I am going to put out some garden lights outside soon. I have two spot lights of 12V 15W each, which are going to be connected in parallel. The wires for these are going to be quite long (from the garage, and across the whole property). I was just wondering what thickness of wires I need for this. Is the voltage and wattage enough information to find this out? I am also going to have four normal garden lights, of 12V 5W each. When everything is connected in parallel, this means I will be using 50W. I want just one wire running from the garage, to the first area with four lamps of total 20W, then another wire running from there, to the two spots of total 30W. How thick must the wires be? And how should I do it with combining wires under the ground? Can I use regular, non isolated "sugar cubes" (that's what they're called in Norway), or will the moist earth lead electricity and create a short circuit? Should I use the (more expensive) isolated ones? It would also be cool to add some potentiometers to the lamps. Will that work ok? When the wattage is so high, do I need some "special potentiometres", or are the ones I nicked out of an old portable TV ok?
Oh yeah, and I want to add fuses to the garden lights, just to be on the safe side. But I don't know how many amps. I guess there is some way to calculate that. I have one set of four lamps (total 12V, 20W) and one with two lamps (total 12V, 30W). I want to add a fuse to each set. (two fuses). Can you tell me which fuses to use from this site: http://www.biltema.no/products/product.asp?iItemId=13898
In answer to your first question since its only 12v volt you can probably join the cable any way you like without short circuits. However you may want to use something that wont corrode in the damp and lead to bad connections. You will probably need potentiometers capable of dealing with a higher current than the ones out of an old tv. Also P=I*V [P] Power(watts) Current(Amps) [V] Voltage(Volts) or I=P/V or V=P/I For the 50 watt set of lights 50/12=4.16 amps so get a fuse a couple of amps above this rating. For the 20W set 20/12 =1.67amps so a fuse of around 3 amps should be ok. However the transformer shopuld be short circuit portected so you proabbly dont need a fuse.
This may sound like a noob question, but how can the transformer supply so many amps, when it says that it uses 0,27 amps?
That must be the input current. Since the input voltage is higher(240v) the input current is lower. In the same way the output voltage is lower and the current is greater. A high voltage and low current will give the same power output as a low voltage and a higher current.
a little tip: instead of the "sugar cubes" (no idea what they are called either...) just solder the wires and use heat shrink.. i did.. been out there the whole winter.. works fine.... But use pretty thick cable.. (4mm2) mabye... the thicker the better... if you use 1,5mm2 you will nothice pretty big difference after 10 metres with 3x20w lights...
Smilodon, at least you know those regular grounded cables which are used for extension cords in Norway. (Vanlige jordede skjøteledninger) Will those be ok? I guess I can solder and heat shrink, even though the neighbors might wonder why I am standing in the middle of the garden soldering the grass . And one more thing - can I let the lamps stand out in the garden at winter time? The two spots are aluminum, so I guess they'll be all right, it's the four plastic ones I am concerned of.
i think those cables should be just fine.. rubbercables is best though... but most works.. it's 12 volts anyway so... about the winter ting: I'm not sure about that... the ones we have in teh garden is homemade... old milk glasses turned upside down.... molded in concrete blocks... then a halogen reflectorbulb is put inside and a plexiblasdisc is "glued" on with silicone... those lies in the flowerbeads (blomsterbed) and shines up in some trees... anyway.. the cables and the lights itself has been underground all winter.. still works fine.. actually it looks really cool in the winter because the heat of the lights melts the snow so that you see small glowing craters in the lawn.. anyway.. remember that aluminium verdigrises (eirer) over time.. the plastic might crack in the heavy snow and the cold.. doesn't the package say something about minimum usage/storage temp.. if not you could always ask where you bought them...
To change the brightness of the lights, why not just use a dimmer switch designed for inductive loads on the mains side of the circuit? You'll certainly not lose so much energy as heat. I dislike using high power resistors in these applications since they are so inefficient. Regarding those "sugar cubes", are you refering to terminal blocks?
