Power Controller

edited January 2023 in General

I am busy putting the finishing design touches on a 3,000L still and am now starting to look at the power controller.

The still is 54KW, 3 phase, 380VAC. There are 6 x 9KW heating elements. The still will be 100% automated where heating output control is 4-20mA to the power controller.

I received my first quote yesterday and the price was scary. It was for a Thyristor control unit.

The quote today was for a fan cooled WATLOW unit model DC32-40S0-0000 and the price was quite reasonable. Now I know WATLOW to be a quality item.

But it got me thinking, ...... what are others using where they accurately control power to the heating elements.

Cheers from sunny SA. Today about 33 deg C.


  • edited January 2023

    I’d say use contactors for 4 of the 5, and just make 1 variable, but contactors are expensive too.

    From a panel perspective, you can just use a 4 position switch for the power, and one rotary knob for the fine control. PLC even easier. Bonus is you can get away with a much smaller variable controller.

  • Thanks @grim . The concept of how I do things is that no element power is at 100% whilst others are say at a lower value. They must all be identical at any one time, hence the fancy controller. The logic behind this is prevention of element burn on. As it is, each of the six 9KW element is at a fantastic value of 4.6 watts/cm2

  • edited January 2023

    Hey @richard,

    That is a pretty big still to be running on electric. Most use steam once you get to that size.

    With 54 kw let's say we start at 70F and start producing around 195f, in a perfect world it would be 4.72 hours just for start up. Being this is not a perfect world and there are heat losses and other inefficiencies that time is just going to go up.

    Sorry for bearing bad news.

  • edited January 2023

    Thanks @WindyCity . Yes you are correct in your comments regarding time. I had overlooked this issue in the initial design but had subsequently corrected it with increased elements. Currently the new design uses 9 x 9KW elements and overcomes time issues. Inefficiencies are overcome due to the still being completely insulated.

    Yes steam can offer faster heat up but unfortunately has limitations in exacting temperature and operation control.

    Regarding heat up time, this is not an issue due to the still being completely automated where I am able to initiate an automated and unattended start up during early hours of the morning. Here I am able to set start up time and to what temperature I wish to heat up to as well as amount of power input, agitator power, temperature at which cooling water automatically comes on etc. There are additional interlocks for safety as well.

  • 6x9 is what I use for 1000L still, I'm glad you're going with 9x9, but your heat up is still going to be (too) long for 3000L.

    Sounds like your elements are going to immersed inside the still rather than a jacket? Honestly, I'd avoid that at all costs, especially for such a large still where you're going to want to run at full power for a long time to get going.

    @grim is right to suggest all but one flipping on/off.

  • edited February 2023

    Thanks @jbierling . Yes inside the vessel. This affords me precise control and also shortens heat up time. My 100% power heat up time to temperature I have at 2'38'' which I don't think is too long. In any case the majority of this time would be done outside of the workday . Other than heat up, I don't / rarely run at 100% power.

    For my existing 700L kettle also automated, below is what my power controller in the high voltage panel looks like. The power output is via a 4-20mA input from the PLC. The system works really well. In this manner, you can run PID loops for heat control. You can see this further below for when I was last running an internal CIP programme.



    800 x 800 - 113K
    800 x 606 - 66K
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