Connect with us

Automation seems easy but what am I missing?!?!

Discussion in 'General Electronics Discussion' started by boyd, Oct 7, 2016.

Scroll to continue with content
  1. boyd

    boyd

    64
    6
    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 [E-mail removed]
     
    Last edited by a moderator: Oct 7, 2016
    chopnhack likes this.
  2. hevans1944

    hevans1944 Hop - AC8NS

    4,562
    2,135
    Jun 21, 2012
    There is a thread here, several years old now, where two Allegro current sensors are used independently to sense motor current in a woodworking shop environment. The circuit accommodates both 220 V AC and 110 V AC power tools simultaneously. When a tool is turned on, the appropriate Allegro output results in a relay being energized to turn on a dust collection system. As long as one or both Allegros sense motor current is present, the dust collector runs. When the last tool is turned off, a time delay is generated to allow the dust collector to clear its ducts and then the dust collector is turned off.

    It's an interesting read and may give you some ideas on how to solve your problem.

    Oh, and welcome to Electronics Point!
     
    chopnhack likes this.
  3. Bluejets

    Bluejets

    4,502
    958
    Oct 5, 2014
    Is there any particular reason why you cannot just use a small standard 240v relay, one on each machine, arranged to come on at the same time you switch the motor of the machine on?
    Cannot see a reason to detect current.
     
  4. Kabelsalat

    Kabelsalat

    153
    28
    Jul 5, 2011
    Is the issue here to detect increased workload of the motor?

    Would it be possible to place and use a load cell instead to detect load?
     
  5. Tha fios agaibh

    Tha fios agaibh

    2,129
    721
    Aug 11, 2014
    Screenshot_2016-10-07-20-39-33-1.png I agree with bluejets that it's better to avoid the current sensor if possible.

    If that's the direction you want to go, I'd probably opt for a off the shelf current sensor like this one from Hawkeye.

    It has adjustable current levels and relay contacts to drive an external contactor or relay.
     
  6. boyd

    boyd

    64
    6
    Oct 7, 2016
    Hi. Hey I can run a relay in parallel with the switched load cant I? Like the largest machine I have will draw almost 40A on start before dropping to roughly 9A. A relay plugged into that would be ok wouldn't it?

    To be honest, for some blind reason I was trying to avoid tapping into the 230vac and keeping everything low voltage. But the reality of putting in a straight 230v relay to switch the solenoids directly from another power source has really what I have come too. And I am not sure why I was so worried about 230v anyway!!! I am electrical and know how to make things safe. Must have been in a short sighted bubble ha ha. I guess I had visions of running 230v wires all through my workshop where that is not the case.

    I dont have much experience with relays but will look on aliexpress for one. Most of the relays I have seen are low voltage input high voltage rating switching. All I need is a cheap 230vac solid state relay to switch 24vdc for my solenoids. Does anybody know of the cheapest easiest to purchase?

    Oh BTW I did get contacted by someone who has developed a current sensing board which would have been perfect although its US$319 - wow. I am hoping the whole project will cost less than that ha. Very nice unit though but I would need at least two of them I have a lot of machinery.

    Oh and BTW, the reason I am doing this is I worked out that if I automate my extraction system from what I am doing currently I will save approx 37 hours a year ha

    Best Regards and looking forward to any more responses or ideas. Boyd
     
  7. Bluejets

    Bluejets

    4,502
    958
    Oct 5, 2014
    Does not matter what current the machine draws as you are just powering a relay (240v) off the motor drive or similar. i.e. it's a voltage operated device.

    Contacts on the relay (common and normally open)will be voltage free at this stage.

    Connect all your contacts in parallel so if any machine comes on the low voltage will switch your solenoid or whatever.

    One important precaution,
    ..........................................be sure to give your low voltage wiring sufficient isolation from the 240v wiring.
    What I mean by that is, run double insulated wiring (preferably rated at 400v) into each 240v enclosure for your low voltage wiring. You do not want any internal cabinet faults livening up your low voltage with 240V.
     
  8. Tha fios agaibh

    Tha fios agaibh

    2,129
    721
    Aug 11, 2014
    Sorry, but the fact that your not familiar with relays isn't exactly a ringing endorsement of your qualifications.

