VFD Gurus, quick question.

[Phillip Gregory]

The consequent pole motor in your motor is a constant torque device at 60 Hz and below, just like a VFD. Your motor makes 4.57 ft-lb of maximum torque, and since horsepower = (torque * rpm)/5252, having the same torque at twice the RPM equals twice the horsepower. That is why the spec plate on the motor lists exactly half the horsepower at 900 rpm as it does at 1800 rpm. Running the motor in high speed (4 pole) mode at 60 Hz will give you 1.5 hp at 1800 rpm, and at 30 Hz will give you 3/4 hp at 900 rpm, exactly as if you had the motor wired to run using all consequent poles at 60 Hz. Note that the VFD is a constant horsepower device above line frequency and line voltage, so if you wired your motor low speed and gave it 120 Hz, it will still make 3/4 hp as you would need twice the line voltage (480 volts) to make 1 1/2 hp in low speed mode. That is why wiring the motor in high speed mode and reducing the frequency is the way to go.

Note that some consequent pole motors are constant horsepower- you would wire those up low speed and then increase the frequency to 120 Hz for high speed mode rather than wiring them up high speed and decreasing the frequency for low speed mode. Doing that would preserve the greater low-speed torque/power of the motor.

[Malcolm McLeod]

I did not do it that way because I drill some big holes in steel on occasion and wanted to take advantage of the motors low speed. I did it as David suggested, and I am the only one in the shop so it will not be an issue.

I commission a lot of VFDs in my job. Were it mine, I'd wire the motor to run at 'high' speed (for torque), directly to the VFD as recommended. Then use both 'on'
positions of the switch as the low voltage 'run' command (as Philip suggested), setup via the program. (Or, just use one contact in the switch for simplicity?) Program the VFD to run from 10hz minimum to 60Hz maximum.

I'd probably keep the Reeves drive. Let's assume for the moment you leave it in it's mid-range speed position.

1. Flip the switch to 'run'.
2. Use the VFD's keypad to select your desired speed.
- - If at 10hz its's still too fast, use the Reeves to decrease it further.
- - If at 60hz it's still too slow, use the Reeve's to increase it further.
3. Work.
4. Flip the switch to 'off'. Done.

The duty cycle on a DP is much too low to worry about heat unless you are in a nearly continuous process/production. .....See Dan Friedrichs' recent thread about his DP!!!

If you are in production environment, don't skimp. Ditch the Reeve's drive; install a fixed ratio V-belt system that gives you the maximum RPM needed in your process at 100% of motor's rated RPM. Buy a USA VFD (i.e. Allen-Bradley or Toshiba) and (Baldor) inverter-duty motor. You won't ever look back.

[Phillip Gregory]

I commission a lot of VFDs in my job. Were it mine, I'd wire the motor to run at 'high' speed (for torque), directly to the VFD as recommended. Then use both 'on'
positions of the switch as the low voltage 'run' command (as Philip suggested), setup via the program. (Or, just use one contact in the switch for simplicity?) Program the VFD to run from 10hz minimum to 60Hz maximum.

The drum switch is a maintained contact switch. The drum switch Clausing used has eight contacts, and many are jumpered to properly couple/uncouple the "extra" three leads coming from the middle of the windings to have the motor run in high or low speed mode. (There is a schematic on the inside of the cover of the drum switch stating which contacts are jumpered and which switches are open and closed in fast speed and slow speed settings.) The VFD will need to look for the "run" command from both the fast and slow positions but get a second signal from either one of these to tell the VFD to operate at a frequency other than default. Thus you will need to jumper across the output of one closed in fast position and one closed in slow position switch to properly get a run signal. I had to move some of the jumpers around to do this on my unit. I then set the default speed of the VFD to 60 Hz and used a signal from a closed in slow position switch to tell the VFD to run at 30 Hz instead as long as the VFD kept receiving that signal. That was the easiest way to do it with my VFD (TECO L510) and it only took three wires from the switch to the VFD to carry all of the signals. I can provide pictures, a schematic, and the values of the various VFD parameters if anybody needs it.

[Malcolm McLeod]

The drum switch is a maintained contact switch. The drum switch Clausing used has eight contacts, and many are jumpered to properly couple/uncouple the "extra" three leads coming from the middle of the windings to have the motor run in high or low speed mode. (There is a schematic on the inside of the cover of the drum switch stating which contacts are jumpered and which switches are open and closed in fast speed and slow speed settings.) The VFD will need to look for the "run" command from both the fast and slow positions but get a second signal from either one of these to tell the VFD to operate at a frequency other than default. Thus you will need to jumper across the output of one closed in fast position and one closed in slow position switch to properly get a run signal. I had to move some of the jumpers around to do this on my unit. I then set the default speed of the VFD to 60 Hz and used a signal from a closed in slow position switch to tell the VFD to run at 30 Hz instead as long as the VFD kept receiving that signal. That was the easiest way to do it with my VFD (TECO L510) and it only took three wires from the switch to the VFD to carry all of the signals. I can provide pictures, a schematic, and the values of the various VFD parameters if anybody needs it.

My basic assumption here is that the OP wants to simplify the DP. With that as the objective, I was advocating the use of only 1 N. O. contact in the drum switch (or 2 - if you want to signal the VFD to run with the switch moved to the 'low' OR 'high' position). This contact would break the low voltage 'run' input to the VFD (assumed to be 24Vdc, but may vary by VFD manufacturer). The drum switch would have no line voltage run thru it at all; it simply becomes an input signal device to the VFD's control terminal, providing only an On/Off command to the VFD.

You'd supply line voltage to the VFD, and then direct wire the motor to the VFD using the high speed taps (and wire nuts as needed).

95% (?) of all operations could probably be accomplished with the speed adjustment of the VFD - and never touch the Reeve's drive. Simple.

Even simpler is to get rid of the drum switch and the Reeve's drive. Install a VFD to provide all switching, variable speed control, and OL protection to the motor; and it's keypad is all the interface you need.
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I'm headed down Dan's path; looking for the right 3-phase motor and playing with how I might mount and couple the motor as direct-drive (no belts/sheaves) on my old Central Machinery DP.