DIY electricity

This guest post is by Papabear and entry in our non-fiction writing contest.

The Dallas Observer published a report1 recently that Texas has worst electric grid in the nation. This was based on a North American Electric Reliability Corp report2. That’s not very encouraging. They are also reporting that there is the possibility of rolling blackouts in 2013.

For a couple of years I have had the interest in setting up a backup power system for home use. There is a mobile system that provides power for work a couple of times per month, and is a backup system when at home. It provided power for 2 freezers, a refrigerator and a fan during 3 days of outage one summer several years ago. But we really want a system that has the specific purpose of supporting the house.

When looking for a mobile 120 volt (V) system I did talk to an “expert” who wanted to sell the best system that they had. He wanted to get me excited about selling power back to the electric company. After redirecting the talk with the expert to a mobile plan, and taking some of his advice, it proved to be an exercise in frustration.

Not wanting another talk with another overconfident salesman I decided to plan the home system. One essential requirement is to start with home power needs. There are charts available that will show what most appliances consume. Another way is to check the sticker on the appliance and see what the manufacturer states is the power usage. Another way is to use a meter that will measure the power usage. The most well known and used is a meter called Kill-A-Watt. There are other brands that perform the same function. Plug it into a 120V outlet, plug your appliance into it and let it run for a day or two. It does not store the information so you must write it down before unplugging. Check the number of watts (W) that it has used, the total time that it was plugged in and do the appropriate math for 1 day of consumption.

Example: our medium size freezer was tested for 2.76 days giving us an average consumption of .938 KW per day.

Doing this with each 120V appliance can give a measure of our household needs. Remember that the appliances may not be all running at the same time. The total consumption will be one of the concerns in picking batteries and charging them.

How do you pick a battery system? Let’s look at some battery definitions.

Cold Cranking Amps
Cold Cranking Amps is a rating used in the battery industry to define a battery’s ability to start an engine in cold temperatures. The rating is the number of amps a new, fully charged battery can deliver at 0° Fahrenheit for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. The higher the CCA rating, the greater the starting power of the battery.

Open Circuit Voltage (O.C.V.)
The voltage of a battery when it is not delivering or receiving power. It is 2.11 volts for a fully charged battery cell.

Reserve Capacity (RC)
Reserve Capacity, (RC) is a battery industry rating, defining a battery’s ability to power a vehicle with an inoperative alternator or fan belt. The rating is the number of minutes a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery.

RC is the number of minutes a new, fully charged battery at 80 degrees F will sustain a discharge load of 25 amps to a cut-off voltage of 1.75 volts per cell (10.5V on 12V battery). This battery rating measures more of a continuous load on the battery and is a much better indicator of how it will operate bilge pumps. An RC number given in the specification indicates that it is more than just a cranking battery and probably a hybrid starting battery. This is a very useful rating for a boater.

Reserve capacity is directly, though not completely, related to battery plate size and quality. As a general rule, cranking batteries have little reserve capacity after cranking operation unless they have thicker plates. If they have thicker plates, it will have a lower CCA rating.

Amp-Hour battery rating: AH is a common battery rating for batteries. Amp-hour rating of battery capacity is calculated by multiplying the current (in amperes) by time (in hours) that the current is drawn. Variations of the amp-hour battery rating is the most used rating. It most commonly signifies a deep cycle, marine or industrial battery.

Example: A battery which delivers 2 amperes for 20 hours would have a 40 amp-hour battery rating (2 x 20= 40). This is known as the 20-hour rating versus other ratings based on times such as 5, 8 and 100 hours, but also at different amperage rates. Such ratings are given based on what is considered most useful for the intended application. A battery intended to supply low amperage for long periods, for example, would use the 100 hour method, whereas a 5 hour rating would likely be for a high amperage rate. The 20 hour method is most common.