    If your not qualified, it's best to find someone who is.
    An often overlooked electrical hazard around woodworking equipment is the fact that dust particles can be highly explosive. Something simple like an unsealed door on an electrical panel can be a recipe for disaster.
     
  9. boyd

    boyd

    64
    6
    Oct 7, 2016
    Sorry guys I probably didn't install much confidence in my capabilities. I am actually a ROV technician dealing with 3kv at times and have good knowledge of relays, how they work and what they do. I am also a licensed aircraft engineer and have built several CNC machines from scratch.

    What I meant to say is I dont have much experience sourcing the correct one for purpose at a decent price for quality! I have seen relays for a couple of dollars and relays for US$45 each. Most of the ones I have found have an input of 3-34v and a switching capability of up to 400vdc. So my question was not so much about relays and what they do it was more of a putting it out there of who might save me time trawling through the internet sites for a decent relay which wont cost a fortune.

    BTW I have heard about people using a dust extractor for metal and timber dust being risky. What I have never heard of is an electrical box exploding because of timber shavings. For timber to be explosive it needs to be pretty fine almost like flour. Then you need a good oxygen source and a good ignition. Much like the flour gun mythbusters did. Groan...

    Anyways. If anyone knows of a good relay easily accessible and cheap please let me know. Also hearing what Bluejets said, definitely a relay with good protection and proper insulation. I am pretty anal about that for sure so thanks for the confirmation. I would hate to have my lines become hot due to a breakdown.
     
  10. Tha fios agaibh

    Tha fios agaibh

    2,129
    721
    Aug 11, 2014
    @boyd Fair enough, I just want things accomplished safety.
    You need to look at your maximum load, and size your IEC contactor (relay) for at least that much amperage depending on the duty of your dc.
    Use a type 3 contactor that's rated to break motor running current. Obviously, follow your local tap rules, overcurrent (fusing) and overload protection (separate thermal overloads may be needed)
    There are auxiliary contacts that can be used for your solenoid or whatever.
    I think your thinking about a solid state relay, sounds like you just need a magnetic relay to do the job.
     
  11. boyd

    boyd

    64
    6
    Oct 7, 2016

    Hi. Yep all good. I would have thought that my trying to keep the 230vac isolated from my little automation system might have indicated where I was at with safety. There are a lot of variables I need to consider and I need to work it out to create a system which will work reliably yet also NOT have my 3hp extractor constantly switching on/off so will be adding in a timer. Plus I will be adding in a selector switch. I have two 3hp extractors and need to have a separation between treated and non treated timber.

    Hey but if anyone knows of a good reliable 230v input switching relay for cheap available please let me know. I have all the 24vdc stuff sorted. Aliexpress is sometimes a difficult search!! Regards Boyd
     
  12. Bluejets

    Bluejets

    4,502
    958
    Oct 5, 2014
    Sorry but you lost me there.........no idea where the timer comes in or where you get constantly switching on off from. Need for selector switch also eludes me.
    Seems a lot you are not telling us or you've managed to get things A-up.
     
  13. chopnhack

    chopnhack

    1,573
    354
    Apr 28, 2014
    I think what Boyd is getting at is that he needs a delay in his off time for his D.C. (dust collector) so that it doesn't bounce on and off as machines are cycled. A delay on would be wise too so that you don't have a dip in voltage as your tool powers on simultaneously with the extractor.

    Boyd, what product was mentioned at $300? Maybe there's a market for my board lol.
     
    hevans1944 likes this.
  14. Minder

    Minder

    3,046
    644
    Apr 24, 2015
    You can pick up cheap contactors on ebay, My favourite brand is the DIN style by Telemecanique, they can be fitted with all kinds of auxiliaries down to the simple N.O/N.C. contact style.
    For a non invasive current sensors, there is the Honeywell CSDA range, there is also the ACS712 for an invasive type, but possesses very high voltage isolation by way of Hall effect sensor, you can get a whole board off ebay for <$2.00.
    The CDSA comes in simple level or analogue detection.
    For the ACS712 the analogue would need to be converted to a simple set level switch if needed.
    Available up to 40/50 amps IIRC.
    M.
     
  15. chopnhack

    chopnhack

    1,573
    354
    Apr 28, 2014
    30A is the max in the ACS712, but it can take 100A surges which makes it quite impressive in my opinion. Also makes it well suited for motor sensing, allowing for those peaks at startup.
     
