AC to AC relay for Landscape Lights

[cbarria]

I need to take a 3V-9V AC input and drive a 120V AC transformer. The relay should be NO and close the 120V circuit when it gets a voltage in the 3-9 range. I've not been able to find something that will fit this application. It will sit indoors in a garage.

I've seen relays that will take a minimum of 24V, so perhaps a step-up transformer could work as well.

Any recommendations on where to get these components?

 

[AnalogKid]

What is the source of the 3-9 Vac?
How much current at 120 Vac does the relay need to switch?
How fast does the relay need to turn off after the 3-9 Vac goes away?

The low voltage AC source current or power sets a limit on what relay coils are possible candidates.
The AC load current gives us a feel for the size of the relay, and the size of the relay coil power required.
One approach is a rectifier and filter capacitor driving a DC coil relay. Many 12 Vdc coil relays pull in at 9 V.

Another option is a solid state relay. Again depending on size, these come with input voltage ranges of something like 3 to 32 V dc at very low current. Some take AC control directly.

ak

 

[cbarria]

What is the source of the 3-9 Vac?
How much current at 120 Vac does the relay need to switch?
How fast does the relay need to turn off after the 3-9 Vac goes away?

The low voltage AC source current or power sets a limit on what relay coils are possible candidates.
The AC load current gives us a feel for the size of the relay, and the size of the relay coil power required.
One approach is a rectifier and filter capacitor driving a DC coil relay. Many 12 Vdc coil relays pull in at 9 V.

Another option is a solid state relay. Again depending on size, these come with input voltage ranges of something like 3 to 32 V dc at very low current. Some take AC control directly.

ak

The source is coming from a lights controller.(transformer). The relay needs to switch a max of 3A. Up to a second or so would be tolerable.

 

[cbarria]

This is the closest one Ive found at 6V AC

http://www.nteinc.com/relay_web/pdf/R02.pdf

 

[AnalogKid]

R02−11A10−6 looks like it meets your requirements it you can get it 6 Vac. Why does you AC source vary over such a wide range?

A hockey puck SSR should be around $5 surplus, $21 new at Digi-Key.
https://www.ebay.com/itm/SSR-25DA-S...hash=item33dcc05e58:m:m8kg6JUBoNr9oo_zHCRoXyQ

Where are you located?

ak

 

[cbarria]

R02−11A10−6 looks like it meets your requirements it you can get it 6 Vac. Why does you AC source vary over such a wide range?

A hockey puck SSR should be around $5 surplus, $21 new at Digi-Key.
https://www.ebay.com/itm/SSR-25DA-S...hash=item33dcc05e58:m:m8kg6JUBoNr9oo_zHCRoXyQ

Where are you located?

ak

Atlanta, Georgia

The prior installer used a low voltage wire from one of the light transformers to drive a relay switch on the other unit. The transformer has 3 settings, 3V, 6V, and 9V. It is used as a dimmer for the lights and to control the relay switch that failed. The two units are probably 40ft apart.

 

[Bluejets]

Maybe rectify 9v ac and drive a 12v dc relay? A layout circuit would be helpful.

 

[(*steve*)]

If the lights are switching rapidly (and from your comment it sounds like they're not) then a solid state relay would be an ideal solution.

Otherwise, I'd go with rectifying the low voltage AC and choosing a filter capacitor large enough to stop the relay chattering, but small enough to cause it to drop out quickly. Something between 10uF and 100uF would probably be suitable.

If you get a small bridge rectifier you won't have to worry about connecting up a stack of diodes and the whole thing may be rigid enough to just solder to the relay.

Please be careful because the 120VAC will be wired very close to the low voltage. If they touch it could be VERY bad news for you.

Incidentally, this is another reason I like SSR's, the terminals are often spread very widely and there is little possibility of shorting input to output.

 

[AnalogKid]

Since response time is not critical (post #3), why not just one diode? That plus 100 uF would yield a turn off time of about 0.1 s for 10 mA SSR input current.

ak