Marine:  It seems as if every battery manufacturer today sells “marine” batteries but, as mentioned earlier, many such take considerable liberty with the term. Some marine batteries are deep cycle, others are hybrids, while others are pure hokum. True marine batteries are designed for dual use of engine starting and house service and are therefore hybrids (not true deep cycle). These will have spongy, porous plates that are significantly thicker than automotive batteries. They will be larger and heavier than auto batteries. A true marine battery will tolerate up to 50% discharge, whereas a deep-cycle and industrials tolerates up to 80%, whereas an auto battery will quickly die at such discharge rates. Numerous batteries found in small boats will be labeled “auto/marine” and the only way to tell the type is by cutting it open and examining the plates unless you are buying a reputable brand, but it’s still a pretty good bet that any battery so labeled isn’t going to be very good. There are also very many brand names of this type, and also many of low quality.

Deep-Cycle:  These batteries are distinguished by having much thicker plates (1/4″ or 0.270″ for Surette), nearly seven times thicker than an automotive battery, but high quality batteries will have solid lead plates versus others made of a lead powder composite. Lead powder plates allow for much more rapid charging but also deteriorate much faster, whereas solid or more dense and thicker plates are slower charging but have much longer service life.

Deep cycle batteries withstand greater abuse and thousands of charging cycles and have much greater service life than the other two types. They do not, however, have as great cranking or burst power, being designed to provide power over longer periods of time. These are best for use with inverter systems. They are identifiable by their cost of 2-3 times that of other types and 20 hour AH ratings. The number of brand names of this type is relatively small since the cost is higher. Good quality ones are usually not found in discount stores or mass retail outlets.

Golf Cart batteries are generally a quasi-deep cycle similar to marine, and though not as good as batteries with solid plates, they are better than the auto/marine types. Usually set up in banks of six volt batteries, these have a greater number of plates to provide longer periods of use under a constant power demand and deep discharging. T-105, US2200 and GC-4 are common identifiers. These batteries can discharge up to 80% without being damaged. They are not better for use with inverters than true deep cycle batteries.

Industrial Batteries :  “Industrial” or “commercial” has long been used as a designation for deep cycle batteries used in fork lifts, sweepers, floor cleaners and similar battery powered machinery. Similar to golf cart but usually true deep cycle types with much heavier and pure lead plates up to around 0.270″ thick. These batteries can discharge up to 80% without being damaged.

Yet another type name has crept into the lexicon recently, is the RV type. Most RV types sold are cranking batteries or hybrids as indicated by their higher cranking power but lower reserve power.

Obviously, the deep-cycle is the preferred battery type for marine use but for its one drawback of being less able to provide high cranking power. This is overcome simply by increasing battery size.

AGM Batteries

AGM stands for Absorbed Glass Mat which contains the electrolyte absorbed in a mesh of Boron-Silicate glass fibers. Thus there is no fluid electrolyte to leak or spill nor will they suffer from freeze damage. There are two big advantages of this type. First, it can be charged with conventional chargers without fear of damage from modest overcharging. Second, water loss is reportedly reduced by 99% because hydrogen and oxygen are recombined within the battery. Further, this type has a modestly lower self discharge rate of 1-3% versus up to 15% with standard lead-acid batteries. The AGM is a true no maintenance battery. It otherwise has similar characteristics as the standard lead-acid battery. They have yet to see much use in boats, probably due to the higher cost. These are widely used in battery back up power systems and solar systems.

The down side is the cost of around 2-3 times comparable standard batteries. Thus their greatest benefit is for installations where it is hard or impossible to ventilate charging fumes such as the interiors of sail boats.

So which one?

The battery type that you pick will usually be determined by the available budget. Getting the biggest and best there is may be nice but won’t help a bit if it means going into debt to do it. Also, with multiple batteries in a battery pack they should all be purchased at about the same time and be the same type/kind. Never mix older batteries with newer ones. The older ones will degrade the new ones. It goes without saying, but let’s say it anyway: never depend on a single battery of any kind.

Searching online shows the full range of battery types. The true deep cycle batteries have AH ratings that are high but so is the price tag. Many of the lead-acid and AGM batteries are 6V which means you would need to buy them in pairs. One pair would be hooked up in series to make 12V. That means positive post of one 6V battery to the negative post of the other, and negative post of the first battery to the positive post of the other.

1x1.trans DIY electricity

Normally individual 12V batteries will be cabled together in parallel. What this means is that the positive connections will all be linked and all the negative connections will be link as well. In this way your 12V battery pack will give you a combined reserve power.

