Newbie needing motor guidance
 

Ok guys I just joined the forum. I have a 2002 36V EZGO PDS. I am upgrading it. It's a lifted cart with stock everything else. I just bought an Alltrax 600 amp PDS controller, heavy duty solenoid, and 2 gauge wires. I'm starting with this. I should have it installed this weekend.

Next I want a motor. I would like 25mph. I have been reading about the D&D, Plumquick, GE, etc... I have 23" wheels so to attain 25mph, I need at least 4600 RPM+, but I dont' want to kill all my torque either.

Lastly I will go 48V, so the motor needs to be 36v and 48v compatible like the controller.

What are your suggestions??

Re: Newbie needing motor guidance
 

Since you already have 23" tires, it's a bit late to have concerns about killing the torque, since you've already killed 22% of it.

Unless your tires are the low pressure type (<10PSI max inflation pressure), you might reach about 25MPH feeding your stock PDS motor at 36V through a DCX600 (turned down to 400A because a stock PDS motor can't tolerate a steady diet of 500A, much less 600A)

A stock, standard speed, PDS motor maxes out at about 5600 RPM at 36V, but the 22% torque loss from the 23" tires will knock that down to about 4400, or about 24.2 MPH. Of course the torque curve isn't linear, so it might be a bit faster, or slower, than that.

The D&D motor I'm running gets me about 28 MPH on 17" tires at 42V.

With 23", steer clear of high speed motors, you need a standard speed, or high torque. My motor is standard speed with +30% on the torque.

Re: Newbie needing motor guidance
 

JohhnieB is the right, he has helped me and spot on. I have the Altrax 500 setup from Scotty. Both the before mentioned have a wealth of knowledge, so listen up.:mrgreen: I'm getting 26 mph with the stock motor at 42 volts and happy on my 23" tires! Next upgrade is a torque motor just need to figure out which one! LOL

Re: Newbie needing motor guidance
 

That's all great stuff. When I say 23" tires, that's the diameter, on 14" rims. Something seems off with the speed. My max speed straight and level is 17 mph per my GPS. When I go up hill it dies off very quckly. I must have like a 2.5 hp motor. I could never touch 25 mph on my stock motor and 23" tires. I have new 2 gauge cables.

The stock motor is temporary. I'm will go very easy with the Alltrax 600 controller until I find the right motor. I do see where the high torque motos put out a lot of HP, but they are limited to 14-18mph and spin low RPM's. I need 25 mph consistently, which is about 4600 RPM on 23" tires. I assume either a D&D or GE can do this?

Re: Newbie needing motor guidance
 

Wheel (Rim) size is mostly cosmetic. When I say tire height, I mean tire's true vertical diameter when mounted on cart, inflated to max recommended inflation pressure embossed on the sidewall and measured with driver onboard. Measuring with a yardstick and level is close enough for most purposes, by for greater accuracy, measure the distance traveled from tire's BDC (Bottom Dead Center) to BDC for several tire rotations to get the average circumference and divide by Pi.

The tire size embossed on the sidewall is very, very approximate and can be off by an inch or more in either direction. IE: My tires are stamped 18X8.50-8 indicating they are 18" tall, but the distance from BDC to BDC after four revolutions is 214.125", so the have a dynamic diameter of 17.039526", which I round off to 17" unless I'm doing exacting stuff.

Doing 17MPH with 23" tires and a stock PDS controller may or may not be consistent with what the top speed ought to be. It depends on which performance chip is installed, if any. If the controller is in the All Terrain (Golf) or Steep Hill performance modes, the speed on stock height tires would be about 13.5 MPH, so with true 23" tires 17MPH would be about right.

All carts slow on inclines, but the taller the tires are, the more the cart slows going up hills.

With 23" road tires, a PDS cart with an Alltrax DCX or XCT controller might not do 25MPH with a 36V battery pack, but it will with a 42V pack or with a 48V pack.

The speeds listed on the D&D website are for motors installed EZGO PDS carts with a stock controller, a 36V battery pack and 18" tires. With 23" tires the speed would be about 28% faster mathematically, but won't be quite that fast due to the torque loss inherent in the incresaesd tire height.

Since you are looking for a consistent (cruising) speed of 25MPH, you will want a top speed a bit higher than that so you aren't running wide open all the time. To do that, you'll probably have to up the pack voltage to 42V or 48V.

Find out what the top speed is once you have the DCX600 installed and we can calculate how much the 23" tires are holding your cart back.

Re: Newbie needing motor guidance
 

So I got the Alltrax 600 installed yesterday. I will take it out this afternoon. Even though it's a 600 amp controller, it came with a 400 amp fuse to go on the negative battery end. I'm confused???

Re: Newbie needing motor guidance
 

You are not alone in the confusion about fuses, most people don't understand what they are or how they work. :mrgreen:

A fuse is a fire protection device rather than an equipment protection device. In other words, its purpose is to prevent a catastrophic equipment failure from causing a fire.

Electrically, a fuse is a piece of wire with enough resistance in it to generate enough heat to melt open if enough current (amps) is passed through it. Since it takes time to get the wire hot enough to melt, the higher the current, the faster is melts open and the lower the current, the longer it takes.

To melt open the ANN400 you have in 0.01 seconds, you will have to pass over 3,500 Amps through it.

As you can see on the chart in the attached ANN specs, a ANN400 will pass 650A for 100 seconds and a DCX600 will only pass 600A for a maximum of 120 seconds, so the is little, if any, danger of the DCX600 blowing the ANN400 fuse during normal operation.

FWIW: I was using a ANN250 with a DCX400 when I exploded the armature of a stock PDS motor, shorting the controller's output. I had to replace both motor and controller, but the fuse is still intact. Basically the 400A controller protected the 250A "very fast acting" fuse. :lol:

Re: Newbie needing motor guidance
 

The DCX is a good control but, a word of caution.
The DCX version has no rpm monitoring - which means you can over-speed the motor running downhill which will result in a catastrophic motor event.
So while you are watching the GPS, be sure to limit your downhill speed to your flat ground speed. Motor lock ups at high speed can be dangerous as well as expensive since the DCX also has no short protection on the output side.

Re: Newbie needing motor guidance
 

Scotty, that is what has me nervous about going to a 48v pack (from 36v). I know mph but not in how they come from the rpm's...

I know Scotty and Johnnie have a differing opinion of max rpms... But for the sake of it, since the dcx can not monitor the rpm, How fast (mph) equals rpm?

Is there a chart out there? (Johnnie? lol)

So with a stock PDS motor, a dcx400 powered with a 48v pack, stock tires (18")... it should go about "x" mph (32?) churning how many rpm?

Say you move up to 20" tires how much does that effect the rpm?

Or in Iflyasa's case 25" tires?

Another words, when or at what mph becomes too fast for the motor?

Maybe the best way put is, what should one limit their mph to to prevent motor damage?

Then again why limit it, burn it up buy bigger and better? HA- wheres the money tree... lol!

Re: Newbie needing motor guidance
 

I constructed a spreadsheet that calculates Tire height vs Differential gear ratio vs Motor RPM vs Cart speed for me. :mrgreen:

Without the motor being RPM limited by the controller and in a typical two-passenger PDS cart with a top, but no windshield, a stock, standard speed 36V PDS motor will spin at about 5600RPM with a 36V battery pack, which is 24.1MPH on 18" tires.

If up the pack voltage 36V to to 42V, that is a 16.7% increase in voltage, which ups high end torque by a similar amount, so the max rpm also increases by roughly the same percentage as long as the mechanical drag stays the same. That means the max RPM should be 5600 + 16.7% or 6532RPM, which is 28.1 MPH on 18" tires.

If up the pack voltage from 36V to to 48V, the pack voltage is increased by 33.3% and the max RPM climbs to 7465RPM, which is 32.1 MPH on 18" tires.

When you increase the tire height, the cart travels further for each tire revolution, so the cart speed is faster at a given RPM, but increasing tire height also reduces the amount of torque available where rubber meets road, which is effectively increasing the mechanical drag on the motor, so it will not reach as high of a RPM for the same applied voltage.

Due to the field weakening (Field Mapping) process, a SepEx motor's Torque vs RPM vs Voltage curve isn't linear, but if it were, the max RPM would be rough the same percentage lower as the torque loss caused by the increased tire height.

Based on that assumption, the 10% torque loss of 20" tires would limit the motor to about 5879RPM at 42V, which is 28.1MPH on 20" tires, and about 6809RPM at 48V, which is 32.9MPH on 20" tires. However, the high end torque of a SepEx motor is not linear and the max RPM reached at 42V and 48V will be higher. I just don't know how much without having access to the actual Torque vs RPM of the specific motor.


Since it is a direct drive system, the motor RPM vs Cart Speed is 232.3RPM per MPH for 18" tires and 209.1RPM per MPH for 20" tires, so if you know the cart speed (GPS), you can calculate the motor RPM.