3 Phase Motors Speed Control

[Jamie3032]

Hi, Does anybody know of any alternative to governing the speed of a 3 phase motor than a frequency inverter? Thanks in advance, Jamie

 

[Jamie3032]

Yes it can easily be controlled via a potentiometer and since the motor you want to speed control seems pretty small, it would not cost more than a couple of hundred pounds to source/install

Thanks for all the advice, do you have any recommendations for a frequency inverter to use for this application @ 1.1KW

 

[westmac]

It depends on the reputation/support you want from the manufacturer. We use both ABB and Danfoss inverters depending on the customer.

 

[Jamie3032]

Yes, I have had some involvement with both ABB and mitsubishi AC Inverters, as this job is on a tight budget I was hoping that somebody may have a cost effective solution with regards to a cheap no frills inverter, thanks again

 

[Knobhead]

The motor is already in place D.O.L. , the budget is the main issue here, I wouldnt think that there will be any need for feedback or any kind of ramping up/down of speeds, just a means of governing the speed of the bandsaw blade for cutting different materials

Hold it right there!

Have you spoken to the manufacturers about this. You're entering a legal nightmare.

 

[Marvo]

You could see if one of these would be suitable. I'm not sure if they're any cheaper than a low-end inverter drive though.

 

[clematis432]

Something to consider Jamie, is that the speed of the motor must not be able to be increased by any operator above the rated speed of it.
It,s important that you are competent in the setting of a VSD

 

[westmac]

In this particular instance you have a good point but its shocking the amount of motors that are run approaching 2x their nominal speed these days.

 

[Jamie3032]

Hold it right there!

Have you spoken to the manufacturers about this. You're entering a legal nightmare.

Could you explain this further please Tony, im not sure what you mean by a legal nightmare?

The inverter is to be programmed to run between its manufacturers operating speeds of 710RPM (Low Speed) and 1420RPM (High Speed) (it is 2 speed motor c/w 6 windings) the idea being to govern the speed between these 2 parameters only using the 6 windings of the Motor (High Speed) Cheers

 

[Marvo]

I think Tony's concern is that if you alter the function or operation of a piece of machinery you may find yourself liable if there's an accident or failure and you weren't qualified to make the design changes.

It's a valid point.

 

[Knobhead]

Cheers Marvo.

Jamie, you really do need to speak to the manufacturers and also you're complience with the new machine tools ledgislation.

I was busy working on something so didn't get back.

 

[Jamie3032]

Cheers Marvo.

Jamie, you really do need to speak to the manufacturers and also you're complience with the new machine tools ledgislation.

I was busy working on something so didn't get back.

Thanks Tony, I will get in touch with them (that is if they are still in business, the machine itself is quite old)

 

[Darkwood]

Could you explain this further please Tony, im not sure what you mean by a legal nightmare?

The inverter is to be programmed to run between its manufacturers operating speeds of 710RPM (Low Speed) and 1420RPM (High Speed) (it is 2 speed motor c/w 6 windings) the idea being to govern the speed between these 2 parameters only using the 6 windings of the Motor (High Speed) Cheers

Im assuming you have 2 distinct speed settings already regarding it been a 2 speed motor, be careful here the winding resistances for each speed will be different and you cant simply attach a VSD to do this variable speed range, the torque of both speeds as is will be suited to the job hand and if you wire as in slow config and overspeed you could get torque collapse and vice versa by connecting at fast speed and under-speeding you could end up with lack of torque if drive isnt set up carefully.
Their are drives which can run multiple motors or if you choose 2 speed motors where you set up different drive parameters according to the motor slow/fast speed selection but in asking the general question in the first place i would consider it beyond your experience.
Lastly i must agree with Tony if you alter or add to a existing designed machine then you hold responsibilty for the safety of the machine and that it complies with all relevent reg's and you void the manufacturers of the cover or design.

 

[Jamie3032]

Yes there are 2 distinct speed settings as is usually found on a 2 speed motor and yes there is going to be different winding resistances as is the norm with a 2 speed 6 winding motor. In actual fact my first question was whether anybody had any experience with alternatives to frequency inverters for governing the speeds of a 3 phase motor and not how to set one up but thank you for the groundless assumption. Also as stated the machine itself is quite old, there is therefore no manufacturers warranty applicable, I believe that this is an issue that can be discussed with the customer, cheers

 

[Darkwood]

Sorry Jamie wasn't trying to undermine your intellect and experience it probably came across wrong but as re' your OP then i see no-one has mentioned variable speed gears although this is a late suggestion and not a cheap route either so probably out of the question or if the speed change is occasional then a multi-head pulley if belt driven which is the cheapest under existing set up, and as goes other options i would consider there to be limited as VSD give alot for its buck with overload settings etc as i now assume you already know.

 

[Knobhead]

If the machine is old and you make any alteration, then I'm sorry but ALL the control and safety systems must be to the 2008 (I think) woodworking machinery standards (legislation). Plus a whole load of other regulation, all of which are legislation and therefore mandatory.

PS Chuck the 17th away it doesn't apply.