Automation. Sometimes simple things just miss us. Looking for advice please.

Thread Starter


Joined Oct 7, 2016
Hi from New Zealand,

I am slightly into electronics having built 4 CNC machines which the last two are working wonderfully. I am on a new project now but seem to be stumped on what is the best and cheapest solution for what I want to do.

Having worked in the ROV industry and having also very limited experience in electronics I have so much going on with ideas I am completely missing the point.

Short story:

1. I have 10 woodworking machines in my workshop running on 230v.
2. I want to install a current sensor on each machine which, when turned on will activate a relay to supply 24vdc to a pneumatic solenoid which will then open a gate via a pneumatic miniature cylinder for my extraction system particular to that machine, and also activate a common relay to start the 230v 3hp dust extractor.
3. When the machine is turned off, the pneumatic ram will spring shut with loss of 24vdc to the solenoid and the extractor will shutdown.

I seem to be having trouble working out how to convert the small voltage (milli volts) from a non evasive current sensor to enough voltage to operate a relay. It seems so simple yet I am unsure where to start.

Everything else, the physical gates, pneumatic rams, solenoids, air supply is no problem. Just the sensor to the relay. I was considering a circuit using a transistor with an arduino board but feel that’s over the top.

What do you think? Would you mind giving me an idea to work on? Warm regards Boyd
I had these[full_desc]=Y&s[sku]=Y&s[match]=all&s[cid]=0 in my bag of tricks for you.

The deal is some require power, some don't and you might have to hunt for something. They all have a maximum and you have to just use one of the wires. It can be wrapped around the sensor multiple times to increase sensitivity (1x, 2x etc) . You can't exceed the maximum current.

You don't need a current sensor.

This is something different.

I/O modules is yet another way.

In SOME cases you can fit this stuff in the breaker box if all the ducks are in a row so to speak. You typically have one wire you can run the wire through the sensor. You just have to make sure everything else is up to code with mixed low and high voltage wiring. let's just say you have a sub-panel in the shop. You can put everything in a NEMA enclosure and pass it through to the power source.

DIN rail terminals and devices is the erector set of the control engineer. You add wire raceways etc.

There could be an odd device that won't fit into the scheme of things.

Your problem is a little more complex than you imagine. The machine has to open the gate too.

A single box measuring current is a good start. Now throw a 10 HP 3 phase gizmo and you have to use something else.

In the US, we have what's called class II wiring. It has to be power limited to 100 W and usually around 24 V or so, so no conduit is required, but you don't want a board to bang into it either. I had to buy a FAP power distribution panel for what I needed to do. I could logically control one of the 8 or 16 outputs.

Hint: This company: Let's just say, it saves a LOT of work. Only issue i had was operating some strobes because of surge current. They were from the same manufacturer, but a different design. The newer ones had less kick to them. So, you may have an interface to the gate valves. You might want to use air cylinders too. ASCO has some nice manifoldable valves. I just had to clean them first to operate on Argon without an oiler. Air can be a lot easier. You can change the rate they close and open and the valves I used had a manual control on the valve too.

So, you have two things at this point, A way to activate a valve and a way to monitor if a machine is turned on. 24 VDC is the standard. I used AC maybe because I didn't know any better.

If your the only one operating the machines that's one thing. The downstream side could also get messy. e.g. a VFD on your vacuum.
You might need some interlocks of some sort.

let's add one more detail - the ability to use an RF switched hose. e.g. A hand power tool or a temporary tool or use it when one is broke. I don't know.

Let's hope you don't need to disable tools when too many are in use?

NOW what?

You can't be turning off the vacuum all of the time, so it needs to run longer than the last user. In fact it might run at different times depending on how far away it is. It may need a port that needs to be controlled open (not just on and off). It also might need outside air. Yep, I'm complicating stuff on purpose.

In simple terms, you want to turn the vac when you use a piece of equipment and open it;s corresponding hose. Not exactly!

When you turn that equipment off and it's the only one, you have to let it run for a while until person A gets to machine B. Only if he doesn't do that would you want to shut down. You may need velocity control (fan speed) and//or a controllable gate or even a port that goes no where but can be opened partially. A VSD (Variable speed drive cuts noise down and your electric bill).

Then you can get really fancy and every so often run with everything open and measure the static pressure or measure the current that the motor draws. Save this info and do it every day at some pre-determined time. You can definately determine filter change/clean times and look at the general performance.

You may even need a way to reverse the system?

Anyway food for thought.

it's all over the map and it's meant to be to give you ideas. the one thing you don't want is to keep restarting the dust collector when you move from machine A to B in 30 sec after turning off machine A.

You do want to know when the dust collector needs maintenence.

