GerryR

The VFD can operate in "constant torque " mode if the motor is designed for VFD operation (because of both voltage and current (heating) requirements needed to accomplish this). However, you can set the VFD to run with a standard 3 ph motor, and you can set it to run just like a DC "servo" with an external (foot) speed control. I have a 1 hp, 3 ph, 230 VAC, 1725 rpm motor to which I added a 5:1 gear reducer, and then did a further reduction through the pulley, giving about a 7:1 total reduction. I made a foot control (could have bought one, but had what I needed to make one) and can vary the speed from 0 to about 240 strokes per minute (which totally suits my needs). With the reduction, the motor is at ample speed at low strokes per minute to prevent any over-heating and there is ample torque to sew 3/8 leather. If by chance I need to go faster, I can reset the upper frequency limit in the VFD and drive the motor in "constant hp" mode (lose some torque) and move along, for example on thinner, garment material. My point is that the VFD is as versatile as a DC drive if set up properly. I am not that familiar with the so-called DC servo's sold for sewing machines, but unless there is some sort of feedback from an encoder (which I tend to doubt because of their low cost), it is not a true "servo" but merely a "variable speed" DC drive. So again, the VFD, I believe, is a viable option, especially if you already have the motor, which the OP does have. The DC servos that boast needle position capability, I assume, do have some form of positional feedback encoder or sensors, and would be more inline with a true "servo" system.

You're forgiven, but yes, mechanically speaking.

I believe the OP bought a machine with the 3 ph motor on it. It may be less expensive to just replace it with the "correct" motor, but these are just some options if he wants to keep everything "original." With the VFD, you don't lose any torque, as it generates 3 ph out from the 1 ph in. Also, if the motor can take it, from the rated RPM on down, it can be set to run in constant-torque mode, so you get good torque at low RPM's. If you want to run above the rated RPM's, it will then run in constant-horsepower mode, and the torque drops off accordingly. But it gives a lot of options, not the least of which is variable speed. The phase converters (not the rotary converters, which generate all 3 phases) just start the motor, and then the motor runs single phase at 2/3 the rated power.

For $117.00 shipped, you can get a VFD (Variable Frequency Drive) that will convert your 220 VAC 1 ph input to 220 VAC 3 ph output to the motor. It will also give you speed control of the motor, I just put one of these on my Singer 153 W... but have been using them for years, installing them in factories and mills requiring motor speed control and 1ph to 3 ph conversion. Here's the link: http://www.automatio...0_VAC)/GS1-20P5 If you decide to get one and need some guidance in hooking it up, contact me. I hope this helps. Gerry pcox, The 4 wires have 220 (nominal) between any two of 3 wires, and the 4th wire is ground; no 120 VAC in a 220 VAC, 3 phase system.

Thanks Wiz. Gerry

Thanks Eric. So I assume from your answer that there are thinner belts available. Would you know a source? Gerry

First, greetings to all. I have a Singer 153 W... and was wondering if a standard "A" belt is OK to use from the motor to the drive pulley on the machine, or are there special belts for this purpose? The "A" belt appears to fit the groove OK, but the belt stands proud of the pulley by approximately 1/8 inch. I seem to recall a thread where a 7/16 inch wide belt was mentioned but was unable to locate that thread again and cannot find that size belt listed anywhere. Any input will be appreciated. Thank you. Gerry