Think of it this way: parallel connection increases amperage, series increases voltage. Standard battery cables are ok to use. Try to keep them all the same length. If your batteries have screw terminals connect to those instead of the battery post.

How many is enough?

There is no easy answer for this question. If you listen to the solar experts they will tell you to buy 2 times the number of batteries that you think you will need. Their justification is that you should not use more than 50% of the battery’s reserve so that you do not shorten its life.

In the beginning I used a single battery for mobile power. Yeah, that was dumb. It was adequate for the task but that was all. For extended use I replaced the single battery with 3 deep cycle/marine batteries of the same size. That number was based on available space and budget. Using that trio in parallel connection has shown itself to be a good choice for the task. Based on personal experience, decide how much battery power is needed to meet your expected daily power consumption then add at least 20%. The extra should be enough cover what you did not plan for.

Deep cycle batteries typically have a life span of 4-5 years. Expect to replace them. Knowing that their end of life is coming you could plan your next purchase 1-2 years in advance, using that as the time to make an expansion in capacity if need be.

Is there any maintenance?

With a lead-acid battery, which are sometimes called a flooded lead battery, you must periodically check the fluid level. This means opening a plug and viewing the level. If the fluid level is below a marker then you must fill it until it reaches the marker. In most cases there is a ring at the end of a short column. The fluid must touch the ring. Fill the battery with distilled water. Do not use tap water, filtered water or purified water. There will be minerals in it that will shorten the life of the battery. AGM batteries do not have a level to be checked.

Over time all batteries will collect dust on the top. Wipe the dust off as there is a very small possibility that it will conduct power between posts. Also check the connections to make sure they are still tight. Check the terminals and cables for any sign of corrosion.

How to use the batteries

There are 12V appliances available. If you want to get ideas go to a large truck stop and look at the 12V accessories that are offered for the truckers. There are fans, slow cookers, toaster ovens and coffee makers just to name a few. At RV stores you can also see small refrigerators, lights and other accessories. Online searches can turn up major items such as deep freeze and larger refrigerators3.

Feeding 12V power into your home is not difficult. There are 2 basic plans: feed power from the battery pack directly to the location of the appliance, or feed power to a point where it is distributed as needed. The 2nd method is similar to the load center for your household current. We are planning on having some 12V products so a load center will be part of this plan. Electronics supply stores often sell camera systems. One accessory for the security cameras is a 12V power load center that is fed from a built in transformer.

This should be easily adaptable as a load center for a 12V system. The 2 terminal blocks at the top of the box are for connecting the devices needing power. You can make one of these yourself or buy one.

1x1.trans DIY electricity

Most of the time we will need 120V power for the existing appliances. There will be a need for an inverter. It will take the 12V power and produce the 120V that need. Since we have estimated or measured the amount of the appliances will use we can use this to decide how large of an inverter is needed.

The 120V power that comes into our homes is alternating current (AC). It is graphically illustrated as a sine wave because the power flows forward then backward by the same amount. In the USA this flow, or cycle, occur 60 times per second. In many other countries it cycles 50 times per second.

1x1.trans DIY electricity

Inverters are made to produce either step wave or sine wave. A step wave imitates the 60 cycle sine wave but in incremental steps. The sine wave inverter makes a smooth flow of power. If your power needs include medical devices such as a CPAP machine then you will want a sine wave inverter for the device power supply. Note that the sine wave inverters are more expensive than the step wave inverters. You can run 2 inverters, step wave and sine wave, from the same battery pack if need be.

The first mobile inverter I had was a 1000W major brand that came from the solar expert’s store. It proved to be completely inadequate. What I later learned was that the total wattage is split among the outlets. So if the inverter produces a total of 1000 watts and has 2 outlets, each outlet can support a load of 500W. Some inverters have 2 values in their specifications: continuous load and surge. In that case the surge amount is divided by the number of outlets. So if the inverter has a 1250W capacity with 2000W surge each outlet will have a capacity of 1000W. Unless the inverter specs show a surge, there is none. The total value is all you have to work with.

Many inverters have LED indicators that show the amount of power that is being taken from the batteries and voltage level. Most will also have cooling fans that are thermally controlled. Those that do not specifically say they have thermally controlled fans will keep the fans running all of the time. This means that the inverter is taking power from the batteries when it may not be needed. Most inverters will also have a low power shutoff. If the voltage drops below 10.5V the inverter will not run.

