Low Max RPM Alltrax XCT500 Admiral B2 Motor

[scottyb]

I don't think this motor is supposed to make 27-28 mph.
B2 is a high torque motor.

[JohnnieB]

The wrong field map was probably weakening the field more than the correct one does. Excessive weakening of the field causes sever overheating and heat kills motors.

As Scotty said, the Admiral B2 is a high torque motor, meaning it is physically wound so the electromagnetic field generated by the field windings is relatively strong with respect to the electromagnetic field generated by the armature windings, so it has more low end torque and less top speed than a stock PDS motor. With a 36V battery pack and stock height tires, the cart ought to reach a top speed on level pavement from 18MPH to 20MPH. That means the max motor RPM with a 36V battery pack is from 4182RPM to 4646RPM. That in turn means the max speed for your cart with 20" tall tires is from 20.0MPH to 22.2MPH on level pavement (11% speed gain).

To increase your speed, you need to increase the battery pack voltage or tire height.

Going to 48V will up the max RPM by 33.3%, but the max recommended RPM for the B2 is 6000RPM, so your carts max speed at 48V (without exceeding max RPM or field weakening) on 20" tires is up to about 28.7MPH.

[wbhess]

Man there is so much to learn with these carts. If I made two 1/8 mile runs at 25mph, do you think I damaged my motor? So, going to 48v will help me achieve 25+-mph without hurting the motor? Will I have to change the field map when going to 48v?

[JohnnieB]

Originally Posted by wbhess

1. Man there is so much to learn with these carts.
2. If I made two 1/8 mile runs at 25mph, do you think I damaged my motor?
3. So, going to 48v will help me achieve 25+-mph without hurting the motor?
4. Will I have to change the field map when going to 48v?

1. You've got that right. I'm still learning and I've been working on electronic and electromechanical stuff for nearly 60 years.

2. Since it is still running, you probably only shortened its life a few months out of about twenty years or more. Heat kills motors, but it is a slow death unless a catastrophic failure occurs at the time the overheating occurred.

3. Actually, your motor will be happier on 48V because it will have fewer amps flowing through it to do the same amount of work. The work done by a motor is measured in Watts and Watts are Volts time Amps, so a task that requires 1800W takes 50A at 36V and only 37.5A at 48V. If the motor is 80% efficient, 10A is converted to heat at 36V while 7.5A is converted to heat at 48V. Making the benefit more significant, heat is generated at the square of amps flow through a resistance.

4. No. Or at least I've never heard of different field maps for the same motor at 36V and 48V.

[scottyb]

4. Alltrax did have some voltage specific maps for the same motor for the DCX controls. There may be one or two for the new controls. But that's not typical