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Automatic Dust Collection Design #1: Introduction

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Blog entry by kinger posted 08-16-2015 08:09 PM 1323 reads 6 times favorited 8 comments Add to Favorites Watch
no previous part Part 1 of Automatic Dust Collection Design series Part 2: Opening the Black box »

Back in November of 2014 I posted a project showing the system I had made to control my shop-vac for automated dust collection. You can see the project here:

Click for details

After posting, there were several people asking me for the schematics so they can build their own. So instead of only posting the schematics I drew up, I though it would be a good idea to provide a little additional explanation for everyone else that might not have as much experience with electronics. I don’t believe its a complicated design and there is no special code to write. Its a pure analog circuit that I hope can help simplify the use of your dust collection system.

Now for two disclaimers, one serious and the other not as much…..

  1. Here it is, you knew it was coming…...Danger: Hazardous voltage 120 Volts not only startles you but can kill you. The sole purpose of this system is to turn on and off your dust collector. It does this by applying 120VAC and hence there are several parts of the circuit that are HOT with 120 volts. If you do not feel comfortable with building these types of circuits or know general practice of working with electricity I would not recommend you attempt to build this system.
  2. Now the second disclaimer, I am an engineer and this is my first blog post. I am good with numbers and not so much with words. So I apologize up front if I am not explaining something clearly or well enough. I always despised writing papers in college and always preferred the math proofs or diff eq side of things. So with that said, I will try to be as detailed as possible but please tell me if I didn’t explain something enough.

Update on the system. Since the project posting, I have moved into a new house and have since purchased a new Powermatic PM1300TX dust collector. It is worlds beyond the shop vac in terms of power and suction but sadly due to its infrared remote control and timer box, it isn’t compatible with my automatic dust collection system. Once I complete this write up of the first system my plan is to design a second version that can integrate into the control box of the PM1300tx and control by means of 220v.

Concept of the System
What we want to do is turn on the dust collector when a tool turns on. It may be a black box to some, but if we start at what we know and break it down its not too mysterious. So first we must determine the inputs and outputs to our system. The inputs are to “know” when the tool turned on and the output is to turn on the dust collector. Sounds simple right. The first part, “knowing” when the tool turned on can be accomplished by detecting the current that is drawn when the tool is operating. That is the one “flowing” quantity of electricity that is somewhat easily detected. The second part, is to apply power to the dust collector. This is accomplished by using a relay to apply 120v to the dust collector. Just like when you press the Green “ON” button on the shop vac, the relay applies 120v to the shop vac motor.

For the input to the system, detecting when the tool is turned on, I decided to use a hall effect current sensor package which can be found on amazon for about $10. The IC part number is ACS712 and looks like this:

Tip: I recommend the sensor that has screw type terminals instead of compression pin terminals. They are much more secure and carry the current more safely.

I wanted a voltage that is proportional to the current being drawn by the tool. The current sensor is just a little IC that does exactly that by means of the hall effect. Read more here if you’re interested in the details. The sensor is bi-directional and therefore can measure current in both directions. We only need measurements in one direction but this has to be taken into account to interface to the next step…the “processing” of the signal. The output is 0-5 volts DC and is proportional to the current being drawn from -30 to 30 amps. So when the tool is off and no current is being drawn it will put out 2.5 volts. Alternatively when 30 amps is being drawn it will output ~4.5 volts and when -30 amps is being drawn it will put out ~0 volts. And in between those values the voltage output follows a linear path. See below graph (snap shot taken from ACS712 data sheet) :

For the output of the system, where we apply voltage to the shop vac, a simple electro-mechanical relay will due the trick. A relay is just a electronically controlled switch. Read more about them here. I happened to have a Omron relay from my electronics stash which worked perfectly. The part number I used was G2RL-1ATP5-E. It has a 12VDC coil and contacts that can handle 16A at 250VDC. Looks like the following:

The way it works is if you apply 12VDC (or whatever the coil voltage is) to the coil, the contacts are connected together. When no voltage is applied to the coil, the contacts are not connected. Therefore we can apply voltage to the shop vac motor by applying 12 volts on the relay coil.

At this point we know when the tool is on and how to turn on the dust collector but there is still a bit of “processing” we need to do to interface the input to the output. That will come in the next post. I’ll post schematics in the end tying it all together. For all those who made it this far, thanks for reading!



8 comments so far

View Redoak49's profile

Redoak49

1964 posts in 1456 days


#1 posted 08-16-2015 09:22 PM

I will be watching for the rest of the series…thanks

View kaerlighedsbamsen's profile

kaerlighedsbamsen

1177 posts in 1181 days


#2 posted 08-16-2015 10:13 PM

Hey that was super fast writing! Think that you make this stuff quite understandable for a non-engineer as myself.
Looking forward to the read more!

-- "Do or Do not. There is no try." - Yoda

View Deycart's profile

Deycart

444 posts in 1725 days


#3 posted 08-17-2015 05:01 AM

I am studying EE and a few credits away from graduation. Why would you want a proportional response from a tool? I would just want to know if it was “drawing” current(on). Different tools will pull different amounts and at different loads (turn on, during a heavy load like a thick board of dense wood, free spin).

Why not just “OR” all the outputs from the current sensing board to turn on the vac?

What about using individual relays and a solenoid to pop open the blast gates to your not wasting your suction on tools that are not on?

