Remote controlling star delta starter

RF Lighting · 12 Dec 2010

Evening.

I have just wired a vacuum pump to a star delta starter which all works fine.

It's a bog standard starter with start and stop buttons on the front.

There is another machine that is part of this installation which is required to switch the pump on and off. All this machine has is a normally open pair of contacts to turn the pump on and off.

I'm a bit unsure of how to wire it. Switching the contactor on is not a problem, but getting it to stop again is, as the contactor latches.

I was thinking a DPDT relay would do it and use one side to break the stop circuit and the other side make the start circuit when the main control machine is calling for the pump to be on.

I require the buttons on the front of the contactor to still work as a manual override.

Here is the diagram of the the control circuit as it is at the moment.

Sorry about the state of it. I dropped it in cow poo.

Any help would be much appreciated.

tonyelectric · 12 Dec 2010

Milking machine is it?

Your reasoning with the relay sounds right to me, i've never wired a remote that way but have done remote button start and stop, in that case you need a normally open switch to start and a normally closed one in the stop circuit.

RF Lighting · 12 Dec 2010

Yeah it's the vac pump in a milking parlour.

I've sat down and had a think and I think a relay should work.

I've done plenty with normal remote buttons, but never tried to control it quite like this, and just couldn't get my head round it on site today.

My only concern is whether the contactor will hold in with the on relay when the stop circuit is broken. I guess it should if I break it in the right place?

electronicsuk · 12 Dec 2010

As long as the relay contacts are in parallel with the local start switch, the emergency stop will function normally. As the stop button on the contactor is almost certainly going to be NC (i.e. breaks when pressed), wiring a relay in series with this switch will result in the local start switch on the contactor failing to work properly, as the relay contacts will be holding the coil circuit open.

I don't see why you should need to mess about with a DPDT relay - if you break into the control wiring in the right place, it should be possible to use your NO dry contacts to power up the coil while retaining the E-stop functionality. EDIT: No, that's a stupid idea, as I seem to have completely forgotten about the latch contacts

Adam_151 · 12 Dec 2010

Yeah, with just a relay across the start button, it'll be as if its beeing held down whilethe other machine that is calling it is running, so that if you were to hit the stop button manually on the starter, it would stop, but as soon as released would be called to start again!

I reckon you want to put the stop line through normally open contacts on the relay as you suggest, and also install a timer relay module, which one powered will close over the start button for a second or two and then release

Also if there is any emergency stop switches, these will need a little consideration so that it cannot be restarted remotely when they have been pushed (I imagine locking buttons which require a key to pop them back out would be ideal)

electronicsuk · 12 Dec 2010

Adam_151 said:
I reckon you want to put the stop line through normally open contacts on the relay as you suggest, and also install a timer relay module, which one powered will close over the start button for a second or two and then release

Stop line through NO contacts? Not sure I follow...

In any case, double throw relay onto two timers set to fire off a very short pulse across the start/stop buttons should work with minimal interference to the existing controls.

Adam_151 · 13 Dec 2010

Scrub that, he probabaly wants to be able to manually stop/start it even when the external machine isn't calling for it to run, rather than just when it is... So it would be no good anyhow

I'll look at this tommorow when I'm less tired

Spark123 · 13 Dec 2010

Easiest way would be to take the latching out of the star-delta circuit and have an auxiliary circuit doing the latching business. The latching circuit can then control the star delta starter by means of a dry contact, then parallel the auxiliary from the other machine across this dry contact.

Where the emergency stops go in the circuit is another matter, really speaking if the machines are common then the emergency stop should kill both machines so they can't start up without manually restarting them.

bernardgreen · 13 Dec 2010

Before you design the ciruit you need to be clear as to the way the manual controls and the "automatic" control from the other machine are prioritised.

Which, if either, has over-riding control of the pump.

The original post suggests they are to have equal priority.

To give both equal priority the contact closure from the other machine has to be processed with at least two relays to provide two pairs of contacts.

The first contact pair is normally open and closes for a brief period when the machine contact closes. This is wired in paralle with the manual start button The second contact pair is normally closed and opens for a brief period when the machine contact opens. This is wired in series with the manual stop button.

Two relays are controlled by the contac in the machine. One operates without delay and the other is a slow to operate or has a delay circuit.

The contacts of these relays are wired to provide the "start" and "stop" contacts. The duration for which these "buttons" are operated is the difference in operating times of the two relays.

IF this is what is needed then I can post the circuit later today when I have access to a scanner

ColJack · 13 Dec 2010

you'll need a time delay on the contacts so that the stop circuit closes a second before the start contact does or it might not work reliably..

ricicle · 13 Dec 2010

ColJack said:
you'll need a time delay on the contacts so that the stop circuit closes a second before the start contact does or it might not work reliably..

It won't be a problem in a hard wired circuit.

SgtTrojan · 13 Dec 2010

The problem here is that RF has been milking over these drawings by the looks of it

Cow poo my udders

mikhailfaradayski · 13 Dec 2010

As Bernard suggests, how the machine and the pump interact with each other needs to be understood before the logic of the wiring can be completed.

e.g. making the assumption that the machine may have an emergency stop button fitted somewhere, what would be the desired effect when the e-stop is pressed, should the pump be allowed to carry on, or should it be shut down aswell?

ericmark · 13 Dec 2010

Looking at the diagram, I think we have the following:-
S11.0 is stop button
S11.1 is start button
The remote needs to be is series with S11.0 and parallel with S11.1 so both stop and start will work.
If you break the connection as it leaves terminal 22 on S11.0 and divert both removed cable and connection to remote plus the common rail which connects to terminal 14 on S11.1 then the three wires will work from the remote.

I have found in the past when using remote control very quickly it becomes cheaper to use a PLC. Every box and switch costs and with a PLC it means two wire remote can be used instead of three.

Not sure what you intend with latching relay. The latch must be part of contactor Q11 as once the stop button is pushed the latch must release. I have used aux contacts on the contactor in the past but unless very simple it is so easy to make a mistake and with hard wiring so hard to correct. I take my hat of to those years ago who would wire very complex cabinets. Much easier now with the laptop.

Stop control

ericmark
13 Dec 2010
1

bernardgreen · 13 Dec 2010

If the machine has equal priorty with the manual buttons then this arangement of two relays should work to start the pump when the contact in the machine closes and stop the pump when the contact in the machine opens.

One relay or contactor " fast " is operated by the contact in the machine and a second relay or contactor operation and release is delayed by about one second. This delay would be by diode - resistor - capacitor if DC was avialable or by slow acting auxillary contact on FAST if only AC is available.

Fast relay operates when the machines "run" contact is closed.

With FAST operated the START button is shorted out to start the pump and when SLOW operates the short is removed.

FAST releases when the machine's run contact opens and the ciruit through the STOP button is open circuited. This open circuit is removed when SLOW releases.

There is a transient break in the STOP circuit when SLOW operates at the end of the START pulse. This might be a problem if the contactors in the control ciruit are fast to release. Make before break contacts on SLOW would remove that problem.

This is better

Untitled

bernardgreen
14 Dec 2010
1

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Remote controlling star delta starter

tonyelectric

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