Single phase motor blows fuses under load

blackbird307 · Aug 9, 2015

I apologize, this isn't really a PLC question, but I am asking since this is probably the only place I know where I can get a reliable answer to a question like this. I have a single phase 115V motor which runs fine.... until I put a load onto it. It blows all my fuses, 20A, and 25A regardless. Obviously the inrush current drawn by the motor is WAY too high for any fuse I throw in. What is the best solution without overhauling my entire electrical. Should I use a soft starter? Where would I get one for single phase motors? Motor runs a hydraulic lift. Motor specs weren't anywhere on the product description when I initially purchased... or the manual.

Motor is rated at
3450 RPM
1.0 HP
110V
60Hz
Frame 56
Amp: 15A
MAX AMB40

Thanks

mendonsy · Aug 9, 2015

With a rated current of 15 amps the starting current will be somewhere between 60 and 90 amps. Fuses tend to be much faster acting than a circuit breaker so there is a possibility you could get away with running it from a 20 amp circuit breaker. "D curve" circuit breakers are made for similar loads.

blackbird307 · Aug 9, 2015

Hmmm... I just have a fuse box... I guess I couldn't just eliminate the fuse with a short in the socket, like a plug (im sure something like that exists), and just place the breaker beside the motor? Since it's the only thing that draws from the circuit?

Seems kind of crazy, but I might have no choice.

milldrone · Aug 9, 2015

blackbird307 said:
I have a single phase 115V motor which runs fine.... until I put a load onto it. It blows all my fuses, 20A, and 25A regardless. Obviously the inrush current drawn by the motor is WAY too high for any fuse I throw in. What is the best solution without overhauling my entire electrical. Should I use a soft starter? Where would I get one for single phase motors? Motor runs a hydraulic lift. Motor specs weren't anywhere on the product description when I initially purchased... or the manual.

1. It sounds like you have tested the motor when it's not coupled to any load (I'm presuming you uncoupled the pump from the motor).

2. You mention inrush, is this one of those hydraulic units for a scissor lift or a car lift? When the motor runs it pumps fluid into a cylinder and when you want to lower you actuate a valve is this correct?

3. Is the motor shaft very short and have a slot like for a screwdriver? The pump would have a blade to engage the motor slot.

4. Have you tried powering the pump with a cordless drill?

Perhaps my presumptions are all wrong. Can you energize the motor and put a load on it with some other means?

mendonsy · Aug 9, 2015

I would suggest running a properly protected 40 or 50 amp fused circuit from your fuse panel to the motor with #8 wire then using a 20 amp D curve circuit breaker at the motor.
http://www.factorymation.com/s.nl/it.A/id.5687/.f

blackbird307 · Aug 9, 2015

milldrone said:
1. It sounds like you have tested the motor when it's not coupled to any load (I'm presuming you uncoupled the pump from the motor).

2. You mention inrush, is this one of those hydraulic units for a scissor lift or a car lift? When the motor runs it pumps fluid into a cylinder and when you want to lower you actuate a valve is this correct?

3. Is the motor shaft very short and have a slot like for a screwdriver? The pump would have a blade to engage the motor slot.

4. Have you tried powering the pump with a cordless drill?

Perhaps my presumptions are all wrong. Can you energize the motor and put a load on it with some other means?

It is for cars. I am not too sure what you mean by uncoupled motor with pump? You mean the centrifuge (or whatever it is)? I am unsure how exactly it works since the entire thing is in an enclosure, and I would have to disassemble it to see for sure, there is a hydraulic line which runs to the cylinder. I was able to operate the lift with myself standing onto it. But as soon as I drive a car onto it weighing a couple thousand pounds, the load is too much for the fuse. The lift lowers when a valve is actuated.

Basically after I replace the fuse, try it out again, the lift moves like an inch then fuse blows. The lift is rated for 8000lbs.

DickDV · Aug 9, 2015

Do I understand correctly that the motor will start and run the lift pump as long as there is no load on the lift? If that is so, forget softstarting. It's already started and running successfully.
Is it possible that the system is designed for an 1800rpm motor and it has been replaced with a 3600rpm motor? Or even if it is designed for 3600rpm, you could change to a motor of same hp in the same frame but 1800rpm. This doubles the torque available for pumping but will reduce your lift speed a bit.

The NEC dictates what fuse is correct for this motor. I would suggest a time delay, probably 30amp fuse. If it blows this fuse, the motor is seriously overloaded and the problem is more about sizing than overcurrent.

Highland Controls · Aug 9, 2015

I don't think you are talking about inrush here. Is the motor running before you try to move the lift? What is the rating of the lift?

blackbird307 · Aug 9, 2015

Sorry, the lift operates with a single push button, as soon as that is pressed the motor starts and the lift moves. But in my case the lift starts moving and fuse blows less than a second after started.

DickDV said:
The NEC dictates what fuse is correct for this motor. I would suggest a time delay, probably 30amp fuse. If it blows this fuse, the motor is seriously overloaded and the problem is more about sizing than overcurrent.

I may try this out first, cross my fingers it works since it doesn't look like I have too many options right now.

milldrone · Aug 9, 2015

DickDV said:
Is it possible that the system is designed for an 1800rpm motor and it has been replaced with a 3600rpm motor? Or even if it is designed for 3600rpm, you could change to a motor of same hp in the same frame but 1800rpm. This doubles the torque available for pumping but will reduce your lift speed a bit.

Plus 1 to this.

Ronnie Sullivan · Aug 10, 2015

Maybe it's not the motor. You press the button and it blows the fuse. Could be the valve solenoid or the relay.

JesperMP · Aug 10, 2015

Measure the current.

DwSoFt · Aug 10, 2015

It sounds to me like you need to get a licensed Electrician in there to troubleshoot it further...

JRB · Aug 10, 2015

Shorted RUN capacitor?

Racer5039 · Aug 10, 2015

If the valve did not open, the motor has to bypass all pressure. Also check voltage drop. What size wire to the list? Corded or hard wired?
+ 1 for Lic. Electrician

Single phase motor blows fuses under load

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