  16. Minder

    Minder

    3,046
    644
    Apr 24, 2015
    The only down side I have to the ebay $2.00 board versions is the tiny (15a) terminals they use for the current, I would up them to at least 25/30amp.
    M.
     
  17. boyd

    boyd

    64
    6
    Oct 7, 2016
    Good morning! Thanks so much for the info. Yes correct I wish to have a timer delay on the shutdown of my extractor so when I switch machines within less than 30 seconds it is not constantly shutting down only to restart.

    The extractors (I have two) are 3hp so draw a bit of current on start before they settle down. The reason I am looking also at switching between extractors is sometimes I use treated timber and sometimes (usually) native which is great to put back into the ground. So wish to seperate them.

    In all I am buying 10 16mm 100mm stroke pneumatic cylinders which will open a plastic gate of my design inserted into the 100mm extraction piping in my workshop. I have a 20" thicknesser and when it is running taking a full cut, it (extraction) needs to be isolated due to the massive amount of shavings it produces. And some of my machines are 12m away from the extractor which also need everything shut to achieve decent extraction. Like I mentioned before, if I have this system all automated I will be saving a week each year where I can sit on the beach here in Nelson with a glass of cocktail with a little umbrella sticking out of it lol.

    So these spring return pneumatic cylinders will be operated with 24vdc solenoids. In all, 10 cylinders, 5 solenoids (I have 5 already) 40m of 6mm hose, all the pneumatic fittings I need comes to US$119 delivered to New Zealand! Cheap huh.

    I did wake up with a question this morning though. If I was to put a relay in parallel with the output contacts of a machine switch, when the machine is running down will it generate a back current through the relay keeping it closed for a short period of time?

    I also thought about putting a cap between the inputs of the relay that will hold it closed for a short period of time after shutdown but a cap wouldn't hold a relay closed for very long would it?

    The current sensing board I was talking about was offered from a nice guy Bradly at http://measure-current.com/?page_id=395 I didn't pursue what the DIY kit would cost as I am only looking at spending such a small amount of money on this.

    Ok I am going to look into the products you guys have kindly offered up. And appreciate the time spent!
     
  18. chopnhack

    chopnhack

    1,573
    354
    Apr 28, 2014
    Yikes, that would be an impressive mountain of shavings to witness!! Are you a subcontractor for the mill?

    Beautiful and the best case for automation, cheers!!!

    I don't think so - you would need some type of μcu to handle the timing. Arduino's are dirt cheap, you can use one and interface it with enough relays to get the job done. The programming shouldn't be too difficult either since you won't have too many situations

    Thanks for the link, one of my project ideas apparently has already been conquered by sir Bradly, LOL - great minds think alike.

    Do let us know how you get on!
     
  19. boyd

    boyd

    64
    6
    Oct 7, 2016
    Ummm. I just realised something. All I need from each machine is 24vdc when I switch it on. How does it sound if I was to place a 230vac to 24vdc adaptor into each machine?

    I could do it proper and find a product made for purpose. Or go down to my local recycling shop and purchase 10 24vdc power supplies for $2 each.

    But it would be way cooler if I can find an adaptor which will put out 24vdc when I switch my machine on. Then use that 24vdc to operate the relay to start the extractor and open the solenoid for the appropiate pneumatic valve.

    Something like this https://www.aliexpress.com/item/Fre..._1&btsid=9b2a1dce-272d-422e-ba99-f5be58b980a5

    What do you think?? Was it staring me in the face all this time?
     
  20. chopnhack

    chopnhack

    1,573
    354
    Apr 28, 2014
    Well, you could put a transformer into each machine just past the power switch such that the transformer energizes with the machine, but you still would need to work out timing, which can still be done, the 24vdc can be the start signal. You would then need to keep each 24vdc pulse separate so that you could use each one as a logic signal and to operate the gates individually. For example, if you have one machine dedicated to treated lumber, that 24vdc signal would only power on the extractor dedicated to pt solely. Also timing can be achieved by polling the pins that receives the presence or absence of the 24 vdc. Of course an arduino will need an interface, as it only accepts logic level inputs, but that shouldn't be too much of a problem to step down.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-