Anyone got any experience with contactors ?

[robgraham]

I bought a second hand woodworking lathe some months ago which came with an ABB contactor switch (type A12-30-10). I didn't consider it necessary to have a contactor and an 2kw electronic controller for the lathe, so re-directed the starter for driving my circular saw. This had a contactor in a home made box so there was an attraction in having a pukka device.

I'd checked the new contactor's operation sometime back and was a bit suspicious that it was a bit sluggish in pulling in. This is now confirmed when connected to the 2kw motor for the saw. Sometimes it will operate OK and the saw starts up fine, otherwise there is a lot of chattering, sparking, chuntering from the saw motor and nothing happens.

I jury rigged the original contactor to see if it is something to do with the change of site and it operates fine - pulls in perfectly each time.

This is a 240v single phase system.

Anyone any ideas before I go the the bother of fitting the old, and operating, contactor into the 'new' starter box, and dumping the 'new' one.

Thanks Rob

[BigWallop]

Have you checked that the coil voltage is actually 240Vac / dc and not 24Vac / dc?

Is this contactor dual 1ph and 3ph operable? (3pole - 4pole construction)

Did you mark and copy the exact wiring plan / configuration before you transfered the contactor?

So many questions, so little knowledge of this particular peice of equipment. :-)

[Andrew Mawson]

construction)

If the coil was 24v it would be toast now - possibly though it is

415v?????

AWEM

[Rob G]

It looks like my mistake !! Everything pointed to this being a 240v set up, but I've now noticed a '440v' which I hadn't spotted before and didn't in all truth look for ! Doubly confirmed by checking the coil resistances - 1770R and 800R.

I bought the whole lathe and controller package at quite a good price from a guy who was a metal working enthusiast who had gone into wood turning. He didn't actually say so but I think he gave up in disgust as there were so many things wrong with the electrical/electronics that I wonder if he ever actually got the lathe working properly - and this contactor is another anomaly !

My apologies for having bothered you. A case of jumping in with 'phone a friend' before thinking it out yourself !

Now to find a solution !

Rob

[PeterC]

Sure the lathe isn't 3 phase? :-)

[BigWallop]

The only thing I can think of is this

But it's very expensive. :-(

[Rob G]

Yes it is - 240v 3ph from a 1 to 3ph inverter. As I said I really don't understand how the seller ever got this system working - the starter switch fed the inverter with the emergency switch killing the starter: crude when the inverter has all these facilities in it.

Thoroughly recommend these inverters - once you've gone up the required learning curve they really are great for running a 3 ph motor at variable speed.

Rob

[Harry Bloomfield]

The reason it has a contactor, may be for safety reasons - as in a no volt release, so it doesn't start up when power is restored.

Check the coil voltage is the correct voltage and ac or dc. Check it actually on the mains supply rather than fed from an inverter. I also once came across a sluggish contactor which was sluggish because it was choked up with oily wood shavings.

[Rob G]

tomorrow.

I would like to think that the electronics is programmed to not restart the motor after a power failure. On the other hand it may well be a user programmable option - fan drives might for instance be better if they restarted automatically whereas machines like lathes would not.

Rob

[mick]

One of the common arrangements in 3-phase "boxed" contactors, with buttons on them, is to use a coil with a voltage around 400v, operated across the incoming phases. Trying to use one of those on 230v would give symptoms similar to those that you are getting. There is insufficient magnetism to completely close the contacts and they burn up!

The A12-30-10 has 3 main poles and one normally open auxiliary. IIRC the main poles are 1-2 3-4 5-6, the coil is A1-A2 and the auxiliary is 13-14 (although I may be wrong on some of those - the catalogue is at work). They are sold in a range of coil voltages, and the voltage/frequency is marked on the coil, visible through a window on one side of the contactor IIRC. The A12 bit is the contactor rating. In this case it's 11A AC3 (motors inching & plugging). If you are tracing the wiring note that there are A2 terminals at both top and bottom (internally linked) to make wiring easier.

You have to have a means of disconnection (i.e. a contactor) with an electronic controller because they don't isolate the motor so can't be used with an emergency stop system safely. Some of the controllers actually include their own contactor inside the housing.

[PCPaul]

On a related note I've just got into electric radio control planes again after a long break - they now use 3ph AC brushless motors instead of the old brushed DC jobs. The on-topic bit is that they now have tiny electronic speed controllers which don't have the problems DC controllers had - since they are only effectively PWM switching three sets of DC to get the 'phases' the controller itself needs no heatsinking and uses very little power.

If anyone needs a small motor with very high power/weight (150W from a

1.5" diameter 1" end to end motor, up to 1KW or so if you want) with a simple speed controller then they are well worth a look.

The electronic speed controller (ESC) takes RC servo control signals, but that's basically a variable length pulse train - you can get 'servo testers' which would just give you a knob to twist. And any number of microcontroller boards will drive them directly...

The ESC is programmable as well - several levels of soft starting, motor braking, low battery protection etc etc. And no end of gearboxes, toothed belt drive pulleys etc. available if you need them.

I'll shut up now. ;-)