Can someone explain what an RC network is and what it does? I understand that it is good to have an RC network across the coils of contactors that are controlled by a plc or some other sort of electronics to dampen the arcing of the relay. Is this correct? How necessary is this? How do you design an effective RC network?
RC network design
- Thread starter lesmar96
- Start date
My applications would be mostly AC suppression.
The reason I ask is because one of my customers is using a temp controller to control heats and blowers on a plastic extruder line. The relay contacts of the temp controller control contactors and relays for the heats and blowers. But the temp controllers only last a few days. In a couple days, the output of the temp controller quits working. Some tech support told me that it needs to have an RC network or it will blow out the electronics in the temp controller from all the switching. But I need help to know how to build an effective RC network.
The reason I ask is because one of my customers is using a temp controller to control heats and blowers on a plastic extruder line. The relay contacts of the temp controller control contactors and relays for the heats and blowers. But the temp controllers only last a few days. In a couple days, the output of the temp controller quits working. Some tech support told me that it needs to have an RC network or it will blow out the electronics in the temp controller from all the switching. But I need help to know how to build an effective RC network.
Typically you want a RC/Diode Suppression to protect the outputs of a PLC. They are also a good practice just to suppress noise if you have a lot of AC coils on a circuit. Are you burning out the Temperature Controllers (Watlow comes to mind) or are you burning out something else?
If the Temperature Controller is a "simple device", such as a simple on/off contactor, then I could see suppression being of value, but again mainly to protect the control that engages a relay.
DC circuits are now a days, protected by built in diodes, we like them because they also indicate state, but AC relays/circuits often do not have this protection integrated.
What device is burning out? A model would be great, just for clarity.
If the Temperature Controller is a "simple device", such as a simple on/off contactor, then I could see suppression being of value, but again mainly to protect the control that engages a relay.
DC circuits are now a days, protected by built in diodes, we like them because they also indicate state, but AC relays/circuits often do not have this protection integrated.
What device is burning out? A model would be great, just for clarity.
Gene Bond
Member
My bet is that the relay is wearing out, but could be the arc from the contactor coil is blowing the contact.
'Quencharc' is a brand name r/c all-in-one device that comes to mind, it's UL Listed for this purpose. In the old days, we always just hooked a 150 ohm 1/2 watt resistor in series with a .1uf capacitor across the 120v coils...
'Quencharc' is a brand name r/c all-in-one device that comes to mind, it's UL Listed for this purpose. In the old days, we always just hooked a 150 ohm 1/2 watt resistor in series with a .1uf capacitor across the 120v coils...
GaryS
Member
RC Networks only work on AC coils to select the correct one in hit and miss thing.
I get it from the manufacture that the way to select is get bunch of different ones and try them out to see what works.
fir what I see in the post you are having trouble burning out power relays on the heaters.
I would change the out for solid state relays with zero crossing . I think you will find that it will solve the problem. years ago the used mercury relays for heating applications du to the short cycling but I don't recommend them. I have seen them explode and spray the mercury all over the inside of the panel. a real mess to clean up. the solid state relays can handle the short cycle with out any problems and you don't have the voltage spikes that you have with mechanical relay coils.
I get it from the manufacture that the way to select is get bunch of different ones and try them out to see what works.
fir what I see in the post you are having trouble burning out power relays on the heaters.
I would change the out for solid state relays with zero crossing . I think you will find that it will solve the problem. years ago the used mercury relays for heating applications du to the short cycling but I don't recommend them. I have seen them explode and spray the mercury all over the inside of the panel. a real mess to clean up. the solid state relays can handle the short cycle with out any problems and you don't have the voltage spikes that you have with mechanical relay coils.
Given a quick search:
Here is an Allen-Bradley part to get you started. It's expensive, like everything AB sells, but you get what you pay for. Let me pull up your doc's and see what they specify. Keep in mind there is RC supression and there is MOV, I would guess you'll end up with metal-oxide varistor (MOV), but both serve the purpose.
https://www.rexelusa.com/usr/Root-Category/Power-Distribution/Power-Quality-Protection/Surge-Protection-%26-Power-Quality/Surge-Protection---Panel-Mount/Allen-Bradley-199-FSMA10-VARISTOR-SURGE/p/71169
Here is an Allen-Bradley part to get you started. It's expensive, like everything AB sells, but you get what you pay for. Let me pull up your doc's and see what they specify. Keep in mind there is RC supression and there is MOV, I would guess you'll end up with metal-oxide varistor (MOV), but both serve the purpose.
https://www.rexelusa.com/usr/Root-Category/Power-Distribution/Power-Quality-Protection/Surge-Protection-%26-Power-Quality/Surge-Protection---Panel-Mount/Allen-Bradley-199-FSMA10-VARISTOR-SURGE/p/71169
I agree with both @Gene Bond @GaryS. I think it depends on the level of effort ($$$) you want to put into a solution. I would contact the manufacturer and buy one from them direct, unless you want the home-brew solution, like the resistor / capacitor from Allied or Digikey as @Gene Suggested, no offense, but it's all you get in a canned package from a vendor (MOV excluded).
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Solid State will burn out even faster without the right protection, if I understand your schematic correctly. I think you are using the heaters in a Pulse Modified Control, where that device could be firing a coil on and off very often, depending on the setup.
PID can be both Analog or Pulse Modulated, so you are running in Pulse Modulated, and that's why it's burning out the controller. Your Microwave (well up till the newest ones) and your Forced Air Furnace both run Pulse Modulated, they run 100% for x period of time. The quicker that turns on and off, the more significant that suppression becomes.
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