Motor feed and capacitor

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Willtom

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Richmond, Va
I ran into this the other day at work. I got a service call to look at a boat lift with motors not working properly. There are 2 3/4 horsepower motors feed by a 240 volt 20 amp circuit. I was told the motors where originally wired 120 and have been changed to 240. I was wondering if the capacitors needed to be changed also. They currently thave 165 volt capacitors and I was thinking a 20 amps gfi breaker seemed a little low also. Any thoughts?
 

ActionDave

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First thing is to find out if it's a motor problem or a circuit problem. If two motors are tripping one breaker I would look at the branch circuit wiring first.

If it is the motor the first thing I would do is check amps on the whole motor and then the starting winding.
 

Willtom

Member
Location
Richmond, Va
The circuit seems fine I was also able to verify with a different circuit near by the same problem. It seems like the motors where caused great the circuit to be overloaded and trip. I took an amperage reading any when you turn the motors on the amperage jumps up to around 35 Amps then the circuit will trip.
 

jim dungar

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... when you turn the motors on the amperage jumps up to around 35 Amps then the circuit will trip.

It is not unusual to have a breaker carry about 6X for roughly 20 secs, and 1.5X for over a minute. How long does it take it take before tripping? If it holds for more than a minute, my guess is that the motor is not getting up to speed due to something mechanical.

Did the owner get a new boat? Is it possible that the lift is getting old (it may have been moved, otherwise why change the voltage), has the pulley system been properly greased?
 

Willtom

Member
Location
Richmond, Va
I'm not there today I was just there for a couple hours yesterday as a third opinion. I'm just trying to wrap my head around what was going on. Trying to figure out what else I could have done to figure out the problem in the time I was there. I did uncouple the motor and I'd didn't seem to make a difference it still acted the same and tripped.
 

Willtom

Member
Location
Richmond, Va
It is not unusual to have a breaker carry about 6X for roughly 20 secs, and 1.5X for over a minute. How long does it take it take before tripping? If it holds for more than a minute, my guess is that the motor is not getting up to speed due to something mechanical.

Did the owner get a new boat? Is it possible that the lift is getting old (it may have been moved, otherwise why change the voltage), has the pulley system been properly greased?


The he boat lift is fairly new and there was no boat on the lift just the lift itself. The breaker did not hold very long maybe ten or 15 seconds. It seemed like the motors just would get up to speed. That's what made me think the capacitors could be wrong. I had read some where that you should use a 330 volt capacitor when using 240 volts.
 

Willtom

Member
Location
Richmond, Va
It is not unusual to have a breaker carry about 6X for roughly 20 secs, and 1.5X for over a minute. How long does it take it take before tripping? If it holds for more than a minute, my guess is that the motor is not getting up to speed due to something mechanical.

Did the owner get a new boat? Is it possible that the lift is getting old (it may have been moved, otherwise why change the voltage), has the pulley system been properly greased?


As as for the voltage change. From what I was told the company who installed the lift and motors thought they where being wired for 120 volt but the guys who did the electrical work decide to use 240 volts.
 

ActionDave

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It's possible that the start winding is not dropping out of the circuit. You can check with your amp clamp around one of the leads going to the starting cap, it should only have current for a couple of seconds at the most.

It could also be the leads are not made up correctly or a bad starting cap. It could be a bad bearing. It's not the voltage rating of the capacitor.
 

Jraef

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But as to you question on the caps, if it only has one cap, that's a start cap only, meaning it is a Cap Start / Induction Run (CSIR) and it would only be in the 120V circuit regardless of how it runs, so 165V is typical for that.
motcon2.jpg

Needing a 330V cap is if you have a Cap Start / Cap Run (CSCR), because the Run capacitor will be in the circuit the whole time and see 240V; but even on those, the start cap can still be 165V.

I agree with Action Dave, from the description of what happened here most likely the centrifugal switch is stuck and not dropping the Start cap and winding out of the circuit. A lot of times people will complain about a motor becoming "weak" so some DIY guy or handyman will assume that changing to 240V will make it "stronger" (which is BS). But if the problem was the centrifugal switch all along, that just makes it worse.
 

jim dungar

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Wisconsin
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Jraef

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