Transcript
A “CEDIA” Low-Voltage Initiative Proposal TR December '08 TIP-of-the-Month Copyright 2008, Training Reels and Grayson Evans
This month’s TIP is really a follow-on article to our August ‘08 solar electrical system “tip”. This article picks up where the other article left off in terms of power distribution.
H Somewhere in the mid 1980’s, the NAHB Research Center in Washington was run by a guy I knew (whose name I can’t seem to dig up) who had a wacky vision. His idea was to reinvent the way electrical power was distributed throughout the home. They called it Smart Home (not to be confused with the Disney movie of the same name or other stuff that uses that name now). I think it was the first use of the name. It worked something like this. Electrical power was distributed from a central “power server” in the house to each outlet. A “Smart Home” compliant appliance that plugged into the outlet (using a new 4 contact plug—2 pins for power, 2 for data), would signal the “power server” that it was Smart Home compliant and that it needed so-and-so amount of power at 120 volts A.C. for example. Or it might say it needed 30 watts at 12V D.C. The “power server” would then energize the outlet with the correct power and monitor the current draw. If the draw was exceeded, or went to zero, power was immediately removed. The big advantage of the system was that it was very safe (no voltage at the outlet unless asked for by a plugged in device), and energy efficient (since inherently low-voltage devices didn’t need to convert high-voltage A.C. down to low-voltage D.C. for example). To do this, the center came up with a whole new wiring infrastructure for the home (new outlets, new wires, new everything). Needless to say, it was an overly ambitious project and totally naive. But, believe it or not, it got great financial support—mostly from appliance manufacturers—for many years.
KThe concepts were not at fault and the reasons for the project were admirable. It just had two MAJOR problems. 1) the technology to do it was either nonexistent or prohibitively expensive, and 2) it had to rely on electrical contractors to install it. Never mind. Fast forward twenty years. Some of this technology sounds not only more feasible, but familiar. Actually we have a similar technology already in use in offices and homes now, albeit on a less ambitious scale. Can you guess what it is? 802.3af, aka, PoE (Power over Ethernet). PoE is a DC power on demand technology that works almost exactly like the Smart Home project envisioned. There is a “power server” device (usually built into a data switch) that can furnish 48V D.C. at various power levels to any 802.3af compliant device that plugs into a connected ethernet wall jack. Attached devices execute a simple protocol (by presenting different resistive loads to the server) to tell the PoE server how much power to deliver.
A Solar Marriage In a previous “blog” on Solar Panel installation (and newsletter article), I discussed the problem of converting the output of the solar panels to usable power for the home. The problem is that solar panels output DC (usually at 12 or 24 volts). Great for charging batteries, but useless (as is) for anything in the home. So the 24V DC from the panels/ batteries has to be converted to 120V A.C. at enough power to supply a lot of stuff in the home. This is obviously inefficient and wastes a sizable percentage of the energy as heat, and the equipment is expensive, large, and subject to failures (due to heat).
Typical power loss from solor panels/batteries to the load (electronic device). Numbers shown are for a typical 120W device such as a DVD player or small receiver.
The compounding ironic problem is that a lot of the stuff in the home (electronic equipment in particular) works natively off low-voltage D.C. So the power has to be reconverted back to low-voltage DC. The diagram below illustrates the problem for a simple electronic device such as a DVD player that only draws 150 watts. If you assume the DC-AC inverter (required to convert the 24V from the batteries to 120 V A.C. for the house) is 80% efficient at best, and the power supply to convert the A.C. back to low voltage is 75% efficient on average, then the batteries/solar panel needs to supply about 250 watts. The difference (100 watts) is lost as heat. My point is that solar power and a low-voltage power on demand technology like 802.3af are really made for each other. Why not just keep everything at a low voltage? We’re stuck with A.C. in the home because the electrical utility needs AC power distribution so it can use transformers to manipulate power on the grid (trading off current for voltage on long distance transmission lines), stepping voltage up and down to make power distribution easier and more efficient. Everything as been designed to
use it out of necessity, but hardly anything works better with it (vs. D.C.). Everything we install (that I can think of), works off low voltage D.C. The ubiquitous “wall wart” power supplies are everywhere. What a pain. (Admittedly, high current loads over 10 amps such as air-conditioning equipment, dryers, stoves, etc. benefit from higher voltage)
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Implementation So the point of all this is that I think our industry is not only in a great position to take on the energy generation part of energy management (solar generation - panel and equipment installation), but the efficient distribution of electrical energy in the home as well. I propose that our industry initiate a new way to wire electrical distribution for the home by providing low voltage outlets where electronic equipment is likely to be located in the home, especially A/V equipment. We now have everything it takes: low cost easily available technology (parts, IC’s, hardware, etc.), and an industry to design and install it reliably. This creates an opportunity. Time to take advantage of it.
Basic LV distribution scheme. LV distribution panel incorporates fused branch circuits just like a standard electrical panel. More than one LV outlet can be wired to a branch circuit. Branch circuits can be rated and fused for 10 or 20 Amp service. 12 or 14 gauge speaker cable can be used for branch wiring.
At first this can be just an “uncontrolled” distribution of 24V DC co-located with existing 110V AC outlets (Phase 1) This would incorporate a simple low-voltage “load panel” with LV outlet (see diagram above). Outlets would use the same connectors as the load panels, the Anderson PowerPole connectors (see photos). These are “off the shelf” inexpensive items. Many types of equipment can be powered directly without any modification if it uses external 12 or 24 V power.
LV distribution panel. Each branch is fused using standard auto electrical fuses. Branch circuits use industry standard PowerPole connectors.
Why 24 volts and not 12 volts? The primary reason is that solar panels are typically wired to furnish 24 volts and storage batteries are configured for the same voltage. But secondly, it’s the same reason that PoE uses 48 volts: to allow for voltage drop in the cable from source to load—the same problem we have with speaker cable. A 200W load that could operate over a 12V to 24V range would draw, on average, 10-12 amps. Assuming the LV distribution is wired with 14 gauge “speaker cable”, this would generate about a 6V voltage drop yielding 14 volts or so at the device. 12 gauge cable would be even better of course. Anderson PowerPole connectors are both the male and female end. They are keyed and interlocking.
Phase 2 would incorporate a true PoE style power on demand system. My guess is that existing PoE ethernet chips can be adapted with almost no change since the protocol for determining how much power is needed to the device is very simple.
We Have the Clout There is NO question our industry is big enough to get the “chicken and egg” problem off “top dead center” by getting the infrastructure started. 1. It’s very easy, 2. It solves a lot of problems, 3. It drastically increases energy efficiency, 4. It is a natural solar energy system extension. 5. It provides true benefit to the customer. 6. It is an additional service you can easily provide.
Yes, this is a long term project. It will need 5 years to get imbedded. And it requires some interest and cooperation from equipment manufacturers. But something that allows manufacturers to make products cheaper for a change by eliminating unnecessary power supply components (instead of adding more features) usually gets their interest. If you would like to know more about how to make this work, send me an email. If any of you were around (past puberty) during the Smart Home days, please send me your favorite Smart Home story! Do you remember the Smart Home cable and insulation displacement connectors? What was AMP thinking??
N If you have any questions about anything in this TIP or solar power/power distribution in general, drop me an e-mail at
[email protected] I will actually answer it! NEXT MONTH TIPs on job site practices. Catch you next month….Grayson For many more Training Reels TIPS, visit www.trainingdept.com/html/support.html
