SHTF Electricity Basics, by M.N.

Monday, Jul 25, 2011

Most of us are accustomed to having safe, easy, instant access to electricity. After a disaster electrical power is low on the hierarchy of needs.  On the other hand, avoiding electricity may become a priority.  Damp clothes and wet, lacerated skin make us much more vulnerable to electrocution.  By definition, improvised or post disaster grid power won’t be as safe as we’re used to today.   After a disaster, electricity becomes an elemental threat that can kill you dead if you miscalculate.

If you’re lucky enough to be able to prepare a bastion with solar and generator power, do a good job now and you won’t have to worry later. Many of us don’t have the means to make this choice, and will instead make do with a combination of bugging out or bugging in.  What follows are my suggestions gained from experience doing off grid solar work in the Third World, disaster relief and maintaining remote scientific equipment.  I am not a licensed electrician.

If you find yourself needing AC power in a location you haven’t prepared, or your existing environment has suddenly changed for the wetter and worse and you want to improvise a solution, stop!  Turn off AC breakers and avoid AC power until you have the time and mental space to make sure things are done right. In the mean time, if you've prepared, an affordable toolbox-sized 12 volt DC power system can keep you in charged AA batteries, light and radio communications. It is possible to hurt yourself with a low voltage system, but the starting risks are much lower than with 120 VAC. You’ll also have the benefit of traveling with a system you prepared and know you can rely on. Home Power magazine's web site and the Internet have plenty of advice for building portable DC photovoltaic (PV) power systems, so I’ll cover aspects unique to this audience. The product links are examples rather than specific product recommendations.

Must-Have Tools

Multimeters help make safe improvisation possible.  You can buy a simple meter for AC/DC Volt-Ohm meter for around $5 on eBay and not much more at a local Radio Shack. Used ones will work fine. Buy a stack of them, so that you can afford mistakes and to allow for wear and tear on their test leads. Older analog panel [pivoting needle] volt meters that don’t need a battery are more repairable, but less protected against humidity and drops.

Splicing Wires 
Plan A is to buy a butane powered soldering iron and learn to solder. Learn how from YouTube or at Sparkfun.com. First practice getting two wires to stay connected and how to solder a wire to a copper pad. That will cover most of the repairs or modifications you may need to do.  12 volt and A-battery powered soldering irons exist, but a butane soldering iron has consistently worked best for me outdoors.  

Plan B is to stock up on [solderless] splicing hardware.  For temporary work, I prefer Euro style terminal connector blocks. These are fully insulated devices that let you securely join two wires using a flat blade screwdriver. They’re hard to use incorrectly. Wire nuts work too, but be sure stock up on tape to use with them.   A cheap and sturdy screw driver spice for larger wire can be found in your hardware store as a “well pipe waterproof splice kit”.  If you need waterproofing and strain relief, then wrap the wire in self-fusing silicone tape. This tape stores well for several years in Ziploc bags or in a heat sealed plastic.

Strongly Recommended Tools
At some point you’ll need a tool that requires a 17.1 volt proprietary battery.  DC-DC switching converters are the solution for using a standard battery with this tool.   Most readers have used an adapter to drop a 12 volt battery down to something safe for a cell phone or radio. Older models got very hot to the touch, as they converted excess voltage (and half of the precious watts) into heat. Newer models use a “Buck Converter” which can be more than 90% efficient.  If you need to get from a pair of AA batteries to 5 volts, you need a “Boost Converter” to increase the voltage.  Some circuit designs combine the two. A “Buck/Boost” allows 9-16 volt input to produce a constant 12 volts output.  The catch is that Buck and Boost converters require the output to be 1-3 volts different from the Input. So you may not be able to get from 12 volts to 11. Buck/Boost circuits tend to allow a smaller input range, and usually handle fewer watts than comparable dedicated Buck or Boost circuits. 

Commercial DC/DC products exist, but tend to require small proprietary parts too easily lost in an emergency. I recommend buying parts used for industrial prototyping. These tend to be made in China using the exact reference specifications of the DC-DC chip maker.  Look for models that allow a screwdriver to change the output voltage, and if possible, allow you to set the output current (this reduces the number of fuses required). Well-built models include heat sinks, potting/ plastic to protect the circuit, and ideally screw terminals for the inputs and outputs. I’ve had good luck with models from xscyz.com. Keywords to look for on eBay or other sites are LM2577 (boost) and  LM2596 (buck). With a current limiting Boost converter and a multimeter, you could permanently power that 17.1 volt device directly from a 12 volt solar panel or a handful of double AA batteries.

Fuses exist to reduce the risk to you and to equipment you won’t be able to replace in an emergency.  This includes things like wires we now take for granted.  For DC systems, put fuses at the battery, between strings of batteries, and on the cord of every item you can’t replace. Put fuses between the solar panel and the power plug used to connect it to the charge controller. ATC automotive blade type fuses have many advantages:  They’re easy to use, water resistant holders are cheap, and you can get them in a wide variety of amperages down to 1 amp.  ATC form- factor circuit breakers are available.  Standardize and stock up, particularly on the small sizes that make debugging short circuits safer for your equipment.

