forum.cncdrive.com

I would like to enable UCCNC control of my dust collector using M7
From the AXBB-E manual I can see this should be a relatively simple matter of adding relays connected to the appropriate port 2 digital outputs. However I am no electrical engineer and there seem to be a number of details that need to be got right. So I am posting my conclusions here so you can correct any mistakes before it acts as a guide to others.

Controlling a 1HP (750w) Dust extractor
Clearly I need to fit a relay to convert the 24v AXBB-E digital output to 220-240 AC (UK mains). However the extractor has an induction motor and is therefore an inductive load, which is bad for relays as the start up current can be 5-10times normal. With bigger inductive loads (I have a 3kw dust extractor in the main workshop) you need a proper DOL contactor to switch the load, but for a 750w motor at 240v, normal current is only 3A and so start up currents are 15-30A.
I have seen advice that recommends fitting additional components to further protect the relay from the start up current. This can be a diode or capacitor or capacitor-resistor circuit. But any novice who has ever been told by an electronics engineer to 'just fit a diode' has normally failed when faced by a choice of hundreds to chose from before they even starting to worrying about which way around it should go! However there do seem to be 'snubbers' available specifically for this purpose and you just have to get the correct voltage (I believe).

Selecting components
So I think I need a 24v 240v 16-30A relay. Relay seem to range from a few £ to around £100.
(https://www.ebay.co.uk/itm/125658993541?) These chinese made pcbs are very cheap (<£10) and meet the spec but my control cabinet has DIN rails and I would like to keep things tidy and professional (and more reliable?) (24V DC Relay Module 240VAC 30A)
(https://uk.rs-online.com/web/p/contactors/1881602) These seem to be the proper industrial solution but are £50 (Finder 22 Series Contactor, 24 V ac/dc Coil, 2 Pole, 25 A)

so (https://uk.rs-online.com/web/p/electrom ... ys/7943721?) these seem to be the happy medium at just over £10 (Phoenix Contact DIN Rail Mount Interface Relay)

Now I am not sure of I need a snubber/ Surge Suppressor like (https://uk.rs-online.com/web/p/surge-su ... ts/9055771) this. The data sheet for eth Phoenix seems to mention something about suppression already

Is this the right relay and approach, or have I missed something still?

Hopefully this is useful to you,

I'm switching a 3hp dust collector with a solid state relay, I tried a cheap ebay 25 amp relay which burned out quite quickly. I read up on all you're talking about and just decided to try a much beefier relay, I think I got a ~60a with a heat sink from ebay or amazon for $40 or so. Has been operating for a long time no problem. You may consider just sizing up.

Thanks, real world experience is always valuable.

So your 3hp (2.2kw) motorr on 220v would from my reading have been pulling around 50amp on start,.so not surprising your first solution gave up! So certainly recognize the sense in spending some money to be sure the second time. However was hoping someone who really understands could save me some money.

Well to control my Spindle/Router motor I have a small 24 volt plug in relay mounted inside my control box. It has both contacts in parallel to handle the 6 amp load but its only switched on and off once or twice in a project. That is the type of relay I would use to switch an external heavy duty relay lLike you need, I would never use the standard output of a UC whatever to switch that large relay. Yes I am a electrician and have been since 1962, not a Residential Romex runner but industrial.

Thanks for the reply, but to my ear there is not enough detail to make sense of your response. Can you fill in the blanks

wmgeorge wrote:Well to control my Spindle/Router motor I have a small 24 volt plug in relay.

What spec? 24vdc coil sure, 240v 6a load? Example please if possible

wmgeorge wrote:but its only switched on and off once or twice in a project.

Same for a dust extractor so same.

wmgeorge wrote:use to switch an external heavy duty relay lLike you need

Ok so you recommend a two stage approach. Familiar with that for bigger motors where a contactor is required. However in UK at least with 220-240v supply there are not contactors available for less than 1.5hp so do I get the smallest I can find or use a second relay, this time 240vac coil, 240v 20a load? and does that need a suppressor/snubber?

wmgeorge wrote:Yes I am a electrician and have been since 1962, not a Residential Romex runner but industrial.

Respect, you have forgotten far more than I have ever known on this topic (I trained in mechanical engineering, work in software). I appreciate you sharing your expertise, but again for the slow kid please

Small plug in relay 10 amps per pole. Yes 24 vdc coil. Your switching the coil voltage of the larger relay I would suggest another transformer on your mains 240 vac to 24 vac a HVAC contactor as we use here would switch 30 - 40 amps no issues. Stubber Nope nothing else needed.

https://www.amazon.com/Industrial-Gener ... r=8-4&th=1


https://www.amazon.com/Packard-C230A-Po ... 08&sr=8-11