Shared 'dry contacts'

[ptonsparky]

Change of plans now that 2000' of wire is buried. nice We have a pair of #12 control wires in the raceway that were not needed originally.

Point A has control and dry contacts. Point B has a control and dry contacts. I would like to parallel the two contacts so that if either closes, it cycles both controls.
Workable or will one interfer with the other? That and distance laying directly next to 480.

 

[gadfly56]

I think you can do this with an auxiliary relay and power supply at each end. Have to think about it. And you may have too much voltage drop to make it work. Hmmmmmm...

Does the dry contact at each end act as an output or input?

 

[texie]

I don't think I would do this with AC. I think DC is a much safer bet.

 

[hbiss]

Little confused. Dry contacts are just switch contacts and as such will do nothing until you put them in a circuit with a voltage source and a load for the contacts to control.

Point A has control and dry contacts. Point B has a control and dry contacts. I would like to parallel the two contacts so that if either closes, it cycles both controls.

You mention controls and I take that to mean that they each provide a control voltage of some sort. Do these controls have auxiliary dry contacts on each that you are wanting to use? If you do parallel them, how do you propose to wire the loop to control the controllers since they both provide voltage?

If I'm correct, I would simply provide a relay at both controllers, the coils controlled by the dry contact loop.

I would do some calculations first, 4000' of #12, and coil current of the relays you want to use will give you the needed transformer voltage. Don't know if DC will make any difference. I don't think the 480 will be a problem. One good thing is that the #12 is already run so you can play with it.

Keep in mind that this is really a no brainer. POTS telephone lines do exactly the same thing over miles of 22GA wire under 12Kv and higher primaries.

-Hal

 

[hillbilly1]

Change of plans now that 2000' of wire is buried. nice We have a pair of #12 control wires in the raceway that were not needed originally.

Point A has control and dry contacts. Point B has a control and dry contacts. I would like to parallel the two contacts so that if either closes, it cycles both controls.
Workable or will one interfer with the other? That and distance laying directly next to 480.

Not going to work due to paralleling power supplies of both controllers, well, I say it won’t work, electrically it could work, but not a good idea.

 

[__dan]

You could add a ballasting resistor to the coil to mitigate induced voltage causing pull in of the control relays.

 

[hillbilly1]

You could add a ballasting resistor to the coil to mitigate induced voltage causing pull in of the control relays.

I like your thinking, kinda like fire alarm horn and strobe circuits, send dc one way to verify loop, send it the other way to fire the horn and strobe (except this is a relay) ?

 

[ptonsparky]

I was making it too hard. Typical. Point A will supply us 24VDC, run it out 2000' through a set of NO contacts controlled at Point B, then back through another NO set of contacts controlled at point A. If both closed we get a run command. Either drops or fails to close we get a stop command.

 

[hillbilly1]

I was making it too hard. Typical. Point A will supply us 24VDC, run it out 2000' through a set of NO contacts controlled at Point B, then back through another NO set of contacts controlled at point A. If both closed we get a run command. Either drops or fails to close we get a stop command.

But you said you only have two wires? And you were starting controllers at both ends.

 

[ptonsparky]

I like your thinking, kinda like fire alarm horn and strobe circuits, send dc one way to verify loop, send it the other way to fire the horn and strobe (except this is a relay) ?

Pretty much.

We had a full pivot and two pivot corners that were going to run separately from one well. None at the same time. Turns out well pumps way too much water and unless we added $xx,xxx VFD we were going to exceed psi rating of 30 year old buried pipe. We were set up as requested originally to run one corner or the other with radio controls. Two transmitters with one receiver at the well. We should be able to return one transmitter now.

 

[__dan]

Drawing needs a slight modification. If A.sense closes, B.operate is OK as is.

If B.sense closes and powers the B.sense coil, it should not cause the polarity reversing relay to toggle, which the above drawing shows. Slight modification, probably one more relay and another blocking diode needed.

 

[ptonsparky]

But you said you only have two wires? And you were starting controllers at both ends.

Yes, each pivot motor will start on pressure from the remote well, closing a well relay. Each pivot has a safety circuit that will trip open the well relay circuit should something go wrong. The radio transmitter and receiver talk so it knows when the well has started and allows for time to elapse before sending a Stop. System will attempt restart at each POCO cycle of power.

No,...

 

[Jraef]

Carlo Gavazzi makes a product called "Dupline" that is a 2 wire communication system wherein you would have a module at either end talking to the other one with the two wires, telling each other what to do. it's perfect for that sort of thing.

Dupline from Carlo Gavazzi

Carlo Gavazzi Dupline.

www.gavazzionline.com

 

[tom baker]

yes it would be. I used a product called Electromatic 30 years ago, and the logo is very similar to the Carlo Gavazzi. I am sure its the same product, it used a signal key for each channel, 2 wire, very simple.

 

[Jraef]

yes it would be. I used a product called Electromatic 30 years ago, and the logo is very similar to the Carlo Gavazzi. I am sure its the same product, it used a signal key for each channel, 2 wire, very simple.

Carlo Gavazzi bought Electromatic maybe 20 years ago (or more, I'm losing track now). It's still the same Dupline system. I couldn't for the life of me remember the original company name though, so thanks for that, saves me from waking up in the middle of the night with that answer.

 

[tom baker]

It was a good product and its not very well known. Interesting how large the product line is now. it would be a good application for this system.

 

[gar]

200409-14219 EDT

I can not understand this thread.

First, I don't like the name dry contact. Just call it a contact.

So we are dealing with two separate normally open contacts. Each is in a different location. The spacing is about 2000', and two wires exist between these two locations.

At each location there is some sort of controller that requires a contact closure to make it do its function.

Note: my use of the word contact means an electrical device with two terminals that has two states, open and closed (high impedance and low impedance), and is electrically isolated from anything else until explicitly connected to something else.

The desired function of the contacts is that both originally stated contacts must be closed to perform some system function. This is the logical "AND" function. This is accomplished by connecting two NO (normally open) contacts in series.

Thus, we create a circuit with the two contacts in series, and interconnected by the two #12 wires. #12 copper wire is about 1.5 ohms per 1000'. Thus, wire loop resistance is about 6 ohms.

A 24 V DC P&B KUP relay coil resistance is is about 450 ohms. Thus, two relays in series is 900 ohms. Wire resistance is insignificant. With this series combination you would use a 48 V DC source.

Because it is a wet environment it would be better to use reed or solid state relays. If there is a noise problem place capacitors across the relay coils.

.

 

[hbiss]

I would like to parallel the two contacts so that if either closes, it cycles both controls.

The desired function of the contacts is that both originally stated contacts must be closed to perform some system function. This is the logical "AND" function.

No. He want's a logical "OR" function.

-Hal

 

[gar]

200409-

hbiss:

See post Tuesday 2:06 PM. A logical AND.

..

 

[gar]

200409-1619 EDT

If he really wants logical OR, then complement the inputs and outputs. In other words input contacts are normally closed as are the outputs.

.