Outdoor Low Voltage Transformer - Page 1
Forum section: electronics / general

author: MeganVonTincan
author_rank: Newbie
timestamp: August 20, 2016, 06:40:19 pm
content: I have an outdoor, low voltage transformer (Malibu ML200RT) (http://www.intermatic.com/~/media/intermatic/documentation/obsolete/powerpacks-instructions/ml200rt.pdf) that I'm using for a small electronics project I'm building. Does anyone know why the instructions would state toKeep a minimum of 10 feet (3 m) of wire between the power pack and the first fixture."? Could it be to add some capacitance to the circuit for stability?

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 23, 2016, 06:49:08 pm
content: I smell rotten fish. The people that wrote that manual know little about electical. They are just blurting safety requirements to cover their asses.As evidenced clearly by this statement: "However, lamps eventually burn out and operating with one lamp can shorten the life of the others. IT IS IMPORTANT TO REPLACE BURNED OUT LAMPS PROMPTLY."No, no it's not important at all, because if all the other bulbs are already blown, how are we "shortening the life" of the others by leaving one on?Just use a GFI if you can and don't worry about their weird requirements about wire length and stuff.

author: SeanB
author_rank: Super Contributor
timestamp: August 23, 2016, 06:56:47 pm
content: 3m between power pack and the pond, so it is not subjected to excess moisture from the evaporation off the pond, and is far enough to comply with regulations regarding electrical equipment and water.The replace lamps promptly is simply because the output is not regulated, and is 12VAC only with the rated load, rising above it with lower load. Thus if a single lamp burns out the others will have the voltage increased by the regulation figure, so they now have a higher voltage, and thus a shorter life. They can often be 14VAC or a little above at zero load.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 23, 2016, 07:36:29 pm
content: They said operating with only one lamp, thus only one working bulb (terrible wording if they meant otherwise). But why would they have a 14V output? If they were accounting for drop in the wires why would they force you to put 200W through two terminals?I would think you would have different branches on the system all coming back to the transformer on their own taps. If the transformer dropped that much it would get hot.

author: LaurentR
author_rank: Frequent Contributor
timestamp: August 23, 2016, 09:02:21 pm
content: Even for modestly-sized incandescent LV lighting installations, you have to worry about IR drop.A 14AWG wire (fairly typical for these and recommended in the manual) is 8.3mOhm/m. For a 200W load, that's 1.4V of IR drop per 10m (small distance for a backyard), definitely noticeableThat's why:* Most 12V lighting transformers, even professional ones have multiple 200W or 300W channels instead of fewer 600W or 1200W ones.* Higher-end lighting transformers commonly have multiple taps for each branch (e.g. 14, 15, 16, 17, 18V) so that you can cancel out IR drop at the transformer.* 12AWG is commonly sold for lighting and 10AWG often installed by professionals (that's a lot of copper to do a backyard - sometimes more expensive than the lighting appliances themselves).* When building the topology, you try to group the lamps close to each other on each branch so that most of the IR drop is before the first bulb, you have even illumination of all the bulbs and you can adjust voltage at the first bulb by changing the tap at the transformer.* LED lights are awesome...So the Intermatic transformer from the OP is pretty standard for a lower end transformer. If it had just 12V, in most installations, it would be too dim. But then at 14V, especially if you have a light load or little wiring, bulbs are going to have a much shorter life. No easy way to deal with it.

author: ez24
author_rank: Super Contributor
timestamp: August 23, 2016, 10:33:44 pm
content: The way I read this"Mount power pack at least 10 feet (3 m) from pool or spa."is use common sense and don't get it wet