Author Topic: Using a 48v motor with a 36v battery  (Read 13088 times)

Offline MrEverfresh

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Using a 48v motor with a 36v battery
« on: September 13, 2015, 07:27:44 PM »
Hi,

I am part of a senior design team creating a solar powered boat from the ground up.  We have been searching hard to find a motor that will work for our purposes, and for the power we need, the 48v motors seem to be the way we want to go (5kw for the endurance race and 2 - 5kw for the sprint).  The problem, however, is that the competition rules specify that we must have not more than 36 volts for our source voltage (we plan to utilize 3 - 12 volt batteries).  So we are wondering what sort of efficiency losses we might expect, and if there is a way to calculate this loss.  For the endurance race, we only plan to use 1/2 of the 5kW power for maximum efficiency, but for the sprint we plan to use as much power as we can get out of the double motor set-up.  Any help on determining what sort of losses might be seen by using 36v on a 48v motor would be greatly appreciated!  Can we just control our amps to ensure we are getting peak efficiency out of the motor?  Are there other consideration factors?

Offline Bikemad

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Re: Using a 48v motor with a 36v battery
« Reply #1 on: September 14, 2015, 03:14:52 PM »
Hi andto the forum.

Running the 48V motor at a lower voltage should not make a great difference to the efficiency of the motor but you will only produce 75% of the power and maximum rpm on 36V compared to 48V.

Without running the motor on a dynomometer at both voltages and comparing the two different sets of figures, I don't know how you could calculate any efficiency losses.

I have just compared the dynomometer results for the Magic Pie motor on 36V and 48V and the maximum efficiency of the motor is 78% on 48V and 77.2% on 36V.

The overall efficiency (and speed) will depend on many factors, including the size, weight and drag of the boat and also the gear reduction, propeller diameter/pitch/blade section etc. and the amount of current being drawn.

You will obviously need an effecient three phase Brushless motor controller that is capable of running on the lower voltage too, as I don't know if the VEC500 controller will operate on 36V.

Alan
 
« Last Edit: July 02, 2017, 03:44:16 PM by Bikemad »