in my woodworking shop, I installed a dust collection system with several 'branches' to be able to have dust collection at every stationary machine.
These 'branches' get opened of closed by blast gates. These are successfully controlled by the arduino mega 2560. I am able to select the gates using an IR remote.
Now the question:
I would like my system to 'auto-select' the blast gate when a machine is activated. So in essence, I simply need to detect current flowing through the power cable of my machines.
Most of my machines run on 240V, 2 of them on 350V.
I thought of optocouplers, hall effect sensors and reed switches.
Research led me to believe that the easiest way to achieve my goal is using a hall effect sensor module like the ASC712. (Using the ACS712 Hall Effect Current Sensor Module (part 1) - YouTube). It's readily available, still quite cheap and easy to install...(I know it' is a bit overkill, because I don't need to measure the current, I simply need to detect the ON/OFFstate.)
But can these components handle these voltages (240-350AC) and currents (unable to determine how many amps my tablesaw produces, but I imagine it's quite a lot) and do a sufficient job?
Any thoughts?
Use a current transformer. These are noninvasive (surround a wire) and are safe to use at those voltages. I use the CS60-010L or CS60-050L from CoilCraft, and you may get free samples from them: Current Sense Transformers & Sensors | Coilcraft
Thanks for the reply.
I tought about using these.
Downside is the size (would like to have something smaller). And also price: I could buy one in my region from amazon for 8.99 euro (10 usd) and I would need 10 in my shop...
A relay with a 240 or 350V coil would be the simplest solution and it would provide isolation. (But, 350VAC relays are not common... I've never seen one, but I've never looked for one either.)
An opto-isolator can work but you need a series resistor to drop the input-voltage. (The LED inside runs somewhere around 2V, so a resistor is standard even in 5V or 12V applications.) The opto-isolator is usually rated for a couple-thousand volts of isolation. You need a high-power resistor and the resistor generates heat... i.e. 240V at 10mA is 2.4 Watts, and that would burn-up an everyday 1/4W resistor.
Another option would be a regular step-down transformer. (And a rectifier and possibly some voltage-protection on the secondary.) It could be the smallest transformer you can find (low power & current rating since you'll only be sensing the voltage and not drawing any significant current.) As you may know, the primary and secondary of a transformer are electrically isolated so you and your Arduino are safe from the lethal voltages.
And also price: I could buy one in my region from amazon for 8.99 euro (10 usd) and I would need 10 in my shop...
An opto-isolator and resistor might be the lowest-cost solution, but 5W resistors aren't "free" like regular resistors. Or, you might find some cheap relays....
By the time you add some kind of housing & connectors & wiring, the costs are going to add-up and you're probably going to spend a couple-hundred Euro no matter how you do it.
Why not simple voltage detection? You can build a non-contact voltage detector that works for anything from 100 to 500 volts AC for a couple of dollars in parts that will interface directly to your Mega.
Just Google "non contact voltage detection arduino". There was a simple three transistor (BC547's) circuit on hack-a-day. Lots more out there.
jremington:
The CS60-010L is only 19x14x20 millimeters, and that is a problem?
that indeed is no problem. The ones I checked out were all around 57x32mm.
This might indeed be the most effective solution!
Will check out the non-contact voltage detectors avr_fred mentioned.
avr_fred:
Why not simple voltage detection? You can build a non-contact voltage detector that works for anything from 100 to 500 volts AC for a couple of dollars in parts that will interface directly to your Mega.
Just Google "non contact voltage detection arduino". There was a simple three transistor (BC547's) circuit on hack-a-day. Lots more out there.
Could you please elaborate? I don't see how this would work.
This might make me sound really dumb (and correct me if I'm wrong), but...
I follow the reasoning with 110V where there is a 'hot' wire and a neutral. If you would measure a voltage of 110V on the neutral side, it would indicate that the machine is turned on.
But with 240V, the voltage is always present on every wire since (with 240VAC) there is no neutral. There are 2 phases and a ground.
So for example: if you would measure near a socket (doesn't matter which side), you would always measure voltage. Even when there is nothing plugged in.
More specifically, if my machine is plugged in, but not switched on, voltage will still be present on every wire, no? So you would always get 'affirmative' feedback from the voltage meter.