Air cylinders may be more useful. You can have air to open, air to close and spring to open, spring to close etc.

Synchonous motors work well. In a home system the controller can basically control static pressure by knowing current. and vary the speed of the VFD accordingly. Bypass dampers may not be required, because the motor is doing all of the work. Changing it's speed based on the load.

System restrictions like a bad filter can be found if all the dampers are open and it characterizes the system daily and looks for a substantial change in static pressure. Actually, that how my home system works. Every day at 1 pm, the furnace runs about a 5 minutes test where it assumes all dampers are open. if it were a zoned system, it would open all zones. You get a notice when to change the filter and when you do change it, you reset it back to 0% of capacity. The filter is changed about every 6 months and may take up to 45 minutes to do so.

Velocity sensors and dust don't get along. I know. They have to be cleaned. I'll tell you that ones with numbers makes life a LOT easier.
the air cleaner i use is this one:|3149|aprilaire 5000||S||114735734218&gclid=CNGHtqKGyM8CFUEmhgodzWEJXg The element comes compacted and then the electronic portion has to be cleaned which attracts the smaller stuff. The furnace tells you when it's dirty.

Let's add one more wrinkle and that is the air supply and exhaust. Had a lab running with 100% make up air

Thinking cap on. Don't throw any ideas out right away. So...
What would i like to have if I had all the money and time in the world?
What must I have
What do i need?
What would i like to have?
What do i need now.

What you will find is that there are things that could cost you so little money when done in the initial stage. let's just say it's running of wires.
Running one cable is almost the same as running 5. So, you add the "hooks" for a possible upgrade. Sizing an enclosure might be way big for the initial project, but adding one later will cost tons.

You may already have air. This might give you an opportunity to upgrade with auto-drain valves and condensation removal and get the leaks fixed.

it's probably best to centrally locate the sensors. Think like how a "small" non-automatic generator panel is sometimes added for critical loads. You take wires out of the main fuse box, run it to mini transfer breakers and then back in.

Here's another sensor. You see how stuff gets messy quickly.

This website tries, but doesn't even come close. Sensors in wireless out. Closed system. What else is new.
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Thread Starter


Joined Oct 7, 2016
Hi. Hey. Thanks so much for your time taken to write to me. I need to read it again to digest all.

Where I am at now!

I have bought 10 cheap 12vdc power supplies which I will install in each machine paraelle with the output of the on/off switch. US$1.70ea. These will output directly to a relay bank which controls the 12vdc to larger 80A SSRs to switch on/off the 2.2kw extractors. (the 40A ones were counterfeit and just latched on permanently)

The 12vdc for each machine also runs to a totally separate relay bank which controls a 24vdc pneumatic solenoid bank thus sending a pressure line to double, single operation, one way spring return cylinders which physically open. This is up and running and works! I attached a pic of my design which I cut out on my CNC router.

I bought some timing delay boards off aliexpress which worked exactly as I wanted them too! But, unfortunately, they were 12vdc boards. If I input 12vdc, the board would run the relay but one of the components of the board would overheat and start smoking. So I would down the voltage, but then the relay would not have enough voltage to close the gates?!?! Weird. Perhaps the board(s) is faulty. All four I bought did the same. Not sure what to do there. If this board worked, I would be done and dusted and happy.

I am wondering if I need to remove a jumper so the logic of the board can operate off 5vdc and it takes power from somewhere else to run the 12vdc relay? A shame because it took a while to suss out this board which actually operated in opposite to what I needed. It at first would delay BEFORE switching the relay on. But once I worked out and moved a jumper it smoked. It was several weeks ago now and I have forgotten what I did.

But all in all, I have sorted this project. Its only the time-off delay I am having trouble with.

All is good though. All 230vac to the extractors is well grounded and isolated and covered in a proper box.

Best Regards


Thread Starter


Joined Oct 7, 2016
Yes. Definitely 12vdc. Measured with my meter and they have an adjustment which I was able to wind down to just under 10. I was able to wind down the voltage so the relay wouldn't latch, and wind it back up until it did latch, but then the board smoked.

Actually I didn't measure the voltage whilst under load though.

I will research more.

Thread Starter


Joined Oct 7, 2016
Hey so I originally wired up this board and it did the opposite to my needs. .Apply vcc and the relay took whatever setting before it latched. Then it stooddown for the same time before relatching on vcc. So basically did the opposite to what I wanted.

Then I moved or removed (cant remember) a jumper.

The board then operated the way I wanted it too but one of the couplers started overheating. Then it fully smoked. I am wondering that the board has had the incorrect rated component installed for the sequence I need.

If I lower the voltage its ok but not enough to work the relay?

Hmmm? Thoughts?