There are inverters that go to 240V of you have a need. These can be used on a well pump for example. These require 24V supplied by the batteries.

Inverters can power devices that are plugged directly into them. A good extension cord running between the inverter and the appliance is one method of doing this. Another is to connect to the household wiring via a transfer switch. The transfer switch is usually an external switch that cuts out grid power and supplies power from the inverter.

Ways to recharge them.

Charging batteries is not done at 12V. Most charging methods will be about 15.5V. Most charging systems talk about charging in amps not watts. There is an easy way to convert:

Amps x Volts = Watts

This first one may sound silly but the basic battery charger found in most automotive or farm stores will work. If your backup power system is waiting for the next grid outage this will keep the batteries peaked. Make sure that it is an automatic charger as they will start at their maximum value and make the charging current taper to a minimum until the battery system is fully charged. It will then act like a “maintainer” to keep the batteries from self discharging. A trickle charger is the same thing as a maintainer. It puts a very small amount of amps, usually 1A, when the battery needs it. This also works if your power system is on light duty until the next outage.

The next type of the charging method would be 12V automotive alternator that is mounted on an exercise bicycle or some similar device. There are a couple of alternators to choose from but the easiest to work with is a model that has an internal regulator. Another way is to use a small gas engine to run the 12V alternator. There is a web site4 that shows how to make your own small engine charger, and sells parts to do this with.

Many of the AC producing gas generators, usually those below 4000W, have a connection for 12V. The documentation for these generators say 2 things that are of interest: the 12V connections are only for charging batteries and they are not regulated. Using the 12V output from one of these generators to the batteries would easily lead to an overcharge situation which would be very bad for the batteries. To prevent this means connecting an automotive regulator to the 12V output then connecting the regulator to the 12V battery pack.

So at this point you might wonder, if there is an AC generator why use the inverter? If your batteries are very low connect the AC appliances to the generator while the batteries are charging. Unless there is an unlimited supply of fuel for the generator, and it is completely silent, you will not want to have it running all the time.

Next up in the power chain would be a windmill. They are great for producing power, can be configured for 12V or 24V and have very little upkeep. One little problem: they require a minimum of 10 mph of constant wind speed in order to produce electricity. Some of us cannot get that much wind speed. A secondary problem is visibility. They are up in the air, rotating blades, acting like a beacon to anyone who is without power.

Finally there are photovoltaic or solar panels. In most towns and cities they can be seen attached to the flashing stop signs or school zone signs. It is the same concept as home use.

Solar panels can be purchased in single panels or in sets. They are as small as 5W or currently as large as 290W. The choice is not easy and neither is the price. When selecting panels remember that the higher values may mean a faster charge but the batteries usually respond better to a slow steady charge. The maximum power of any panel will be achieved when the panel is in “ideal” position. Ok, what does that mean? Simply put, the panel must be directly facing the sun. In other words if the panel is perpendicular with the sun then it is directly facing the sun. When the sunlight strikes the panel at an angle the power output drops. Open circuit voltage for solar panels can be anywhere from 17.2V up.

In the 1980s there were experiments done with solar panels. One of these tests was to devise tracking systems so that the panels were kept facing the sun. Most of the early methods proved to be difficult to work with. Another thing that was done was to place the panels at an angle that more closely matched that of the sun. For example: if the location was Denver, CO the latitude5 is 39 degrees meaning that the panels should be mounted at the same angle from horizontal. Today people generally point them in a south facing compass direction and put them at a 45 degree angle. Not ideal for maximum utilization but its easy. Modern tracking systems are available.

Another possibility is to have multiple panels but not all pointed at the same compass direction. Place them at several compass directions so that a lower peak current will occur and be spread out over a longer time. For example, if there are 5 panels in the solar array place each of them at 5 compass angles along the path of the sun. With solar panels it is possible to mix panels with different output.

The solar panel approach will require a charge controller. This is a device that takes the input from the panels and feeds it to the battery system until the batteries are charged. The smallest one will handle a total of 105W, or 7A. Better ones can support 30A or more, and will show the state of charge of the batteries. All of the charge controllers prevent the batteries from discharging through the solar panels when the sun is down.

