Speed control and on off switch for 12v dc motor

Discussion in 'General Electronics Chat' started by Aburrell, Feb 9, 2018.

  1. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    Hello
    I need to be able to turn on and off and vary the speed of a 12v motor, driving a diaphragm pump. The motor will plugged into the mains.
    I have no idea how to go about building it. I have looked in the forums and largely couldn't find a solution or I just didn't understand the responses.

    Should I be on and is there a site catering for people like me who've no idea.

    I have found some circuit boards on Amazon that seem to want to give me what I am looking for.

    Thank you

    Andrew
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    You haven't given us much to go on. What is the full motor spec (power, current)? Can you post links to the motor/pump/circuit boards?
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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  4. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    I have an exhaust fan I use as a blower with water misters. I can control the motor speed from full on to very slow to off; and vice versa. They sell them. Just ask for a blower motor speed controller. Let me peruse one of the local home improvement store websites and see if I can spot one for you. No need to build anything, just a little wiring up work.

    [edit] OK, here's one that operates on 120 VAC and is good for 2.5 amps (that's 300 watts) for about $40.

    https://www.lowes.com/pd/SUNCOURT-Duct-Fan-Controller/3228002
     
  5. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    After looking a little closer at the specs and questions others have asked, this might not be quite what you may need. Since we don't know the power rating of your fan, watts, VA's, horsepower - etc. knowing exactly what you need is at best guesswork on our part. The fan I mentioned that I use is a fairly significant motor - but I can't tell you the specs. As an (originally) exhaust fan, this thing moves air. Largely the reason why I use it outdoors. It can move air across the back yard. Set up a sprayer in the moving air column and you get a significant amount of cooling a good distance away, especially in my dry climate.
     
  6. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    Hi
    Here's the pump details:

    Specification:

    Voltage 12V when: power is 5W / H
    Outlet diameter: Inner: 6mm/0.24”
    Outer: 9mm/0.35”
    Operating voltage Working power Flow Maximum suction
    DC6-12V 5W/H 1.6-1.7Min 1.2M
    Features:
    It applies to: the towers, changing the water tank, pumping device
    It can used for Water or Air.

    This came with no circuit boards.
     
  7. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    I bought it from EBAY. I'm assuming I can't show the product for fear of contravening site regulations.
     
  8. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    You're allowed to.

    [edit] In fact, many sites like it when you direct someone to their web page.
     
  9. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    LOL. I'm sure they do like it.
     
  10. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    Suddenly I'm realizing that I was getting caught up in the "Mains" part of your question. The end result is you want to control a 12 volt motor. So assuming you're going to use a transformer or repurposed wall wart, you can probably go with PWM (Pulse Width Modulation). Wall warts for phones put out 5 volts. But some put out 9 volts, more for cordless phones and such, and some from old printers may put out 12 volts. At 5 watts your current needs are (5÷12=) 0.42 amps (or 420 milli amps).

    I've gone to Xfinity from time to time and asked if I could have an old power supply someone returned with their modem or cable box. I often get one or two for free, and they're typically 3 to 5 amps capable; far more power than what you need to run this pump. Now, concerning PWM, you can build something yourself, it's not difficult; OR you can go to an automotive junk yard and pull the dash board light dimmer controller from a wrecked modern car. I'm sure they won't charge much. Maybe a couple bucks, maybe five. If they want more than that - just go to another yard. Anyway, I have one of these from my wife's Toyota Celica. It provides path to ground. Let me elaborate: Power goes to the bulb, then to the dimmer then to ground. The dimmer itself needs 12 volts, so as you turn it up or down the lights (in your case the motor) will brighten or dim (or speed up or slow down). As for completely off, some cars won't go completely out. The one out of the Toyota does. It reaches a point where the PWM simply shuts off. Now, that IS going to be using a small amount of power when in operation, even when at zero. So you'll probably want to use a switch to control the on and off part of your system.

    Funny, I just went to Xfinity four months ago and picked up two power supplies. Their ratings are:
    Input; 100 to 240 VAC 0.9 amps 50/60 Hz.
    Output; 12V, 3A

    I'm sure that will give you plenty of power. A power supply for free and a dimmer from a junk yard for a few bucks and a little time pulling one out - sounds like a winner to me. Odd thing; I have that dimmer and have never used it on anything. At least not yet. Maybe on a model railroad. Maybe.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Those pumps show a 1.2amp rating so you do not need alot in the way of power supply.
    You can get the 555 PWM controllers on ebay (182304262165) for ~$2 to $5 .00.
    Max.
     
  12. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    Thanks all you lot.
     
  13. Aburrell

    Thread Starter New Member

    Dec 28, 2017
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    I've got my hands on a 500 mA power supply.
     
  14. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    That MIGHT be big enough. Don't see why it wouldn't work. But then again, we're not figuring in for overhead stuff like the current needed by the PWM. A good general rule is always to give yourself a buffer of at least twice what you need when practical. Assuming your PWM draws only 80 mA (milli-amps) you'd be right at the threshold of whether your system will work or not. I don't know what to expect from a PWM module from e-Bay or Amazon. Right now I have a few other things going on that need my attention, otherwise I'd look that information up for you. But I would recommend at least 1 amp power supply.
     
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  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Although 0.42A may be the current when running, the start-up current of the pump is likely to be several times that. Even a 1A supply might not cope with the start-up surge; but you could strike lucky.
     
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