Shared 'dry contacts'

[hbiss]

I too gave up. Originally there was to be two NO contacts in parallel then series then timers then one-shots. My head hurts.

Normally I would be looking for a sequence of operation or a reference design, the way everyone else does it. That's the place to start.

Exactly. Tell us what equipment there is and how everything is supposed to operate.

-Hal

 

[ptonsparky]

All you need to know is: I have a timer that uses a NO switch wired to terminal 5 & 6 to start that timer sequence.

Now, add an identical timer using the same NO switch wired to its terminal 5&6.

Will they both start their respective timer sequence?

 

[hillbilly1]

All you need to know is: I have a timer that uses a NO switch wired to terminal 5 & 6 to start that timer sequence.

Now, add an identical timer using the same NO switch wired to its terminal 5&6.

Will they both start their respective timer sequence?

Maybe, but you are paralleling each timers start circuit voltage, it may cause false starts if the other timers electronics interferes with the trigger signal.

 

[ptonsparky]

Maybe, but you are paralleling each timers start circuit voltage, it may cause false starts if the other timers electronics interferes with the trigger signal.

That is what I was concerned with.

 

[texie]

That is what I was concerned with.

I think this could let the magic smoke out as each relay has it's own power source.

 

[gar]

200410-20111 EDT

ptonsparky:

You have no way of knowing what will happen until you know how the time delay relay works.

Since only a contact closure between pins 5 and 6 is required to initiate timing this means there is some other source of power to the time delay relay. You also need to know if contact closure between 5 and 6 is required after initiation of timing and thereafter until the timer output is to be dropped.

For a low cost timer it is likely that there is no electrical isolation between the power source to the timer and the terminals 5 and 6, and therefore, if the timers are powered from separate electrical sources you may not be able to parallel the two sets of terminals 5 and 6.

To make decisions you need to know your products.

.

 

[hillbilly1]

Modern timers are usually electronic, so that input is most likely only a few volts, and is looking for that voltage to go "low" to trigger timing. So I figure it probably will not smoke it, but may give erratic operation. Someone with far more electronics experience could probably give a better answer.

 

[gar]

200410-2345 EDT

ptonsparky:

If you have only one pump, and need a delay to start, then why do you need two timers?

.

 

[hbiss]

For a low cost timer it is likely that there is no electrical isolation between the power source to the timer and the terminals 5 and 6, and therefore, if the timers are powered from separate electrical sources you may not be able to parallel the two sets of terminals 5 and 6.

What the heck are terminals 5 and 6??? How about a model number and diagram of the timer.

-Hal

 

[ptonsparky]

https://www.ametekncc.com/-/media/ametekncc/downloads/industrialcontrols/timedelayrelays/timedelayrelays_multi-time%20range%20function%20tmm%20series.pdf

 

[ActionDave]

What the heck are terminals 5 and 6??? How about a model number and diagram of the timer.

-Hal

It's the pins on a standard ice cube relay. 2 and 7 are the coil, 1 is common to 3 and 4, 8 is common to 5 and 6, each are NC and NO respectively.

 

[ptonsparky]

Not the same because it uses supplied power via 7.

H3CR-A Solid-state Multi-functional Timers/Specifications | OMRON Industrial Automation

Solid-state Multi-functional Timers Multiple Operating Modes and Multiple Time Ranges. DIN 48 x 48-mm Multifunctional Timer.

www.ia.omron.com

 

[kwired]

It's the pins on a standard ice cube relay. 2 and 7 are the coil, 1 is common to 3 and 4, 8 is common to 5 and 6, each are NC and NO respectively.

Except his plug in relay is a timing device and terminals 5 and 6 are not contacts but rather the "input terminals" to initiate a function of the device.

 

[kwired]

I think this could let the magic smoke out as each relay has it's own power source.

Probably lets the smoke out if this function is on AC current and the two AC currents are out of phase with one another.

Otherwise it may simply cause undesired operation if conditions are right. I think I have seen case where the so called "common" terminal of two such timers are tied together, but pretty sure there was still separate contact for each timer in that application, or maybe even was a situation of common tied to a common terminal on another control relay but double throw contact was selecting which timer gets a signal - or something to that effect.

 

[gar]

200412-1130 EDT

ptonsparky:

I am confused. So I will outline what I believe is the layout and problem.

1. There is one water pump that supplies two pivots (water sprinklers).

2. Water pressure is too high, if only one pivot is using water. Pressure is OK, if both pivots are using water.

3. The pump is close to one pivot, and 2000' from the other pivot.

4. Two single conductor #12 copper wires are available between the two pivots. A total loop resistance of 4*1.5 = 6 ohms will result.

5. At each pivot there is an isolated NO contact that closes and remains closed when its pivot wants water.

6. The pivot needs feedback that the pump is pumping, or at least that the pump has been told to pump. A pressure switch at each pivot could provide this information, or an electrical signal via the #12 copper loop could be used.

7. There may be some reason to want some time delay to actual pump start once it is known that both pivots want water.

8. If either or both pivots don't want water, then the pump stops.

9. Why would you need more than one time delay?

Am I missing anything.

.
.

 

[ptonsparky]

200412-1130 EDT

ptonsparky:

I am confused. So I will outline what I believe is the layout and problem.

