% right maintaining a higher voltage thru the race is a distinct advantage!Comment
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I posted a thread a short while ago asking about efficiency differences between larger and smaller props. I was hoping that this kind of info would creep into the conversation. But it didn’t... The thread was left with the impression that the larger prop is more efficient, which it is from strictly a prop’s perspective. But there is the electrical perspective and that was explained very well here! Thanks to Larry and Terry for that insight.Comment
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There is some guess work and a balancing act that happens. Sometimes you have the right prop for a boat and the wrong motor. Sometimes you have the right motor but can't quite settle on a happy prop. A larger prop will typically have more blade in the water and accelerate better. If you don't give rip about acceleration go with the tiny prop and high rpm. For ovals and especially offshore you're forever throttling to turn and then accelerating again.
Back in the dark ages when we ran Nimh some of us would use a gear box. Ed Hughey was the absolute king of the gear drive. Later the Turbo trans from Fine Design. Sometimes we let a motor scream and gear down so we could turn a big fat prop. Fat prop comes out of a corner better. It was also better for the Lemans starts we were doing at the time too. That drag race to the first turn sucked if you were running high kv and a tiny prop. Eventually you would get to the same speeds. Watts are watts and all but it was too late. You were running in slop left behind the guys that had a better hole shot. It's like big fat tires on a F1 car or skinny tires on a land speed record car. You don't need big fat tires on a speeder.Noisy personComment
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Less amps=more volts=more rpms?
Higher mah and C ratings allow more volts to potentially be drawn?Comment
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You don’t “draw” volts, you draw amps... you’re looking at it backwards. Volts is like line pressure in a water line. The water flow rate is like amps. MAH is an expression of the amp draw capacity. C Rate is the highest amp draw you should make and still maintain 3.7V out. The discussion is saying get batts with higher mah to keep off the lower voltage part of the discharge curve. So you have to understand you don’t “use” voltage, you use amps. Amps being delivered at a higher voltage creates more power, V X A = Watts.Comment
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