Single phase motor blows fuses under load

[blackbird307]

Alright, so I tried the 30A time delay. It worked for the duration of the time, but still blew. Car moved a little, once again, but longer before blowing, by a few seconds. The motor sounded like it was having a really hard time. I don't understand.... this lift supports weights up to 8000lbs, and my car isn't half that. The motor shouldn't be drawing that much current under regular operation. I am going to see if changing motor to one of less rpm, yet same hp and see if that helps.

I would measure the current with my oscilloscope, but I don't have a current clamp with a BNC connector.

I was thinking of using one leg of a 60A 220 and connecting it to the motor. I have a plug and a bunch of wire. Would anyone here object to that? Maybe first figure out why the motor is working so hard.

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

Corded

 

[GlenGineer]

I was thinking of using one leg of a 60A 220 and connecting it to the motor. I have a plug and a bunch of wire. Would anyone here object to that? Maybe first figure out why the motor is working so hard.Corded

Yes figure it out! A time delay fuse is the appropriate device to use for this application. I believe the code calls for a maximum of 125% FLA for time delay fuses (although the NEC is not in from of me). Using the wrong voltage, RPM, or too high a fuse is a big problem. The fuses are there to save motors, to prevent fires, and to protect personnel.

I will not agree with others about a licenced electrician. Most of the ones I met can tell you a lot about house wiring...very little about motors and connected mechanical systems. If the motor runs OK without a load (normally we would at this point check amps on the motor and expect it to be extremely low) then I would look at the pump, the valve, the hose and the overpressure return valves. I would check to make sure there is hydraulic fluid (although I doubt this is the problem). You have to make a list of what it could be and figure out ways to test whether or not that is your problem.

Years ago I produced a new hydraulicly powered lifting device. I had the plants hydraulics expert look over the hydraulic power unit and asked him "what is this...do we need that" questions". My electrician stepped up and put it together. Unfortunately the info the hydraulic expert gave us was wrong. The electrician tried to run it but kept blowing fuses and finally burned out the hydraulic pump. As it turned out there was an overpressure return valve that was disabled. So the pump would be on but the control valve was closed and the pressure was just building. When the pressure got too high fuses blew and eventually the pump failed.

So check your hydraulic system.

 

[Racer5039]

One leg of a 30Amp 220 is only going to be 120V. Why would you do that? Did this lift ever work right? do you know if the motor is wired for 120 or 220 volt? I would be checking that first before I started throwing parts at it like an IBM repair man. If you don't know whats wrong, You will spend a lot of cash before you get lucky.

 

[JesperMP]

Since you replaced the fuse for a slow blow version, and experienced that the time was longer before the fuse blew, we can rule out a short-circuit.
And since it is a 1-phase system, we can also rule out such things as a missing phase.

It is almost certainly a mechanical problem. So dont hire a certified electrician. Hire a mechanic

 

[milldrone]

Alright, so I tried the 30A time delay. Car moved a little, once again, but longer before blowing, by a few seconds. The motor sounded like it was having a really hard time.

While performing this test did you notice some of the timing of the details you mentioned.

"The car moved a little" and you mentioned the "motor sounded like it was having a really hard time". Did the car stop moving and then the "hard time" noise start then, or did the motor have the "hard time sound from the beginning?

 

[dlweber]

I was thinking of using one leg of a 60A 220 and connecting it to the motor. I have a plug and a bunch of wire. Would anyone here object to that? Maybe first figure out why the motor is working so hard.

You mentioned that this is a 115V motor, if you have it plugged into a house hold outlet you are already using one leg of 220. The (american) residential wiring that I know of is single phase 220 that splits its legs in your breaker panel to get the 110-120V, So I would have no objections, other than you are already doing what you want other than breaker/fuse size

 

[mendonsy]

While performing this test did you notice some of the timing of the details you mentioned.

"The car moved a little" and you mentioned the "motor sounded like it was having a really hard time". Did the car stop moving and then the "hard time" noise start then, or did the motor have the "hard time sound from the beginning?

It sounds like your real problem is a mechanical or hydraulic issue with the lift. If the motor is having problems with lifting the load then it will draw well over the nameplate current.

If you can locate a clamp-on amp meter it would be very useful to know how much current the motor draws when you operate the lift empty and loaded.

 

[jraef]

Alright, so I tried the 30A time delay. It worked for the duration of the time, but still blew. Car moved a little, once again, but longer before blowing, by a few seconds. The motor sounded like it was having a really hard time. I don't understand.... this lift supports weights up to 8000lbs, and my car isn't half that. The motor shouldn't be drawing that much current under regular operation. I am going to see if changing motor to one of less rpm, yet same hp and see if that helps.

