VFD & Inverter questions

[Ex contributorParticipant @mgnbuk]

John.

You can access a .pdf copy of the SEM MT range technical manual here.

That motor requires 20A to generate it's rated torque, so quite a meaty drive on a single phase supply + it is a constant torque motor, where there is no constant power range – much like the DC motors fitted to Chinese mini-lathes but much, much gruntier & more robust.

A 3 phase 1 KW 4 pole motor generates approx 6.6 Nm & a 1.5 Kw motor approx 9.9 Nm at rated speed, so such a replacement would be either a bit less or a bit more than you have at the moment. Runnning a 50 Hz 4 pole motor at around 138Hz would get you the same 4000 rpm top speed. The DC motor is capable of sitting stalled all day generating it's rated 8.5Nm with a suitable drive, which a 3 phase motor on an inverter would be decidedly unhappy doing – if you do a lot of lower speed running, fitting a separate blower to cool the motor in place of the rotor fan would help here . The reality is that the Parker SSD drive will probably be a fairly basic device (though I note that there are wires to the tachogenerator for speed feedback) & probably will have a miniumum speed setting above stalled.

I'm not up on how much a 1 / 1.5Kw 3 phase motor & inverter would cost at the moment, though probably not much more than your quoted DC drive replacement. As I am aware that spares for the SEM MT range are OOP & increasingly difficult to obtain now, and that may help sway your decision – and when parts were readily available they were pricey. The last tachogenerator armature I bought (15 years or more ago) was over £350 +Vat IIRC (they can go open circuit on one or more windings – only solution when that happens is to fit a replacement).

HTH

Nigel B.

[ManofkentParticipant @manofkent]

Nigel

Many thanks for all this information which is very helpful.

It reminded me that my Harrison L5 lathe (now long gone) was powered by a 1.1kw motor and was plenty powerful enough – so a 1.5 kw will give me power to spare.

Now I just have to work out how to fit the motor in the lathe…

Thanks once again

John

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