Motor Problem; won't work under load

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brantmacga

brantmacga

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Location
Georgia
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Former Child
Here's what is happening:

A.O.Smith 1HP, 115V-

Connected to a pulley and gearbox, this setup is rated to lift 4k lbs.
The load it is trying to lift is 3.3k lbs.

This boat lift came as a pre-assembled setup w/ a drum switch and 120v GFCI cord cap. From the service, I ran approx 40' to a sub-panel w/ #10. From there, I went to the dock another 50' w/ #12 feeding a GFCI recep. The owner brought me a remote control setup to replace the drum switch. The lift was never operated under load w/ the drum switch.

The boat was put on yesterday and one the hoist reaches the boat, the motor hiccups and grinds to a halt. Voltage drop was around 20v at the controller. I had some 8-3UF on the truck, so I ran that from the sub-panel to the motor and again got 20v drop.

The run capacitor checked out fine, so any ideas as to what may be happening? I disconnected the control also and wired directly to the motor. I get the same result.

I took the motor to the shop, but I don't know when I'll here back from them. I'm not so much of a motor specialist other than making connections, changing direction, etc. . . Just wondering if someone had any thoughts on it. All connections were correct.

-------- Edit to add: - I made a post awhile back about a feeder getting cut; this was from the same job. The EGC connected to this motor was energized for at least a couple of days. I don't think the neutral was energized because the PCB in the lift controller wasn't fried.
 
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Brant, try the experiment again (maybe with someone at the switch so you don't burn up the motor between tests).

This time, measure the voltage at every accessible point. You know it drops to 100 at the motor. What about at the panel? Check both incoming and outgoing terminals.

If you get excessive drop even at the sub-panel line terminals, check the next place upstream: at the sub's feed. Keep going until you find a place voltage doesn't drop.

You can also check across suspect connections and devices, as you would across a fuse, such as from the sub's line terminals to the branch's load terminals.

One more thing: can you rewire the motor for 240v, as well as the supply chain?
 
Jraef said:
Could be that the start (centrifugal) switch on the motor is not opening up at speed, leaving the start cap in the circuit when it is no longer needed.
Click to expand...
I would think that this condition would continue to attempt to supply starting torque at less than running speed.

It may be more likely that the start winding is not being energized. That would lead to an easily-stalled motor, if it starts at all.
 
In order of probability (at least my guess today):
1. Marginal on wire. Can the motor be connected for 240V?

2. Bearings or bushings in the gearhead. If the unit is not new, the bushings/bearings cn drag.

carl
 
1) voltage drop @ the sub-panel w/ motor running was a 2-3V less than at the motor.

2) The motor could be connected 240V if the customer is willing to pay for the new line to be pulled from the panel. 120v is what I sent down there because it came w/ a 120V drum switch connected from the factory. The new remote can go 120/240.

3) Nameplate rating was 13.something amps.

thanks for the replies. I've just been trying to think if there's something I screwed up here. i'm pretty sure I'm in the clear. This thing was ordered from somewhere out of state, so there is no local warranty service. Its not the owners fault, and i don't think its mine; but its electric, and I'm the electrician so its pinned on me to make it right. I hope to have a final answer from the armature shop by tomorrow afternoon. I'll let you know what they find.
 
brantmacga said:
1) voltage drop @ the sub-panel w/ motor running was a 2-3V less than at the motor.
Click to expand...
This makes me think the feeder to the subpanel may have an issue or is undersized for the new load.
2) The motor could be connected 240V if the customer is willing to pay for the new line to be pulled from the panel. 120v is what I sent down there because it came w/ a 120V drum switch connected from the factory. The new remote can go 120/240.

3) Nameplate rating was 13.something amps.
Click to expand...
Per motor? Is this a 1-motor or 2-motor lift? Most of the lifts I've seen have 2 motors.
 
I think your wire size is fine with the given motor data.

2-3 volt drop from sub panel to motor tells me the amps are within range of the motor load, say 15 amps or less.

The #8 would have helped maybe by a couple of volts, but verified there was not a problem with the #12.

The 103 volts at the sub-panel is a problem. With only 14 amps, this should not be the case. If you start out at 117.5 volts, the sub-panel should be near 116 volts.

Check the #10 and the panel it comes from. I would also take an amp reading at the motor and the sub-panel and the main panel.
 
brantmacga said:
2) The motor could be connected 240V if the customer is willing to pay for the new line to be pulled from the panel. 120v is what I sent down there because it came w/ a 120V drum switch connected from the factory. The new remote can go 120/240.
Click to expand...
If the motor(s) is the only load on the line, just re-color the white and land it on a 2-pole breaker. Doubling the voltage halves the current, eliminating the need to upsize anything.

However, the excess drop at the panel means you need to keep checking upstream. The voltage drop may be on the #10 feeder, but it may not be.
 
crossman said:
I'm guessing it is a mechanical problem in the drive/gear reduction assembly.
Click to expand...

Owner just called and said he was on the phone w/ the manufacturer. They said, and this is a quote, "that is an extremely tough motor. If it runs at all, nothing is wrong internally." They went on to say that either it is "starving for voltage" (obviously) or the pulley size needs to be changed. So, crossman may have nailed it. Yay.
 
crossman said:
I'm guessing it is a mechanical problem in the drive/gear reduction assembly.
Click to expand...
But that does not explain the voltage drop problem. There was only a 2-3 volt drop from the motor to subpanel, indicating the amp draw was ok below the subpanel.

The gear would not explain 103 volts at the subpanel.

I can think of one other explanation, but would first like to hear back from brantmacga on the amp readings and what is going on ahead of the subpanel.
 
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