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  1. #16
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    Quote Originally Posted by BobL View Post
    Sorry to drag this out but can I ask if the connection between the impeller and filter housing has been modified? The reason I'm asking relates to the currents drawn by the DC you are observing.
    Absolutely bog standard. I think I removed the cross bar that "protects" the impellar against impacts, but thats it.

    I re-razzled the cleaner and re-ran the tests.

    5.54 amps and only 1100 watts.

    Its supposed to be a 2HP motor. It claims to be 9A on the plate.....

    I'm very surprised at the lack of draw. A dud?

    IMG_20190523_200437.jpg IMG_20190523_200559.jpg


    Here is a video of the thing starting up


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  3. #17
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    Quote Originally Posted by woodPixel View Post
    Absolutely bog standard. I think I removed the cross bar that "protects" the impellar against impacts, but thats it.
    I re-razzled the cleaner and re-ran the tests.
    5.54 amps and only 1100 watts.

    Its supposed to be a 2HP motor. It claims to be 9A on the plate.....
    9A sounds a tad high, 9A is usually what 3HP motors draw.

    What the lowish currents you see demonstrate is that the ducting between the impeller and the filter housing is acting as a bit of a bottle neck.
    If this was attended to I'd expect the running current with clean PFs to get close to 6A - this would then make it 2HP which is the motors rating so it would be working to its capacity.

  4. #18
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    This morning it occurred to me I already had the basic Arduino parts to have a crack at mocking up an "auto shop vac start" when the "power tool starts up".

    There would be a cheaper way to do this with analog parts but the Arduino programability provides extra flexibility and information if required.

    Here's the basic prototype
    A is a $5 Arduino clone micorcontroller
    R is a $5 250V 10A optically isolated relay that provides power via mains to the shop vac.
    P is a $2 potentiometer that allows for setting the delay time the shop vac keeps running after rtes power tool is turned off
    C is a $12 20A current sensor to measure the current through the power tool (in my case I uses a 150W incandescent lamp as a load).
    AM is an ammeter to cross check the currents with what the Arduino was saying..
    "To MM" was the output of R connected to the resistance setting on a multimeter to check the relay contacts were opening and closing as required.
    For another $2 I could add a 2 x 16 character LCD display to show a bit more about what is going on.
    About 80 lines of code and it was done.

    It turns out the Arduino current sensor samples current instantaneously. As the AC current varies widely during its AC cycle. To get around this you have to average the absolute value of the current about 100 times and convert to RMS to get close to a reliable reading. All good maths fun when you know what to do.

    IMG_3710p.jpg

    Packaging it into a box with a couple of GPOS is another story, and I'm not going to bother doing thi until I have a need as I don't use shop vacs on power tools,

  5. #19
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    I found some slim line (skirting board) 10A GPOs online so decided to make the prototype into a real thing.

    The box material looks black but is made from offcuts of 5mm thick smokey grey acrylic.
    The black knob on the LHS sets the delay time.
    The GPO on the RHS is the master and the one on the left is the slave.
    I chose to use GPOs with switches so either can be turned off in an emergency.
    Complete2.JPG

    The screen is a tad hard to read from a distance so that's why I added the RED LED to show the master GPO is activeComplete.JPG

    For anyone that's interested BELOW is what the guts looks like.
    Note use of old 9V mobile phone adapter(bottom RHS) to power the micro-controller.
    $47 TOTAL worth of parts - the GPOs were the most expensive components ($8.50 each)
    Even if it were made using all analog parts it would not be much cheaper in terms of parts.
    The advantage of using a micro controller is the programming flexibility and ability to then drive a $2 .screen to display current and delay time.

    guts.jpg

  6. #20
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    Mate! You are really cranking out those arduino jobs!

  7. #21
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    DISCLAIMER

    No liability is accepted by UBeaut or the Wood Working Forum's administrators
    or moderators for advice offered by members posting replies
    or asking questions regarding electrical work.
    We strongly advise contacting a Licensed Tradeperson for all electrical work.
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    Members following such information do so at their own risk

  8. #22
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    Quote Originally Posted by woodPixel View Post
    Mate! You are really cranking out those arduino jobs!
    Cheers WP. Yeah some of this is related to not having enough energy to stand up for lengthy periods in my shed.

