AC Diodes?????

[gerryr1gerryr1]

Hi there hope someone can help me.

I have a 16 station AC OpenSprinkler V 2.3 with 16 stations.

It operates through a master panel with LED warning lights to indicate stations that are on.

I wish to add a second 24 vac power source to enable manual on/off each station completely separate from OpenSprinkler.

This circuit would also have a separate LED to indicate Manual power is on as opposed to power from OS.

I do not wish to use the manual function of OS for this purpose.

My problem is that with 2 separate LED’s ( one OS the other Manual) I get feedback of current to the LED’s so that both LED’s are lit no matter which source of power is on.

With DC I could overcome this with a diode, but how do I overcome this problem with the AC power supply.

Hope someone can assist

Thanks

[sakos]

Driving a single valve by two independent AC sources directly is a really bad design. If both sources are active (manual and OS) it may cause a short circuit with 50% probability. I highly recommend to avoid this setup.
To separate the two systems you should use one relay per station. This will atuomatically solve your LED problem as well. You need 24V AC relays with NO/NC/COM contacts.

See this picture as a guide.

Device=valve, V1 sine, V2 sine are the station outputs of the two controller.
Dual contact is not necessary in 24V AC setup The common wire can be directly connected of the two systems.

[gerryr1gerryr1]

Thank you Sarkos. That should solve my problem. Appreciate your reply

[gerryr1gerryr1]

Just priced up 18 24 vac coil relays and bases at about A$ 130 to A$150.

Would the attached sketch work ?? It would cost only a few diodes and caps.

The DC output would be fine cause most of my existing solenoids are DC.

Tested it on LC Spice and it seems OK but I really know nothing about this stuff so would appreciate a comment from someone more knowledgeable than myself.

Thanks

Attachments:

1. Snap_2015.12.02-16.17.01_002.pdf

[sakos]

The connection of Opensprinkler and the manual timer is not detailed enough on this drawing. Anyway, this setup should work. You do not need diodes D5..D8. D6 and D7 do nothing in this setup hence can be omitted. D5 and D8 can be replaced with a short circuit. D3 and D4 diodes makes the work, however they provide only half-wave operation. C1 shall be dimensioned according to this.
The D1 and D2 LEDs need a serial resistor.

[gerryr1gerryr1]

Thank you Sakos. Appreciate your comments and help

[gerryr1gerryr1]

Have another question.

What is the minimum AC voltage required to operate open sprinkler.

Could the open sprinkle input voltage be say 14, 16, 18, or 20 vac?

[Ray]

I agree with sakos that having two power adapters operating the same valve can lead to the risk of shorting the two adapters: the issue happens if both OpenSprinkler and your manual switch are switching on the valve at the same time, that’s equivalent to connect the two transformers wire to wire (i.e. in parallel). If they are synchronized in phase, this is fine, but if the phase is reversed, it will burn the transformers. However, if you can guarantee that they won’t turn on the same valve at the same time, it should be ok.

The way OpenSprinkler working internally is that one wire of 24VAC transformer is connected to the COM (common) wire, and the other goes to circuit ground. Each valve has one wire connected to the COM wire, and the other wire connected to a triac. The triac acts as a switch to ground. So when the triac is on, it directs the second wire of the valve to ground, thus completing the circuit and the valve turns on.

If you just want to add a manual switch to a station, you can add a switch between the station terminal to circuit ground (on the orange terminal block the wire closer to the USB port is circuit ground). That way, when the switch is on, it bypasses the triac and turns on the valve. This will be pretty easy and safe as there is no second transformer involved.

[Ray]

Regarding the minimum AC voltage question: 18 to 20VAC should be fine (the circuit uses a switching regulator that accepts a wide range of input voltage). Below that the voltage will not be sufficient to switch on a valve (because standard 24VAC valves typically do not work with voltage under 18VAC).

[gerryr1gerryr1]

Sorry to be a pain but would this work?

I would prefer a 24 vdc output as all my existing relays and solenoids are 24 vdc.

As I see it all output from the opensprinkler would be converted to near perfect 24 vdc
by C1 and D1 and then D3 and D4 would stop the backwash of current from either power source
thus solving the LED issue I originally had.

Although unintended there exists a possibility that the same circuit could be powered from 2 power sources
at the same time, through accident, but is this a great issue with DC???

The system would be intended to drive only the solenoids or relays anything requiring more than 50 mA would be switched via relay.

I hope you guys could add your wisdom and point out the flaws cause I am a REAL amateur at this.

Thanks

Attachments:

1. 

   Open.jpg
   

[sakos]

Should work.

[gerryr1gerryr1]

Thanks for you input. Appreciated.

Query closed satisfactorily

[Author]

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