There is a small amount of upkeep with solar panels. You must keep the surface clean. Dust and dirt that accumulates will cut down on the amount of sunlight that the panels get.

Now what?

Let’s look at all this as 2 possible choices – one where finances are unlimited, and the other where there is a budget.

Open ended system.

Description Type Quantity

AGM batteries 210AH 8
Inverter 7000W 24V 1
Transfer switch 1
Solar Panels 95W 12
Charge controller 24V 1
Tracking system 1

The batteries would be wired into a 24V system in order to feed the inverter. The transfer switch would perform the cutover during a grid failure. The tracking system would make sure that maximum power is delivered to the batteries.

While convenient it becomes too easy to live in the house with a full power system. It does not give incentive to conserve during difficult times. The movement of the tracking system may attract attention.

Budget system.

Description Type Quantity

Deep cycle/marine batteries #29 5
Inverter 3000W 12V 1
Solar Panels 40W 5
Charge controller 1

The budget system would be manually connected to appliances. It is possible to run some things, such as freezer and/or refrigerator from the inverter all the time. That way there is no loss of food in the event of an outage while away from home. The panels do not all have to be purchased at the same time, plus they could be mixed with smaller ones that turn up on sale.


I do not have all the answers. This discussion does not include all the possibilities or all the details. Any product that may appear in a web link is not an endorsement.

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This contest will end on December 16 2012 – prizes include:

Well what are you waiting for – email your entries today. But please read the rules first… 1x1.trans DIY electricity

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  1. Wow!im gonna have to read this again! Just the info on batteries was making my head spin. I had no idea that there were so many varieties. It seems to make the most sense to me to run 12 volt into your house and use 12volt appliances as much as possible. I was a long haul trucker for more than 30 years and I can tell from firsthand experience that they work well. I’ve made coffe,cooked meals,kept frozen food frozen and lived a comfortable from the cab of a truck,using 12 volt appliances. Very interesting article.

    • BC,
      Any info or advice on 12V appliances you can give us beginners would be great.

      • BC, I second Papabear–your insights on 12V appliances would be much appreciated!

        • robert in mid michigan says:

          believe it or not truck stops carry most of these at a relativly good price. you need to do some research but i loved my fridge and microwave on the road saved me a ton of cash not having to eat out twice a day

  2. “The Dallas Observer published a report1 recently that Texas has worst electric grid in the nation. This was based on a North American Electric Reliability Corp report2. That’s not very encouraging. They are also reporting that there is the possibility of rolling blackouts in 2013.”

    What else you got form Pravda err… the Dallas Observer.. to make the case for “has worst electric grid in the nation”? Nothing in NERC specifies this. Besides, if you’re basing potential electricity investments based on what you read in the D.O. then you should be pursuing power supplies based on unicorn farts and Obama rainbow energy (as the other five readers of the Dallas Observer are).

    The possibility of rolling blackouts in Texas in 2013 is primarily due to reinstatement of CSAPR (EPA imposed restrictions) taking out somewhere between 1.2 and 1.4 giga-watts of electricity – nothing to do with the electrical grid per se since that energy is being willfully killed solely due to some ink on paper somewhere. A severe drought (2011-like) is not predicted for 2013 so no power plants will shut down due to loss of water for cooling or generation (as was in 2011). Plus ERCOT is better off today to handle disruption than it was in 2011.

    Don’t get me wrong – I have a somewhat mid-to-small sized 12Vdc system set up in my house in DFW suburbia and applaude the rest of your submission (very informational!!), but you could have not have led your article with a more worse source of information than if you were deliberately trying to sabatage it.

    • Keep in mind that there are only 3 power grids in the country. One in the east, one in the west, and Texas. Texas has it’s own grid which gives it some interesting possibilities, since in general it is not subject to a lot of federal regulations because there is no interstate commerce involved. With the amount of natural fuels in Texas, their only problem would be the federal EPA, so I don’t know what the criteria for being the worst electric grid in the nation means. Would be interesting to see how they decided this.

      • OP,
        One thing hurting Texas is the EPA mandate that coal fired power plants be shut down. That will restrict production here, just as it is in the other 2 grids.

