Temperature control of 3 phase heaters

strantor

Joined Oct 3, 2010
6,782
Ok thanks. But I guess I still need to figure out why this happened too. the third phase was only giving me 230v between the first two instead of 400. I've checked the circuit and wiring and it looks ok.
Your heater element probably needs to be replaced. Resistive loads don't just occasionally trip overloads, and they also shouldn't be prone to welding contacts (as opposed to inductive loads like motors). If you have tripping/welding then something is wrong with the load.
 

Thread Starter

JonathanL

Joined Jun 12, 2020
16
Yeah I'll be checking the load when the system cools down and is emptied out. I have a feeling the element may have failed
 

bassbindevil

Joined Jan 23, 2014
824
Maybe the emergency override relay could be connected to a simple mechanical thermostat or thermal fuse. Like the ones in a microwave oven, which open if someone warms a muffin for 15 minutes instead of 15 seconds.
 

THICKO

Joined Jun 10, 2016
17
Strictly speaking you should have 2 independent circuits,
one as control, one as alarm, both driving separate contactors.
There should be 2 sensors.
You can also create an alarm condition by monitoring the aux
contact of the control contactor and the state of the controller.
output. That way you determine whether the contactor is releasing
when the control signal is off. You use an XOR circuit to do it.
IE. contactor on + controller on = OK
contactor off + controller off = OK
Any other state is a fault.

Just my 2c of course.
 

Kevoh24

Joined Jan 1, 2021
2
Hi guys

I am looking for some help on a system which I have here. There is a temperature probe in a tank which is monitoring the temp of a liquid and the controller output is switching a 3 phase contactor on and off when the temp of the liquid drops below the setpoint and then switches the contactor back off when the setpoint is reached again. The problem is now that over the weekend the contactor welded closed and kept heating the liquid which had to be dumped. There is an over temp alarm relay output on the controller which was not connected to the circuit therefore no failsafe. I need to configure this now so that the contactor coil switches on and off as normal through the relay output of the controller for when it drops below setpoint and then switch off when setpoint is reached. But i also must now get the over temp alarm into the circuit to switch the contactor off as well. I am a little confused as to how to go about this as in should i install a safety contactor so that if contacts weld shut no power will flow, should I put in a safety relay, or change the type of temp controller with different outputs instead of relay outputs. Or maybe a logic module of some sort? The temp controller in question is an Omron E5CSV
Change the contactor itself to a bigger one putting into consideration the current. It seems that the heaters are drawing too much current therefore making the contactor to weld.
 
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