1987 EZGO Marathon Will Not Go Up Inclines

[mr_six_79]

I have a 1987 EZGO Marathon that runs fine on flat ground and downhill, but once you try to go up the slightest incline, the cart stalls and jerks. I have installed a new 500A controller, a heavy duty solenoid, heavy duty F/R switch, Brand new batteries, and new 4 AWG cables throughout. Anybody got any ideas before I start surgery on this thing?

 

[HotRodCarts]

I'd start with hooking a multi-meter up to the battery pack and see how low the voltage is dropping when going up an incline. Also make sure ALL the cables are clean and tight.

 

[Reevesj79]

.

 

[mr_six_79]

Voltage drops to 32.2. Battery pack shows 39.6 at rest. Cables were installed less than a month ago. All clean and all tight.

 

[Rstaley]

You almost have to have a battery issue. 32.2 is very low for a battery pack under a normal load. Under normal circumstances, the pack might drop 35.5 or so, just for a second until the motor had a chance to pick up speed, but not 32.2. Put your meter on each battery individually while testing and see which one (or more) is “dropping out”. I’d be suspicious of your meter also. 39.6 is high, unless you testing right after the charger has been removed and the surface charge hasn’t had time to reside. Good luck, Ron.

 

[mr_six_79]

The batteries were installed less than a week ago. Checked them with another meter and an hour after unplugging the charger. At rest they show 38.7, and drop to 34.8 while trying to go up an incline.

 

[Patrick L]

Those new numbers sound more in line too me. But I'd like to see those numbers individually just to make sure. The cart will surely slow down on hills, especially considering the grade, but, shouldn't get jerky or stop. I wonder if the controller may be overheating and dropping out. What system does this monster have ? It kinda sounds like its a series with the mechanical F/R switch.
This is my take anyway, but, there are other fellas that know more than I do.

 

[mr_six_79]

It is a series motor with mechanical F/R. It has always slowed down a little going uphill but just recently developed the problem I mentioned. I should also probably mention that I use this cart for hunting, so it is being driven off road almost entirely. Nothing extreme though, just gravel roads.

 

[Rstaley]

What about the tire situation, Did you make any changes there. The size of the tires will make a big difference to the overall gear ratio to the ground. Also, tire inflation makes a big difference to the “rolling resistance” of the cart. Just curious. Ron.

 

[Rstaley]

The only other things that I can think of are:

1 Is the controller programmable? Might be missing something there.

2 Are you sure the throttle is being recognized as “wide open” at its most depressed position?

 

[mr_six_79]

Tires are the same ones I’ve had on it since I got the cart. I keep the pressure checked in them so they stay inflated. The controller is not programmable. It’s a Curtis 500A. Not sure what you mean about the throttle.

 

[Rstaley]

When you move the accelerator to its maximum position (“pedal to the metal”), that position must be relayed to the motor speed controller. I think that in your case, the linkage turns the shaft of a potentiometer that varies its resistance from 0 to 5k ohms. I would just make sure that the potentiometer is actually being fully turned to that position. By the way, a bigger controller won’t speed up the cart unless the old one had some problems. Once the controller reaches 100% pulse width modulation, the rest is up to the motor. If you replace the motor with one that will provide more speed and torque, and “needs” more current to get to 100%, then the larger controller will have a major impact. You can’t make a light bulb glow any brighter by using a bigger switch, unless the old switch wasn’t doing its job. The motor determines the speed, unless the controller can't supply the current it needs.

 

[mr_six_79]

Gotcha. I’ll check the potentiometer to make sure it’s working properly. I’m assuming a simple resistance test will work. The motor is the next upgrade coming. Not as concerned with speed as I am with torque.

 

[mr_six_79]

Potentiometer shows 6.7K ohms fully depressed.

 

[HotRodCarts]

The potentiometer shouldn't be over 5K - 5.5K maximum at full throttle so that may be your problem.

 

[mr_six_79]

I have a spare cart for parts and it had a potentiometer on it. Checked it and it reads 5.6k ohms. Swapped it out and still have the same issue. I’m thinking it’s going bad also so I’m ordering a new one. We’ll see what happens.

 

[HotRodCarts]

Try going up a hill at 1/2 to 3/4 throttle and see if it makes any difference.

 

[mr_six_79]

I think I might have found the problem. Just got curious and pulled the motor and whatever this used to be was rattling around inside.

 

[Rstaley]

Wow! It looks like remnants of your brushes. I think you are certainly on to something. They can be replaced, but if you intend to upgrade the motor anyway, this would sure be a good time to do it. As the brushes loose surface area to “contact’ the armature, you lose all kinds of efficiency. I say contact in quotes because I have read many an engineering document that says that once the armature starts to spin, the brushes are actually “riding” on a “cloud” of gas being emitted by them, and not actually touching anymore. Anyway, the more surface area, the more efficient they are. Congrats, I think you found it. With the new motor, you will certainly have justification for your “killer” controller. Good luck, Ron.

 

[mr_six_79]

It is what is left of a brush and another one of them that was still intact is almost gone. Just ordered a new high torque motor so we’ll see how that goes. I’m replacing the potentiometer also. Might as well since everything else is “new”. Thanks for the help.