  3. This is the kind of information I need!


  4. Really a good article for those of us who don’t really understand electricity all that well. Worthwhile to print out. Thanks for the information.

  5. tnprepper says:

    The picture and text for connecting batteries in series is wrong. Only connect one positive post to the negative post of the other battery. The two free posts become your positive and negative terminals.

  6. With all due respect, I am sure that your diagram for wiring batteries in series is incorrect. The way it is shown, the batteries are shorted out. With a series configuration (supposing Battery “A” and “B”) one “load” wire would attach to battery “A” neg. Then battery “A” pos. would attach to battery “B” neg. and finally the other “load” wire would attach to battery “B” pos.(think of how flashlight batteries are installed). Hope this helps.

    • With all due respect to you guys posting that the wiring diagram is wrong… you are incorrect. The 6 volt batteries are wired in “series” not in parallel and the diagram is correct for the purpose.

      With batteries wired in series, the positive from one battery is connected to the negative terminal of the other. The remaining free positive terminal and negative terminal are used to connect to your 12 volt system. Creating 12 Volts from two 6 Volt batteries.

      See you can learn something here everyday…

  7. DIY Electricity entry has a incorrect illustration for the 12V series connection. As shown, the two 6V batteries are shorted together.
    Should be minus of one connected to positive of other, the other terminal on each battery are the plus/minus 12V output.

  8. HomeINsteader says:

    OH, WOW! This is great. Thanks, Papabear!

  9. HomeINsteader says:

    M.D. – have you noticed how “nasty” people are getting, even on here? It can only get worse.

  10. Great post, obviously someone who has a few more brain cells than I do wrote it. :)

    This is nice to keep for a reference, thanks for taking the time to write it up.


  11. Outstanding Article! You have really boiled this down to the nuts and bolts. Very good! I had to print this one to keep as a reference. Now I have a MUCH better idea, on what I need to look for in consumption, and equipment. Thanks!!!

  12. HomeINsteader says:

    I hear you, M.D.

  13. Look at the Iron Edison battery. They can’t be overcharged, they can be fully discharged. They last 25-40 years. The electrolite is water and potash.

    • Prep Now,
      I left the Iron Edison out intentionally. For someone starting to build a backup system the cost alone would scare them away. Aside from that they are outstanding batteries.

      • Papabear, I appreciate you sticking with the range of choices most likely to be in folks’ ordinary budgets. You’ve shared so much information that there’s a lot to digest, for me at least. Thank you for all your good work on this.

        Do you think there’d be some use in a separate post on the Iron Edison?

        Seems like several segments of the Pack could find that helpful in the near term–like those with a nest egg and concerned about inflation. Or those with retirement accounts who might be weighing early withdrawals.

        And then there are always those of us who’ll choose one of the options in this article as Plan A. . . but wonder if they could do anything now to make it easier to upgrade in the future, in case that becomes a more viable option.

  14. Everyone please keep in mind that it’s called “electrical theory” because we don’t really “know” all there is to know about electricity. Please be careful when your “DYI”ing electricity.

    • I’m not sure what we don’t know. That being said, explanation to a layman still requires some skill.

    • Cityboy,
      I have wired 12V in cars, 120/240 in houses. There is nothing to be afraid of. Buy you are correct in saying to be careful. Get careless with household current and it can bite you or burn down your house. The wires on top of the pole…… defintely keep your distance. Those are in the 10s of thousands of volts.

  15. New prepper says:

    Great timing. I am doing a site evauluation this next week. Your article cleared up many of the things I have been trying to learn. Will be looking into micro-hydro as the primary means of producing power. Lot for me to learn and grasp.

  16. SurvivorDan says:

    Related subject. I just ordered 2 new portable solar chargers from Walmart.
    I’m jumping the gun as I haven’t received them yet and tested them but they look like they have potential for what they are designed for , re-charging cell phones and led lights. On the cheap at about $40 each. Will post a review after I receive them.

    I’m too technologically challenged to comment on this article.
    Got lost around…”f the inverter has a 1250W capacity with 2000W surge each outlet will have a capacity of 1000W. Unless the inverter specs show a surge, there is none. The total value is all you have to work with.”

    Guns, combatives and survival techniques I know a thing or two about. If it has anything to do with electricity , I will have to kidnap the author and imprison him at my survival Retreat.

