1. Home
  2. ⚙ Model Engineering in the UK
  3. Slow induction motor

Slow induction motor

I have an old Clarke motor (1/5 HP, 0.15 KW, 240 v, 1.8 A, 1400 rpm, type 5DB, single phase according to the rating plate,) that only runs at

400 rpm whether loaded or unloaded. I am looking for suggestions for why it is slow, and how I can rectify the fault.

My inspection of the motor reveals that: [1] It has no brushes so I guess it is an induction motor. [2] It has a 8 microFarad external capacitor which suggests it is a run capacitor not a start capacitor from what I have gleaned from the internet. [3] The bearings are not binding or rough, and the spindle is free to turn. [4] A cheap multimeter test of the disconnected capacitor gives a gradually increasing resistance up to 20 ohms. [5] A cheap multimeter test of the windings from the capacitor terminals reads 58 ohms.

Any clues folks?

Reply to
Clifford Coggin
Loading thread data ...

I would take a look and see if there is a centrifugal switch that is stuck on. Richard

Reply to
Richard

Possibly a permanent split capacitor motor and those, as well as shaded pole motors, can be speed controlled to a degree by varying the voltage so maybe the motor is somehow getting supplied a reduced voltage.

Reply to
David Billington

Assuming DC tests your multimeter should show a resistance reading approaching infinity asymptotically. 20 ohms is a long way short of infinity !!!!

Andrew

Reply to
Andrew Mawson

That's the first thing I looked for, but there is no centrifugal switch.

Reply to
Clifford Coggin

If that is the case the motor is junk and I need a new one.

Reply to
Clifford Coggin

It may have gone to a higher reading if I had continued the test, but I stopped after 10 seconds or so because the increase was so gradual. Are you suggesting a faulty capacitor or a useless meter?

Reply to
Clifford Coggin

Either is a possibility - your meter is easily tested against a known resistance. What resistance range was it switched to.

Andrew

Reply to
Andrew Mawson

I was just wondering if you had checked the supply voltage at the motor terminals. It used to be that Machinemart sold single phase motors were all PSC motors so not a good start-up torque but good for some applications.

Reply to
David Billington

I am not an electrician and don't have any known resistances. The meter is auto ranging so I can't answer your second question.

I shall order a new capacitor in the hope that it will solve the problem. If it doesn't, the motor is destined for the bin as I don't intend to spend any more time on the job.

Thanks for your help Andrew.

Reply to
Clifford Coggin

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.