1990 Electric EZGO 36 Volt Speed

[Rodney Hardegree]

Earlier this year I purchased a 1990 36 Volt EZGO. I had to have the controller rebuilt and installed all new battery cables. The batteries are about 3 years old and charge up to 38.0 - 38.2 volts. I have an old timer based Lester charger, so it doesn't automatically shut off at full charge and I have to estimate how long to charge. Anyway, I finally got around to testing the speed of my cart with a gps and it goes around 10 mph on a hard flat surface and got up to 11 mph with wind at my back (little slower on grass). I thought I read that these should go about 14 mph, so I read some posts about ones that run slow and did a few of the tests suggested. One such post said to test voltage at full speed between main battery pack, B- and B+, and M- and B+ with the last test determining how much voltage is being supplied to the motor. My resting state charge at the beginning of the test was about 37.7 volts. All three described tests at full speed had a voltage of 34.8 to 34.9, so it seams that cables are good and controller is supplying full voltage under load to the motor. Is it running slower than 14 mph just because it's and old cart or is there something else I can check? The batteries aren't the best, would new batteries help any with speed or would they just give me longer run times? And finally if the answer is it's just an old cart and thus old motor, would a new 36 volt motor get me up to 14 or 15 mph?
Thanks in advance for any help!

[JohnnieB]

A 1990 EZGO would be a Marathon body style. (Three batteries on either side and controller in middle.)

I'm not sure if the top speed on those was much more than about 12 MPH or so, but I might be mistaken.

At 37.7V, the batteries are only about 80% charged, so cart won't reach its top speed, but the volt drop was what you were testing for.

With fully charged batteries (38.2V), measure the voltage between the B- and M- terminals on the controller when running at top speed on level pavement. You should measure slightly above zero volts. (The MOSFETs will drop in the neighborhood of 0.1V per 100A flowing through the controller, and that ought to be what the reading is.)

IF you measure more than 0.1V or so when at max speed, the controller's PWM output is not going all the way to 100% duty cycle, which is likely to be a throttle issue.

Also, inflate your tires to max pressure stamped on sidewalls to get max speed.

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If the existing motor hasn't been serviced (Brushes, bearing and thorough cleaning) in the last 10 years, it is due, which may help in the speed department.

[cgtech]

Overall battery charging & health is first in my mind. Your battery numbers were pitiful. Maybe the charger isn't working in the time you give it, maybe you have a failing battery. You gotta get them voltages up. And 34v at full cruising speed, doesn't look good to me.

[Rodney Hardegree]

The initial tests I performed were not on fully charged batteries, but were to test if the battery cables were limiting voltage or if the controller was not passing full voltage to the motor all under load as suggested on another thread by JohnnieB. Since all the results were the same then it eliminated cables and the controller not passing full voltage. The voltage drop at full speed was 2.9 volts. CGTECH - what is an acceptable voltage drop under load at full speed?

I've charged up the batteries and will perform more test soon.
Thanks for the help thus far.

[Rodney Hardegree]

JohnnieB - yes it's a Marathon and layout is as you described. Tires were aired up before the first speed test. I charged batteries last night and resting state charge is 38.2. Top speed is still 10 - 11 mph.

The main battery pack at full speed now drops to 35.9 volts. That's a voltage drop of 2.3 volts under load at full throttle. Yesterday when starting with a battery pack at 37.7 volts I was getting a 2.9 volt drop at full throttle.

I performed the additional test suggested by testing voltage between B- and M- at full speed. With the peddle to the floor the DVM showed 0.0 volts. Don't know if this is relevant but with the key on and in Neutral it showed 16.9 volts and when switched to Forward it showed 30.1 volts, then drops to 0.0 at full throttle. Does this mean all is okay with the throttle?

Any idea what ball park cost is for having the motor serviced as you described?

[JohnnieB]

The 0.0V at max speed tells us the controller is passing all the power is can get from the battery to the motor. So we now know the throttle is telling the controller to go to 100% throughput and the controller is doing what it is told.

In other words, we've pretty much eliminated the controller and throttle from the list of things that is keeping the speed down to 10-11 MPH.

That leaves the motor, the batteries or mechanical drag.