Obtain several microprocessor-controlled DC-powered chargers for AA batteries. You’ll want the ability to charge just one AA or handfuls at the same time.  

Nice to haves:
For circuits below 1 amp, manufacturers use cylindrical glass fuses in too many different sizes. Whenever possible I avoid them by switching to a self-resetting fuse called a Polymeric Positive Temperate Coefficient (PPTC) thermistor. These devices get hot and trip like a circuit breaker when there’s a problem. After power is removed, the PPTC will cool down and reset.  You can buy radial  PPTCs from Digikey.com or Mouser.com for about 40 cents each. If you're very lucky, there's a local electronics supply or television repair shop selling them near you.  PPTCs can be used in parallel, but may not be appropriate in very hot or cold conditions.

Many SurvivalBlog readers have already discovered Anderson Power Pole connectors. By combining colors and polarization you can make a DC power system that’s hard to assemble incorrectly. I use yellow and black connectors for the solar panel to the charge control, then red and black for the charge control to battery. I use color beside black to mean 12 volts. With 5 volts I use violet and place the color above black. This looks different and is impossible to plug into 12 volts.  This is not the Anderson standard, but I try to use polarization for things that would be disastrous to plug together, and colors for reminders that are protected by a fuse and can wait until I have a light.  

Buy an older copy of the book Illustrated Guide to the National Electrical Code (NEC). You may never need it, but a used copy is less than $10, and you’ll have the answers.  Mirrors of MikeHolt.com and the John Wiles Code Corner would also be useful.

Thanks to car culture, there is a wide choice of waterproof 12 volt LED light strips.  I find that most of these crack and fail within a few years. I’ve found the UV-stabilized strip lighting for ponds seems to wear better.

A non contact voltage tester like a Fluke AC Non-Contact Voltage Testeris handy today, and could be a lifesaver when testing if pipes or other unexpected items are electrified.  A ubiquitous receptacle tester is a more simple way to do the most useful AC checks around a house.

The last and most optional part is a DC watt meter like the "Watt's Up". These devices measure voltage and current, but also keep track of watt hours used. Track the power put into your battery by day to know your power ration at night.

Saving your life with a multi-meter
Fallen and flooded power lines are obvious threats, but there are two subtle AC power problems likely to increase after an emergency: poorly installed systems and grounding issues.  The good news is that checking for these problems is fast and simple.  You may not have the luxury of fixing things, but you can quickly leave or reduce your risks.  

The normal NEMA ("surprised face" style) North American wall outlet has three wires: The tall slot is the neutral wire, the short slot is the hot wire and the round one is a ground.  If you look at a light bulb socket, the outside rim is the neutral, and the inner dot the hot wire.  Modern appliances will have the outside metal shell connected to ground.

If everything is built to code, back at your circuit panel, the neutral wire is connected to the ground line and a big copper spike in the earth.  This makes sure that when you stand on a wet floor and touch the outside of a light bulb socket, the neutral line will have a better connection to the earth than your body and you won’t get shocked (as badly).

In practice, people frequently wire things backwards so that the outside of the light is hot and your body is the best path to ground. This is particularly common on cheap generators that require some assembly.  Dangerous inside a dry room, but suicidal outside after a hurricane.

Having multiple connections to ground can be dangerous. A common example is a site between two widely spaced generators or long extension cords between houses. Under the wrong circumstances, simply touching both grounding wires can give you a shock, and touching the ground from one and neutral from the other is likely to be fatal.  The fast fix is to remove all connections to one power source from your area. All other solutions are more complicated, requiring study and spare equipment you might not have.

To find out if you have a wiring problem, first pause and reflect if you can test a socket without increasing your risk and if you are certain you can test without your body becoming part of an electrical circuit. If so, use a receptacle tester or follow your multimeter’s instructions to measure AC voltage. There should be roughly 120 volts between neutral and hot.  If it’s down around 90 and you’re using a lot of power, someone probably disabled a circuit breaker and your risk is higher. If there’s .05 or zero volts you probably don’t have a real ground spike connection.  This is common with inverters.  If there are 90+ volts between neutral and ground, measure hot to ground. The circuit is probably installed backwards.

If there are more than 2-3 volts between neutral and ground in an average house, there had better be a good reason. Sadly, there are both legitimate reasons and dangerous reasons, which is why we have electricians and the NEC. The danger increases with the voltage. Above 5 volts, you almost certainly aren’t getting the protection you and your equipment want.

Finally, measure voltage between the plug ground and water pipes or other metal things that are likely to connect to the ground. If you might have two sources of power, measure the voltage between ground plug holes.  Anything above 2-3 volts between grounds is cause for concern.

