Contactor Questions

[n00b 0f l337]

Working out a PID and contactor, not sure If I need another piece or if I'm doing it right, so asking :) A contactor is basically a relay from what I know, so I don't think I need another relay.

I'm trying to set the PID to trigger the Contactor, the PID has two junction outputs that can be set as relays or "PID Relay" not sure the difference, and one output to SSR. Thats a solid state relay, not sure how it differs from a Contactor though. Does anyone know where I wire it up?

Bazx I've seen you use Contactors, any wiring schematic for them to your PID?

[mytekcontrols]

On the PID temperature controllers I have used in the past, the SSR output is normally meant to be used for situations that will require rapid cycling of a control device (something that a very low mass would require in order to maintain a tight temperature).

It is basically a solid state switch, so there would be no contact arcing to worry about. However if I remember correctly, this output can not handle very many amps (maybe 1-3 amps). The relay outputs can normally handle 10 amps. So if your control device falls within the current capabilities of the SSR, then I'd say use the SSR. Otherwise you'll either need to boost it externally, by using an external relay, or just use the relay output of the controller if its current rating suits your needs.

As to wiring; both the relay and the SSR outputs are treated as a basic switch, so just wire it in series with what you want to control.

[n00b 0f l337]

So wire one terminal to each of the trigger terminals of the contactor? I guess my question is, should the relay option be able to trigger the contactor which will then cut the 2nd stage compressor in on the cascade I'm working on?

[DetroitAC]

Relays and contactors are rated differently, contactors are used to switch power to motors, whereas relays may only have their rating for resistive loads, and not inductive loads (like an AC motor).

I would bet that a compressor on a cascade would be too much for the relay in a PID (but you have the specs), so you're heading down the right path of using a contactor. Electrically, you can wire them as if they're a relay like mytek said.

[wdrzal]

Do you know what the coil voltage of the contactor is ???? You must supply that voltage for the coil to hold the points closed. or change the coil.

[mytekcontrols]

Actually relays can also be rated both resistively and inductively when it comes to current handling of the contacts. And relays are used all the time in inductive load applications. I think the big difference is that contactors typically have been manufactured in much higher ampacity then most relays, may have better release capabilities, and are primarily used in high current 3 phase motor control applications.

In fact, a lot of the AC units out there with remote controllers, are using relays to switch the power for the compressor and fan motors. So if it works for an standard AC unit, then it should also work for your modified AC beasty as well.

Now back to your question Adam: Check out this post (http://www.xtremesystems.org/forums/showthread.php?t=183010) for an idea of how to wire a controller to a contactor. Just substitute your PID's SSR or relay contact for the time delay relay shown in the posted diagram I gave a link to.

[wdrzal]

A relay and a contactor are same thing. Before the age of solid state relays (no moving parts) all relay/contactors where electro/mechanical. Usually a lower current and/or voltage is generally used as a control circuit to energize the magnetic coil to close the contacts(electro/mechanical) thus energizing the main load. Usually the main load is a higher amperage.

[[XC] Hicks121]

A relay and a contactor are same thing. Before the age of solid state relays (no moving parts) all relay/contactors where electro/mechanical. Usually a lower current and/or voltage is generally used as a control circuit to energize the magnetic coil to close the contacts(electro/mechanical) thus energizing the main load. Usually the main load is a higher amperage.

QFT!

Typically a relay is used for lower current draw situations. Where as a contactor can go up to 1000+amps & they are customizable with aux contacts & many other controll related things. They also can be made into a starter, but I wont get into that.

[n00b 0f l337]

The coil I believe is 110V 50/60Hz. So I guess I need a relay to take the output voltage from the PID, and use it to connect 110V to the contactor, to close 110V to the compressor... Hmmm odd, for some reason I thought since it would handle a SSR it might handle a contactor, guess I was wrong. Or am I better off dumping the contactor and going with the relay Mytek posted?

[n00b 0f l337]

Okay it says the relays are rated for 3A at 240VAC. So I guess that means I screwed up my knowledge lol, not to trigger a relay, but it has the relay built in. Okay so PID closes relay, and it can handle a 3A load. So now how might I get that to handle a compressor.... Unless, what if I ran a powerline from wall thru the contactor and through the relay all in series. Thus the relay closes the circuit.
Right? Thus my problem right now is theres no voltage in my wiring :P

[boshuter]

I think you are still missing the purpose of the external relay/contactor. All the relay output of the controller has to do is energize the external relay, it doesn't matter how large of a load that relay is going to control.

You wire the output from the pid to energize the relay, your mains power will go through the second side of the external relay.

Think of a relay as 2 separate circuits, one low volt/amp side and one high volt/amp side. The low side requires very little volt/amps to work and it doesn't matter what the load is on the second side.

It just allows you to control a high amp load with a very small amp.

[n00b 0f l337]

Yep figured it out, was forgetting a mains connection :)

[mytekcontrols]

Yep figured it out, was forgetting a mains connection
I was hoping that you would. :up:

Otherwise I was about to whip out the DeltaCad and draw you a complete circuit diagram for your specific situation.

And yes Walt is correct; a contactor is a relay, but as Hicks pointed out, it is a special type usually associated with motor control. Although it doesn't have to be (I've used them for shutting off the main power on vacuum system power supplies when a safety switch was opened).

[n00b 0f l337]

They're great though, simple concept brought to a beautiful tech level.

[wdrzal]

Noob if I was you go to radio shack and get a electrical/electronics beginners kit with a bread board and manual. Learn how to use capacitance & resistance to control electron flow. Learn AC & DC, analog & digital inputs and outputs.Basic wave forms and logic. Build a temp controller,clock ,radio, transmitter etc.....It much easier if you got the basics down first..Otherwise you will probably ruin a lot of expensive electronics. It will be worth your time....

While wiring a contactor is easy enough. Control strategies can be very complex.especially when mixing analog and digital and using a wide variety of different voltages,loads & switching gear. Just Manually setting the gains on a PID or setting up a frequency drive takes some advanced know how.You can't guess,or POOF a few hundred/thousand dollars of trash.

[n00b 0f l337]

I've been doing those kits since I was 6.
The output for this PID stated that it provides a signal voltage, thus I thought I was going to need a separate relay, but was willing to try just a contactor to start, then found that it doesn't mention that the signal is for SSR only, and that the other relays are normal relays ;)
I'm not an electronics guy by far, but I manage without zapping myself everytime ;)