Electrical help needed/explained

[scottstribling]

I have attached a working diagram of my control box. Everything works. I have made 6 batches with it. I am just fine tuning things. I am trying to control my boil rate a little better. To have it simmer rather than a vigorous roll. I have adjusted the duty cycle on the PID to 55%, manually and it does the trick but I still have the pulsing of the element of and on. I decided to add a potentiometer to the mix. I added it to the PID SSR out pin (7+) that goes to the element selector switch. It is a 5k Ohm, 1/2 watt. Resistance is 0 - 5.11 ohms. The PID pin 7+ has 23.4v going to the pot switch at the pot switch it stays 23.4v until resistance is added. Rotating the switch to a 2.37 ohm resistance the voltage drops to 5.6v. There Boil Element is a 240v, 5500w element. When the pot switch has a resistance of 2.37 ohms and the output to the SSR is 5.6v, one leg of the Boil Element stays at 120v and the other leg drops to 0v. If I continue to turn up the resistance on the pot switch, anything greater than 2.37v and the voltage going to the SSR drops below 5.5v, the element shuts off, but both legs of the Boil Element maintain 120v, with the one that had 0v to come back live with 120v. I am perplexed by this. Im not an electrical whiz, basic knowledge with help from this page and PJ. I have went through a test boil cycle with this setup and none of the wires or hardware gets above 115F except the heat sync for the SSR.

 

[Brumateur]

The SSR you have can not be controlled by potentiometer. It works just like On/Off switch. If voltage on control terminal is high enough it switches ON, if voltage is below threshold SSR switches Off.

To have gradual boiling control you need a PWM circuit with duty cycle around 1 sec.
If you are using Auber PID you can reduce cycle time to 1-2 seconds to mitigate pulsing effect.

 

[scottstribling]

Yea, with all that crazy stuff going on I am forgoing the pot switch. I have adjusted the PID (Auber Syl2352) for the boil. I have it in manual mode and set to 100% duty cycle until it starts rolling, then manual reduce it to 55%. This provides a good simmer but the element still cycles on and off. I was trying to alleviate that and control the power not the cycle. I thought about a switch on one of the 120v legs and just run the element (5500w) at half of its rated wattage. Would have to add a relay that would shut the leg down when kettle reached boil temp. Any ideas.......I read your quote....not keeping it simple. Thanks.

 

[Bobby_M]

Don't take this the wrong way but you're barking up the wrong tree. You can't switch one of the legs to get 120v. You would have to switch one of the element terminals from one of the L1 or L2 hot legs to a Neutral in order to get 120v. If you just break one of the legs with a switch you get zero volts at the element.

Also, if you DO switch one element terminal to neutral to give it 120 volts, the element puts out one quarter of the wattage, not half. I don't think you'll maintain a boil that way.

If you want to smooth out the boil surging, Brumateur had it right. First, be sure you have the duty cycle at minimum setting of 2 seconds. In that case, your manual setting of 50% would put it on for one second and off for one second. If that's is still too surgy *it shouldn't be, you would want to add a VSSR inline with the leg that goes through your regular SSR. A potentiometer hangs off the VSSR (which is a different kind of device than a regular SSR) and what the potentiometer does is actually limit how long the power is applied every 1/60th of a second. As you can imagine, it's so fast that there is no surging.

 

[scottstribling]

Loud and clear! Thanks guys!