Hello Jim,
I enjoyed the article regarding off-grid power by Roger A. I’d like to add a few points about the elimination of phantom loads and the use of inverters.
As defined by the author, “phantom loads are created by appliances that have been designed to still need electricity while nominally switched off.”
The elimination of these phantom loads reduces electrical needs in two ways; by eliminating the power needed by the appliance and the potential of being able to turn off the inverter. As pointed out in the article, inverters draw an average of 25 watts just to operate. Running 24/7 this can be a huge load for an off-grid system.
Jim, you suggested using a switched power strip for appliances with phantom loads. Excellent advice. Unfortunately, esthetics and forgetting to turn the strip off after using the appliance can reduce its effectiveness.
I’ve lived off-grid twelve years now. Here’s what I’ve learned to eliminate phantom loads.
Anything with a plug that includes a digital clock is a phantom load. Microwave ovens and clothes washing machines that use dial-timers are still available. Most of these appliances use no power when they are “off.” Speaking of digital clocks, use a battery powered travel type alarm instead of the plug in type. Cordless shavers, toothbrushes and cordless power tools are okay, but should only be plugged in when the inverter is operating, for example in the evening when lights are needed. The chargers on some cordless devices can be destroyed when used with modified sine wave inverters. This is not an issue with true sine wave inverters.
The “entertainment center” (television, DVD, satellite dish receiver, etc.) is best served with a power strip. That dratted television is mostly a waste of time anyway, but I digress. The computer and its accessories should be plugged into a power strip, which is switched off when not in use.
Battery powered outdoor lighting units with LEDs and a motion detector work well for specific areas.
Refrigeration is tricky. I use a Sun Frost refrigerator/freezer. It’s a DC model, which means it runs directly off the batteries and no inverter is needed. These boxy units are available in 12 and 24 volts DC. They are very efficient and have a reputation for reliability. However, the non-standard size and high cost is off-putting to some.
Cordless phones and answering machines can be bought off-the-shelf, and then powered right off the battery system with an appropriate DC to DC converter. These are the devices you plug into your car’s cigarette lighter (12 volt DC) to charge your cell phone. Lighting can be had from 12 volt compact fluorescents or 12 volt LEDs. Pumping surface water (from tanks, pools or lakes) to a pressure tank or garden can be done with a DC pump. I’ve had good luck with Shurflo pumps. Available in both 12 and 24 volts DC, they are noisy and don’t tolerate any solids in the water, but are reliable and easy to maintain.
One important caveat when using low voltage DC is to fuse every single device. If you’ve ever dropped a tool across a car battery and watched it vaporize in an adrenalin-inducing instant, you’ll understand the importance. This can be as simple as an appropriate sized in-line fuse from an auto parts store.
Using low voltage DC calls for short wire runs from the batteries to the device and appropriately sized wiring.
Besides helping to eliminate phantom loads, there is another advantage in powering some appliances by DC, especially refrigerators, pumps and lights. Should the inverter fail, you would still have refrigeration, running water and lighting. Best Regards, – Dave S.
Jim,
Greetings from the suborned state of Colorado.
I’ve rewired a few houses, and while I’m not an electrician – I always used one to inspect my work – also swapped out a lot of panels on aluminum wired condo’s for fellow homeowners…
Overloading a circuit has been a problem for all types of wiring since electricity was invented, circuit breakers are there to insure that the line draw never exceeds a certain level the level and draw are calculated based on expansion and heat loss for the types of wires used. As the following chart shows, nearly all aluminum alloys have a rating of 13 (yes it’s a measurement, but for comparative purposes that’s not important) whereas most copper alloys run around 9. The difference actually isn’t that great, platinum has a much better rating, but is also much more expensive. The other factor that is overlooked is the ductility of various metals.
The fire problem was only peripherally caused by overloading, the more typical problem has to do with aluminum wiring and it’s expansion when heated and it’s ductility when expanded. Simply put, when aluminum heats up it expands but when it cools down the metal loses it’s “memory” and does not shrink back to it’s original shape. The ductility (or, essentially, the ability of a metal to return to it’s original form) of aluminum is fairly low, meaning that a given shear force (force exerted along a perpendicular axis) needed to cause aluminum to separate is lower – and it’s higher for things like iron – but even more importantly is the deformity curve, for a given force a deformity is a permanent displacement of material for a given force, the curve for iron looks flat until you hit the absolute sheer strength (that needed to separate it), iron will resist deforming almost up to the actual point of sheer. The curve for aluminum is fairly constant for deformity, at very low forces aluminum deforms permanently.
This permanent deformity problem only crops up over time, and only crops up at junctions where the wire is fastened, like the service box where the circuit breakers are and points in the loops where power is drawn out (outlets), it gets really bad if you join copper wire to aluminum as the copper expansion contributes to the aluminum deformation under heat/expansion stresses. Joints where a steel screw join with aluminum don’t exhibit the same deformation problems as those where copper is joined to aluminum.
so what is the real cause of fires in aluminum wired homes? Well, it’s easy, over time the aluminum deforms and when it cools it fails to resume it’s former shape. Screws like those used in outlets fasten the aluminum to the (usually) bronze or copper outlet or to the bronze/copper end of the circuit breaker. The steel screw has a very high deformation curve so as the aluminum wire expands with heat in response to load and other environmental factors, the steel or bronze screws resist doing the same thing, and the aluminum deforms on a microscopic scale while the other materials generally don’t deform. So expand/contract, over time and use causes a slight gap between the aluminum wire and the outlet box or connector, when there is a slight gap the electric current arcs across the gap (because it’s still close enough to do so) and eats away a little at the aluminum as the heat of the arc attempts to deposit the aluminum on the bronze/copper fixture – this weld fails as the metals are incompatible and the aluminum is lost – creating a bigger gap. At some point the arcing will start to create flashing and the erosion rate increases – until one of two things happen. The circuit fails due to the gap or the materials surrounding the junction catch fire. If you’ve used steel junction boxes and your main panel isn’t directly in contact with your siding the failure isn’t catastrophic – but wait – a lot of junctions happen behind walls, such as when someone doesn’t have enough wire to make a full circuit (or are using up short lengths of wire) and these places are hidden and usually not protected by a steel junction box – the heat hits the building materials and you have a fire.
But overloading isn’t the primary cause, it’s the nature of the materials and their application that is the primary cause – overloading just makes it happen faster! – Jim H. in Colorado