I have a lighting issue at my ski place that I need to solve.
If the weather’s good, we just drive up, unlock the gate (in the car’s headlight), and wait for the motion detector lights to kick on.
If there’s a little bit of snow – say, 3″ or so – the Outback handles it fine, and I get out the snowblowblower and clean off the driveway. Except once I get about 50′ away from the house, I can’t see anything any more, and snowblowing in the dark isn’t a lot of fun.
If there’s more snow, we can’t get into the driveway, and have to park out in front, unload in the dark, and then walk across the meadow and through the woods to the house. In the dark.
Seems like we need some lights.
The first choice is whether to go with line voltage or low voltage. Really simple in this case – I need to get the power to two locations about 150′ from the house, and I need to get the lights up into the air. That means a whole lot of trenching through the woods and putting up poles to attach the lights to. Or, it’s running some zip cord through the woods and then mounting some lights up in the trees. So, we’re going the low voltage route.
Which has some problems of it’s own. One of resistance.
The transformer for the system will mount in the house, and that means about 150′ of wire to each of two remote locations. Let’s say we buy 12 gauge wire, just to make it easy. We have 300′ of wire total, and if we look up the resistance, we find that it’s 1.588 ohms/1000 ft, putting us right about 0.5 ohms for the 300′ of wire.
That doesn’t seem like a lot of resistance, so let’s look at some numbers. If we want to run two 20 Watt lights, that will take 40 / 12 = 3.3 amps, so we’ll lose 0.5 * 3.3 or 1.6 volts. With 12 volts running into the run at the start, that means we have 10.4 volts into the lights. If they’re halogen lights, they don’t like that – halogens require full voltage or their lives are reduced considerably. If we bump up to 2 50 watt lights, it’s much worse – we’re pulling 8 amps and losing a full 4 volts in the wire.
The professional low voltage transformers have taps at higher voltages, so we’d hook up the 14 volt tap for the 20W lights, and the 16 volt tap for 50W lights. Unfortunately, the pro transformers are fair bit more expensive than the ones I’d like to buy. Another option would be to go with thicker wire 10 gauge only has about 2/3 of the resistance, but it’s also half again as much copper, so it’s a lot pricier.
As an alternative, let’s consider a system with LED bulbs instead of halogen ones. You can now find 3-5W LED MR16 lamps that in the $20 range, producing the same amount of light as a 20W (ish) halogen. It’s about 5 times more efficient, which means that if you put two of those out, you are only pulling 1 amp, and you only lose 0.5 V. I can probably step down to a smaller wire gauge with the right transformer.
Not sure which way I’m going to go yet. But I do have the control system designed. That’s up next…
So, what do you think ?