Amp Hogs for Motors

[kojo]

I've seen posts on here before about some motors being amp hogs. How do you know if a motor is a "amp hog" or not. Do you look for a specific HP to RPM comparison. Thanks for any input guys.

[JohnnieB]

I suspect most of the "Amp-Hog" motors are in carts with Tall, Wide, Low-Pressure tires.

Traction motors have a sweet-spot on the Torque/RPM curve and if you aren't running at or near the sweet-spot, the motor will not be operating at its greatest efficiently. The sweet-spot is when the Torque multiplied by the RPM produces the highest number, which should coincide with peak HP. However, always take an electric motor manufacturer's HP rating with a grain of salt because there different ways of calculating the HP of electric motors.

Basically, HP is a subjective calculation while Torque and RPM are quantitative measurements, so use them to pick a suitable motor for your application and leave the HP numbers to the advertizing brochures.

[kojo]

Thanks for the input JohnnieB., I have 23x10.5x12 Desert Fox tires now but,I kinda want to go with a 23x8x12 or a 24x8x12. So a size like these shouldn't be as bad as the wider Desert Fox tire should they? Thanks again Johnnie B..

[JohnnieB]

I know nothing about Desert Fox tires, but I suspect the narrower tread width would be easier to turn.

What is the max inflation pressure?

[kojo]

JohnnieB., sorry for the late reply but, the cold inflation is 20psi & it reads never to exceed 36psi. Thanks for the help.

[sportcoupe]

Typically you want a golf cart motor to pull no more then 60-70 amps at full speed cruse if you want your batteries to last more then 2 years. I would define an "amp hog" motor as one that pulls much more then that, say 90-120 amps at full speed cruse.

A stock motor and stock controller with stock tires can be an amp hog if you add a set of high speed 6:1 gears. That combo will net 110-120 amps at full speed cruse (in a pds cart). I have tested this combo myself.

Larger tires are also like a small gear change resulting in higher then normal amp draw but not as drastic as 6:1 gears.

Picking the wrong aftermarket motor for your combination on a modified cart can easily result in an amp hog so it's best to consult the motor builder with your expected usage in order to get a motor that will last long and perform.

[JohnnieB]

Originally Posted by kojo

JohnnieB., sorry for the late reply but, the cold inflation is 20psi & it reads never to exceed 36psi. Thanks for the help.

That sounds like it might be a decent general purpose tire for a combination of non-extreme on-road and non-extreme off-road usage.

Golf cart tires isn't my long suit by any means, but from what I've read here on this forum and in other places on-line, it is the low pressure tires that reek the most havoc with top speed and run-time. If you drive through deep mud and sand, a high floatation (wide - low inflation pressure) tires may be beneficial, but you'll pay the price while driving on terra firma. The same is true with tread patterns, ones that will get your cart through a swamp, will shake you and your cart to pieces on dry ground.

As sportcoupe mentioned, the differential gear ratio as well as the tire height effect cart performance. The combination of the two is the final drive ratio.

Basically, a motor that is an amp-hog in one cart may not be an amp-hog in a cart with different final drive ratio and tire type and pack voltage and controller.

[kojo]

Thanks guys for the help on this. Guess I'll just tell them what I've got, what my goal is, and see what they recommend.