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Newbie Help - 24vac circuit.

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cgiles75

New Member
All,

This is my first post and i could use the help of the masters to find the answer. I know just enough about electronics to be dangerous but AC has never been my forte.

The schematic is attached but is probably clear as mud so I'll explain. This is a water topoff setup for a reef aquarium. Solenoid A and B are turned on/off by a float switch. What I want to happen is if either A or B is closed, C also closes but not the other. Basically either A-C is on or B-C is on but not A-B-C. Right now when I close one all three close. I have a good idea how to stop this with DC but AC has me stumped. I know relay is the best solution but I'm having trouble finding a source for a relay that will work.

Any suggestions are greatly appreciated.

**broken link removed**
 
XOR together (via logic or DIODE) the A and B output and use this to then drive the C solenoid
 
You have not made it clear. Please use the term "powered up" instead of "close" as a solenoid can be energised to open or close.

When flow switch(es) operates, either A, B or both A & B will be powered up.

When A has power, you want C has power.

When B has power , you want C also has power, but what happens when both flow switches operates and both A & B has power? Do you want C without power in this case? If so, try the following circuit.
 

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Hi eblc1388,

Your relay circuit is of course faultless.
Yes, it is not clear from the first post exactly what is needed,
but i think you have covered it.

Hi cgiles75,

In your post you said that you thought a relay would be the answer,
well you are almost correct, but this requirement cannot be met
with one relay, it needs two relays, as shown by eblc1388.
Unless your float switches have more contacts than you have shown.

If your float switches have break contacts (NC) as well as make
contacts (NO) then it should be possible to arrange a suitable
circuit using just the float switches.

If a circuit like this is chosen, then check that the float switches
are the break-before-make type, it is extremely unlikely that they
will be the make-before-break type, but check anyway as that would
blow fuses.

Switches that include both Normally Open and Normally Closed are
very common, if you check, the ones you have may have both.
Typically they have three connections, but only use two.

Regards, John :)
 

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Thanks for the help guys. I'll start looking for a suitable relay. If anyone has a good source for such a relay please let me know.

Thanks again...
 
Hi cgiles75,

You will need two 24VAC relays,
Or,
float switches with c/o contacts.

John :)
 
Hi cgiles75,

Hi
So you're going to try and find a relay for this then ... ?
yeah, i wanna get right on with it.
You will need two relays, you realise that don't you ?
Yes, of course !
You said 'a relay' so i wondered if you knew you need two ...
I meant a suitable TYPE of relay, i know i will need two of them
Ok, so long as you know.

Have you considered that it might be possible with just the float switches ?
What do you mean?
I mean with no relays, just the float switches and the solenoids.
No, i had not considered that.
Well it would depend on the type of float switches.
How can a float switch decide whether or not to engage an extra solenoid ?
Quite.
Surely it must have a relay, for the third solenoid ?
Well not necessarily ...
And whats it got to do with the type of float switches, they just
float up and operate, ... right ?

Yes, but some include an extra contact which isn't used much, one
that opens when the switch operates.
Whatever for? surely you only need one that makes contact? ...
Depends. You might want a pump to stop when something is full, that sort of thing.
You might need a "make" when its up to level, or you
might need a "break" when its up to level. Depends what you're doing.
Some float switches allow for both choices. Its not unusal at all.
I see, so my float switches could have an extra contact ... ?
They could have, yes.

If they have contacts like that, they're called change-over cantacts.
C/O for short.
So how would that help anyway?
If they were c/o type they be arranged to operate the third solenoid
without any relays involved.
Could they ?
yes.
So how can i tell if my float switches are this type or not ?
You would have to have a close look at them, right where the wires
join on to contacts themselves, and see if there are three points for
connections, but only two being used with wires on them.
And if there is?
If there is then they are probably c/o type.
And if there isn't?
Then you will have to use two relays to do the switching.
Two?
yes two
I know, I know, just kidding

will it mean getting my hands dirty ... ?
It might, are they that clean now ?
Oh all right, i'll check it out

Okay, let us know then ...
John :)
 
They picked up their unfinished conversation later that day....

I still have some doubts about your proposed circuit.

Let's hear them.

You are connecting the AC supply across the C/O contact.

Yep. Is there a problem?

No. But I never see any circuit connected up like this.

There will always be exceptions. Trust me.

Will there be an arc when the flow switch operates and the contact moves?

Sure there is.

Is it possible that the arc is still there when the contact reach the other position?

Could be. Might be, why ask?

What will happen to the arc in this situation?

#%^%$@$%&((&*^%&...Carrier lost......
 
Hi eblc1388,

Not quite the person i had hoped to hear from, but a valid point.
If the solenoids are large there may be a problem.
Yes there would be a spark as with any contact.

Like most of the questions here, not quite enough information.
Its low voltage stuff, i would be happy with a fuse just in case.

If the float switches are maybe some distance off, or way down in
holes, then i would go for the two-relay option rather than disturb
the float switches.

As a general rule i try to be minimalistic with circuit arrangements.
Sometimes thats not always a good idea.

Regards, John :)
 
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