Dimming landscape light transformers?


Senior Member
I want to dim some landscape lighting. They are powered by the standard 12VAC magnetic transformer. Anybody with experience or advice on this?

I consulted SmartHome.com and am confused. It appears that all the xxLinc v1 stuff supported dimming. It appears that the KeyPadLinc v1 and v2 support dimming. But the LampLinc v2 and SwitchLinc v2 do NOT. As far as I know, they all use a similar triac for dimming. Why the discrepancy, especially among the v2 stuff?

From the v1 docs:
SwitchLinc PLC Dimmer can control low voltage halogen (e.g. track) or other low voltage lights. (Note: works with most magnetic and dimmable electronic transformers.) Also, SwitchLinc PLC can control your ceiling fan. (Note: some motors may produce a subtle humming sound.)
From the v2 docs:
Dimming an inductive load, such as a fan or transformer, could cause damage to the dimmer,the load device, or both. If the manufacturer of the load device does not recommend dimming, use a non-dimming INSTEON switch such as SwitchLinc V2 Relay.
Freewire's FWLROD outdoor lamp receiver is a 500w outdoor low voltage dimmer.

Freewire uses standard X10 commands, and can be trained from X10 products. I've seen a kit online with two FWLROD units, an indoor lamp module, a remote and a transceiver for under 35 dollars. Remember that Freewire transceivers and remotes are not interchangeable with X10, they will control X10 devices, but an X10 transceiver will not receive Freewire signals, and Freewire transceivers do not receive standard X10 remotes. The lamp modules and appliance modules however work as standard X10 devices.
I assume you want to be able to control the dim level, but you could also replace the bulbs with lower wattage if you want the level to always be a lower level.

I have my landscape transformer on an appliance switch and haven't tried to dim them. I have dimmed other magnetic transformers to no good effect. Both switches and transformer burn outs.

This doesn't answer your question directly, but I can confirm the V1 Switchlinc's can dim low voltage transformers.

I have a 2386 that is controlling a 500w Intermatic low voltage transformer for my outside lights in the front yard.

The dimming capability is nice because they turn on at dusk to 60% and then ramp to full when motion is detected on the front path, or when one of our RFID tags (car or personal) approach the house... 10mins, they dim back down.

I also have them dim to 30% when we go to bed and they stay this way until dawn.

Has been working really well for over a year.

I thought dimming a transformer was a huge no no and caused heat buildup but if Paul has been doing it for a year without damage it must work?
I may be wrong, but I have always understood that dimming a magnetic (transformer based) low voltage supply is fine. The only downside is that it does not ramp the light output in a very linear fashion, as you would see with standard line-voltage incandescent lights. IOW, you might find that the lights appear to be off at a 40% dim. Depends on your installation.

But dimming an electronic (voltage regulator) can only be done if the manufacturer states that it is dimable, or you must buy a special electronic dimmer. And none of the Smarthome dimmers are electronic capable.
"Dimming" a transformer is a no-no because your typical triac dimming circuit does this by switching out part of the sine wave that goes to the load, so your transformer is not getting a sine wave anymore and will likely overheat.
I was a bit suspicious at first, but the Switchlinc docs said it would work so I gave it a try. I kept a close eye on it for the first few weeks and the only ill effect I noticed was that the motor on the built in mechanical timer would buzz and hum at low dim levels.

It wasn't needed any more, so I opened up the tranformer and diconnected it.

The transformer doesn't seem to get any warmer when running at 60% for hours at a time than it did before I connected it to the Switchlinc and the lighing load is close to the 500 watt rating of the transformer.

I also have a light in the house with a transformer driving 12v halogen lights and it works great on a Switchlinc too?

For those of you looking for a good selection of electronic and magnetic transformers, I've bought a few from CCL-Light with great results. And they claim all their electronic transformers to be compatible with standard dimmers (like Switchlincs).
Well, I finally got an "official" answer from SmartHome. It still sounds like a YMMV. Upon re-reading the V2 docs, they don't say that they do NOT support it, just a kind of "be careful".


The lamplinc V2 (http://www.smarthome.com/2456D3.HTML) supports dimming. The Appliancelinc (http://www.smarthome.com/2456s3.HTML) is the one that is only on and off. Same thing with the switches. The switchlinc V2 Dimmer does accept dimming commands (www.smarthome.com/2476d.html) while the Switchlinc V2 Relay does not (www.smarthome.com/2476s.html). What the quote is referring to is the fact that for example, if you dim something to the point where it can't cool itself down, you may hurt it, or limit it's life. This is also true for the V1 dimmer when used with inductive loads. I hope this helps.


Luis H.
Smarthome, Inc.