Two Speed Pump Motor Issue

[Jarheadforlife]

I have a two speed 240V pump motor on a boat that will start in low and switch over to high with no problem, but will not start in high speed.
I've replaced the cap just for GP (the old one tested in tolerance) but it didn't change the symptoms. I've cleaned the contacts for the high-speed winding and still no change. Any thoughts before I pull it out? It's not easy to get to.

 

[ActionDave]

If you can get an amp meter around the wires going to the starting switch on the motor you can see if there's anything different between starting on low vs high.

End play in the bearings might be just enough for motor to drag on high speed start.

 

[Deltaforce]

I have a two speed 240V pump motor on a boat that will start in low and switch over to high with no problem, but will not start in high speed.
I've replaced the cap just for GP (the old one tested in tolerance) but it didn't change the symptoms. I've cleaned the contacts for the high-speed winding and still no change. Any thoughts before I pull it out? It's not easy to get to.

ChatGPT from

- *Capacitor Functionality*: You've replaced the capacitor, but it's worth double-checking if it's the right type and value for your motor's high-speed operation.
- *Winding Issues*: There might be a problem with the high-speed winding itself, like an open circuit or insulation issue, preventing it from starting directly in high.
- *Contactors/Switches*: Although you've cleaned the contacts for the high-speed winding, ensure they're functioning properly and making good connections when switching to high.
- *Voltage Drop*: High inrush current when trying to start in high speed might be causing a significant voltage drop, especially if your boat's electrical system isn't robust enough.
- *Mechanical Load*: Consider if there's excessive mechanical load or binding that's preventing high-speed start but allows low-speed start and switching.
- *Control Circuit*: Check if there's a specific control circuit or relay involved in switching speeds; maybe there's an issue there affecting high-speed start.

Next Steps
- *Check Voltage*: Measure voltage at the motor terminals when attempting to start in high speed to see if there's a significant drop.
- *Inspect Wiring*: Look for any signs of damage or loose connections specific to the high-speed circuit.
- *Consult Manual*: Refer to the motor's documentation or manufacturer's troubleshooting guides if available.

 

[ptonsparky]

RTFM, Consult Manual, should be higher on the list although that would be typical for most of us. ChatGPT is learning from us after all.

Application of volt and amp meters should have been used from the start. More information is better at times.

 

[Jraef]

So some assumptions on the details left out:
1. This is a single phase AC capacitor start 2 speed motor.
2. There is only one capacitor and it has only one cap value on it, with only 2 wires going to it.
3. It was previously working to start on either speed and no longer does.
4. You have a mechanical switch for changing the speeds, not mag contactors controlled by a switch.

The issue is, there are basically two ways of having a 2 speed single phase motor: there are two capacitance that are put in series for the low speed, in which case if one was bad, it would only work in high speed, or the main winding is split, so in low speed you only energized half of the winding, then all of it in high. So if it only starts in low, and half of the winding was bad, it wouldn’t run in high. So if it just will not START in high, but RUNS at high speed after starting in low, then the problem must reside in the speed selection system external to the motor.

But this brings up point 3 above. If it PREVIOUSLY worked to start in high and no longer does, then you need a wiring diagram to diagnose the problem. If it is new and you are WANTING it to start in high, the problem may be that it was never designed to do so. It’s very common to do that on 2 speed motors, especially those with a single capacitor and a split winding. That’s about point 4, because that is typically done via contactors and a timer. Starting in low is direct, but if you want to start in high, it goes through a timer that always starts in low and only allows switching to high AFTER the centrifugal switch takes the start cap out of the circuit.