1. There is one water pump that supplies two pivots (water sprinklers).
Normally one pump, one pivot.

2. Water pressure is too high, if only one pivot is using water. Pressure is OK, if both pivots are using water.

3. The pump is close to one pivot, and 2000' from the other pivot.
1300 and 2500 rounded to nearest 100.

4. Two single conductor #12 copper wires are available between the two pivots. A total loop resistance of 4*1.5 = 6 ohms will result.
5*1.5=7.5

5. At each pivot there is an isolated NO contact that closes and remains closed when its pivot wants water.
No. Each pivot will start on pressure up from well.

6. The pivot needs feedback that the pump is pumping, or at least that the pump has been told to pump. A pressure switch at each pivot could provide this information, or an electrical signal via the #12 copper loop could be used.

In the original setup prior to change, one pivot or the other would run. Not both. A radio transmitter from each pivot would communicate with a receiver at the well. The well starts with no input from the chosen pivot. Valves and power were to be manually set to operate with one or the other pivot. The R&T communicate when the well starts. A delay of 15 minutes is allowed for pressure to rise and oil hydraulic pressures to prove within limits. R&T verify interlocks, allowing continued operation.

7. There may be some reason to want some time delay to actual pump start once it is known that both pivots want water.

The pivot(s) always want water. They wait until pressure is up before starting movement.

8. If either or both pivots don't want water, then the pump stops.

The pump must stop if either pivot fails to operate as designed. Meaning, for some reason it has stopped moving. 350 GPM is a lot of water to apply in the same area for hours.


9. Why would you need more than one time delay?

I know I don't now. We did away with the timers entirely. My 1st thoughts were to momentarily (one shot) a control contact at Pivot A if B went down or B if A. The initiation contacts 5&6 would have been paralleled, one set at each pivot point. That was the basis for the original question.

Am I missing anything.

.
.

 

[kwired]

200412-1130 EDT

ptonsparky:

I am confused. So I will outline what I believe is the layout and problem.

1. There is one water pump that supplies two pivots (water sprinklers).

2. Water pressure is too high, if only one pivot is using water. Pressure is OK, if both pivots are using water.

3. The pump is close to one pivot, and 2000' from the other pivot.

4. Two single conductor #12 copper wires are available between the two pivots. A total loop resistance of 4*1.5 = 6 ohms will result.

5. At each pivot there is an isolated NO contact that closes and remains closed when its pivot wants water.

6. The pivot needs feedback that the pump is pumping, or at least that the pump has been told to pump. A pressure switch at each pivot could provide this information, or an electrical signal via the #12 copper loop could be used.

7. There may be some reason to want some time delay to actual pump start once it is known that both pivots want water.

8. If either or both pivots don't want water, then the pump stops.

9. Why would you need more than one time delay?

Am I missing anything.

.
.

I don't know I have all the details but I am familiar with kind of thing he is working on.

He said one "full pivot" and two "corner pivots"

Guessing full means full quarter section of land and the "corner pivots" are smaller systems that are watering places the "full system" doesn't reach.

The well is probably sized to supply the full system. Is oversized for the small systems, but using two of those smaller systems at same time gets at least much closer to well design.

Likely there is manually actuated valves or even reconnection of piping sections when running the full system vs the corner pivots.

The corner pivots need interlocked somehow with well so that if one would shut down the well will shut down, otherwise you continue to pump water through a system that is not moving and this will overwater that area of the field, and worse yet if you are injecting fertilizer or pesticides into the system you over apply to a limited area.

The timers I am guessing is maybe a delay to bypass pressure sensing long enough for normal pressure to build during startup or something of that sort of nature.

 

[tallgirl]

Dry contacts are no longer dry (absence of voltage) once used in a circuit. Voltage is applied to provide a function, whether to power a coil, start a timer, etc. If the control power at both ends is the same circuit or output, then no problem, but if they are different circuits, then they would be paralleled.

My understanding is that "dry contact" refers to any relay, switch, whatever which is not a SOURCE of power under normal conditions. A controller might output 12VDC when some function is performed on whatever controls that. If an application required "dry contacts", that 12VDC could then be used to control the coil on a relay having the appropriate ratings. If the controller only provided "dry contacts", a source of power to control a relay, and another to provide the power, would be required.

Do I have that wrong?

 

[hillbilly1]

My understanding is that "dry contact" refers to any relay, switch, whatever which is not a SOURCE of power under normal conditions. A controller might output 12VDC when some function is performed on whatever controls that. If an application required "dry contacts", that 12VDC could then be used to control the coil on a relay having the appropriate ratings. If the controller only provided "dry contacts", a source of power to control a relay, and another to provide the power, would be required.

Do I have that wrong?

Correct

 

[hbiss]

In electronics we just call contacts "contacts" then go on to describe what they are and how they are connected and operate. The trades use the term "dry contact" to describe a pair of contacts, on usually a switch or relay within a device, that are available for use to control something if you place them in a circuit. So, if you hold a toggle switch in your hand, you have to wire it up to a power source and load for it to control something. The contacts on that switch could be called "dry contacts". Usually dry contacts are used for low voltage control.

-Hal