5 replies to this topic

[Hal Adams]

Hello!
I thought I understood domestic electrics until I came to specifying a soft start switch for a motor! So reckon it is time to ask an expert..

I have a small woodworking workshop in my garage and treated myself to a large dust extractor which I would like to fit a soft start facility.

The plate on the induction motor has the following:

HP (box is blank, but alongside in another box is 2.25KW)
Hz =50
Volts = 240
Amps = 18
Phase = 1
Class = E

This motor is by far the largest of any on my woodworking machines, so I would like the general electricity supply to the house not to suffer each time I switch this thing on. I have laid a dedicated feed to the dust extractor using 6mmsq cable.

Will someone point me in the direction of a suitable soft starter please? Noting that space is a consideration, and to a certain extent, funds. The 18A on the plate - surely (I hope) this is not continuous running is it??

Thanks in advance
Hal

[marke]

Hello Hal

I expect that the 18 Amps is the rated running current of the motor at full load.

What type (design) of motor is it? i.e. capacitor start, capacitor start capacitor run, or induction start.

If the motor is an induction start, (no start capacitor), the results with a soft starter will be somewhat limited.

Best regards,

[Hal Adams]

Thanks Mark - it is induction start. So I have no option but let it hard start?
It is not the end of the world, after all 18A is not exactly a high pull this day and age, but it would be nice to have a nice quiet build up.
Thanks for the information anyway! I have learnt something new.

regards
Hal

[marke]

Hello Hal

If you switch this motor DOL. I would expect that the start current will be in the order of 6 - 8 x 18 Amps i.e. 104 - 144 amps.

If a soft starter would work on this motor, it could drop the start current down to about half of this figure.
I have always found that soft starters work west on capacitor start motors where you can separate the start winding and the run winding, and apply the soft starter to the run winding only.

I have not had good success with induction start motors, some do seem to work OK.

Best regards,

[Hal Adams]

Thanks Mark - it is all a bit of a damp squib really - just fired it up, and the lights hardly flickered!
Still, it was worth asking.

thanks and regards
Hal

[marke]

Hi Hal

If you can get away with it with out a soft starter, then that is great news!!

Best regards,