Centec feed motor starter switch

[PropPeteParticipant @proppete]

I use a static phase inverter to power both motors of my Centec 2b. The motor for the power-driven table is 0.125hp, 1350rpm, FL amps per terminal 0.28A. I believe the existing starter switch for this motor is faulty because after a few minutes use, even with light cutting, the overload protection triggers, though I’m pretty sure the current is not reaching anywhere near full load. Any ideas how I can check this, or what replacement starter I can buy?

[PropPeteParticipant @proppete]

[not done it yetParticipant @notdoneityet]

Hello Pete,

I am wondering if the trip is caused by overload or a low voltage relay (for protection against restarts after power loss).

If the latter, changing around the phase connections to your motor might just sort your problem.

RAB

[PropPeteParticipant @proppete]

Thanks RAB

I eventually measured the currents on each phase and was rather taken aback by how different they were. Benn scratching my head ever since.

I hadn't considered the low voltage relay, and I guess there must be one because the table motor switches off a few seconds after I switch off the main motor. Reminder to myself – stick my head in the casing and sketch out the circuit!

Pete

[not done it yetParticipant @notdoneityet]

Might it be the capacitance values in your converter causing the eneven currents?

I'm no expert on anything but that seems, to me, to be a likely area for investigation.

[john fletcher 1Participant @johnfletcher1]

I also think its the capacitor values. Has all been OK up to now ? Can you check the resistance of the motor windings using an Ohmmeter and it insulation resistance using a "Megger " to illuminate the motor .I have wired three ammeters into a converter circuit and like you, was surprised by the differences in line currents and voltages.I then wired a large rotary switch in circuit so that I could adjusted the capacitors, with the motor running, so that the voltages and currents in each line was about the same. I also found that when the motor sounded/hum normal the capacitance was about right. But, all changed when load was applied. I found the values are only correct for one setting, near enough generally. I think modern converters will have some automatic means of adjusting capacitor values.I've never got round to fitting a pilot motor which idles way behind the lathe cabinet equalising the voltages, but apparently they are a good idea. Think of a triangle with each side of the same length, balanced 60 degrees, then another with un equal sides.I'm pleased Inverters came along.John

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