  17. Cal Hollis says:

    Sorry to have to weigh in, but the series diagram, as shown is only using one battery – the top 6v one. The second battery only has the negative terminal connected and the positive has no connection, therefore an incomplete circuit. In a series circuit, the crossover (pos-neg) connection is NOT used to draw the higher voltage. Not meant to be critical, just a correction.

    One other consideration in using 12v vs 120v via inverter – much heavier wiring is needed for the same load on a 12v compared to the 120v. This can be a really limiting factor on solar panels that are located a distance from the working load. (If nothing else but cost.)

    I would like to throw in another generator option that pretty much goes unconsidered – there are companies that make adapters to allow you to use 3 different fuels – gasoline, natural gas, and propane. The ability to switch fuels with the turning of a valve allows someone to use natural gas if they are connected, if that fails, they could then use gasoline till exhausted (and before the fuel goes bad), then fall to the LP gas (which stores indefinitely) Even with solar panels, I would opt for a secondary backup generator…

    Excellent resource article to explain the various elements people need to decide on a system for backup. Nice to see a no BS presentation on this essential subject.

    • Cal Hollis says:

      Corrected diagram looks great!

    • Cal,
      For long distances with 12V or heavy 12V loads I don’t use conventional wire. I go with welding cable. It is made to carry a lot of current with little loss. That is what connects the inverter to the batteries.

      • You’re also better off keeping the batteris and inverter physically close to avoid the IR losses in whatever cable you use. The 110/220 from the inverter to your load has much lower losses due to the higher voltages, and the significantly lower current.

        • IR losses?

          Okay, from the surfing I did last night, I’m thinking I = current, but the R is for something other than resistance, because that’s “r”.

          I’ve heard some car guys say that the amount of energy needed to power an engine with electric batteries is more than just the amount of electricity it draws when you plug it into charge–that there’s also an incremental amount that is lost in transmission from the power plant.

          So, would what OP mentioned be a similar concept, that since cables don’t conduct perfectly, minimizing the transmission distance means more of the power you generate actually gets to the device you’re trying to run?

          • Lantana, let’s see if this helps.

            Let’s say that you have to walk to the gym to do jumping jacks. You start with an empty backpack but as you walk you pick up rocks and drop them in. The rocks are making you work harder as you walk and you get a little tired. If the distance is short it isn’t much of a problem. If the distance is long it makes you tired because of the distance and because of all the rocks that are going into the pack. It makes you work harder before getting to the gym.

            With electricity passing through wires it meets resistance (adding rocks that make it work harder). Resistance can be good or bad. The good kind does work for us, such as the filament in a light bulb. The bad kind makes things slow down with no productive work (get tired before getting to the gym).

            Electric car motors use direct current (DC). The more distance that the DC travels the more it slows down by being unproductive. There is resistance in the wires (added rocks). When it causes current to slow down the wires get warm. As they get warm there is more resistance (adding even more rocks). When it gets to the electric motor it must produce some work (jumping jacks). The work it produces causes more heat which causes more resistance.

            Charging the car batteries is similar. Alternating current (AC) is coming from the plug that goes to the car. It must be changed to DC, which produces heat as a byproduct of the work being performed. To produce 100% of the DC that the car batteries need there must be more than 100% of the equivalent AC. There are also AC losses from resistance in conversion to DC.

            AC travels long distances much better than DC. Using 12V DC in a car or truck is effective because of the very short distances. Using it in your house is still effective but the distances are longer resulting in a little more cost (or loss) to produce the same amount of work. Sending the DC from your house to a barn 200 yards away is not so good. It would be better to use AC between the house and the barn.

            Thomas Edison and George Westinghouse were in competition with each other. Edison produced 110V DC to distribute to houses while Westinghouse produced AC for distribution. That in itself is a long story. When you get a chance take a look at both of these men in Wikipedia.

            Hope this helps.

          • Lantana,
            First of all, let me apologize for the confusion. I used a common engineering term without first defining it, which is something I beat into all of my firearms instructor candidates. Always define a term before or at least “when” you use it.

