36 Volt EZGO - add battery or buy new motor

[tennesseeboy]

Hi, we have an EZGO TXT PDS 36 Volt cart. I have installed Scottie B’s Alltrax Controller and big solenoid, but I still have the stock motor. We live in a subdivision with lots of hills (some bigger than 25% grade). On the flat ground areas it will fly (~24 mph), but on a couple of the hills it really slows down. I have stock wheel/tire size and my batteries are brand new.

Would I get more bang for my buck with a new “high torque” motor (~$500) or by adding a battery and buying a new charger (~$350)? I don’t want to fly up the hills, but I don’t want to lose much of my flat ground speed either.

On a side note, do they make cool little “plug-ins” for the alltrax to “divert” some of the power to the torque curve?

Lastly, my stock motor is around 2 HP I think, and the high torque motor is 7 or 8 HP. Do they make one somewhere in the middle? Or is it best just to get the high torque version?

Thanks!


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[JohnnieB]

All electric carts slow down going uphills. Carts with series drives slow the most and carts with AC drive slow the least, while carts with SepEx drives (like we have) fall between those two extremes.

In very general terms. motors are wound for higher torque with lower speed or higher speed with lower torque and the stock motors found on carts are a compromise of the two extremes, however that rule of thumb is for motors in the same size cases and you can get aftermarket golf cart motors in longer than stock cases the can have stock speed with greater than stock torque. The D&D I'm running has more or less stock speed with about 30% more torque.

I'm also running a 42V battery pack, so my cart does not slow all that much on hills, but it still slows down to less than 20MPH on a ~25% grade. I have it RPM limited to 25MPH (6150RPM on 17" tall tires), so it doesn't slow at all om mild hills.

I'd probably go to 42V with the stock motor first and start saving for a better motor later on.

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The are some boxes that allow you to have more than one user profile, but they only turn things down so the wife and kids can drive, or road vs golf course vs off road and differences like that.

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HP is a meaningless quantity, unless it is associated with a RPM.
Mechanical HP = Torque X RPM / 5252.
Electrical HP = Volts X Amps / 746 X motor efficiency.

My motor varies from about 2.3HP at 6500RPM up to about 14.5HP at 1500RPM.

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Basically, you've got some homework to do.

[tennesseeboy]

Thanks JohnnieB, I live your super detailed answers, they’re crazy helpful.

I guess the question underneath my other questions is how can I tell if my motor is degrading? Do they normally gradually die or all at once? It’s about a 13 year old cart I think.

Also, if I opt for the motor, how much speed will I lose with my setup?


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[JohnnieB]

Brush type DC motors can last for decades, but they do need to be serviced every ten years or so. They brushes wear down and the conductive carbon dust from the brushes gets all over the innards, which can provide alternate paths for the amps going to the motor, so performance lessens. Also the bearing dries out. At 13 or so years, your motor probably could use a good cleaning, new brushes and bearing and the commutator may need some attention.

As long as you stay with stock height (18") tires and no rear seat, and don't want to spin the motor faster than about 6000RPM (Just under 26MPH on 18" tires), the stock PDS motor ought to last another 13 years after it has been serviced.

Going to 42V will up the torque by nearly 17% so it won't slow as much on the hills.

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The motor ought to be the last thing replaced/upgraded. That way you'll have a better idea of what is needed for your cart and terrain. If you install tall tire or a rear seat, the motor needed will be different than what is needed for stock height tires and no rear seat.

[tennesseeboy]

I have a Madjax rear seat kit, that’s probably not helping. I called our local golf cart shop and he quoted me on a motor cleaning. It’s basically an hours labor plus any parts, not too bad.

Thanks for the help brother!


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[JohnnieB]

Originally Posted by tennesseeboy

I have a Madjax rear seat kit, that’s probably not helping. I called our local golf cart shop and he quoted me on a motor cleaning. It’s basically an hours labor plus any parts, not too bad.

Thanks for the help brother!


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You'll most likely want new brushes and bearing.

Have a rear seat is somewhat akin to carrying an additional passenger with you all the time. Slighty lower top speed, slows more on hills and a bit more wear and tear on the motor.

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Something else to check. The ten High current cables. Are any getting more than about 10°F above ambient after climbing some hills?

A ~13 year old cart puts it back in the era when EZGO used a mix of 6Ga and 4Ga cables. They should all be 4Ga or thicker. Cables where the first thing I replaced on my cart and it was only 3 years old when I acquired it.

BTW: I was born in Sparta.

[tennesseeboy]

Sparta, awesome!! Not too far from here.

I had 4 ga. Battery cables and 2 ga. everything else, but this week I swapped the battery cables over to 2 ga., too, and I might be crazy, but it seemed to help some lol.

I’m still a little torn, though. If I get my motor cleaned, new brushes, new bearing and labor, and add a battery, I’ll be in it about the same amount of cash as a new motor. Can I go wrong either way?


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[JohnnieB]

My first upgrade was going to 2Ga cable with silver soldered terminals throughout and the cart was only 3 years old when I bought it. Due to the stock PDS controller limiting the motor to 4400RPM, the top speed stayed the same, but there was a noticeable improvement in low end torque and acceleration.

I had access to a device that accurately measured resistance down to 1 Milli-Ohm and the longest 2Ga cable toggled between 0.000Ω and 0.001Ω, so my guess the cable had about 0.0005Ω of resistance. The resistance of a 2Ga copper conductor is 0.0001563Ω/foot, so the cable including the soldered on terminals was pretty close to the intrinsic resistance of the copper conductor itself. The longest 3 year old OEM cable was about 0.005Ω, so there were about 166W of energy per 100A of current draw being converted into heat by the cables instead of being converted into torque by the motor.

Whatever you decide to do with the motor, go to 42V. If the budget is tight, run the stock PDS motor as is for now and replace it down the road a ways.

With 18" tall tires (stock height - but measure the height, the numbers on the sidewalls are approximate at best) and 42V and the RPM limit set to 6500RPM, your cart will do about 28MPH on level pavement, which is actually too fast for a vehicle with mechanical brakes on the rear wheels only.

As for what motor to buy later on, one that has stock speed and greater than stock torque. An aftermarket motor that has stock speed and is in a longer than stock case will fill that bill, (A stock PDS motor is 8.5" long. See attached drawing)

[tennesseeboy]

Awesome, your answers are as educational as they are helpful man.

I found one more thing that may be contributing to my hill climbing woes. The Max Voltage that my batteries will charge to is 40 Volts. I thought I read somewhere you said that they should charge up to 44’ish volts. I’ve tried two separate chargers with the same results. Is the there something on my cart I can check with a voltmeter to see what’s up?

Thanks.


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[tennesseeboy]

Originally Posted by tennesseeboy

Awesome, your answers are as educational as they are helpful man.

I found one more thing that may be contributing to my hill climbing woes. The Max Voltage that my batteries will charge to is 40 Volts. I thought I read somewhere you said that they should charge up to 44’ish volts. I’ve tried two separate chargers with the same results. Is the there something on my cart I can check with a voltmeter to see what’s up?

Thanks.


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Disregard, I just read the thread explains charge voltage and 12-hrs-later settles voltage. I’ll check those.


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