motor heat help

[kojo]

Well yurtle, went down the driveway and was hearing a little humming sound then hit the highway and it sounded like a ticking sound so I turned back around and put it in the garage.

[yurtle]

Bummer. Maybe put it on jack stands and have someone press the gas slowly, and use a wood or metal dowel to see if you can narrow down where the sound is coming from.

[kojo]

Thanks man, I'll try that tomorrow. Does it sound like the bearing to you yurtle?

[yurtle]

I've only had one bad bearing before, and it was a sealed axle bearing. It made a grinding noise, but the motor bearing is more enclosed, so not sure what it would sound like. I can't remember how hot mine's been, but I had it get close to yours. On a series motor, the bearing is a sealed bearing, so I guess the grease or the seal could have gotten hot enough to allow the grease to "escape" letting it run dry. I was actually surprised at how "low" Alltrax' recommended temp was, since I always thought the winding insulation would be the weak link. I guess it's also possible the brush holder could have sustained damage, but you'd think it wouldn't run if that had happened. The only other thing I can think of is the commutator is some sort of insulated material. I suppose that could have been damaged, and may make a ticking sound.

I'm just guessing. After you determine the sound is the motor, it's not that hard to tear it apart. The Service manual tells how, and the Parts manuals has good diagrams.

[JohnnieB]

If the motor case temperature is 249°F, the motor is getting too hot.

Yurtle is correct, the max temperature for Class-H motor is 180°C (356°F), but that is for the insulation on the wires the Armature and Field (aka Stator) windings are made of.

Since we don't typically have golf cart motors with thermocouples embedding in the windings to measure the insulation temperature directly, we have to measure the insulation temperature indirectly and derate it considerably due to several factors associated with indirect measurements.

The maximum temperature the motor case should reach at its hottest spot, should be 115°C (239°F).
Also, there is a time lag between the max temperature that exists in the windings and max temperature at the case due to the thermal mass of the motor components and the thermal convection rate of the materials used.

When electrical energy (amps) pass through a motor, it is either converted into mechanical energy (torque) or thermal energy (heat). When a motor is spinning at its No-Load RPM for the voltage applied, very little of the electrical energy is converted to heat, but when a mechanical load is applied to the motor (drag) the heat generated will increase exponentially with the RPM reduction from the No-Load RPM for the applied voltage.

Basically, the greater the mechanical drag on the motor, the hotter it will run.

Sounds like you lost a bearing or something someplace, which is making the motor work harder and get hotter.

[yurtle]

Originally Posted by JohnnieB

The maximum temperature the motor case should reach at its hottest spot, should be 115°C (239°F).

That sounds more reasonable than Altrax' recommendation, and would allow the wet finger sizzle test, if you have no other way of measuring temp.

[yurtle]

The time lag works for cooling off as well. The outside of the case may cool off faster than the inside of the motor. There is a lot of thermal mass on the laminations of the rotor and stator, so if you need to cool off, take that into consideration.

[JohnnieB]

Originally Posted by yurtle

The time lag works for cooling off as well. The outside of the case may cool off faster than the inside of the motor. There is a lot of thermal mass on the laminations of the rotor and stator, so if you need to cool off, take that into consideration.

I think that was a contributing factor for the motor I exploded. It was at about 220°F when I got to the shooting range and it was busy, so I only spent a few minutes there before heading home. Up a steep hill and then down the other side, where I lost the motor.

[kojo]

yurtle and JohnnieB, thanks for the replies. I haven't had a chance to check anything today on it, had to put a mandrell on my lawnmower and cut my grass and my mama's grass,and weedeat to. Then my wife was going to help so she got on the lawnmower and went to the backyard and ended up driving into the deck steps and bending the crossover steering bar. So I had to take it off and straighten it out. It looked like a teepee. Talk about Toe out, 'bout 4in. So it's been a rough day. Oh and the batt. died today to. But anyway, thanks for the help fellows, maybe tomorrow I can check some things out.

[cgtech]

Is the tick at a speed the same as one wheel revolution, or more frequent than that? Draw a chaulk mark on the tire, and drive a little, have a friend observe the "1chaulk mark revolution to "click" ratio" if possible. That will help figure out where the noise may be located. This is kinda vauge, but the speed/frequency of the noise can help to figure it out.