4s vs. 6s vs. motor watts

[siberianhusky]

Say you have a Pair of Leopard 4074s, 1500kv & 2200kv, on 6s and 4s respectively they turn almost the same rpm.
The motors have the same watt rating.
Should the 6s setup be faster? Logic says no with respect to the output of the motors or does the watt rating really mean nothing? or do people choose to ignore it?
I realize you drop your amperage by raising the voltage but you still end up with the same amount of watts being produced!
Been reading a lot of threads in the last year or so that have the general theme that 6s is a magic ticket to go faster regardless of the power rating of the motor.
Am I looking at this all wrong or something? I'm still of the mind set that to go faster you need a more powerful/bigger motor not simply more voltage.
I don't think any of the SAW stuff applies here, that is it's own whole area of experimental pyrotechnics/theoretical physics/voodoo!
Cheers

[kevinpratt823]

Watts is still watts, and can be looked at as "work a motor can do". 746 watts= 1 horsepower. Horsepower is a function of the combination of tourque and rpm. You can do the same work with lots of tourque and less rpm, or lots of rpm and less tourque, typically with gearing, which in our boating case is props. Watts is a function of amps multipled by volts, so you can do the same work with high voltage and low amperage that you could with low voltage and high amperage. So I would venture to say that if both motors have the same wattage rating, and you have them turning the same rpm, they will put out close to the same tourque.
The other factors come in, though, such as heat loss, and ripple currents etc. Higher current creates higher heat, which is energy from the battery dissipating into the air/water instead of being converted into motion by the motor. Higher voltage/lower kv means lower amperage, which is better all around, as it creates less heat losses, less signifigant ripple(I believe), and less other undesireable stuff(technical term).
Sorry, you seem to understand most of this already, but some may not. In a nutshell, I think you could make both setups go the same speed to a point, but then your equipment will limit you on the 4s system, as you would be doing the work with amperage, and your batteries, wiring/connections, and ESC would be maxed out far sooner than if you did it with a higher voltage, you may be able to prop up a bit more on 6s without running the equip to the limit.

[siberianhusky]

Here is what I'm getting at, the leopard is rated at 1500watts 2000 burst.
@ 4s thats 104.16 amps, easy on the equipment, well under the rating of a 180 amp esc and 40 C batteries.
@ 6s thats 68.81 amps yes even easier on the equipment.
Evidently most everybody including me is blowing these watt ratings right out of the water but putting say 150 amps through it on 6s is more than 3000 watts! Double what the motor is rated for.
I agree that running 6s may allow you to prop up a bit, but is it really the magic ticket to the speeds some people are trying to achieve?
Not trying to be an ass but it seems that this has really come about since the Spartan was released, their speed claims seem to be the new standard that everybody expects a boat to run. And we know how that turned out for them at the beginning.....

[HTVboats]

Recently in testing for time trials with P & Q outboard tunnels we tried a 4S and 6S setup on the same hull with 1515 1Y & 1.5Y Neu's. Same 2500watt motors 2200 & 1500 kv respectively and same esc and timming settings. Normally for Q we use a larger hull and 1600kv 1521 Castle power but for 1/4 mile the lesser 1515 handled turns better. Anyway unloaded RPM for 4S is 32560 and Q at 33300. Using 45c/5000ma Hyperions the only difference is the single 4S pack vs 2 3S 5000's in series. More weight and potential enery in the 6S setup. Speed and times were very similar with the edge going to the 6S Q setup using the same props. The 6S could pull more prop pitch and diameter giving it a further top end edge. (2-3mph) As was previously stated the 4S created more heat. If i were not concerned with class requirements I would run the 6S using the same wattage motors. Not a tripple blind test just my observations.
Mic

[kevinpratt823]

I guess it is also relative to the size of the boat. I'm pretty sure I can run down any 6s Spartan with my 4s Impulse 31 with 4082, but in my 36" DF cat, 6s/1600kv is much more neccesary to achieve higher speeds, as my Genesis on 4s/2000kv doesn't even come close to it.

[iamandrew]

Yeah but everyone on this site is OH I HAVE A BOAT IT HAS TO RUN 6 S!!!!

ITS 6S doods, everyone get with it! you all want 2 3S packs in series, and enjoy your 1 or 2 minutes of run time, and then an hour cleaning the boat.

because hey, why have 10 min or run time with two packs in parallel?!

[kevinpratt823]

Yeah but everyone on this site is OH I HAVE A BOAT IT HAS TO RUN 6 S!!!!

ITS 6S doods, everyone get with it! you all want 2 3S packs in series, and enjoy your 1 or 2 minutes of run time, and then an hour cleaning the boat.

because hey, why have 10 min or run time with two packs in parallel?!

