Recent content by Guineafowl

Results: Capacitance (uF):Current U:Current V:Current W: 013.413.18.3 1212.812.68.0 209.410.07.2 359.310.57.0 It looks like a low point around the 20 uF mark. At this level, subjectively, the motor sounds happier and gets less hot. Phase balance looks better, too. Increasing to 35...

Ok, well I have 30 uF and 20 uF coming, so that will give me the range 12-50 uF. Checking for motor voltage spikes, I assume my Fluke 87V on peak detect should spot them?

An interesting short article on self-excitation in pf-corrected induction motors: https://nepsi.com/resource/Self-Excitation Concerns.pdf The key point is, if the capacitive reactance is greater than the motor magnetising reactance, as when the cap is deliberately under-sized, the resonant...

I’ve had the motor apart for testing the windings and changing the bearings: It’s dual voltage, ie 230V delta or 400V star. Latter configuration currently. No internal switch.

As soon as power is cut, the motor stops dead from the friction. Does that allay any fears? I’d guess that, at switch-off, we’ll be left with three LC tanks, complicated by the rotor nearby. Would they just ring down to nothing? The motor being fairly modern and dual voltage/frequency, I...

I’ve ordered three ##450V, 30\mu F## capacitors, having approached the calculation differently and got the same answer: At ##400V, 11A, 50Hz, cos\phi=0.65, \phi=49.5°##: ##|S| = \sqrt 3 VI = 7.62 kVA## ##P = |S|cos\phi = 4.95 kW## ##Q = Ptan\phi = 5.80 kVAR## The above with a ##cos\phi## of...

Thanks, I’ll get some EP grease. The only problem is, the lubricator is an oil reservoir, 11, and a tight-fitting felt wick, 9, which might just clean away the grease as it goes. I wonder if I could mix up some EP with the normal oil and try that? The phosphor bronze lift nuts, acting on the...

The screw is on the right, and turns the other screw via two 90deg gearboxes and a driveshaft under the lift area. The lift nut is no. 19 and it lifts the squarish bracket (12), which in turn lifts the carriage with the arms that contact the car (not shown). Above all that is the autolubricator...

Ok, so a cosphi of 0.65 gives an angle of 49.5 degrees: $$Z=36.4\Omega <49.5° = 23.6 +j27.7\Omega$$ $$C=\frac 1 {2\pi f 27.7} = 115 \mu F$$

VFD manual should be linked in the first post. Yes, I thought lifting the car slower might reduce the loading of the system. Or, running at 60Hz might improve the power factor, according to the motor plate. All doable with a twiddle of a pot. It seems very inefficient. Lifting a 2-tonne car at...

As a first attempt, looking at the motor plate (connected in star): $$Z=\frac V I = \frac {400} {11} = 36.4\Omega$$ Find capacitor with Xc of that value at 50Hz: $$ C = \frac 1 {2\pi f X_c} = 87\mu F$$

1. Done - it has automatic screw lubricators which have been cleaned out and topped up. 2. Yes, certainly something to try. I assume 3 equal values of capacitance - start at 5uF? As I understand it, the motor is custom-designed to be used for minutes in the hour (pf not a priority), but must...

Motor plate, for interest:

This one is a 3ph 400V in and out model. Can’t be changed. Cheap enough for a punt on this problem; if no go, I can use it for something else. It’s not worth buying a 1ph 230V in, 3ph 230V out model for this one car - it would have to be specced a lot higher than the 3.5kW, given the lift...

Power supply to the 7.5kW rotary is 1ph, 240Vac. Supply voltage drop at full load is within 5%. The rotary outputs (roughly) 415Vac 3ph to the screw-type car lift, capacity 2.7 tonne. The lift motor is a 3.5kW, 50Hz, 4-pole, asynchronous induction motor with a power factor of just 0.65. Phase...