You are correct that in a 220v circuit, there is voltage on both wires. Because both conductors are "hot", both conductors pass through the on/off switch for safety reasons. So, you only need place the monitor on either lead after the switch and it will function correctly for this application.
As a side topic, you explanation of a 120v circuit is flawed. You will not see 120 volts on the neutral conductor when the device is on because all white wires (neutral) are bonded to earth inside your power distribution box. You might be able to measure some voltage on the white wire out at the outlet but this is due to the resistance of the wire itself and the voltage could be calculated with I^2r where I is the current and r is the resistance of the white wire from the outlet to the distribution point where the neutral meets ground.
Speaking of the distribution panel - did you ever wonder why most breakers are single pole but are some that have their handles joined together with a pin or a bracket? The answer is quite simple... As the two pole breakers are suppling 220 volts, the single poles, 110 volts.
avr_fred:
both conductors pass through the on/off switch for safety reasons
Are you sure? Because when you open any light switch for example in Europe, you see 1 phase passing through and only 1 phase is interrupted by the switch.
Also, 'place a monitor [...] after the switch', this would mean internally to the machine, no? For example, inside the handle of my chop saw. Or would you suggest adding a switch to the power cord? Because that's not practical at all.
My asumptions about 120V were indeed incorrect. Since I live in Europe, I had zero knowledge about this...All I knew was what I could quickly find on internet.
The ACS712 and similar are only safe for mains use on a properly designed PCB with cut-outs
under the chip and/or potting, and ideally would use conformal coating too. The issue is the
small size of the package which is SOIC and not really large enough for proper clearance between
high and low voltage sides without some extra measures. Current transformers have to
only go round one conductor, which means again some consideration to mains safety - at least it
is possible for the split-core types to be non-invasive of the inner insulation even if you've removed
the outer sheath. Current transformers must always be operated with an appropriate burden resistor (its best
to get one's with this built in), as failing to do so can generate dangerous levels of voltage and power
on the output.
It had occurred to me that you might be in Europe due to reference to 380 volts (incorrectly mentioned as 350 volts). The CE harmonization has increased that to 400 volts which means your single phase household voltage is 400 / square root(3) = 230 volts. The calculation result is actually 230.95 volts but we round it down for consistency.
Please notice that I said "single phase" above. In Europe, your household voltage is derived from the 400 volt mains with a wye connected distribution transformer. The center point of the three phase windings is connected together which is then grounded directly or though a resistor in series which allows for a small voltage across the resistor where the voltage is proportional to the neutral current. This is sometimes used in industrial systems where the voltage across the resistor is an earth fault trip of the distribution circuit breaker. I don't want to get lost in the weeds here, let's come back to point at hand that I wanted to make.
In your typical 230 volt appliance connection, you have a "hot" wire, usually brown in color and the neutral wire which is blue in color. Please notice that I'm calling the blue wire by its real function - a neutral point which means there should be no voltage present on that wire. This is the same situation as in the US wiring scheme, where we only switch the hot lead/wire since the neutral wire should have no voltage present.
All of the above is all quite pointless since you are 100% correct about having to disassemble the tool to get to the switched wire feeding the motor. So, I'll withdrawal my suggestion, IMO you'll find the cleanest solution is a current transformer over the "hot" phase wire, typically the brown wire. If the device uses 380/400 volt three phase power, any one of the phases should have the same current as the other two. I would suggest that you check this, assume nothing
blokskebeton:
Thanks for the effort you put in to help me solve my problem!
Really appreciate it!
Will indeed probably go with the current transformer.
If you are inclined to experiment, you could make a Rogoskie coil that is a current transformer in the form of a solenoid that can be placed around an AC conductor without having to disconnect anything.
Use a flexible cylinder and wind some number of wire turns around the cylinder. Perhaps 50 turns. Then tape the coil so it won't unwind. Feed one end of the wire back through the cylinder so bot start and end of the winding are available on the same end of the cylinder. Fold the cylinder/coil around the conductor to be measured and you have a one turn to 50 turn current transformer.
You might use a length of heat-shrink tubing as a form for the coil.
