VFD or Soft Start Single Phase Motors

R

rlay002

Member
Location
Michigan
Occupation
Retired
Hi All -

I have a boat hoist that is powered by 2 single phase capacitor start induction motors.

The controller (up/down only) is wired with 220v from the panel through twin contactors with one of the hot legs being constant (orange) and the other switched to separate motor leads for forward and reverse based on up/down toggle (red/black).

The fixed rotor current is 33A (66A total) for each motor which is marginally greater than the maximum pass through current of the Inverter (60A) - resulting in shutdown due to Max Over Current Error. The grid at the location is incredibly unreliable so switching that load to the utility isn't practical.

I am looking for any suggestions for limiting LRC for a few milliseconds to get the motors to SFA of 6.8A each.

Can a soft starter work here or will torque not be sufficient to start the motors under load (FLT 3 ft-lbs, LRT 9 ft-lbs)? If so, How would I size the soft starter - to SFA or LR? Is the SS device upstream of downstream of the contactors? If downstream, does each of the 3 legs need its own device?

I have yet to find a single phase in/out VFD that would work in this application and replacing the motors with 3 phase would be more expensive than switching out the Inverter. Let me know if you have seen anything different.

All of the precious threads on this have been incredibly helpful in getting me this and am hoping you can fill in the missing details detailed above.

Thanks in advance for any insight you can provide.
 
Rather that retype all of this, I’ll just redirect you to this post:

Soft start solutions for 1P induction motors?

Dealing with a limited power situation in which the continuous current on these 1P motors is not an issue, but the inrush hit is. I have seen a few soft start products floating around but I want to know exactly what they are doing internally so I can ensure this is a real solution and not a...
forums.mikeholt.com

As to VFDs, it’s similar problem. There ARE VFDs out there for single phase motors, but not YOUR TYPE of single phase motor.

Most likely, your only options are a bigger inverter, or change out the motors to 3 phase and use VFDs.
 
Thanks. I read that post and was leaning towards replacing the motors and adding a VFD is the way to go. The comparable 3P motor lowers the inrush current substantially.

If I go this route, how do I deal with the 220v contactors used for the switch? Does the VFD come after the contactor and use the 2 legs from the contactors as it's input. If so, how does the VFD remain powered when the switch isn't engaged to reduce start up time and retain settings.
 
With two motors, you might be able to put them both on the same VFD if they're identical, other folks can give you a better answer on that.

Power-
Run un-switched 240v to the VFD, remove the contactors as no longer needed or wire around them, and connect the VFD output straight to the motors. Wire the up/down buttons to a couple of inputs on the VFD (you'll have to program the inputs for those functions) and wire any limit switches in series with the Up/Down buttons. (There are probably some other parameters that ought to be set, also leaving that for others.)

You'll want some sort of disconnect before the VFD.

Question for others- does this setup need a GFCI? I think it's prudent, boat hoists seem to be problematic.
 
Not sure how that would work with the myriad of switches, levelers and limit switche run through the contactors.

The up/down toggle (whether wired or wireless remote) is really forward/reverse with the 3P contactor switching L1 between the T5/8 motor lead using the Red/Black contactor outputs. The other contactor output (orange) is always hot when the switched in either direction.
 
To be honest, I think this is getting out of your depth- those switches are part of the overall control system and need to be integrated with the VFD forward/reverse (up/down) controls, you should not be running the VFD output through the contactors! (All the contactors do is switch the power and select the direction.)
 
Agree. In that context, I was referring to running the 220v output from the contactors to the VFD but then you lose the directional leg and have a start up pause. I have wired similar controls to VFDs before so am not resistant there - the lift resides on a remote location and can say for certain there is no when that could operate/maintain it with everything run through the VFD. Trying to find a more streamlined solution to marginally lowering inrush current.
 
No, you can't have contactors with the VFDs,. Well, you CAN, but you will eventually kill the VFDs. Well... maybe. The issue is, VFDs have what's called a "pre-charge" circuit that prevents the capacitors inside of the VFD from destroying themselves when first powered up. This is done with a little resistor, and a relay that shorts it out a second after power is applied. That little setup is good for about 1,000 operations, which, if you do it once per month, is 83 years. But if you do it twice per day, it's something like 15 months! So how often is the boat hoist used? If this is your personal property and you use it to haul out a couple times per year, then you may never know that the life has been foreshortened.

If you were to try to do it with one VFD, you still need separate OL relays for each motor, it gets more complex than people realize.
 
rlay002 said:
Thanks. I read that post and was leaning towards replacing the motors and adding a VFD is the way to go. The comparable 3P motor lowers the inrush current substantially.

If I go this route, how do I deal with the 220v contactors used for the switch? Does the VFD come after the contactor and use the 2 legs from the contactors as it's input. If so, how does the VFD remain powered when the switch isn't engaged to reduce start up time and retain settings.
Click to expand...
Does the existing setup run both motors simultaneously? If not is there situations where you must run them separately?

If they can always run together you ditch the contactors, the drive output reverses the motors according to what inputs the drive is receiving. If they must run separately at times then you pretty much need a drive for each motor.
 
You must log in or register to reply here.
Top