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A Question About PWM Controllers

Discussion in 'General Electronics Discussion' started by cygnusv, Apr 28, 2020.

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  1. cygnusv

    cygnusv

    76
    14
    Oct 7, 2014
    Hi All
    I'm updating the heating system on our boat. Currently we have a central heating circuit running from a back boiler in a solid fuel fire. I'm updating this system by replacing our small 5KW output stove to one which has better output, but more importantly also has a back boiler mounted inside the fire under the stove top. This will extract a lot more heat for the central heating.

    My problem. I am using a PWM variable controller to manage the speed of the 24 volt circulating pump. The first PWM lasted 2 winters then started 'hunting' and then failed. I replaced the unit with a more expensive unit but this too 'hunts' on occasion. Next winter the system will be carrying much more heat than now and I want to avoid PWM problems by finding something more robust.

    The current PWM I'm using is listed on Ebay UK under search number 323585726803. I had thought of some sort of 'stepped' speed adjuster rather than the variable turn dial. Main thing is that I want to change what I have for something I can have more faith in.

    Does anyone have a suggestion for a switching method that will achieve this. The pump doesn't need to run at high speed, Just enough speed to move the water round the system without the pump waking us up! The pump is directly under our bed..... :)

    Many thanks in advance. Stu
    PS, The circulating pump uses very little current
     
  2. Alec_t

    Alec_t

    2,822
    754
    Jul 7, 2015
    How much is 'very little current'? What is the pump rating? Electric motors have a start-up current which is several times their normal running current, so that may be a possible cause of controller failure.
     
    cygnusv likes this.
  3. cygnusv

    cygnusv

    76
    14
    Oct 7, 2014
    Thanks Alex_t. The pump is rated at 2.2 amps maximum - This is the pump

    https://www.mackengineering.co.uk/cm30p7-1-24-johnson-circulating-pump-24v-mag-drive.html

    The pwm I'm using says its rated at 20 amps, but I don't know at what voltage. I do know that some pumps have up to 5 preset 'clickable' speeds and I'm hoping to find an external switch that I can use that will achieve the same result. If I simply plug the pump into 24 volts it would run great, but we'd never get any kip!

    Many thanks, Stu
     
  4. Frankchie

    Frankchie

    91
    5
    Nov 14, 2017
    Maybe you can get away with a simple adjustable voltage convertor module. The disadvantage compared to a PWM controller is the startup torque is less. But maybe for just moving water you may not need a lot of torque.

    You can probably rig up some lower voltages using batteries to test if the pump runs satisfactory at a lower voltage. Check me, but I think I saw that your pump is rated to run at 12-24 volts although I'm not sure how low a voltage gives a satisfactory noise factor . Running lower than 12v may be possible, but I would not go too much lower than the manufacturer's ratings. Actually I might go lower, but I would not recommend that others do that.

    There are lot's of voltage convertors available just Google "adjustable buck voltage convertor module". Here's one module that seems to meet your requirements.
    https://www.aliexpress.com/item/400...earchweb0_0,searchweb201602_,searchweb201603_
     
  5. Bluejets

    Bluejets

    4,054
    847
    Oct 5, 2014
    PWM retains the torque at low settings.
     
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