# Simple AC circuit help.

#### Sage4ME

Joined Aug 19, 2022
8
Hi all, I am good with DC but not AC. Here is my problem. If I need to heat, cool or raise the humidity of my enclosed environment I need to turn on the mister. I have sensors to monitor all three of these and turn on AC power. How do I make my mister go on if any of these three systems turn on? My mister is another AC powered device. If this was DC I could do this in a flash, I am just not seeing it with an AC circuit.

Thanks all.

#### Sage4ME

Joined Aug 19, 2022
8
Anything more elegant than 6 diodes?

#### Danko

Joined Nov 22, 2017
1,392
To use this I would have to sense all three ac outputs, convert this to dc and then decide witch of the relays to turn on.

#### Ian0

Joined Aug 7, 2020
5,816
Relays with 230V AC coils.

#### Sage4ME

Joined Aug 19, 2022
8
That is good, optical relay to detect one half of the phase. The RC to hold for the second half of the phase then logic to decide what to do with it. It will need relay drivers after the logic, but not seeing the current requirements. If I was doing this commercially this would be a good solution.
As is this is a hobby project.

For $13 each I could just use three misters. Parts not counting PCB or breadboard is looking at over$35.

Cost wise 6 diodes should work. Please tell me if I am wrong about this. As I said I am not good with AC.

My mister is a piezoelectric mister. https://www.amazon.com/dp/B089LDS24S?psc=1&ref=ppx_yo2ov_dt_b_product_details. Hmm $18 not$13.

This is a good solution and I may do it to clean up the system. Trying to do this easy and cheap.

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#### ebeowulf17

Joined Aug 12, 2014
3,306
This solution is bulky, but dead-simple:
Use three mechanical relays, with each coil powered by the output of one of your other devices, and all three output switches wired in parallel such that if any of them is on, it powers the mister.

Thanks.

#### Danko

Joined Nov 22, 2017
1,392
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#### MisterBill2

Joined Jan 23, 2018
12,678
Why are you struggling to switch on the mister like that. Post #1 states that there are three sensors, so why does a mister need to switch on when any of three sensors switch on.

The logic is not clear at all. Certainly the condition might exist where the temperature is correct but the humidity is not, and likewise, the humidity may be as desired but not the temperature.

Thus the motivation is very unclear, what is the actual requirement, never adequately stated???

#### Sage4ME

Joined Aug 19, 2022
8
Why are you struggling to switch on the mister like that. Post #1 states that there are three sensors, so why does a mister need to switch on when any of three sensors switch on.

The logic is not clear at all. Certainly the condition might exist where the temperature is correct but the humidity is not, and likewise, the humidity may be as desired but not the temperature.

Thus the motivation is very unclear, what is the actual requirement, never adequately stated???

I am building an grow environment to simulate the conditions on top of a Tepui.
https://www.worldweatheronline.com/parai-tepui-weather-averages/bolivar/ve.aspx

I am heating / cooling water in the bottom of the tank to control the air temperature. I have found that it takes a significant time for the air temperature to match the water temperature. I have found that if I turn on the mister the two match within 20 minutes. So changing temperature requires the mister to be on. If the humidity is low I need the mister to be on.

I live in a dry climate and the humidity today in the tank with no active controls is 75%, so I could run the mister for 20 or so to hit the desired humidity.

here is some info on what will be growing in there once everything is set up:

Thanks for the interest.

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#### BobTPH

Joined Jun 5, 2013
5,453
Could you run the mister based on a humidity sensor, independent of heating and cooling?

#### MisterBill2

Joined Jan 23, 2018
12,678
OK, the simple scheme will be touse a mains currentsensor which might be as simple as a reed switch with some wire wrapped around it to serve as an energizing coil. Then the reed switch can control the solid state relay as was shown in an earlier post. That arrangement would avoid any changes to either the heater or the cooler. Such a current detector is probably available because the same functionality has been required for sound systems for at least 50 years.

Joined Jan 15, 2015
6,813
Hi all, I am good with DC but not AC. Here is my problem. If I need to heat, cool or raise the humidity of my enclosed environment I need to turn on the mister. I have sensors to monitor all three of these and turn on AC power. How do I make my mister go on if any of these three systems turn on? My mister is another AC powered device. If this was DC I could do this in a flash, I am just not seeing it with an AC circuit.

Thanks all.
Based on your original post. Rather than relays and merely as an example there are SSRs (Solid State Relays) which use an AC control voltage. One such example, and only an example is for example a Crydom A4875. Note the control voltage is 90 to 280 VAC. I am sure but the general idea is the control voltage of a SSR can be AC or DC and a wide range. They are all not limited to 3 to 32 VDC. You can likely find inexpensive versions of what I linked to. If you choose to roll your own there are also plenty of opto-couplers designed to work with AC. That includes AC 50/60 Hz at line voltages of 120 / 240 VAC. Just buy a SSR for your application using a control voltage for your application. Again, the Crydom I suggested is merely an example of a SSR using AC control voltage. Such SSRs are pretty common and with some looking you can find them. There is no need for anything DC or low voltage.

Ron

Joined Jan 15, 2015
6,813
OK, the simple scheme will be touse a mains currentsensor which might be as simple as a reed switch with some wire wrapped around it to serve as an energizing coil.
OK, I have seen this suggested many times as a current sensor. It's not quite that simple. I was involved with reed switch testing for awhile. Unless there is a heavy AC load, really heavy, some wire wrapped around it isn't going to do much of anything. We start getting into Ampere Turns and Tesla or Gauss. This is a good sort of white paper on the subject. Next if we apply an AC current we have a reed switch turning on and off 50 ~ 60 times a second. We were placing a hundred reed switches on a test board inside a coil with a 10" diameter with about 400 turns of AWG 14 magnet (enameled) wire. Using a Variac (auto-transformer) we increased current till we had 5 amps @ 60 Hz. We used a MUX to look at each switch over a period of time while the switches sat in an environmental chamber going through thermal shock. Anyway, here nor there but it is not as simple as wrapping several turns around a reed switch unless you have some very high current. Also keep in mind the switch is going to be turning On/Off at mains frequency unless you power the coil with DC. While it sounds good it is not as easy to get results.

Oh yeah, the test coil looked like this:

Ron

#### MisterBill2

Joined Jan 23, 2018
12,678
OK, so the reed switch is not the best current sensor. So use two series strings of diodes in reverse parallel . Five or six ten amp diodes in each direction should provide enough voltage drop to operate the solid state relay.And that drop should not interfere with the operation of either heating or cooling. That is as simple a system as I can come up with. No complex circuits to build, just diode strings. One more diode if you get a DC operated SSR.

#### Sage4ME

Joined Aug 19, 2022
8
This solution is bulky, but dead-simple:
Use three mechanical relays, with each coil powered by the output of one of your other devices, and all three output switches wired in parallel such that if any of them is on, it powers the mister.

I'm used to using Deltrol relays like this 20601-84 for jobs like this, but you can almost certainly find smaller, cheaper ones if you don't need such high power capacity (I'm guessing an \$18 mister doesn't draw anywhere near 15 amps of power!)

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This is a nice simple solution. 4 modified power cords and 3 relays. Thanks! I am kicking my self for not thinking of it myself.