Forum

multiple elements -...
 

multiple elements - variable power via script and pseudo A-D conversion  

  RSS

(@clearwaterbrewer)
New Member
Joined: 4 months ago
Posts: 3
February 20, 2019 8:01 pm  

I would like to control power with contactors, as heat generation from SSR's for the power level I am using is excessive... 45kw

5x 9kw 3-phase elements controlled by 6 contactors

C1-c4 - 9kw

C5 - 6kw

C6 - 3kw

with this, I should be able to get 3,6,9,12,15,18,21,24,27,30,33,36,39,42,45kw 

Control would be via an analog input on the Mega , could be potentiometer or any analog signal. Could even be a PID PWM  through an analog board back into the Arduino.

 

wondering what the best approach is?

here is one idea:

[PowerLoop]
if "analog_0" value < 15
// zero power
"C1" state = off
"C2" state = off
"C3" state = off
"C4" state = off
"C5" state = off
"C6" state = off
elseif "analog_0" value < 31
// 3kw
"C1" state = off
"C2" state = off
"C3" state = off
"C4" state = off
 "C5" state = off
"C6" state = on
...
...
...
elseif "analog_0" value < 239
// 42kw
"C1" state = on
"C2" state = on
"C3" state = on
"C4" state = on
 "C5" state = on
"C6" state = off
elseif "analog_0" value >= 239
// 45kw
"C1" state = on
"C2" state = on
"C3" state = on
"C4" state = on
 "C5" state = on
"C6" state = on
endif
sleep 10000 // 10 seconds between power changes
goto PowerLoop  
This topic was modified 1 month ago by clearwaterbrewer

Quote
(@pbruno3)
Estimable Member Admin
Joined: 2 years ago
Posts: 212
February 20, 2019 9:22 pm  

Looks like a good idea! But quite possibly your SSR quality is not that great, and upgrading those might be worthwhile?


ReplyQuote
(@clearwaterbrewer)
New Member
Joined: 4 months ago
Posts: 3
February 20, 2019 9:52 pm  

  I need to taper the power off as the pressurized jacket temperature of a bain-marie kettle reaches 240F/15psi...  as the interior of the kettle gets warmer, the delta-T decreases, and I have to reduce power further.

I am drawing 125A on each leg of three phase... so 375A of SSR's are needed (or at least 250A if one leg unswitched by SSR's).  Most people switch one leg of 2 23A 5500w elements, which is just under 50A, this is 5-7 times that heat, no matter how high of quality the SSR's are

Contactors work great and don't generate heat...  I bought a huge watlow power controller that retails for $2700 and can handle about half that current, 65A but it takes up a full 25% of my 24x30x12 panel and won't have clearance to shut the door if any switches are placed in the door...  also, cooling becomes an issue, a fan will just blow moist air over the components, not only is it hot and steamy in FL all by itself,  the work area is frequently even more hot and moist...

 

I have a simple script that works in steps and only reduces power one element at a time at temps of 237,238,239,240 on the jacket temp, but a more robust variable control is desired, maybe even PID that has a 10 second or longer duty cycle...


ReplyQuote
Share: