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sprinkler guy
09-08-2007, 01:44 AM
Have any of you guys ever used any mini-transformers? The little 75 watt or 150 watt units that are about the size of a deck of cards or cigarette box. I have an application where the house has a wall sconce for the patio, but the homeowner built a pergola (patio cover) that now makes the sconce ineffective. I'm only calling out three lights (2 downlights with 18 watt incadescents to soflty light the area, a 20 watt spot over the BBQ) Because of the layout of the hardscape I cannot easily get wire from the existing system.

ar-t
09-08-2007, 12:29 PM
I have a similar job in the wings.

While I have not used any yet, judging from the few I have encountered, they are what we call in the electronics "bidnis" switching power supplies.

From my limited experience with them, you may notice that the voltage readings won't seem right. Since the waveform is not the usual sine wave that meters are calibrated to work with, it will read lower. The waveform is closer to a square wave, and most meters will give erroneous readings with such a waveform. In addition, the frequency they probably operate could be above the useful range of the meter.

I'll know better once I get my hands on hand, and get to futz with it.

NightScenes
09-08-2007, 02:46 PM
I have used them on several occasions. You can purchase them through Terradek, www.terradek.com . I think that they are more of a resistor than a transformer. They work very well and I have not had any problems with them.

ar-t
09-09-2007, 01:56 PM
C'mon...you're joking, right.........you have to be joking.

I hooked up a 75W LighTech (yep, that really is the name......) unit to my 'scope. Interesting waveform, in case anyone cares. I'll post a picture of that if anyone here is interested.

But, as I am most likely the only bona fide nerd, here......I'll hold off unless someone asks.

I can assure you that it is not a resistor.

pete scalia
09-09-2007, 02:17 PM
art I'd like to see your readings. I also cannot read voltage on my meter from these junky electronic transformers. They are a fire waiting to happen. whoever endorses them is crazy. Your right these are definately not resistors whoever said that doesn't know what they are talking about. cheers!

NightScenes
09-09-2007, 05:14 PM
Main Entry: re∑sis∑tor
Pronunciation: ri-'zis-t&r
Function: noun
: a device that has electrical resistance and that is used in an electric circuit for protection, operation, or current control

Main Entry: trans∑form∑er
Pronunciation: tran(t)s-'for-m&r
Function: noun
: one that transforms; specifically : a device employing the principle of mutual induction to convert variations of current in a primary circuit into variations of voltage and current in a secondary circuit


Here is a picture of this "mini transformer" or "resistor". I said that it is more like a resistor because it "appears" to be more like a resistor than what most of us are used to calling a transformer. (no core and coil)

Maybe we should include schematics for everything that we post on these issues? I have been an electrician for over 15 years and know the difference but I didn't think we had to get so technical.

Chris J
09-09-2007, 08:50 PM
Paul,
These things look pretty cool, and I must admit I have never used them or even seen them. But I'm stumped as to how one would control the few lights powered by these devices within the rest of the lighting scheme. In other words, in a typical situation all of the other lights will be coming off of the trans which is probably being controlled by a simple digital timer. How could you add something like this and easily control it along with the rest of the lighting system?
By the way, thanks for the great new info. I'm still learning something new every day (I hope I always keep the attitude of the consummate student).

NightScenes
09-09-2007, 10:39 PM
Chris, I use these for for areas that currently have line voltage. I can install a low voltage fixture and operate it along with the low voltage system via CS. Sometimes I'll replace a corner flood with a spot light.

ar-t
09-09-2007, 10:53 PM
"Lighten up." (I know........horrible pun.)

OK, here are some photos of their output. Sorry for the quality of the pictures, but without a viewing hood for my 'scope, and minimal photography skills.......the best I can do.

Anyway.........the first is the envelope of the output waveform. Horizontal scale is 1 mSec/div.

http://www.data.analogresearch-technology.net/lightech_a.jpg

The portion of the waveform that is intensified is shown in this photo:

http://www.data.analogresearch-technology.net/lightech_b.jpg

Horizontal scale is 20 uSec/div. Basically, the output is a 20 kHz (or so) square wave, that has its amplitude raised and lowered to approximate a sine wave. As opposed to a typical SMPS that will have a square wave output that has its duty cycle altered. Indeed, when measured on a typical DVM, the voltage read 11.7V. The last electronic supply (designed for LV lighting) that I had my hands on measured around 8V. Operating at around 8 kHz.

Yes.....you could hear it, and I felt it was annoying.

pete scalia
09-09-2007, 11:08 PM
art that's what i'm sayin these units should be passed on. look at those puny wires coming out of that box they are just waiting to be overloaded and burned up. just my humble opinion

mgm
09-09-2007, 11:53 PM
I use WAC 75W electronic "transformers" for my LV remodel projects - never had any problems, can be wired to line volt dimmers, have built in short circuit and overload protection and built in "soft start" secondary output.

mgm
09-10-2007, 12:08 AM
oops! should have been 150W not 75W

Chris J
09-10-2007, 12:16 AM
art that's what i'm sayin these units should be passed on. look at those puny wires coming out of that box they are just waiting to be overloaded and burned up. just my humble opinion

puny wires? What are we trying to do here?

