Running 380V 3-phase motor on 230V 1-phase

[jimalmParticipant @jimalm]

Hello all

I have recently bought a Leinen MLZ4S. It was probably ordered by the original owner in 1967, but the inspection certificates are dated in early 1969. My problem is that I only have 230V single-phase power in my workshop. The motor is by Bauknecht. It has 3 speeds and I saw in running on 400V 3-phase mains in Holland when I bought it. I also ran it on the same power in Germany, where I crated it up for shipping to me here in France. As you will see below, it is important to have no doubt about the fact that it really does run on 400V. Oh … and without any smoke or fire!

Now that I have the lathe here, I have been able to get a good photo of the nameplate on the motor (see attatched). The first line of the nameplate specifies the 3-phase input. The next line says, “R55/8/6/4 7s3. Presumably that means (among other things?) the motor runs with 8, 6 or 4 poles. Then there’s a serial number. Then the Insulation Class, etc. Then the nameplate provides separate information for each speed. They are ALL rated 220V!! So how does it run on 400V?? Incidentally, there is only the original switch etc., and no transformer involved.

I have “chatted” extensively with ChatGPT, Google Assistant and Claude AI about this situation. They all demonstrated an ability, very convincingly, to come to different conclusions not only from one AI to another or from one chat to another, but often within a single chat. Of course one has to do one’s own thinking anyway, and especially when chatting with AI, but now I’m wondering if anyone in this group can help me out.

ChatGPT has provided the most logical explanation, which is that the practice in Germany for what gets specified on 3-phase multi-speed motor nameplates has changed since the 1960’s. Back then, they specified winding voltage; now, they specify mains voltage. I say, maybe, maybe not. I have just today seen a photo of the nameplate on another MLZ4S motor perhaps a bit older than mine, also made by Bauknecht, and it specifies 380V for all 3 speeds. Same motor, different nameplates? More likely, different motors, but then, how does my 220V motor run on 380 or 400V?

Any ideas? Or, does anyone have a motor with a nameplate similar to mine and, if so, does it run on 220 or 380V?

Regards

Jim

[timdotdParticipant @timdotd]

My electrical engineering is a little rusty these days, but I read that plate as specifying the voltage for the each one of the individual phases – ie three phases at 220V connected in a star configuration, which means the 3-phase connection is 400V in total.

That said, I’ve never seen a rating plate like that before, so I may be no more reliable than AI..!

[ETA: this might be a Dahlander motor, which varies the speed by switching the internal configuration of the coil connections?]

[noel shelleyParticipant @noelshelley55608]

Interesting ! 220v star at 720rpm but delta 220v for 960rpm and 1360rpm Could well be a Dahlander motor. The data plate is giving basic info but is not a wiring diagram. I have to admit I’ve never seen one like this.  Good luck Noel.

[noel shelley]

On noel shelley Said:

220v star at 720rpm but delta 220v for 960rpm and 1360rpm

Please look again at the picture. It is delta at 720, star at 960 and double star (denoted by the II after the star symbol) at 1360.

What is the body part that is often confused with the elbow?

[John HaineParticipant @johnhaine32865]

Whatever it is, I would be inclined to use the connection for highest speed, 1360, disconnect all the switchery which would be irrelevant, and connect in delta to a VFD.  One reason for getting rid of the switchery is that if you forget and change a switch with a VFD you may well blow it up.

[noel shelleyParticipant @noelshelley55608]

Yes ! Got it back to front, it’s delta and  star 1 and star 11. My fault. Noel.

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