How much can my cart pull?

420ma

93 marathon 48v 500A controller 20" wheels...how much can i reasonably pull. Wondering if I can pull smallish fallen trees out of the woods.

BGW

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sand dune coon

i asked a similar question a couple weeks ago..

http://www.buggiesgonewild.com/elect...ng-weight.html

cgtech

20" rims, or 20" tall tires? There is a big difference.

scottyb

Pulling, towing,dragging ... all of these things are the least recommended activity for an electric golf cart. The problem is the cart is usually going slow which keeps the motor in a high amperage draw mode. Couple this with added load and bigger tires and the motor will draw just a whole lot of amps - especially on 36 volts! The problem is that the motor cannot turn all of the amperage it draws into energy or movement so the wasted amperage is converted to heat. This heat will essentially melt the adhesives that hold the motor components in place. The result is a failed motor and worse, a motor/controller failure.
So you can tow something for a short distance of once in a while, a steady pace of or long towing can have disastrous effects.

Fegarex

At one time you mentioned "safe" and "unsafe" temperatures for a motor. I am hooking up a temperature gauge to monitor mine and would like to know some numbers. Couldn't find the thread again. Since upgrading the controller, solenoid and cables they all run cool as can be but I know the motor can get hot. I need to get a little more mileage on the motor before I can upgrade.

yurtle

It's not quite as simple as it should be. The wire insulation is very happy if it stays below 212° F or 100° C. I'm simplifying to make it easy to remember. Boiling point of water. However, there is a lag between the inside and outside of the case. In fact, you can assume the outside temperature will rise, once there's no air cooling when parked.

I've seen rule of thumb numbers listed here before, so hopefully someone will post "gut" numbers.

scottyb

My gut number is 200º case temp, You can bet it is 40-50º hotter than that at the core. And in my tests the temperature raised exp-proportionately above 200º. Meaning at it took fewer miles to raise the temp from 220-230 than it did from 200-210. And as mentioned the temperature continued to rise as much as 25-30º after the cart was parked. So a motor case that reached say 250 degrees running easily hit 275 case or over 300º core temp before cooling.
And in one test cooled quicker running at medium speed on flat ground than sitting idle.
http://www.buggiesgonewild.com/elect...p-exist-5.html
I hope this helps

yurtle

I have my temp probe on a ring terminal, under a bolt that holds the stator in place.

JohnnieB

The first attachment is a chart showing Max temperatures (in °C) for various motor components, and the second breaks down the max temperatures into hot spot margin, max ambient temperature and permissible rise for the insulation on the wires. Cart motors typically use wires with Class-H insulation for the armature and stator(field) windings.

Unless there's a temperature sensor embedded in the windings, the max temperatures given have to be de-rated for case temperature. I cannot find the source information again, but the max at the case was given as 115°C (239°F), which implies the max rise at the case is 75°C above ambient, or 167°F above whatever the air temperature is at the time, so if it is 70°F in the shade, the absolute max the motor case should be allowed to reach is 237°F.

However, I'd be extremely careful using that number since I exploded a motor (which also took out the controller) when the motor case temperature was probably about 220°F. In addition to the motor already being mighty hot, the windings got hit with a massive heat spike from hard regen braking and was spinning over 8000RPM at time of failure. That RPM translates to about 4000 G's of centrifugal force trying to pull the armature apart and with "glue" holding it together weakened by the excessive heat, the centrifugal force succeeded.

Series drive carts don't have regen braking, but get the armature hot enough and spin it fast enough, the results will be the same.

It is also important to remember the case temperature lags the internal temperature by several minutes and the max case temperature reached is several degrees lower than the max temperature reached by the internal components.

Attached Images

	Max Temp.jpg (64.1 KB, 0 views)
	Motor Insulation.jpg (16.7 KB, 0 views)

Fegarex

Thanks for the replies and links! Good idea on a ring and the gauge I am going to use is along those lines from Amazon

I read the lead can be extended so I chose it for this and it's cool looks!
Hope to make that my weekend project.