ok, lets break it down where you mess up and fix it up.
TheSiege said:
Ok so the voltage is going to dictate speed/RPMs
yes. but, more on that below.
TheSiege said:
The wattage will determine the speed, based on Amps it can handle while the motor is under load. 3000w at 72v will obviously be a lot closer to the designed RPM on flat terrain vs going uphill but a 2000w motor would see more of a speed loss going uphill vs the 3000w motor even at the same voltage.
eeeh, almost. if the motors were identical but just a lower nominal rating you can still push the same amount of power into both motors but you would blow up the 2kW motor if you let it overheat.
TheSiege said:
And the amps really dont play much of a part in the speed/acceleration factor because wattage and voltage is a better measurement for that right?
going in slighty more in detail.
the motor does not give a shit about voltage, just amps.
now comes the:
the but(t) in all this is voltage and RPM. the realtionship is called the Kv of the motor. 10Kv means 10rpm per volt. so put 10 volt on the motor and it will turn at 100rpm. the voltage in the motor is ALWAYS directly related to the Kv. the motor is stationary the voltage in the motor is 0 volts. so you can have a million volts in the battey and floor it. the voltage is still close to zero until the rpms pick up.
now hopefully you start seeing the real problem if you understand ohms law. for POWER to be present (aka: Watts) you need voltage and current. but there are not volts to speak of as the motor is near zero speed wich is a problem. the battery voltage is completly irrelevant at this point as you can probably see now.
so for simplicty sake lets assume the motor is at 1V at a dead stop. if you have a controller capable of doing 100A on the phases you will get 100W at 1rpm of power. but at 10rpm you are already at 1kW of power. (that is about 1kph for a 10" hub motor) at 20kph you are at 200rpm at 2kW and so on. so getting the voltage up high faster is very important unless you want to trow hunderds of amps at the "problem". this is why you see 500A controllers and that is why controllers are rated for amps, not watts.
at the same time the battery only sees that 100W load at a dead stop wich quickly rises into the kW range if you dont limit the battery amps the controller is allowed to pull once you get some speed and the power levels get really "interesting".
TheSiege said:
I am familiar with ohms law and volts/amps/watts, I am just unsure of how it affects DC motor characteristics as a whole.
the motor is 3 phase AC, not DC.
TheSiege said:
That being said, if I was to design a new drive system and I have (4) 48v15ah packs. I would be better off going with 96v30ah and to get a higher top speed. Or I could do a 48v60ah and get a lot more distance.
again, voltage is not relevant. lowering the amps the controller is fed means less voltage drop, thinner cables and a higher voltage means you have a nearly unlimited top speed. so you can cap the speed at a hard (legal) limit and hold it there until the battery drains completly. if the voltage is too low your top speed will reduce when the battery goes lower in charge. so you start with a scooter that can do 50 but as the trip progresses the speed lowers to the low 40's before it conks out. not very pleasant driving.
your range is dicated by the consumption (aka:how fast you are going) and the capacity of the battery. the capacity does not change if you ree-arrange the battery, it just lowers the voltage and potential top speed and makes the experence less pleasant.
TheSiege said:
I keep going back and forth, trying to decide what to do. I can do a 48v w/ batteries rated at 30a,60a, or 90a depending on how I have it configured. 96v w/batteries rated at 30, 60, 90 amps. or lastly, I can use my LiFePo4 cells and do 66v w/50 amp batteries.
I am really trying to get the most range I can get with a realistic top speed in the 38-45mph range. Basically a city scooter that wont slow others down. Can you advise on what wattage motor I should get?
higher wattage motors tend to be more efficient, same goes with higher power controllers.