I would measure the current with my oscilloscope, but I don't have a current clamp with a BNC connector.

I was thinking of using one leg of a 60A 220 and connecting it to the motor. I have a plug and a bunch of wire. Would anyone here object to that? Maybe first figure out why the motor is working so hard.


Corded

Do NOT use one leg of a 60A breaker, it violates code for that motor. You fuses are likely just reacting to a situation that is bordering on starting a fire. Increasing the fuse size just removes that safety factor. 30A is the LARGEST allowable time delay fuse for this motor.

Given that the TD fuse still blew, this is NOT a fuse size issue. Either your motor is damaged, or your hydraulics are not working correctly. It may be that the hydraulics are not working, then because you kept putting in fuses and blowing them, you have now damaged the motor.

Get a hydraulic specialist to come and look at the lift and all of the controls that go with it. If everything is working perfectly, then take the motor out and get it to a motor rewind shop to see if it is damaged.

 

[JRB]

"I was thinking of using one leg of a 60A 220 and connecting it to the motor. I have a plug and a bunch of wire. Would anyone here object to that?
Maybe first figure out why the motor is working so hard".

There is a limit of pressure and flow rate at which a 1HP motor can supply force to lift the car with a given size hydraulic cylinder.
GPM and system pressure determine the pump HP required to lift the load in a hydraulic system. These values can be found in hydraulic
cylinder/motor HP sizing charts. So assuming the motor is good and is the correct RPM and HP for a given system, (many of these lift
pumps are 3450 RPM) -the problem is the motor is drawing in excess of its rated current, but if the motor were to draw nameplate FLA
when the raise button is pressed wth the car on the lift, the existing fuse and circuit size would be adequate. So don't change circuit
protection or circuit size to fix the problem of excess motor current above motor rated FLA. System pressure or GPM must be reduced in
order for the 3450 RPM 1 HP motor to lift the car at 15A.

The motor should NOT draw over ~15A when running, so the 60A circuit is a very bad idea. The motor is already started and the system
is pressurized when the raise button is pressed, so there is no starting current concern requiring an increase in short circuit protection
size to allow for motor start, and the circuit protection size should not be increased to allow for continuous overloading of the motor.
You should be able to use a 20A CB or dual element time delay fuse for this circuit, once the motor amps do not exceed FLA. You don't
want to increase circuit protection size to allow motor current in excess of branch circuit conductor capacity. The only way the motor
can be blowing 30A fuses is if the motor is bad, or overloaded to such an extent by incorrect pump pressure or GPM output that it's nearly
drawing locked rotor current. Since the motor HP is fixed, and GPM and pressure determine HP requirement in a hydraulic system, reduce GPM
or pressure to reduce motor current, then, this circuit should only require a dedicated 20A CB or dual element time delay fused circuit.

Increasing the size of the branch circuit short circuit protection (fuse or CB), will only serve to allow the motor to continually run in excess
of motor FLA, (this has to be corrected, not circuit capacity) which will allow the motor to destroy itself without opening the fuse or tripping
the circuit breaker, if no built in overload protection is provided by the motor.

 

[RussB]

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.

If it is the old screw-in fuse my dad used to use a nickel or was it a penny, under the fuse until he could get to the store to purchase a new one.

 

[saultgeorge]

Check the service factor rating on the nameplate. If it is 1.15 or greater and/or the temp rise is 40 degrees C or less, then the overcurrent protection device may be 140% of FLA. All other motors would be 130% FLA. (NEC 2011 430.32 (C). So your fuses could be 21 amps, which are not made, so one is allowed to go to the next size up, which is 25 amps. Get a dual element time delay fuse to help with the inrush. Of course the same math applies to a circuit breaker.

 

[jrwb4gbm]

Nobody has mentioned it yet but either bad or worn motor and/or pump bearings can display the symptoms you described.

 

[s9k2004]

blackbrd

if your electrical system is working before and all of a sudden your fuse is blowing then you might have some problem with short circuit and you need to consult with legitimate electrician.

since you have written the specs of your motor which i assume the 15amp is the full load current then i would say that you are using under rated fuse. as per nec handbook if you have 15fla, using a fuse, you must be using 45amp. that is 300% of your full load current.

though you still have to go to basic why your fuse is blowing given the fact that it is working before. perhaps you have a short ciruit.

 

[rootboy]

Is it possible that the system is designed for an 1800rpm motor and it has been replaced with a 3600rpm motor?

I'm having trouble wrapping my head around why a 3600 rpm motor is used where a 1800 rpm motor would have been a much better choice as well.

 

[TL140]

When was the last time you checked your filter to the hydraulic system? You may have a dirty filter causing cavitation and therefore the motor to over torque and send your amperage through the roof.