    This was one of the easier ones to prototype but shoe-horning everything into a box is never quite as easy as first envisaged. Making the acrylic box also took a bit longer than I expected and all to save the cost of a box. The sturdy PVC ones with the transparent lids suitable in size for (basic Arduino plus extras) electrical projects used to cost $8 one line but now they cost $12! When I make plastic boxes like these I usually cut and sand plastic to size but this time I decided to use my metal mill instead of sanding. It does a good job of getting the acrylic perfectly square and to size but it takes time and one small slip during gluing up can undo all that good work.

    BTW I should have added a potential DANGER DISCLAIMER. This project is well beyond replacing a mains power plug and should only be attempted by persons with AC mains experience. Given the number of 240V connections involved the potential for significant injury and death is very high. In practical terms what I have made is a working prototyped, safety wise the wiring could could be improved so I would never sell or even give one like this away. I usually avoid mixing mains V and low V (ie 12V) Arduino components in the same box as the potential for accidental cross connection and subsequent damage is high. Usually I split the low and High V into separate boxes.

    FWIW I have no immediate need for this device it was really just to see how easily and cheaply such a device could be made. I will have a bit of a play with it but then I suspect it will live in the back of the cupboard and eventually it will be repurposed for another project.

    Along with VI meters on some machines and other LED indicators, if I leave all my Arduino boxes on, at night the inside of the shed sometimes looks a bit like a sci-fi film set. i usually leave the CO sensor on all the time as it has a Temp/Humidity output. The Auto venter for the compressed air lines has a built in clock so it stays on 24/7 and only vents between 8am and 6pm. The compressed air humidity and temp box is left on 24/7 as it doesn't output any actions. The DC Temp/press monitor runs from a battery and is only used when the DC is running. Dust wise, I use to leave a monitor running 24/7 but now I only turn one on when I'm doing something really dusty. If I remember I will take a photo.
    I often wonder what a potential theif might think if they looked in thru the window.
    Last edited by BobL; 11th July 2019 at 11:39 AM.

  9. #23
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    Quote Originally Posted by BobL View Post
    This morning it occurred to me I already had the basic Arduino parts to have a crack at mocking up an "auto shop vac start" when the "power tool starts up".

    There would be a cheaper way to do this with analog parts but the Arduino programability provides extra flexibility and information if required.
    Packaging it into a box with a couple of GPOS is another story, and I'm not going to bother doing thi until I have a need as I don't use shop vacs on power tools,
    By coincidence the parts for my attempt for an auto start shopvac turned up today. I opted for the analog route. I initially had a timer in the design but found there is about a 4 second delay built in the current sensor module so discarded the timer from the design. Although the relay contacts on the module are rated 240V/10A I doubt that it would last, so I went for a solid state switch. The only down side of this is that with the shopvac running it can get a bit warm if running for a extended period, dissipating about six watts. Considering a better heat sink or a conventional heavier duty relay. As you say Bob the electronics are cheap (under $10) it’s the hardware that costs the most. I also endorse the comments that if you haven’t got the appropriate skills don’t fiddle with 240 volts.

    F6052FA5-1AF7-40F6-9036-4DF5B11AFBC0.jpg

  10. #24
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    Quote Originally Posted by apple8 View Post
    By coincidence the parts for my attempt for an auto start shopvac turned up today. I opted for the analog route. I initially had a timer in the design but found there is about a 4 second delay built in the current sensor module so discarded the timer from the design. Although the relay contacts on the module are rated 240V/10A I doubt that it would last, so I went for a solid state switch. The only down side of this is that with the shopvac running it can get a bit warm if running for a extended period, dissipating about six watts. Considering a better heat sink or a conventional heavier duty relay. As you say Bob the electronics are cheap (under $10) it’s the hardware that costs the most. I also endorse the comments that if you haven’t got the appropriate skills don’t fiddle with 240 volts.
    Looks pretty straightforward, especially if no delay time or current measurement are involved, hence it also should work out a bit cheaper. I assume you will swap out the PS for a small (eg mobile phone) power adapter and then you will need two power points and box of some kind? Do you know what your threshold current is before the current sensing low V relay triggers? Mine jumps around a bit and the switching threshold is under control of the micro controller hence programmable - maybe a toroidal transformer type like yours is more stable? - I have one on my bench right now I am about to test.

    I forgot to add that the max total current of mine is 10A so a medium/small shop vac and low medium wattage power tool at the max. Something like a 2HP DC linked to a 2 or 3HP machine should be run from a 15A GPO.

