Heating Element Control

I started this week on my steam generator build.

Regarding the heating element and its control I have decided to use a 6KW 380VAC 3 phase element. I decided against a single phase 5.5KW element because I feel that it's on the upper acceptable limit for current loading.

I had originally decided to control the heating element with a SSR with 4-20mA from my PLC (I have spare 4-20mA modules in stock). This is fine for single phase but not so fine with 3 phase because it is not readily available for inexpensive solutions. YES you can buy some expensive Thyristor control for 3 phase and 4-20mA control.

So the question is ... without spending serious money, how can you effect PLC heating control with 3 phase.

Some of the guys I have spoken to have suggested 3 x SSR's in series for 4-20mA control of each phase.

Another has suggested a temperature controller (panel door mounted) which has 3 setpoints where you can drop idividual phase at temperature setpoint and then use a single SSR with 4-20mA on the one phase for fine temperature control.

Suggestions ??


452 x 800 - 85K


  • edited August 2017

    Watlow Power Series or Din-A-Mite 3 phase SCR. These both have 0-10v or 4-20ma control input.

    Are you in AU?

    These can be found very inexpensively in the US on Ebay.

  • edited August 2017

    I'll gladly reship one over to you if you can deal with the shipping waits.

    How many amps per leg do you need?

    Here you go, this one is a touch small for 6kw I think, but should squeeze by if you can keep it cool, 4-20ma control, $21usd.


    or this monster at 65 amps

    Watlow DC21-60F0-S000 @ eBay

    You'd need to confirm your wiring diagrams too, for the element, the first one has 3 legs controlled, the second is 2 leg control.

  • looks brilliant thanks. Let me do a little more homework and then I will contact you.

    cheers Richard

  • edited August 2017

    Thanks @grim I managed to come right.

    I managed to get a 4-20mA, 3 phase, 30A controller for a brilliant price. Out of the box brand new and controls all three phases. The company concerned had stopped this particular model and only was now doing +60A as their smallest size. So they gave it to me at cost and at a price that I could not refuse. They have two more at 30A one of which I will take next month. A 50A was marginally more expensive.

    The next one for next month I will use a pot / temperature to control whereas the controller for today will be via my PLC.


    452 x 800 - 79K
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