View Chrisprols's profile

Chrisprols

7 posts in 482 days


#4 posted 08-17-2015 08:58 AM

I’ve been looking for such a solution for a while now. I’m in Europe (France) and got a couple of question :
can you include remarks so one could build such a solution for 220V tools ?
What is the max power for inlet ? (I think I found such equipment but for 500Watts inlet only) ?
Is the ACS712 rated only to 120V or can it take 220v ?
Can you defer a little bit the dust collector switching on and as well defer a little bit (more) when it will switch off ? (the idea would be not to start everything at the same time … and to let the dust collector suck a bit more after you stopped your tool).

View kinger's profile

kinger

39 posts in 1048 days


#5 posted 08-17-2015 12:26 PM



I am studying EE and a few credits away from graduation. Why would you want a proportional response from a tool? I would just want to know if it was “drawing” current(on). Different tools will pull different amounts and at different loads (turn on, during a heavy load like a thick board of dense wood, free spin).

Why not just “OR” all the outputs from the current sensing board to turn on the vac?

What about using individual relays and a solenoid to pop open the blast gates to your not wasting your suction on tools that are not on?

- Deycart

Good questions Deycart, and congrats on your proximity to graduation.

To answer your first question, I have several reasons. But first, a device like you suggest adds a bit more complexity to the system while not adding that much value. Now the value part of that statement is my opinion but let me explain the rest first. So, to get a binary signal (current or no current) you must start by detecting the current. And the only ways to do this is by means of a current transformer, inline resistor, or inline conductor to read the magnetic field from. And naturally, each of these methods output an analog signal. This is to say a current transformer will output a current proportional to the main current but stepped down. A inline resistor will have a proportional voltage and the magnetic field will always vary proportional to the current in the conductor. So no matter what device you use, you must always start from an analog value and then process it further to get whatever information you want. Why not process that analog signal yourself and do something with it to provide some additional feature? For me, the additional feature was the ability to have a strip plugged into the system that had other loads on it. So I had lights, fans and even small tools like a palm sander that I could power with the system but would not trigger the DC to turn on. And only when that specific power tool turned on, it triggered the DC to turn on. I’ll explain this more in the next post.

Secondly, I don’t believe there is a device that will put out a binary signal at the presence of current that would be cost effective, reliable and eliminates nuisance operations. There’s always a balance when it comes to features and cost. I attempted to strike that balance between cost, easily obtainable parts, simplicity and features.

You’re second statement about the OR gate is right on track. After I process and do a little level comparison, everything goes into a OR gate that triggers the output relay.

And you’re third statement is also on track. Its hard to see without a closeup of the board but I have four relays installed on the system. One for operating the DC and three others for operating blast gates, one for each tool. This was an additional feature I provided the ability to add on later once the system was up and running. Since I have moved to a new shop I never populated the board to realize this feature but I have all the necessary components and signal to do so. Maybe on my next version of the system.

View kinger's profile

kinger

39 posts in 1048 days


#6 posted 08-17-2015 12:59 PM



I ve been looking for such a solution for a while now. I m in Europe (France) and got a couple of question :
can you include remarks so one could build such a solution for 220V tools ?

- Chrisprols

Is the ACS712 rated only to 120V or can it take 220v ?

- Chrisprols


Hi Chrisprols, yes I can take that into consideration. It won’t be that hard to modify this for 220v tools. The main difference will be to ensure the output relay and the power supply which provides control power can handle 220V. Otherwise not much else changes. The current sensor can handle 220v since it uses the hall effect to detect current. Its limited by current capacity not by voltage ( it has an isolation voltage of 2.1kV from its current path to measuring circuitry). I’m near certain it can handle 220v but I’ll be testing that later.

What is the max power for inlet ? (I think I found such equipment but for 500Watts inlet only) ?

- Chrisprols


When you say “max power for inlet” do you mean max Dust collector amperage? If so, this is only limited by the output relay used. If you can find a relay with higher contact rating then that’s the solution for larger systems. I just happened to have a relay that could handle 16A so that is what I used.

Can you defer a little bit the dust collector switching on and as well defer a little bit (more) when it will switch off ? (the idea would be not to start everything at the same time … and to let the dust collector suck a bit more after you stopped your tool).

- Chrisprols

Yes this can be done. In the current implementation the system turns off the DC after a set time (adjustable) in order to clear the lines. The same could be done when turning on the system.

View kinger's profile

kinger

39 posts in 1048 days


#7 posted 08-17-2015 01:08 PM



I am studying EE and a few credits away from graduation. Why would you want a proportional response from a tool? I would just want to know if it was “drawing” current(on). Different tools will pull different amounts and at different loads (turn on, during a heavy load like a thick board of dense wood, free spin).

Why not just “OR” all the outputs from the current sensing board to turn on the vac?

What about using individual relays and a solenoid to pop open the blast gates to your not wasting your suction on tools that are not on?

- Deycart

Deycart, I’m glad you asked your question because it made me realize I incorrectly stated the output characteristics of the ACS712. Its a bi-directional current sensor where the output is centered around Vcc/2 when no current is being sensed. This allows Vout to go down for negative current and up for positive current. Blog post updated. Thanks!

View robscastle's profile

robscastle

3393 posts in 1672 days


#8 posted 08-25-2015 08:35 PM

The delayed start would be a bonus as its interesting to see start up inrush currents from motors although a very short duration an excess of 50 Amps at times I think I managed to clamp up to 56Amps at one time but do not have a storage device to show the duration.
I know it was blowing a 10, 15 and sometimes a 25 Amp fuse but not a 15 circuit breaker.

-- Regards Robert

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