# Teach Me: Motor Question



## Guest (Jul 20, 2010)

72 Volts! Maybe. Kelly controller will do fine but make sure you use a good finned heatsink with cooling fan. RPMs are good. What about the brushes? It is a golf cart motor. I'd stick with 48 volts. Kind of small for a vehicle just under 2500 lbs. I use a 9" GE for my little VW Ghia. 

Pete


----------



## rillip3 (Jun 19, 2009)

Doubling the recommended voltage is probably not a great idea. It will likely work, but it will wear down very quickly. If he's asking more than you want to spend, then I don't think you want to buy it and then burn it out early.


----------



## TX_Dj (Jul 25, 2008)

It says 2800 is the RPM at 36v. It says 8000 is the max recommended RPM.

Thus, at 36v, the unloaded RPM voltage constant would be 77.77 RPM per volt. At 72v that means 5599 RPM, well under the max rpm on the label plate.

The real question would be, how many amps will it take before it explodes?

It's an EZ-GO motor, that means it's for a golf cart, which also means it probably has a female spined shaft with no bearing. Not a good fit for most EV conversion setups.


----------



## Ladogaboy (Apr 25, 2010)

Thanks, guys! Good info, TX_Dj.

The RPM per volt equation is really that simple!  Of course, you're right, I have no clue how much amperage it can take or how to figure it out. I thought some of you guys might know. 

The main reason I'm bringing these questions up is because I've been re-inspired to do a dirt-cheap entry-level EV... basically, an NEV that I can use for my <20 mile daily commute on side streets. 

I figure that I can afford to start buying ~ $200-300 worth of parts/equipment a month, but since I'm going cheap, I want to see what the lowest voltage/cheapest system I can get away with is. But I know that going too small on the motor will be a waste of time/money. 

Also, a lot of people in my area are selling lower voltage motors (e.g., forklift/golfcart), but I'm not sure how much the voltage/amperage can safely be increased; how to figure it out just by looking at the motor; and how to actually do it. I guess I'll have to go re-read the forklift motor for EV thread.


----------



## Sunking (Aug 10, 2009)

Well I am real familiar with that motor as I do a lot of golf cart modifications. Short story is the motor is pretty much useless for what you want to do.. It is rated at 2.2 Kw max or about 2.2 HP @ 75% efficiency. The stock Curtis Controller used is 175 amps. 

If you go pushing say 400 amps and up the voltage to 72 volts, most likely will burn the motor out pretty quickly. Unfortunately EZ-GO or GE do not publish any useful information. 

The only good golf cart motor I am aware suitable for an NEV Golf Cart type vehicle is a GE D398 Raptor Motor. This is the largest I am aware of for Golf Carts. You can run it at 48 volts with a 450 amp controller with no problem. I have one in my cart and it gives me about 30 MPH, but it will pop wheelies from a standing start, or climb a tree.


----------



## vpoppv (Jul 27, 2009)

I think the biggest issue with the motor is whether or not it has a shaft bearing. Most golf cart motors don't, and it's a PITA to fabricate a plate that incorporates one. As for size, yeah, it's way too small for a car, but it'll work for a few minutes. My motor seems about similar in size/specs. I'm running 72v and it's a 36v motor. Might blow up tomorrow. Should have blown up the first test drive. Not sure why it's still working. Maybe because I tuck it in at night and read it stories. Seriously, it was built for a vehicle that weighs at most 800lbs, and asking it to move 1,800+lbs, at twice rated voltage, for speeds 10-20mph faster than it was intended is truly an extreme test. I've put 182 miles on it so far.....


----------



## Ladogaboy (Apr 25, 2010)

Okay, so how about this one?

The amperage looks right, but the weight is only listed as 67lbs, which seems light for a DC motor for an EV.

Also, looking at the RPM range, if I use that calculation, it seems that the RPMs would be too high. Assuming that 30V drives the motor at 3,800 RPM, running the motor at 72V would put it well beyond the 8,000 RPM mark. Right?


----------



## Guest (Jul 27, 2010)

Special motor that one is. I have a couple of these. Not Jack Heinz but Starter/Generators. They can do 8000 rpm no problem and they can do up to 12000 in short bursts. They need good external cooling. They do get hot but with decent cooling they do just fine. I am getting ready to test another controller from Kelly for these type motors and they will do regen too. These are sepex motors. At 72 volts and 400 amps my motor pushed my Ghia to 60 mph. Not terrible. With the controller we are hoping for better and to get full regen abilities too. I am going to be hooking up the motor to the buggy this week. 

Pete 

PM me.


----------



## umurali2000 (May 3, 2010)

At 36V the rated speed labeled is 2800 rpm and hence at 72V ( your requirement) the speed shall be 5600 rpm approx. During this the current extracted from the power supply into winding will be more. You have to confirm if the winding is capable of allowing that heavy current as rated. You can rewinding the motor as per your requirement.


----------

