Transformers and Automation Controls

[Eden Lights]

I have a client that has just moved into a new home with Home automation. The home has power outside every few feet for Christmas lighting and has four circuits under the home for landscape lighting. I contacted the electrician today about installing the outlets at specfic locations for the lighting transformers. I also contacted the automation company about controls and getting the circuits operational for the install. The automation company asked me if my transformers could be dimmed? He said that one major company in town installed transformers that couldn't be dimmed? The control system has the feature of a slow ramp up at dusk and ramp down at the preset time, but some transformers didn't work well with this feature. I had planned on using Cast toroid style transformers because of the extra common tap and the performance of the toroids. Anyone know of a type of transformer that can't be dimmed? I have gotten a little worried, this the first install on this brand of controls for me. Thanks for any information you might have.

[sitelights]

I believe the information about non-dimmable transformers given to you was incorrect; the basis for this misinterpretation is simply a bit of confusion about magnetic (MLV) vs. electronic (ELV) transformers. Both types can be dimmed but the proper dimmer must be spec'd as either an MLV or ELV. Home automation implies integration of new or existing controls either by touchpad wall units or via a PC. These controls must be ready for anything: motors, switches, dimmers, etc.; if they were not they would succumb to systems that are truly transparent.

I am only familiar with Lutron's "Homeworks" which will control even fluorescent lighting if the proper ballasts are used.

The concern is more to be directed at staying within the manufacturer's specs in terms of total circuit loads.

There is nothing about a toroidal transformer that would render it undimmable since these are not ELV but MLV. Also, ELV is more associated with compactness thus large ELVs are not practical in low voltage landscape lighting applications unless each fixture has its own ELV transformer. I do not consider other than distributed low voltage to be appropriate in an outdoor setting; with individual ELVs in each fixture what you have is a line voltage lighting system

The ramp up, ramp down feature was actually integrated to enhance home theater lighting. All photocontrolled low voltage lighting ramps up in the sense that the lights come on when there is still light in the sky and are perceived as slowly brightening in the increasing darkness. The ramp down feature can be useful if the transition period is programmable; my interior Lutron four channel dimmers can be set to fade to black over a period of one hour. Talk about subtle.

If you have difficulties with insufficient neutral lugs in your installations it is very simple to add commons. Since the multitaps you are using have extra lugs (unless you use every available tap) you can remove one of the connections to the terminal strip, cap it off and jump or split the common into that vacant lug. Most of these terminal strips have back-to-back torque-down screws at each lug; one screw clamps down the wire from the coil to the back of the lug and the front screws down onto the main low voltage cable that goes to the fixtures. You will have at least one extra lug as detailed below.

Your real problem is with the drop in current through the choke since even at 100% "on" the input to the choke is higher than the output. The degree of current loss is dependent on a number of factors. In general you will lose a volt on the secondary side because the transformer may be seeing only 110v and thus provides only 11v (unloaded) at the 12v tap. Your 12v tap on the Cast toroid (or any other dimmed transformer) will be useless and can be converted to a common.

I happen to know that you are an electrician as well as a low voltage designer/installer but I caution others that unless they are fully aware of what they are doing, don't do it.

There is an exchange on this matter of choked current in the luminaires forum under the title "interior recessed low voltage downlighting" that you may find informative.

[Eden Lights]

Thanks for the reply. After futher discussion with the automation company I will agree that maybe the problem was associated with voltage losses on the primary side hurting his transformers secondary output. My line voltage electrical knowledge is limited, I did managed to pass the exam which I did for liability insurance, new construction permits, and resume purposes. When I spoke of the extra secondary tap I was considering the load on the breaker and not physical terminal size. On the Cast Journeyman series you have a spare common breaker for which to use to get 100% capacity of the transformer. An example would be to have a need for a 120W run on a transformer that has 200W existing on each 25amp breaker. While you have 200 watts of trans. left you only have 100W available on each 25 amp breaker. Yes you could change everything to make it work or just put it on the extra breaker and be on your way. Any thoughts? The soft start or ramp on is a home automation sales pitch " See your lighting slowly become evident as the sun goes down on the horizon" I think photocells have the same effect, but when you have invested 25K+ in automation you want everything on the system.

[sitelights]

I was not aware of the Cast transformer feature you described and so I misinterpreted your question. The extra common breaker is a very user friendly solution to the problem you describe. I'll give their product line further scrutiny.