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Sprinkler Controller

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Yobortsa

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Howdy all,

I'm trying to switch an AC Sprinkler Solenoid using a MAC97A6 Triac using a microcontroller.

I tried with the AC Adapter running through full wave bridge rectifier then into LM2596 based buck converter module (cheap eBay module) to get 5V (end up with about 38V after the rectifier and nice clean 5V after the buck converter).

It works fine if I short the Gate of the Triac to the +5V rail via a 470R resister, but if the microcontroller or a 74HC04 Hex Inverter drives the Triac, it goes On then rattles on-and-off at 50Hz in the Off state.

On the scope, I get nearly 80V point-to-point on the Gate of the triac (on both sides of the resister) so I guess that's the issue.

I also tried with a half wave rectifier (just a 1N4004 diode) and got the same result (not surprisingly I guess because the AC, which is almost 80V Point-to-point, is still running to the solenoid).

So my two questions are:

1. Why does it work if I short to +5V but not via the microcontroller or Hex Inverter?
2. How do I get the microcontroller to reliably switch the AC for the Solenoid using this Triac?

Thanks,

David

sprinkler.JPG
 

spec

Well-Known Member
Most Helpful Member
Hi Yorbortsa,

Give the circuit below a spin.

spec

2016_11_13_Iss1_ETO_SOLENOID_CONTROLLER_VER1.jpg
 
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ronsimpson

Well-Known Member
Most Helpful Member
Spec,

YES. Yesterday, I sat here and tried to say what you so well drew.
Now the why.
In post #1: There are two parts to the circuit.
1) ac24 volts + solenoid + triac
2) SMPS + Micro + triac gate
Problem: the AC and DC parts are not really connected together. The ground of the micro is not connected to either side of the AC part. If you put a AC meter form the micro to either side of the AC you will see there is voltage.
In post #3 the micro's ground is one side of the AC. Now the micro can put current into the triac's input.
 

spec

Well-Known Member
Most Helpful Member
Hi Ron,

Yeah, that is the core of the problem- I almost missed it.:)

spec
 

Yobortsa

Member
Thanks for the replies.

Spec, I tried the circuit and it works like a charm. Appreciate you taking the time to draw so neatly. Max, I might have to order some of those drivers as I still need to connect the controller to my CAN bus which I'm assuming won't work if it's riding up and down on the AC wave. Unless anybody has any alternative suggestions of how to link this unit using Spec's method.

Thanks again,

David
 

spec

Well-Known Member
Most Helpful Member
Thanks for the replies.

Spec, I tried the circuit and it works like a charm. Appreciate you taking the time to draw so neatly. Max, I might have to order some of those drivers as I still need to connect the controller to my CAN bus which I'm assuming won't work if it's riding up and down on the AC wave. Unless anybody has any alternative suggestions of how to link this unit using Spec's method.

Thanks again,

David
No sweat Yobortsa- glad the circuit worked OK.:cool:

The best approach would be to have an isolator coupling to the TRIAC, as Max said in post #2, and then run all the processing functions from an isolated 5V supply. I will give it some thought and probably post a schematic.:)

spec
 

spec

Well-Known Member
Most Helpful Member
Please see schematic of post #11.

Isolated circuit, as promised below.

spec

2016_11_18_Iss1_ETO_ISOLATED_SOLENOID_CONTROLLER_VER3.png
NOTES
(1) R7, D1, & D3 form a snubber, which depending on the voltage rating of the TRIAC will not be required.
(2) The reason why a negative 33V supply is used, is to provide a negative gate trigger which is optimum for TRIACs (some TRIACS do not trigger when MT is negative and trigger is positive)
(3) The MCU and solenoid power supplies are isolated by the optocoupler.

DATASHEETS
(1) http://www.onsemi.com/pub_link/Collateral/MAC97-D.PDF
(2) http://www.vishay.com/docs/83674/sfh619a.pdf
(3) http://www.mouser.com/ds/2/308/1N5333B-D-102336.pdf
 
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ronsimpson

Well-Known Member
Most Helpful Member
Look at vo2223a.
600 volt 1 amp isolated triac.
http://www.vishay.com/docs/81924/vo2223a.pdf
It dose take 10mA to turn on the LED.

I think there are other 1A isolated triacs. I don't think you need high voltage parts if there is a zener/RC or something to keep the voltage spike down.
 
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spec

Well-Known Member
Most Helpful Member
Look at vo2223a.
600 volt 1 amp isolated triac.
http://www.vishay.com/docs/81924/vo2223a.pdf
It dose take 10mA to turn on the LED.

I think there are other 1A isolated triacs. I don't think you need high voltage parts if there is a zener/RC or something to keep the voltage spike down.
That is a bit brilliant Ron.:cool:

You can always pop a transistor (BJT or MOSFET) in the LED side, if the 10mA LED drive current were too high for a particular application.

spec

Vishay application report on optoTRIACS (also zero switching): http://www.vishay.com/docs/84780/appnote34.pdf
 
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