3 phase motor rating.

[Rampage]

Firstly, I'm not doing this, I'm getting someone else to. I'm just interested.

I have a machine arriving which has a largish motor, the plate on it is the one below.
The horsepower is 0.6 but the current stated is 2.4A. This to me doesn't work out, is this the in-rush current?
The motor is approximately 14" diameter and 16" long (complete guess). I'm surprised it's only 0.6hp?

For anyone interested it's from an Aciera F3.

 

[Marvo]

Motor inrush currents are generally calculated using a rule of thumb. The inrush current is over so quickly it shouldn't trip the MCB and especially for smaller motors it doesn't really figure in the circuit design. The current stated on the plate will always be the maximum running current the motor is capable of handling and all the control components would be specified around this figure, not the inrush current. It's worth noting that your motor is wired in star and is rated at 875 RPM so it's possibly 6-pole.

 

[peterb]

...... dont forget about power factor. Esp if its a multipole motor. It may physically that big so it has some more inertia given its for a machine tool.

 

[Darkwood]

I take it rampage you don't do a lot with motors as this is a baby .... when you said largish motor I was expecting 30Kw + ...... did make me chuckle when I saw your pic lol
Horsepower is the work the motor can do and with most induction motors can be related as such to running current but motors are designed and built in many forms and efficiencies so not always as you expect. Sometimes efficiency is sacrificed for durability but I wouldn't concern yourself you got the current rating and that's all you need.
Id expect a standard induction motor of 0.6hp(not a standard rating) at 400v to have a running current of 1.44amps but as I said its not always reliable to use HP to calculate current.

Tony's the man who might be able to expand on this with ref' to your particular motor... im sure he'll drop a comment in.

 

[Knobhead]

0.6HP @ 400V .8PF 80% efficiency comes to 0.96A by my reckoning. 110V gives figures near what you give.

 

[Rampage]

I realised as soon as I posted it that it would be a small motor to some people on here!

I have been given a 4kW Rotary Phase Converter to run this mill and a medium(!) size lathe. I want to change to a digital phase converter as the rotary is so noisy.
So should I use the current rating on the motor or the horsepower on the motor!
Its probably obvious I don't know anything about motors!

 

[clematis432]

I realised as soon as I posted it that it would be a small motor to some people on here!

I have been given a 4kW Rotary Phase Converter to run this mill and a medium(!) size lathe. I want to change to a digital phase converter as the rotary is so noisy.
So should I use the current rating on the motor or the horsepower on the motor!
Its probably obvious I don't know anything about motors!

I would use the current on the motor, that,s what you use when setting motor protection or overloads.

 

[ipf]

I realised as soon as I posted it that it would be a small motor to some people on here!

I have been given a 4kW Rotary Phase Converter to run this mill and a medium(!) size lathe. I want to change to a digital phase converter as the rotary is so noisy.


So should I use the current rating on the motor or the horsepower on the motor!
Its probably obvious I don't know anything about motors!

Did they not go through all this during your training. lol.

 

[t-s]

you would normally use an inverter, the sizes will be in kw or hp just google conversion table if you need it.

 

[Rampage]

Did they not go through all this during your training. lol.

lol, I think this was a 1 day add-on that I didn't take!

 

[Knobhead]

Don’t worry about it.
An inverter would be the best bet, but if you’re stuck with the converter then use it. I hope you’re not paying the leccy bill. A converter is hellishly inefficient.
As has been said the O/L’s must be set to the rating plate.
At the end of the day you can only go by what the manufacturers say.

 

[Rampage]

Don’t worry about it.
An inverter would be the best bet, but if you’re stuck with the converter then use it. I hope you’re not paying the leccy bill. A converter is hellishly inefficient.
As has been said the O/L’s must be set to the rating plate.
At the end of the day you can only go by what the manufacturers say.

Is it inefficient because the motor is always running?
I'm going to try and get a digital one, these are presumably more efficient?

Thanks.

 

[44ALLAN]

My old engineer used to say..............flc + 10% for o/load setting.
Worked fine until someone put hydraulic oil in the o/load dash pots

Just curious but what do other folk set their motor overloads at. ?
Does anyone actually think about it or just accept what their set at !

 

[Knobhead]

You will have mechanical losses as well as electrical. And something called windage (nothing to do with flatulence). It’s the power consumed by the motor/alternator cooling fan/s.
Motor generator sets are by nature inefficient. Much as I like old technology they’ve had their day.

 

[Silly Sausage]

Much as I like old technology they’ve had their day.

A bit like the wife! :-(