Motor plate details

Hello all.

I am considering purchasing a machine that has the following motor plate.

My electrical knowledge is very limited hence the question.

My interpretation of the motor plate is that it shows details for both 3 phase and 1 phase operation and how it should be ‘wired up’ to achieve that. I assume that is what the 3 legged star and delta signs convey. The seller tells me it is 3 phase.

Am I correct in thinking that I can convert this motor to 1 phase operation by just rewireing the motor to cable connection appropriately. All my domestic electrics are 1phase.

Many thanks in advance for any responses.

Alan.

Hello Alan

The motor is 3 phase as indicated where it says 3~

It can be run in delta at 220 - 240 volts but still 3 phase. Single phase to 3 phase inverters are my preferred method for this situation.

Hope this helps

Using a vfd you would connect in delta.

It looks like you are at the stage of “exploring the foot-hills” Craig, so I suggest you have a look at this:

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Edited By Michael Gilligan on 06/11/2022 08:21:38

And rather than referring to it as 'a machine', please give details of make and model number. We can then (hopefully) find a manual or pictures of the machine and advise the minimum necessary to make it work on single phase.

Edited By DC31k on 06/11/2022 08:21:23

It is a 3 phase dual voltage 3/4 Hp 2pole motor ! NOT SINGLE PHASE ! It spins at 2820 rpm. Noel.

It's a three-phase motor that can't simply be wired to run on single-phase mains. But don't panic - there's a choice of magic boxes available to do the conversion, each with pros and cons.

Static Converters use capacitors to fake 3-phase, not accurately, but good enough for most purposes. They're not suitable for machines taking a heavy start-up current like a compressor, but probably OK for a mill, drill or lathe.

Rotary converters use an idler motor to balance the phases, and are a good solution for most machines. Their disadvantages are size (big box), noise, cost (due to the extra motor), and low efficiency. (Efficiency is unlikely to matter unless the machine is run a lot. No-one cares about an extra 25% on a small electricity bill, but 25% on a big one will make your eyes water!)

Electronic 'Variable Frequency Drives' have many advantages such as moderate cost, high efficiency, speed-control, soft-start, and other bells and whistles. They're the preferred choice today unless disqualified by one of their disadvantages! They're components that need to be mounted in a simple box. VFDs are sophisticated tuneable devices with hundreds of parameters; it pays I think to buy new and simple because they come with sensible defaults, in contrast to the older industrial models with inch thick manuals intended for trained installers. Most VFDs can only power one motor; they can't be shared, and their output mustn't be switched. Fitting one to a simple machine is usually straight forward but a complicated lathe with a 3-phase main motor and a 3-phase suds pump with contactor switching phases means a fair bit of rewiring. Not impossible, but not plug and play.

It might be worth getting a quote to have 3-phase installed. Unfortunately prices vary wildly and are often shockingly high. Cost seems to depend on how much physical work is needed to make the connection. Are they simply running a wire from a nearby pole, or will they have to dig a trench along the street, with temporary traffic lights and then mending the tarmac? Complications like crossing a neighbours property push the price up too.

As can be seen much depends on the machine, perhaps machines. It's why DC31k asks for more details.

Dave

Not sure what you mean by exploring the foothills Michael but I'm an industrial electrician by trade and whilst I don't claim to know everything, far from it in fact, I do work with drives and 3 phase on a day to day basis

Hello All.

Many thanks to all who responded to my query.

I now understand what this plate is telling me and have a bit more knowledge about electric motors and their differences and workings, so my query is answered. Many thanks again.

Alan