# Stopping 24v ac

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#### dan33

##### New Member
I don't really know how to ask this question with out showing a diagram so I'll ask it this way. I have a 24v ac circuit say flowing one direction and sometimes the flow could change and go the other way but I want to stop it at a certain point. I need like a check valve of something. Somebody said to use a diode. I did and it seemed like it was going to work cause I did not get a reading on my meter when I applied the 24v through it. So in doing a test I hooked in my 24v solenoid valve after the diode it would just buzz. I was expecting it to do nothing? So I need 24v ac to flow through like normal but not back. If you know what to use It would help a bunch!

Thanks Dan33

#### Mike_2545

##### Super Moderator
The directionality properties of diodes only work with DC. The way you describe what you are doing you are probably getting half wave AC, which is causing the buzzing of the solenoid.

You will have to post a circuit diagram or be more specific about your intentions.

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#### dknguyen

##### Well-Known Member
AC current by definition normally flows through and back. Are you looking for a device that will only let current flow one way? THat is a diode. The other thing you could is to use a bridge-rectifier (Google it) which is 4 diode arranged so that it "inverts" the half of the flow so that all the AC current flows with the same polarity.

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#### crutschow

##### Well-Known Member
Tell us what you are trying to accomplish, not what you think you need.

#### Hero999

##### Banned
I think he's trying to make the equivalent of a diode or but with an AC circuit.

It's not really practical because if there are two AC sources, they both need to be in phase with each other.

#### Mike_2545

##### Super Moderator
Sounds like he needs a relay circuit of some sort, but its impossible to tell this early in the "dig it out of them phase"

##### Banned
We need to come up with an official term for that Mike2545.

#### Mike_2545

##### Super Moderator
Dazed and confused?

Noob is taken.

Lazy, unmotivated?

50 questions?

I'll show you mine, if you show me yours?
(probably not)

What do you think?

##### Banned
Discovery phase =)

#### Mike_2545

##### Super Moderator
Unfortunately we never get to see the Ah-Ha moment. Some even say thank you.

I like the term "discovery phase"

#### dan33

##### New Member
Thanks for the help. Sounds like a diode will not work in my situation I have to keep everything 24v ac.

I like "discovery phase" too

#### Mike_2545

##### Super Moderator
Dan, what exactly are you trying to do? Can you post a schematic of your design?

#### Grossel

##### Well-Known Member
I beleive Dan is realy just asking for a rectifier.

Whe you're talking about current flowing back, you mean AC current i think. By using a rectifier (often 4 diodes) you're geting the current flowing only one way. But the magnitude of the current will still vary, so you get buzzing sound. Put a capacitor in parallell with the soleniod will reduce buzz and shuld improve the magnetic force.

Build or buy a rectifier and put a capacitor in parallell to the solenoid.

Read more abotu rectifiers on Rectifier - Wikipedia, the free encyclopedia.

#### dan33

##### New Member
How do I post a pdf file?

#### dan33

##### New Member
That's what my diagram is.

#### Torben

##### Well-Known Member
How do I post a pdf file?

Write your post in the page that comes up. Then scroll down until you see 'Manage Attachments'. Click it and follow the directions to post your PDF.

Torben

#### dan33

##### New Member
Thanks For the posting help.
Here is my diagram. You can see where I want to put the diode. Thats a float switch, that is in a tank of water turning on the valve [24v solenoid] and the 30 sec on delay is connected to the motor contactor that turns on after 30 sec. Turns off when tank is full.

Then when float switch is in full position it turns on a off delay that opens the valve [24 v solenoid] and runs the motor for 3min then shuts off. [Its doing a flush to the system]

My problem is when the 3min off delay is triggered it opens the valve but also goes up and turns on the 30 sec on delay I thought putting a diode in there of some kind to get away from something mechanical would keep the current from going to the 30 sec delay.

Thanks For Any Help

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#### Diver300

##### Well-Known Member
You might benefit from a small PLC (Programmable logic controller).

If you want to stick to relays, you can't use a diode on AC, as you found out. You need some more relays. You want two things (30 s delay and 3 minute delay, I think) to turn on the solenoid valve but you don't want the 3 minute delay to reactivate the 30 s delay.

Get the 30 s delay to turn on one relay, and the 3 minute delay to turn on another relay. Put one NO (normally open) contact from each relay in parallel and get that to turn on the solenoid valve.