Besides the frame, the next most important component of an electric kart has to be the motor. In order to compete with some of the faster karts out there, I was looking for something in the 15HP-30HP range. Setting aside procurement options, there are two basic types of motors to choose from – Permanent Magnet and Series Wound. Yes. There are also brushless DC motors. But these were expensive and work with AC voltages and multiple phases. I did not want to deal with any of these things (especially the cost).

Permanent Magnet

Permanent magnets are the simpler of the two designs. Permanent magnet motors have fixed permanent magnets as the outer set of magnets. Only the inner set of magnets are electromagnets and are continuously switched in orientation to keep the shaft rotating. (Instead of me explaining in useless detail how a motor actually works, you can look at the wiki article. That should get you a fairly good understanding of how these things work.)

Permanent Magnet motors tend to be smaller and cheaper. Most of the permanent motors today use Neodymium magnets, which are apparently much better than previously used materials. BUT, even with better materials being used today, permanent magnet motors have a problem with heat build-up. Since these motors use permanent magnets, their outer set of magnets suffer from demagnetization. This happens as the magnets reach their Curie temperature. And when the outer magnets lose their magnetic strength, the motor effectively loses power. A further concern is that this magnetization isn’t always reversible to the full extent, so you could do some real damage to the motor if you don’t watch the temperature.

Series Wound

Series wound motors are slightly different in that their outer set of magnets are also electromagnets, instead of permanent magnets. These outer electromagnets are kept configured in a fixed configuration, so logically, they are the same as permanent magnets. However, since these outer magnets are just coils, they can overheat and still not lose magnetic strength. Obviously, there is a point where the temperature is hot enough that it starts fusing the coils of wire, but these temperatures are much higher than the ones that will cause damage to the Permanent Magnet motors. This allows the Series Wound motors to be abused a lot more without permanent damage. The disadvantage of these Series wound motors though is that they tend to be about 20LB heavier. They are also usually more expensive. On a kart, the continuous abuse these motors can handle could possibly outweigh (hah) the weight and price disadvantage, but in my case, I went with the permanent magnet motor – the ME1003 to be specific. I don’t see myself doing full throttle long enough to get the motor too hot. Additionally, a fan might be a cheap / light alternative to paying the weight and money costs with a series wound motor. The permanent magnet motor (ME1003) is also smaller in dimensions compared to the ES-33 motor that I was also considering.

The ES-33 is actually a very good option and has recently also come down in price (annoyingly). But the theoretical power output is still about 10HP less. If it was $625 when I bought the ME1003, I think I might have considered the ES33 more.

Oh well, too late now.

ME1003 Motor Specs

• Power: 11.5KW continuous, 23KW Peak for 1 minute @ 72V
• Voltage: 12-72V
• Speed: 3050RPM @ 72V
• Size: 8″ OD, 7.42″ long (w/o shaft)
• Shaft: 7/8″x 1-5/8″, 3/16″ key

As the power section above says, the motor is capable of doing 23kW (or about 30HP) for a minute. This seems somewhat short, but on a typical autocross track, turns come often. According to the manufacturer of the motor, “The 1 minute rating is caused by heat in the armature and brush holder.  Once it cools down, then you can do it again.” So hopefully, I can abuse the motor right after a turn and let it cool down while braking / during the turn. With the given specs, and using an online calculator, the theoretical top speed of this kart is about 80MPH …

Heh