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SSR-VA / Potentiometer Question

brewsmith
edited August 2015 in Configuration

Building a new control panel at the brewery and have run in to a little issue with my SSRs.

Both hot lines in run through a breaker. One the hot lines through the SSR connected to the pot, then through a contactor to provide a switchable/safe on/off. The other hot runs directly through the same contactor to the element. When I fire everything up, and the pot is dialed all the way down, I still read 120v at the element due to the direct line and it stays that way until the pot is turned up over half way, then the voltage starts to creep up with the dial. Do I need two ssrs to control both legs?

I am assuming I missed something very basic and need another set of 'eyes' on the issue to help, thanks!

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Comments

  • grim
    edited August 2015

    One SSR.

    Do you have 240v across the hot legs at the contactor? If so, good.

    How are you measuring the output voltage of the SSR? It's phase angle, it's not as easy as just hooking up any old AC voltmeter. I'd imagine you'd need to hook up an oscilloscope to do it. Your AC voltmeter is liable to read all sorts of funny numbers. You might get closer if you had a "True RMS" AC voltmeter, but even then it's liable to get thrown off by the choppy waveform. Really easier to measure current at the input to the SSR (NOT THE OUTPUT) and disregard the voltage as irrelevant).

  • grim

    I'd put the contactor on the input to the SSR, not the output, but the contactor shouldn't have a problem.

  • Myles

    You can measure the output current in 1 of the element legs and the voltage BETWEEN the element legs. Even if 1 leg is live and the other is issolated, there is no voltage accross the element as no current flows.

    With a lot of controllers BOTH the output current and the voltage between the element legs change as the pot is turned.

  • Myles

    If you are using single phase it is 1 controller, with 3 phase 400v supplies it is supposed to be 1 controller on each phase.

  • CothermanDistilling

    if the element is not connected, SSR is turned off, and contactor is on, you will have 120V from N/Gnd to either side of the element (one side is connected direct, the other gets leakage current through SSR... (there will be near 0V across the SSR)

    If element IS connected, the SSR is turned off, and the contactor is on, the leakage will be the other way, so to speak, and there will be 240V across the SSR

    the path through the element is what is causing the reading, there is nothing wrong... another SSR just adds more heat in the panel.. I know, that is how mine is and i am going to remove one SSR some day...

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