Huh???
My Impulse runs (2) 4s in paralell, so does the genesis. I have 4000, 5000, and 5300mah sets, and I would agree, the runtime is much more enjoyable, I'm leaning towards a similar 6s setup for the other boat when I can afford some more packs, I've only had it a few weeks and 3s packs is what it came with. FWIW, my Thunder Power 3s 6600mah packs are Identical to their 6s 3300mah pack, the cells are just linked together differently internally(paired in paralell, then series'd together, as opposed to all 6 in series) so the end result is basically the same, it's just a matter of configuring the external wiring differently to get the desired voltage.

[iamandrew]

it was a Jookkke !

[keithbradley]

Higher voltage is typically used to keep current in check, it doesn't neccesarily mean more power/speed.

However, if the math works out the same for both of your setups (kv * v = RPM) while using the constant of 3.7v as "v", expect a little more speed from higher voltage setups. While we normally use 3.7v to calculate RPM, that number is really a variable and it will be higher with the higher voltage/lower kv setups.
Also, it's not unusual for a motor to be less efficient at higher current, so your speed and runtime may benefit at higher voltage.

Keep in mind: If you really are putting the same wattage into both setups, and one of them returns cooler than the other, they are not making the same power at the prop, regardless of what they are drawing/using.

[olwarbirds]

Higher voltage is typically used to keep current in check, it doesn't neccesarily mean more power/speed.

However, if the math works out the same for both of your setups (kv * v = RPM) while using the constant of 3.7v as "v", expect a little more speed from higher voltage setups. While we normally use 3.7v to calculate RPM, that number is really a variable and it will be higher with the higher voltage/lower kv setups.
Also, it's not unusual for a motor to be less efficient at higher current, so your speed and runtime may benefit at higher voltage.

Keep in mind: If you really are putting the same wattage into both setups, and one of them returns cooler than the other, they are not making the same power at the prop, regardless of what they are drawing/using.

totally agree...if a motor is rated for 3-6s its gonna run more efficiently on 6s ...unless you load it up with the wrong prop...your amperage draw will be lower and the whole system should run cooler...and possiibly FASSSTER :) ...DJ

[olwarbirds]

Just to add...we went through all this with edf jets several yrs back...as Keith mentioned same wattage doesnt necessarily mean equal performance....and sometimes more wattage doesnt maker ya faster either, just pulling more amps and getting shorter runs/flights....least the lipos are finally up to the c ratings we need... DJ

[mannytx1]

The 1466Kv (1500Kv) will draw less amps and extend run time.
14.8 volts applied to a 2200Kv motor under a given load might draw 81 amps giving you 1200 watts @ 32560 rpm
22.2 volts applied to 1466Kv motor under the same load would draw only 54 amps giving you 1200 watts @ 32560 rpm
1500Kv

[kevinpratt823]

The 1466Kv (1500Kv) will draw less amps and extend run time.
14.8 volts applied to a 2200Kv motor under a given load might draw 81 amps giving you 1200 watts @ 32560 rpm
22.2 volts applied to 1466Kv motor under the same load would draw only 54 amps giving you 1200 watts @ 32560 rpm
1500Kv

That completely depends on battery capacity and setup. ex:If the 2200kv is running on (2) 4s/5000mah packs in paralell(for 14.8v) would give you more runtime than if the 1466kv was running on (2) 3s/5000mah packs in series(for 22.2v)
If you want runtime, you inevitably have to go with a heavier pack setup.
Some batteries have a watt-hour rating, combining the voltage and milliamp-hours, this is the real power capacity rating, defining how many WATTS it can put out in an hour's time, similar to the way the utility bills you for the electricity in a building or home. Especially in a commercial building, you have various equipment running at various voltages, with various ranges of efficiency. They bill you for kilowatt-hours, not volts, amps or mah.

[keithbradley]

The 1466Kv (1500Kv) will draw less amps and extend run time.
14.8 volts applied to a 2200Kv motor under a given load might draw 81 amps giving you 1200 watts @ 32560 rpm
22.2 volts applied to 1466Kv motor under the same load would draw only 54 amps giving you 1200 watts @ 32560 rpm
1500Kv

While your basic assessment is true, those setups would not perform the same, even when basic formulas show the same theoretical power being consumed. The flaw with your math is in assuming that both setups will see the same voltage per cell. With similar performing cells, the 2nd setup will see a higher relative voltage, resulting in higher theoretical RPM. Loaded RPM will also depend on efficiency.

[bob_t]

Great thread, great information and explanations! This is what makes this group great!

Thanks,
Bob