Current sensing switch

[Munroast]

Is there anything available that will turn an appliance on when another appliance starts?

I would like to get a vacuum cleaner to start up when a bench saw is started. I'm sure it could be wired from the switch in the table saw but I would rather have something easier such as a device hat fits round the cable to the power saw and when that senses current it will switch on the circuit to the vacuum

 

[SFK]

There are one or two.
Search for "Vac auto switch"
This is a good example:
https://www.toolbritannia.co.uk/ele...MI5oytjcq07QIVGO7tCh0V1ATOEAQYAyABEgKuM_D_BwE
and
https://www.amazon.co.uk/Vacuum-Aut...ocphy=1006457&hvtargid=pla-699641852331&psc=1

Fully recommend as these do make a massive improvement to workspace air quality.


I did not buy this as I wanted/needed it to run-on for a programmed amount of time after tool switched off. And I needed an override button to switch vac off when tool on (Vac not always needed), or have vac running when tool off (to clean bench afterwards).

The above linked unit DOES have this. But at the time they did not so had to make my own using an Arduino and relays.
But this is not as simple as using the examples and programs online, as most seemed to be made by programmers who had no knowledge of
- inductive load of vac motors welding relays closed
- Safety of not having vacs turning on, or staying and overheating (see Cutty Shark fire)
- Operating Relays in a manner that minimises arching.
- Safety of separating 5V lines and signal lines from 240V lines

So do recommend and suggest the above linked unit.
SFK

 

[crystal ball]

One of these will do it, will have to be mounted in an enclosure

https://uk.rs-online.com/web/p/monitoring-relays/1026134/

 

[Tigercubrider]

You might find it cheaper just to buy a vacuum with power take off?

 

[scbk]

What about an eon powerdown socket? Don't know what the max wattage is. And there is a 5sec delay on startup.

https://www.ebay.co.uk/itm/4-x-Eon-...idWebWithBBEV2&_trksid=p2047675.c100005.m1851

 

[SFK]

Scbk,
I have tried those.
The 5sec delay makes them useless with a mitre or chop saw. Already finished cutting before it starts the vac.
Sfk

 

[ericmark]

In factories we had extractors that had to be running before the plant would work, dust can explode, so if the dust extraction plant failed, the machines would auto stop.

So the mitre or chop saw should be supplied from the relay which is switched as the vac starts, so unless vac running then the mitre or chop saw can't be used. Your putting the cart before the horse.

 

[SFK]

extractors that had to be running before the plant would work, dust can explode

Agreed and some systems spec ESD safe tubes to be used.

mitre or chop saw should be supplied from the relay which is switched as the vac starts

But on most home workshop systems (which is what I thought Munroist was looking for) with a zero startup time for the Vac to start, the vac is already running before the saw touches the wood.

 

[SUNRAY]

I needed to create a unit to prevent 2 appliances running together. In this case it was 2 pumps which over loaded the drain if both ran.

What I had to hand on site were 24Vac relays. I stripped the coil wire and wound a new coil with 1mm enamelled copper wire until there was enough to operate the relay when wired in series with the appliance. For a Henry I'd suggest using the relay to operate a contactor rather than rely on a relay contact.

Commercially I'd expect to fit an air flow switch in the dust extractor in the saws contactor control circuit.

 

[JohnW2]

... For a Henry I'd suggest using the relay to operate a contactor rather than rely on a relay contact.

That distancing has always rather amused me, and I suspect that it may confuse some people. What is a 'contactor' if not a 'heavy duty' relay - and, perhaps more uncertain/confusing, what about a 'heavy duty relay' (and there are certainly many described in those sort of terms) results in it not being called a 'contactor'?

Kind Regards, John

 

[flameport]

Although their basic function is the same, the standards they are made to are not. BSEN60255 series for relays, BSEN60947 series for contactors.

 

[JohnW2]

Although their basic function is the same, the standards they are made to are not. BSEN60255 series for relays, BSEN60947 series for contactors.

That doesn't surprise me, but I would still be interested to know what the distinction is - or, to put it a different way, how (in general terms) the Standards differ in their requirements.

For example, if an up-market 'heavy duty' relay would not satisfy the Standard applicable to contactors, in what sort of ways might it fail to satisfy them?

Kind Regards, John

 

[SUNRAY]

That doesn't surprise me, but I would still be interested to know what the distinction is - or, to put it a different way, how (in general terms) the Standards differ in their requirements.

For example, if an up-market 'heavy duty' relay would not satisfy the Standard applicable to contactors, in what sort of ways might it fail to satisfy them?

Kind Regards, John

They fail.
I have replace lots of failed relays with contactors.
16A rated relays will not switch 2KW heaters for very long and very reactive devices like transformers/motors burn the contacts even quicker.

 

[JohnW2]

They fail. I have replace lots of failed relays with contactors. 16A rated relays will not switch 2KW heaters for very long and very reactive devices like transformers/motors burn the contacts even quicker.

I'm still not really clear about the distinction - which is why I was asking how the requirements of the Standards differ.

I can't see that it can just be a matter of their switching capabilities. I have in my time seen things which have been 'rated' to switch very high (reactive load) currents, yet have still been described as 'relays'.

Kind Regards, John

 

[SUNRAY]

I imagine it is much to do with switching speed and arc suppression but this is a guess as the unit I created for the pumps was 4 pole 5A rated contacts wired in parallel and the pumps were something sizable ~3KW ish. It ran for months without problem, however the contacts didn't switch the load but if they did I'm convinced they would have burnt out very quickly.