John in CR wrote:Doc,
I think I understand, but you qualified it all with a current limit on the controller. What I'm looking for is, "Which is capable of more power?", assuming current and voltage aren't artificially limited by the controller or batteries.
I think the best answer is to first minimize the creation of heat. I'm going to try some 2 motor alignments that aren't full time 2wd. Doc is trying the switchable windings. There's been talk by a few of cooling systems. I'm sure many are working on a better motor, but they'll be expensive and probably slow to become available. What else can we do without sacrificing performance?...Maybe a braking loaded spring or mechanical device to help bear some of the load of takeoffs...
John, bout the "Which is capable of more power?",
I wrote the answer above.
We know that the power taken by a motor is determined bt the formula of
Voltage x Current = Power
Voltage =Resistor x Current
Voltage = motor load x current that can supply the controller
50A across a 1ohm resistor result to more power (2500W) than
50A across a resistor of 0.4ohm... (1000W)
The resistance of a 5302 is lower than a 5305. So current law can give the answer.
You know that for a given resistor (load) the voltage across it determine a current that cross it... just like a shunt..
So with the resistance that a 5302 have, the voltage that will be across it will be lower for a given current than for the 5305 that have a higher resistance.
The problem is that if you want to do 100V across a 5302 at full throttle.. normally the current would be like
and 100V x 250A would give 25000W.. But this is impossible!
If we use our exemple of the 50A limit controller, the equivalent voltage the controller give will be matched with the load and will by that way also decrease the current...
1: The power the motor have is the current x voltage that the controller send to the motor.
2: The voltage the battery have is not the equivalent voltage the motor will receive.. it depend on the load and the current limit of that controller
3: Power is Current x Voltage... and these two parameter also revelate the resistance (load) the motor have:
4: load = Voltage /current
5: 5302 = low resistsance 5305= higher resistance
6:power of the 5302 is limited by the maximum current the controler can output and with a lower resistance it is is just lower than with the 5305's higher resistance.
To resume.. what limit a motor power are lower resistance winding combined with lower voltage for a given current.
if you put 100V on a 5302 motor and set the current limit to 100A that can handle it, the output power will be less than the same setup on a 5305.
the reason?: the 5302 will reach the 100A limit at 40% throttle and will stop increasing power anyway if you try 100% throttle cause the internal PWM of the controller will limit the duty cycle of the output to sustain the 100A limit.. and the corresponding voltage at output will be like 40V
40V x 100A=4000W
But with a 5305, the 100A limit will be reached furter.. like 80-100% throttle so the corresponding pwm voltage to sustain the current limit at output would be like 80-100V
80V x 100A = 8000W