Most sewing machines make one stitch per hand wheel revolution. Observing needle bar movement with hand wheel rotation, verifies stitches per revolution.
Measuring RPM, provides a means of evaluating machine performance. Listening to a machine, feeling vibrations may be misleading in estimating speed. Measuring power in operation, with maximum controller speed, provides motor output estimation.
The ability to measure RPM of hand wheel and motor provides a method for determination of belt slip.
Pulley sizes of hand wheel and motor, determine drive ratio. RPM ratio follows drive ratio, and should stay nearly constant under load conditions. Ratio can be found by measuring circumferences and dividing hand wheel by motor pulley. An alternative method is mark each and rotate hand, counting turns plus fraction of turns of motor pulley. A Singer 99 has a ratio of slightly more than 3-1. Correct belt adjustment, is just tight enough not to slip. Too tight of belt, stresses motor bearings, and may create enough friction to activate main shaft when hand wheel stop is set for bobbin winding.
Hand wheel speed is easily measured with a DT-2234C digital tachometer.
They are available for about $10 shipped. A reflective adhesive target, marks a spot to trigger tachometer measurements.
Target strips are provided, along with a zipper carry pouch. Since most motor pulleys are shiny, pasting black paper disk with reflective target should work as target. On open spoke hand wheels, blue painters tape with target should work as target. Test button is pressed while pointing tachometer at target, a red LED provides visual feedback indication of aim. LCD display indicates RPM, and updates at a rate of 0.8s per reading. RPM measurement is accurate, viewed on 5 digit display, (+/- 0.05% +1 digit).
A Meterk MK34 power meter was also purchased for about $20.
It measures real power consumption of sewing machine plugged into outlet. The power meter also measures current, line voltage, and power factor. Power in a DC circuit is the product of voltage times current. In AC circuit, the voltage and current “wave forms”, are multiplied to determine real power. Sewing machine motors are inductive devices. When an inductor is energized, current is 90 degrees out of phase with voltage, there is current and voltage, but real power is near zero. A loaded motor draws real power, yet has reactive component for charging magnetic circuit. Measuring only current, results in somewhat meaningless information. A power meter makes measurements, not possible with typical multi-meter.
Power is a measurement of work, and power includes losses. Small motors are inefficient, perhaps around 30-50%, but relative measurements are still useful. Power measurement can indicate if motor achieves desired output. An estimate of motor output is rated current, times voltage. For a 0.6A motor at 120V about 72W.
Motor controls are typically series resistors, serving to reduce voltage and current seen by motor. There is power loss in resistance controller. The power loss is current squared times resistance, or voltage at resistor times current. To eliminate controller loss, an electronic controller was used in tests below. An electronic controller energizes motor for portions of AC wave form, when not energized the loss is near zero, and when fully energized, controller loss is low too.
Singer 201 potted motor and LED light:
Machine mounted in Singer 48 cabinet, smooth operation over complete operating range. Quilt piecing of 2 cotton layers. Machine quickly accelerated is max speed runs. Light on during tests. Potted motor cover waas removed to count motor rotation, Singer 201 has a 5-1 ratio.
LED lamp with 104 elements 2W, in comparison a standard incandescent ~15W. LED has significantly greater lumens.
Measurements w/electronic control:
70 RPM, 20W as slow as controller would allow
300 RPM 34W
600 RPM 57W
1100 RPM 80W, full speed
Measurements w/Singer carbon pile control:
note: controller losses in values below
Slow speed not possible
288 RPM 58W
580 RPM 69W
1100 RPM 80W, full speed
I would like to try several machines to see if results vary, with same model, suggesting need for improvement on lagging machines. My wife tells me when 201’s have a problem. The most common issue is stiff grease in gears. It seems that fibered automotive type bearing is the culprit. Removing old grease and replacing with Vaseline or Tri-Flow grease works wonders. I have heard just SM oil works too.
I hope to do more tests, add to post, as time and location permits. The plan is to use one motor with electronic controller and move it to many machines. The single motor will let me test things like machine mechanical resistances for belted machines. I will compare to Singer 115,127, 99, 201K.
I will also check Singer 101, 15-91, 201 with potted motors.