Chris J
09-10-2007, 12:21 AM
Chris, I use these for for areas that currently have line voltage. I can install a low voltage fixture and operate it along with the low voltage system via CS. Sometimes I'll replace a corner flood with a spot light.

So my assumption is correct? You have to integrate some type of upb device to make it work with the rest of the system?

sprinkler guy
09-10-2007, 03:05 AM
Art,

It has been so many years since I've looked at an occilascope (spelling?) I don't even know what I'm looking at. Are you saying the unit you tested only put out 8volts? The unit that my local Vista rep recommended is supposed to give me 11.8v. And my fixtures are going to be about 10-12 feet from the source, so I'm not too concerened with volt. drop.

sprinkler guy
09-10-2007, 03:08 AM
So my assumption is correct? You have to integrate some type of upb device to make it work with the rest of the system?

Chris,

In my case I am wirng to a junction box that a sconce is currently hooked to. The 3 lights on the pergola will be controlled by a switch inside the house. This patio area is seperate from the rest of the lighting so it won't stand out having the lights manually controlled.

NightScenes
09-10-2007, 08:00 AM
art that's what i'm sayin these units should be passed on. look at those puny wires coming out of that box they are just waiting to be overloaded and burned up. just my humble opinion

75 watts at 12 volts is only 6 amps. How big of a wire do you need for 6 amps?

INTEGRA Bespoke Lighting
09-10-2007, 08:34 AM
I have used hundreds of LighTech 75W electronic transformers here over the past 4 years. I regularly use them to convert old glare bomb coach light installations over to nice, discreet LV fixtures. They work very well. Not a fire hazzard at all if you are specifying and using fully approved devices installed properly. In fact, many of the better units come shipped with a replacable secondary-side fuse. Most have some sort of built in thermal cut off device.

Furthermore, I have installed thousands of interior recessed luminaries that make use of electronic transformers. I have never had a problem with them. The reason I only specifiy electronic transformers in my interiors is that they operate silently. A inductive or magnetic transformer will hum or buzz when they are dimmed. If you have 14 or 20+ pot lights in a ceiling of a great room and you dim the system, the last thing you want to hear is a lot of humming coming from the ceiling. The electronic transformers are silent. What makes them so attractive for outdoor lighting is their very small size.... able to slip a 60w or 75w transformer into a weatherproof junction box opens up a huge amount of opportunities for landscape lighting designers.

LighTech have been the best units I have found so far. Stay away from the cheap offshore product that the big retail box stores carry. They seem to have a pretty high failure rate. You get what you pay for.

ar-t
09-10-2007, 11:40 AM
Art,

It has been so many years since I've looked at an occilascope (spelling?) I don't even know what I'm looking at. Are you saying the unit you tested only put out 8volts? The unit that my local Vista rep recommended is supposed to give me 11.8v. And my fixtures are going to be about 10-12 feet from the source, so I'm not too concerened with volt. drop.

No, it puts out the equivalent of 12V. But because the waveform on some units does not look like a sine wave, your meter will read incorrectly.

Meters are calibrated to read RMS (root mean square) voltage. Think of rms as one of those "area under the curve" things. A square wave with the same peak voltage as a sine wave will read 1.4X higher on a sine wave calibrated meter. So.......a square wave output equivalent to 12V from a typical transformer will read 8.4V on your voltmeter.

It could even read lower, depending on its operating frequency, and the frequency range of your meter. I would like to think that most meters could handle a switcher operating below 100 kHz without skewing the reading.


OK....back to the LighTech......

The waveform is modulated make it look more like a sine wave. So, this particular brand will read properly on your voltmeter.

INTEGRA Bespoke Lighting
09-10-2007, 12:49 PM
Another note about electronic transformers.....

1: they can be dimmed using traditional incandescent dimmers but ideally you should use a electronic ballast dimmer. The main reasons are longevity of the electronic transformer and the output of the transformer.

An electronic ballast dimmer (Lutron DVELV-303P for instance) will provide you with full 0 -100% output. However when you hook up an electronic transformer to an incandescent dimmer the output will be limited from to about 15-85%.

2. An electronic dimmer will not function as the control power source for an inductive (magnetic) relay switch. The waveform output of the electronic transformer is not the same as a magnetic or inductive transformer and as such will not operate a standard relay module. ( I learned this the hard way... by installing an electronic transfromer in a junction box behind a coach light with the intent to have its 12v output trigger the relay module in a remotely located LV lighting transformer, thereby introducing seemless control to a landscape for an elderly client who was not interested in changing outdoor lighting control options)

Have a great day.