Thread Starter


Joined Oct 7, 2016
Actually now I am looking at the unit, it was a NPN transistor that smoked. Its a J3Y.

Now I remember getting the board to work. Then after only a few seconds of the relay latching the component started smoking. So I looked where I bought it and saw on the site I bought it from it was a max continuous consumption 42ma.

I dropped the voltage on my supply to 10.6 or something, the board did everything correct but the voltage was too low to actuate the SRD-12VDC-SL-C. As soon as I turned up the voltage to the point when the board would operate and also operate the SRD-12VDC-SL-C, the J3Y would start to smoke.

I went to calculate the correct resistor to put inline hoping it would still be enough voltage to operate the SRD-12VDC-SL-C. Installed in between the power supply and board. Smoke.

This board:

Is perfect. But it smokes if I put enough voltage on it to operate the main relay.

Hey I am stumped. Is there anyone out there that might know what I can do here? So simple yet so hard!

I have everything sorted except for a simple time/off delay.

Thread Starter


Joined Oct 7, 2016
Hi. I bought these:

They are very cheap. And given I was going to straight hook them up to a SRD-12VDC-SL-C relay for a yes/no contact felt it would be the most robust and cost effective way of my system knowing if a machine had been switched on/off. These relays are simple and basic.

And they work ok.

Its just this board for the time delay off that has thrown me. I am thinking I should just spend a little more on a board. I have so many machines in this project that I dont want to be spending more than a few dollars on a board that will keep a 12dc relay closed for 30-40 seconds once the signal is removed.

Actually thats it in a nutshell. I need a board, that will close a 0-30VDC SSR on a 12vdc input, and keep the SSR running for 30-40 seconds after signal removed. So easy but so hard to do unless I am spending US$40 or so. I have found boards on Aliexpress that do work for a couple of dollars each but then fail. Thats the kind of thing I am looking for. Ones that dont fail ha ha
The supplies that i would have suggested could have been put into a J-box and your basically done. But your done anyway,

What you basically need is a Delay on Break timer. You likely only need one of these.

I guess, the way i would have done it would be basically what you did. Create a low voltage signal as you did.

A really simple way would be the "controller" have a relay for each machine. A more reliable system would have used optocouplers.

Then I would have probably went the DC input BUS IO system, here:

The carrier board + the cheap DC input modules.

Since the transistors only handle 50 mA, you would probably need a little bit of glue logic, but it would have got you, I think, to exactly where you are now.

I need to hunt for my list of possible candidates for a delay on break. One company is SSAC. Solid State Advanced Controls.

Thread Starter


Joined Oct 7, 2016
Cool. Yes I have put in a relay alongside the 12dc power supply for each machine as the two relay banks I am using are just looking for a contact, 4 relays per bank.

So each machine is sending out a make or break to the relay banks already.

I will check out solid state controls. Although its such a shame the little boards I had smoked on 12vdc.

Delay on break. Thats the term. Hey I even thought of the plain delay on break module for bathroom fans!

Thread Starter


Joined Oct 7, 2016
That looks cool. Although I have the benefit of using low voltage which is 10% of the cost. Worse case scenario is I use an arduino board which I can program to do anything I want?
Although I have the benefit of using low voltage which is 10% of the cost
At least you had access to the power. A small vacuum cleaner can be had with a built in current sensor which could be used for small hand tools.
For fun, you could even incorporate an RF remote for any odd devices.

But the general goal is to to close off unused ports and to keep the system running when your moving from machine to machine to avoid unnecessary starts, A single man shop has different requirements than a 5 man shop.

Re-thinking, a relay , a DPDT relay depending on the actuator at each machine or at each actuator, can provide an actuator signal and an ON signal.

All of these ON signals need to somehow activate the blower with a delay on break type of timer.

To round the project out, you should incorporate a bypass damper, so it never sees all dampers closed. Bypass might and should be totally independent and based on Static Pressure.

To ramp it up a notch, the blower could be fitted with a VFD or variable Frequency drive, so that there might be energy savings as well as noise reduction. I think the VFD could eliminate a bypass damper. Carrier does this with their zoned HVAC systems. The motor itself can effectively compute CFM and static pressure with RPM and load current.

What it also does, it every day at 1:00 PM (in later thermostats, the time can be changed), it opens all of the dampers and runs the blower for about 5-10 minutes to allow the system to compute the static pressure under controlled conditions. This is somehow converted to 0-100% filter use. When you change the filter, you RESET the utilization to zero. This is all capabilities available with the fancy ECM motor.
Thinking about what I said, the idea of having a delay on break for every station makes a lot of sense because you can make it so you always always have a damper open. So, I guess it's weird little gotcha.