You now know if the outlet is good, gray area, or obviously bad.  Your safety is up to you. Reflect if near this outlet is likely to get more dangerous (wetter).  Avoid combinations of temporary electricity and any existing plumbing or electrical infrastructure.  Set up the generator powered radio out of reach of the sink and tape over the nearby wall plug.  Put one hand behind your back before flipping circuit breakers, touching new appliances or testing circuits.  This is all common sense, but many of us have to unlearn decades of being lucky breaking the rules. The AC checks show if your environment is really as normal as it seems.  

Photovoltaic Power for the Bug Out Bag
There are four problems to overcome: Getting enough watts from the sun, building something that travels well, keeping it affordable, and having it work when you need it.  

There are some great looking solar chargers that would fit in a normal bug-out bag. Most of them tend to be fragile, non repairable, and have about 5 watts of solar power. When combined with bad weather and poor solar tracking (lashed to a backpack), this frequently isn’t enough to keep up with the demands of flashlights. 

I favor 20 watts in a more luggable 25 pound system using standard parts. I can’t carry it at a dead run, but it travels well by car or bike and I can take it to a new house if need be. Most important, one sunny day can get me several days of power.

Smaller panels cost more than larger ones and need more mounting hardware to be useful.   Unbreakable panels cost 2-4 times more, so I’ve chosen to buy more  breakable panels as spares and trade goods.  Right now the best value /portability compromise is a 20 watt glass panel with a surface measuring about 2 feet by 1 foot. Sandwiching between pegboard and foam insulation protects them. Look for UL-listed panels, since that filters out the most dodgy imports. Using 10 watt panels does allow a wider choice of luggage, so decide if you want cheap containers or cheap panels.

Flexible solar panels are designed to curve around boat decks, not be stuffed into a backpack. I haven’t tried the $400 military models, but the affordable thin film folding designs tend to quickly wear out at the folds and are impossible to repair if pinched. Thin film requires much more surface area per watt.  Since I have to protect the panels anyway, I’ll stick with crystalline ones.

Rigid panels have a second advantage: they’re easier to point at the sun. Tack a nail straight into a flat scrap of wood. Point the nail head at the sun. When the shadow disappears, match the solar panel’s angle to the wood’s. Paying attention and tracking the sun increases your power by 20-50%. A small tracked panel can exceed the output of a larger floppy panel on the ground.

Panels have to be visible to the sky, above grass and not shadowed by bushes. This makes OPSEC difficult, particularly in northern latitudes where the panels must be near vertical.  Camouflage netting works well to cover the sides and back of panels.  Black solar cells flash less than blue ones.  Try to place your panels behind a bush to avoid flashes down hill, and look out for where you can be seen from above.

Batteries
While there are great solar charging lithium battery systems for sale, the price per watt hour is too high for most people.   The best compromise is still a sealed Absorbed Glass Mat (AGM) battery. A 15-20 Amp hour AGM mower battery weighs less than 20 pounds and can survive a few accidentally deep discharges.  When you buy a battery, write the manufacturer’s preferred charging voltage and current on the side of the battery. Print out the data sheet and store it with the battery.

Unfortunately, different brands and models of AGM batteries have different charge voltage limits, and chargers ignoring those limits will damage them.  Everything will work for the short term, but a bad charger can burn out your battery in weeks.  If you aren’t going to be able to produce a spare, spend more on a charge controller that allows you to specify charge voltages or has an AGM setting matching your battery. The Xantrex (formerly Trace) C12 is the only low watt commercial controller I know of that doesn’t require a computer and will work with any battery.

MPPT charge controllers are  advertised as increasing daily watts by 10-20%. I find the true advantage is being able to get from zero watts to barely useful (AA charging) watts with shadowed panels. I’ve bought no-name MPPT controllers that worked, but they wouldn’t be my choice for an emergency. A solid state PWM charger is a better bet.

Charging cordless electric hand tools requires compromises.  Manufacturers of lithium-ion power tools love to create bulky and expensive cradles for 12 volt tool chargers. Using an AC charger with a 150-300 watt pure sine inverter has more general utility for same price and bulk, but is 30% less efficient in charging the tool [than a DC-to-DC vehicle charger.] Cheap modified sine inverters have been known to kill DeWalt and other brands of AC-to-DC microprocessor-controlled battery chargers.  I’ve tried using small lithium ion chargers intended for remote control hobbyists, but fear I’d use them incorrectly under pressure. A DC to DC converter will charge NiMH tools, but manufacturer's own chargers seem to be the only good choice for lithium battery packs.

There are two phases for keeping your solar suitcase useful when you need it:

1.) Put a small solar panel out today. Even positioned flat in a bad site, it will recharge your AA batteries. This will familiarize you with the system and keep it topped up.

2.) After the SHTF, constantly disable unneeded power draws. Most small inverters draw 5 watts when idling.

Hopefully the Morningstar SureSine inverter will spur competitors.  I’ve accidentally killed batteries by leaving just the wattmeter and charge controller status lights plugged in for a few weeks. I now disconnect the battery when I know I won’t be using panels for a few days.

Be careful and be prepared!


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