I agree with your philosophy with regards to Nucs. I think that is where you can really make a big difference in yields. I did get a number of 4 frame medium nucs through winter last year with good insulation. That isn’t bad for Michigan. I’ve got a number of 4 frame mediums out there right now, but this has been a much colder winter. Without electric heat I’m expecting a near 100% loss of those small nucs. I would have to trek a mile through knee high snow to check on them so I don’t know how they’re really doing at this point. If I was a betting man, I would bet on 100% losses. We’ve had so many nights below 0F this winter, it’s ridiculous.
With regard to the computer power supply, they are a good low cost source for 12volts DC and a lot of amps (20+). You can buy them cheaply from most online computer retailers (under $40). However there are some complications (of course!). Computer power supplies aren’t designed to run in sub zero (0F) weather! They use electrolytic capacitors to filter the output voltage. The dielectric in those capacitors are water based and water freezes at 32F. The caps don’t actually freeze at low temps, but their ESR goes up and that causes all sorts of potential problems. Hence, if you’re going to heat your nucs from a computer power supply (sitting outside), you’re probably going to have to put the power supply inside an insulted box too. That’s what I did.
A power supply is never 100% efficient and the energy that is lost shows up as heat. If you put an insulted box over a computer power supply in your bee yard (assuming we’re talking outside here), that waste heat from the electronics can keep the power supply from freezing. That is what I did. There are photos of that somewhere on my photobucket page.
If your nucs are close to a building with 120VAC power, then it might be feasible to run the power supply inside your building and use heavy gauge landscape wiring (10 gauge) out to your nucs. However, that is going to start causing new problems if your nucs are more than about 50 feet from your power supply. Any current flowing over any wire drops voltage. Speaker wire is way too thin to use in most cases. I used 100 feet of 10 gauge landscape wire in my first attempt and only had 10 volts by the time the power got to the nucs. A loss of 2 measly volts might not seem like much until you look at the bee heating power you lose.
A 2volt drop over your supply wire is a 16% loss in voltage, but that generates a 30% drop in the power (heat) available for your bees. For example, assume you build your resistors to generate 12 watts of heat from a 12volt supply. That would require a 12 Ohm resistor. (Power = Voltage x Voltage / Resistance. 12watts = 12v x 12v/12r ). Now if you lose 2 volts in your supply wires (speaker, landscaping, whatever), your power available at the bee heater drops to 10vx10v/12r = 8.33 watts. A whopping 30% less than you expected.
Lesson is, a voltage drop in a low voltage system is a real power/heat killer! This whole voltage drop over a wire problem is why Tesla won and Edison lost in the AC vs DC power wars a century ago. How do you get around this problem? You really can’t, you just have to compromise your layout around the laws of physics. If you go with a low voltage DC power supply, you’re going to want to keep the lines between it and the nucs from getting very long. That might require moving the power supply outside.
Yeah, there are some ‘tricks’ you need to apply to a computer power supply as well. They’re designed to run inside computers, not bee hives. First trick is you need to jumper the motherboard connector on the power supply to power up. Just plugging in a computer power supply doesn’t turn it on. I’ve got a photo of the jumper somewhere in my photobucket library; you could also search the internet. I don’t remember the pin #s as I’m typing right now. Next, many modern power supplies require a minimum load to run. You may need to connect up an extra 12VDC computer cooling fan to draw enough load; a few hundred milliamps is usually enough. I did have to connect a fan to keep my supply running.
Once you have the supply working, you’ll need to tap into the 12volt line and ground to connect your speaker wire/landscape wire to. I soldered my wire directly to the power supply to reduce the voltage drop at the junction. Remember any voltage losses in a low voltage system really wrecks your bee heat. I did use wire nuts at the other end of the hookup wire to connect the bee heaters up. I didn’t solder everything because you don’t want to make the system too hard to repair if something fails at -10F.
Ideally you would regulate the amount of heat you give each nuc with a small controller of some sort. I used a custom built 8bit microcontroller and a thermistor for that. I can program in a hive temperature and the controller will modulate the wattage output until that temperature is met. You can buy various prebuilt controllers for probably $50+. I happened to build mine from scratch for about $5 in parts. The controller is probably the biggest problem for the average beek. They’re really pretty simple things, but it does require a little experience to be competent working with them. Again, find some 16 year old neighborhood computer geek and he could set you up with no problem.