Connect with us

Programmable Interval Power Timer for Bubble Machine

Discussion in 'General Electronics Discussion' started by thepassion2010, Aug 11, 2012.

  1. thepassion2010

    thepassion2010

    2
    0
    Aug 11, 2012
    Hello,

    I'm working on a project at Burning Man this year and need to find a way to efficiently use our high-output bubble machine that is part of a large art installation. We are trying to minimize the amount of re-filling of the bubble fluid.

    The machine can run as soon as it's plugged into an outlet, and it will stop as soon as it's unplugged. I'm searching for a "Programmable Interval Power Timer" that will allow me to do the following example:

    Run power to machine for 5 minutes, Cut Power to Machine for 10 minutes, Run power to machine for 5 minutes, Cut power for 10 minutes..... repeat, etc...

    Is there something out there that is even close to this pattern? Any help is is greatly appreciated, thanks.

    -Dave
     
  2. thepassion2010

    thepassion2010

    2
    0
    Aug 11, 2012
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Nice work Harald!

    I'm going to be starting on a similar project to cycle a kitchen appliance on and off using a cycle time around 10 seconds.

    We have a toastie pie maker that has a fixed thermosat, and I like to reuse it for reheating my health food (pies and sausage rolls :) but it gets too hot. So I want to build an in-line cyclic mains power switch with a duty cycle adjustable between roughly 5% and 95%.

    I plan to start a thread in the Project Logs forum with my proposed schematic and design ideas. I will post again on this thread when it's ready for feedback. The project name will be notsohot.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
  5. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    A standard thermostat control as used for hot plates will do what you want and go from 0% to 100%.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Is that comment meant for me? You mean I could modify the toasted sandwich maker so it uses an adjustable thermostat instead of a fixed one?
     
  7. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Kris,
    Yes, its for you, I looked at the end of the thread, I did not realise that you had hi-jacked it.
    You do not need to modify the toaster, you will need to put the thermostat in a properly insulated box but that will be no more difficult than making a box for your circuit.
    Duke
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Erm, the thermostat has to be able to detect the temperature of the appliance! If I just put it in an external box, it will never get hot and will never turn off!
     
  9. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Kris,
    That is not the specification of the original requirement.
    The circuit you show uses a 555 to alter the on/off times which a standard thermostat can do. The toaster will get hotter if you turn the control up and will get cooler if you turn the control down.
    Duke
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    What I mean is that a thermostat will only cycle a heating appliance on and off if there is a thermal connection from the appliance to the thermostat. A thermostat in an independent box won't work, because there is no feedback from the heating element in the appliance to the thermostat. The thermostat will stay at room temperature and the appliance will never turn off. That's why I plan to use simple adjustable duty cycle control.

    I started a thread in Project Logs for my project, which has similar requirements to the requirements in this thread but is a separate project. I linked to that thread a few posts back.
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

    9,131
    1,842
    Nov 17, 2011
    If you don't need exact control but can live with an approximate setting, you can use a dimmer (with suitable rating). The thermal inertia of an electric heater will average the power.
     
  12. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Kris,
    You may be thinking of oven thermostats which have a temperature sensor.
    The thermostatic controls for hot plates do not have feedback, they rely on a small internal heater bending a bi-metallic strip.

    Harald's solution is good if you can find a dimmer with sufficient current capability.
    Duke
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Duke, I see. What you describe is not really a thermostat, it's a self-contained on-off cycler device that uses heat internally. I would like to use solid state switching at zero-crossings instead of contacts, but I will look into this option; thanks for the suggestion.

    Harald, I decided against using a standard dimmer with conduction angle control because of the horrible things it does to the current waveform that's imposed on the mains supply, especially with a >2kW load! My current design is effectively a dimmer, but it operates at the half-cycle level; it turns the load on and off at zero crossings only. With an on-off cycle time of about seven seconds, it also relies on the thermal inertia of the appliance, but avoids the interference, harmonics and power factor problems of conduction angle control. Would you agree with my reasoning here?
     
  14. Harald Kapp

    Harald Kapp Moderator Moderator

    9,131
    1,842
    Nov 17, 2011
    Kris, using a zero crossing switch is a very good idea!

    Years ago I tried to build something similar to operate a 115 V popcorn machine from 230 V. Since the popcorn machine had a motor I could not use the long cyce time. Instead I opted for a zero crossing switch with a duty cycle of 1:4 (thus making the effective voltage 115 V). I didn't succeed then, One triac after the other blew to pieces. Probably some kind of current limiting should have been employed to limit the surge current at turn-on.
    You might want/need to incorporate something similar, e.g. an NTC?
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    That's interesting. I wonder what the underlying reason was. Did you always feed positive and negative half-cycles through in pairs? I think you would probably have to. I don't know how a motor would respond to having every second cycle missing... my gut feeling is that it wouldn't like it.

    I intend to use my circuit with heating loads only, which will only be resistive, so I don't think I need any kind of current surge limiting or suppression around the triac. I guess I will find out!
     
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

ā€œā€

-