electric go-cart design

[fzn10]

im looking to design a cheap 2hp electric go cart. Iv been googling around, and most go-carts tend to use a brushless dc motor. Was wondering why they wouldnt use three-phase induction motors as they are more rugged and cheaper as well. I know they require more sophisticated mehtods of speed control. Can any one please elaborate on which acutally has a better overall choice. Cause im stuck in choosing between the two.

Thanks

 

[dknguyen]

A 3-phase motor is AC which is hard to do with batteries which are inherently DC. (Have you even considered how you are going to convert the DC from a battery to AC? Extra stuff = less efficiency and more money.). And as you said, harder to do speed control with...like REALLY expensive in some cases compared to DC.

Also, AC motors may be cheaper than DC motors. And AC motors may be more rugged than brushed DC motors. But I doubt they are more rugged than brushless DC motors.

AC motors tend to be better suited for constant speed tasks. To control speed on AC motors is very not straightforward compared to DC motors.

 

[Oznog]

As mentioned DC is very simple to power. If it doesn't need to reverse, it's a single transistor.
AC induction motors have a much more difficult driver, usually 6 transistors. The proper way to drive them is somewhat motor-specific as well.

That's not to say an AC drive isn't a GREAT project! It's more difficult but you'll learn more. I suspect your cart could outperform a DC motor. Also, if you're doing this as an alternative energy project, DC motors don't really do regenerative braking whereas AC motors do. While this doesn't come up much in a go-kart, it's a very important principle.

 

[fzn10]

Thanks, it does seem that brushless motors are a better choice, think ill go for that. but why than do they tend to use AC machines in hybird cars and EV's

 

[Sig239]

Hello fzn10
A quick google turned up this link **broken link removed** about regenerative braking. It's a great concept. It would be nice to be able to convert low levels of heat back into electricity as well, or at least reuse it.

 

[stevez]

When I think of "gokart" I envision something relatively fast and lightweight. Hav e you done some preliminary math to see how heavy this thing might be? I have not - so my suggestion isn't some subtle way of saying it will come out too heavy. 2 HP may be enough but you might want to estimate how long you want it to run then back your way into the size of battery. Clearly the math works for longer term uses as you see the electric wheelchairs with considerable range - and electric golf carts.

The low cost of the AC motor might be offset by the rest of the system costs but maybe not. While not free, variable frequency drives aren't all that expensive. The convert incoming AC to DC anyway so maybe it would work. I'd be inclined to see if I could pirate the drive out of an electric golf cart or electric wheelchair.