Answer to another set of posts.

Hi, I have not been able to remember the person who got back to me about arc suppression on relays and thanks to Carl for the info on the Thorn DC motor speed controllers. Recapping the controllers did the trick and having one of the DC motors overhauled did the trick.
The subject of Arc suppression on relay contact was solved by a .1ufd capacitor in series with a 100ohm resistor across the contacts. I had a strange occurrence when I tried the same thing across the temperature controller contacts that the temperature controller overrode the set values. I had to remove the capacitor and resistor from the controller. The capacitor and resistor were across the internal contacts using the external screw contacts I have yet to determine the best solution I will let everyone know how I got on. I would like to hear any thoughts on the subject.
 
No problems...DC drives a great bit of control kit. ..As for the snubber network resetting the values on the temperature controller. That is a bit strange almost suggests that there is some type of feedback to the electronics. If I remember there was some talk about SCR instead of a contactor/Relay. You are probably putting some noise on the supply to the temperature controller...if you can maybe put it on a different phase line....or scope it up and see what's going on
 
No problems...DC drives a great bit of control kit. ..As for the snubber network resetting the values on the temperature controller. That is a bit strange almost suggests that there is some type of feedback to the electronics. If I remember there was some talk about SCR instead of a contactor/Relay. You are probably putting some noise on the supply to the temperature controller...if you can maybe put it on a different phase line....or scope it up and see what's going on
Sorry I have confused the conversation on the DC controller which is all good but the issue is separate it involves the temperature controllers for the heater bands on one of the plastic extrusion machines which had separate relays for each heater band the relays had their contacts paralleled together to reduce the current flow on each contact which resulted with the burning of the contacts due to arcing still happening. The snubber network on the relay contacts fixed the arcing problem. The issue seems to have arisen when I tried the same system on the temperature control relay built into the temperature controller contacts the is where it came unstuck even though the contacts were independent of the mains supply and the relay coil supply was from its own built-in power system. The 230 volts was a separate feed to one side of the relay contacts which fed the auxiliary relay for switching the heater bands on and off. The snubber network some how allowed enough current to flow to either keep the relay energised or some other occurrence happening.
 
I don't follow what you've done but doesn't seem to make sense. ...not all snubbers are equal. Have you googled a device called MOV "in snubber circuit" this is a different take on the snubber circuits, you could combine the resistor-capacitor circuit and MOV.
If it's possible you could measure the inductance and resistance of the circuit, then you could calculate a snubber circuit if I remember correctly Semikron used to have some docs on how to do this. Alternatively, you could download a simulation package like Scilab and build the circuit in the xcos package and then calculate the value of the "best snubber network"
Or just simply phone up one of the MOV suppliers and ask them for a recommended MOV...for sure they will have all the relevant tools at hand to give you the best solution. MOV cost pennies, but they do like to explode or certainly, they used to in the day maybe they have gotten better...
Saying all that you are still probably better off with a SCR device....if you are battling with how to implement this just pm me send a circuit/schematic over and we can figure it out shouldn't be too difficult
 
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