Replies

1. 
   RyanBrant | Jan 28, 2005 01:01pm | #1

   You want quality transformers and lights.  We use Justin transformers and several different light manufacturers.  A 600W trans. is around $500 I think.  Avoid Malibu lights and Home Depot.  Transformer quality is not interchangeable.  Go to a professional dealer.  Out here in CA, landscape and irrigation supply stores stock higher quality products.  Better transformers last longer, are more dependable, and offer options like light sensors in addition to timers.  But that doesn't mean you can't use a switch to operate the transformer's outlet.

   Sorry, I can't answer your amperage question.  But with regards to voltage, the transformer will only deliver what it's asked to.  If you exceed the wattage capability of your transformer, its voltage output will decrease.

   Wire gauge is important because LV lighting is very susceptible to voltage drop.  We rarely use anything smaller than 12 ga.  If your lights are on one single line, the end light will receive fewer volts than the first and will likely appear dimmer, especially with 8x50W lights.  Over 100' you'll want to increase your wire gauge.  Consider running two lines to the 8 lights for example.  One run does 4-5 lights and the longer run handles the balance.  Light run optimally around 11 volts actually.  As you hook them up, you can test to see how the voltage decreases with distance and the load prior to your testing point.

   Consider multi-tap transformers.  They have outputs or 11, 12, 13, 14, and even 15 watts.  Two runs of 4x50W each might actaully start with different taps, say 12 and 13 volts, if one run is longer.  The higher tap compensates for the voltage drop.

   Good luck

1. 
   bchanson | Jan 29, 2005 10:02pm | #2

   thanks for the info. I'm staying clear of HD. In the last couple of days I spoke to a couple of different lighting stores and they echoed your advice.

2. 
   bchanson | Jan 29, 2005 10:25pm | #3

   i'm still curious about the technical questions about ####transformer. The sales guys I talked to seemed to know about the mechanics of putting the system together, but didn't seem to have much info on the technical aspects.

   This brought up a couple of more general questions for me.

   Is a 600W output, for example, from the transformer equal to a 600W draw on the circuit on the line side?

   If you have 12V running 600W of lights, that means a lot of amps - 50. That would explain why you need such thick wire for LV systems (10 or even 8 ga.) But LV systems are not (as I understand) subject to the same restrictions as regular line voltage in terms of splicing, heating etc. For example, LV splices don't have to be made in a j-box and the cable can be run in exposed places where romex would not be allowed. Is this simply because the low voltage doesn't pose a risk to people? No one is going to be electrocuted from 12 volts?

   Just a few questions I have all in the quest for knowledge.

   Thanks in advance.

1. 
   tufenhundel | Jan 30, 2005 12:10am | #4

   A 600W xformer should give you that at the output. And since nothing is 100% efficient, at max output the xformer will demand a bit more than 600W from the line (some heat loss from the windings).As far as splicing, unless I am correctly by the trades, my understanding is LV is safer electrocution-wise, hence reduced splicing requirements.

2. 
   RyanBrant | Jan 30, 2005 09:19pm | #5

   I believe a 600W output draw is the same as a 600W output on the line side prior to the transformer.  However, I believe this only matters in terms of KWh consumption.  I'm only the foreman, so I don't know some of these specifics.  Sorry.  However you are right in that the reduction in voltage results in a proportional increase in amperage.  Hence the larger cable.  But you'll hopefully never try to run 600W off of one LV line - that would require a 6ga line.  Best to split your load into zones that combine load and distance somewhat equally.

   Transformers are quite simple to operate - plug it in and screw down the two LV leads under the terminal screws:  one labeled "Common" and the other labeled with a voltage "13V" on a multi-tap transformer.

   Transformers operate by photocell, timer, or by switch; i.e., the outlet itself is switched like that lamp in the living room.  The switch can be hardwired or operated using a X-10 system, which does require the switch and outlet to be on the same circuit.  In CA, no house youger than 60 has a basement, so we mount almost all transformers outside.  And because they are also plugged in 24/7, they require a weatherproof outlet cover - a bulbous plastic cover that covers the 3 pronged plug completely.  Not the spring loaded outlet cover most has come with.  They leave the outlet exposed when in use.

   It's true the 12V in an LV system poses no risk.  When on, the two leads will spark a little, like a fizzle, if touched together.  They will not explode in a blinding ball of white light like line voltage will.  We have seen LV melted where the mow and blow guy line trimmed into LV line and the two wires slowly shorted each other and melted together.  This shorted the fuse in the transformer.  LV requires no J-boxes and there is no required burial depth.  But if we're doing the irriagion system as well, we run it those trenches - about 12" deep.  But it makes sense to protect these line with depth, because if you ever cut it gardening or digging, finding that cut can be like a needle in a haystack.  Conduit is not required, except underneath sidewalks, and only for the common sense of future needs.

   For our connections, we strip and wire nut the splices.  Some fixtures come with wire nuts that are pre-filled with siicone.  They work and are available off the shelf.  They are light blue and are made by Kings Innovations or something liike that.  We don't use them very much because they're fairly expensive, like $3 for six.  Instead, after making the splice, we dip the entire splice into PlastiDip, which is liquid plastic and available off the shelf.  It hardens around the splice.  I wish we used the blue siliconed wire nuts more.  Even after a year or two, the dipped connections show oxidation.  But dipped connections that have been underground for ten years still work, so it can't by all that bad.

   Hope this helps.

3. 
   DanH | Jan 30, 2005 11:08pm | #6

   There's a hell of a lot of difference in quality of transformers in general. This translates into hum, heat generation (and power loss), short lifetime, etc. But I can't tell you specifically which brands are likely to be good/bad, as I don't have much experience with them in the low voltage lighting arena.

   In general a transformer has less than 5% loss (usually much less), so as a first approximation you can consider input power = output power.

   The wire for low-voltage should be essentially the same size as for 120V, for a given amperage. For 12V equipment, the amperage will be 10 times greater than the same wattage equipment at 120V, and the wiring needs to be able to handle 10 times as much current.

   However, a lot of the wire sold for low-voltage applications is undersized and will have excessive heat losses.

4. 
   Jamie_Buxton | Jan 30, 2005 11:51pm | #7

   There's two things which can make the low voltage to run your lamps.  One is a true transformer, and the other is an electronic power supply.   Even vendors sometimes confuse them.  A true transformer has a great big hunk of iron and lots of copper in it, and is big and heavy.  An electronic supply is much more like what runs your computer.  It is lighter and smaller than a transformer.   For high powers -- like 500W -- the electronic supply is also going to be less expensive than a transformer.

1. 
   DanH | Jan 31, 2005 12:43am | #8

   However, the true transformer will be more efficient and produce less heat. Also probably last longer, if it's halfway decent quality.