  11. #25
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  12. #26
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    That Jaycar one looks like good value but I also note it is being discontinued hence the low price - I also prefer slaves to have their own switches like the Bunnings one. These units are both designed for domestic use so perhaps suit a a small shop vac and sander, and maybe that's all the OPs has. Being 10A max devices they won't handle a larger shop vac or 2HP DC, together with say a 2HP machine. I haven't programmed it in to mine yet yet but (like the Amazon model) the slave "on" should be delayed for about a second after the master had fired up to allow for excessive start up currents. Likewise no opportunity to delay turning off afterwards. They also would be more useful if the slaves could be easily reconfigured as a normal power points, so some sort of a bypass switch would be useful, something I was going to add to my 15A version.

  13. #27
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    T
    Quote Originally Posted by BobL View Post
    Looks pretty straightforward, especially if no delay time or current measurement are involved, hence it also should work out a bit cheaper. I assume you will swap out the PS for a small (eg mobile phone) power adapter and then you will need two power points and box of some kind? Do you know what your threshold current is before the current sensing low V relay triggers? Mine jumps around a bit and the switching threshold is under control of the micro controller hence programmable - maybe a toroidal transformer type like yours is more stable? - I have one on my bench right now I am about to test.

    I forgot to add that the max total current of mine is 10A so a medium/small shop vac and low medium wattage power tool at the max. Something like a 2HP DC linked to a 2 or 3HP machine should be run from a 15A GPO.
    i could use a small PS but I might try this baby AC/DC converter. The load at 5V is 80Ma. 2CF04AB0-7EDC-4632-B8CD-E96D49D14BB2.jpg

    I’m looking at options for a box and will probably follow your lead on power points.

    The current sensor is supposedly adjustable from zero to 5 amps via a pot and mine seem to be set at about 250mA and it seems consistent. It’s probably high enough to avoid triggers from any induced noise etc and the tools I’m using with the shopvac are 2A plus, so I’ll leave it as it is.

  14. #28
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    Quote Originally Posted by apple8 View Post
    T

    i could use a small PS but I might try this baby AC/DC converter. The load at 5V is 80Ma.
    Looks useful

    I’m looking at options for a box and will probably follow your lead on power points. .
    Let me know if you need the links

    The current sensor is supposedly adjustable from zero to 5 amps via a pot and mine seem to be set at about 250mA and it seems consistent. It’s probably high enough to avoid triggers from any induced noise etc and the tools I’m using with the shopvac are 2A plus, so I’ll leave it as it is.
    .

    The very cheap ($2) current sensor I'm using actually outputs around 100 mA when there is no current through the sensor, It's a +/-20A sensor so when connected to a 10 bit ADC, 1 bit corresponds to 40mA so the 100 mA @ zero current corresponds to 2.5 bits. I can program this out to zero but the problem is it drifts around by +/- a bit so I might have to use something 250mA as well.

  15. #29
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    I have a clutch of these little fellows for low demand 5V applications:

    Screenshot 2019-06-13 11.01.27.png

  16. #30
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    Quote Originally Posted by Bernmc View Post
    I have a clutch of these little fellows for low demand 5V applications:
    Thanks for the link. I have plenty of spare mobile phone chargers but its good too know that low cost options are available.

    I have been experimenting with a coil from a VI panel meter and it's output is much more stable than the hall effect unit I currently have in my setup so I will be replacing it with the coil.

    The hall effect sensor has a fixed 20A current max centred with the current Zero fixed at 2.5V.
    So, +20A = 5V output and -20A = 0V output.
    On a 10 bit ADC (~1000 AADC levels) such as the Arduino I'm using has, 20A split across 500 output levels equates to 40 mA per level, so the smallest current difference it could measure based on a single ADC value was 40 mA.
    The voltage is of course AC, so has to be sampled and converted to RMS to get a single current measurement.
    I was sampling 1000 times in one second and averaging the values and converting to RMS - this increased the sensitivity of the measurements but the drift was all over the place by as much as 100mA.

    OTOH the coil is much more stable and has far less drift.
    The coil outputs ~1V per 50mA of 240V AC current and is centred on 0V output so 5V output would represent 100A!
    To improve the sensitivity I placed the coil output across a simple 4:1 resistor pair and put the Aduino input across the smaller R so that 20A equates to ~5V which is the Arduino analog post FS input.
    This means each ADC step now equals 20mV but by sampling 1000 times a second combined with much better signal stability results in a 2 sigma variation of about 0.4mA
    This is overkill but its nice to know this level is achievable. OF course if a more sensitive coil a corresponding improvement can be achieved.
    I will probably set the lowest current display and decision making at 1mA.

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