            Actually the ‘R’ in IR stands for resistance, and the ‘I’ stands for current. The resistance of a wire or cable is based on its size and the material from which it is made. The welding cable recommended by Papabear is a large diameter cable generally constructed of copper, which is highly conductive, and therefore that cable has a lower resistance per foot (smaller R value) than something like the standard 12 gauge copper used to wire your house. As Papabear stated in his other reply, the current (electrons flowing through the wire) generates heat when flowing through the wire. In a highly conductive wire, it generates less heat, and in a less conductive wire like nichrome (which glows red in an electric heater) or tungsten (which glows white in a light bulb). In the heater and the light bulb we want to use the power to generate heat; however, in a wire used for transmitting power we do not, since that heat is wasted energy.

            So for the explanation of IR loss we have to do a little bit of math, using Ohms law. I will try to keep it as simple as I can but feel free to ask questions if it gets confusing. Since P=EI (Power in watts = Voltage times Current) or E=IR (voltage equals current times resistance), we can calculate power in terms of only current an resistance by replacing the ‘E’ in the power formula with IR from the basic Ohms law formula, which gives us an alternative power formula of P=IIR (Power in watts equals current times current times resistance). Since the power in a cable is simply wasted heat, we want to minimize that power.

            The simplest way to do this is by making the Resistance value as small as possible. This can be done by using a low resistance wire like the welding cable, and/or making the cable as short as possible. Another way is to make the current (I) as low as possible, and we can do this by raising the voltage.

            Remembering that P=EI, and assuming that we want to deliver 1200 watts of power, then a 12 volt system will need to deliver 100 amps but a 120 volt system will have to deliver only 10 amps. So the higher the voltage, the lower the current required. Looking at the alternative power equation of P=IIR then the 12 volt IR loss is 100x100xR or 10000xR while the power lost in the cable to heat at 120 volts is only 10x10xR or 100xr which is 100 times less loss and heat generated.

            These calculations are pretty much the same for both AC and DC, but the advantage of AC is that a simple component known as a transformer can change the voltage from one value to another, while DC cannot perform this action. In AC transmission systems, the cross country and lines down the street are at significantly higher voltages then the 110/220 coming into your house, courtesy of the transformer on the pole outside of your house.

            For instance, a few miles from my house is a set of transmission lines running at 765,000 volts. When carrying 1 Amp, this is 765,000 watts or enough power to supply 15 homes each drawing 200 Amps. Higher voltages can deliver more power at longer distances; however, any voltage over 50 volts should only be handled by persons who know what they’re doing.

  18. Tactical G-Ma says:

    It is a great article but probably a bit confusing for the Novice. The diagram is assuming one will be connecting the 6v batteries in series to a load or in parallel with other batteries. Keep this article and if you decide to set up a bank of batteries, maybe Papabear can be persuaded to go over your schematics before you blow yourself up!

  19. MD, thanks for re-doing that battery series diagram.

  20. Good article, and really appreciate the definitions.

    I use the Kill-A-Watt all of the time to watch equipment in both the summer and winter. Equipment like freezers can use significantly different amounts of power based on the seasons.

    Another place to start might be with your local electric company. My co-op leases high end UPS units (1500 or 2100) to business clients for two years and then retires them. I have purchased several for a great price and the batteries still lasted at least 3 years. These use a charger to keep the batteries charged, and an inverter to power the equipment, making the equipment capable so riding through the little power glitches, or setting down sanely in an extended power failure.

  21. Papabear, I really like your article–it is so well laid out, with the defined terms and helpful examples.

    Two questions for you (and others who know):

    How do guys (and those savvy gals out there) first learn this stuff? Was this covered in shop classes while the girls were in home ec? At the knee of your dad/uncle/grandfather/big brother out in the garage? Genetic memory passed through the male line?

    And, for those of us who only know that V, W and A are measurements (but not what they measure) and what batteries do (make things work!) but not how, where can we find the classes for Electricity 101 and Batteries 101?

    I asked my DH, but he doesn’t remember not knowing the basics. And following his explanation is like trying to drink from a fire hydrant.

    • Lantana,

      For many of us learning about this, or anything else, it isn’t in a single class anywhere. It is a combination of watching others, asking, reading and doing.

      It took a long time (years) to put all the pieces together for me to understand what I was doing. Some parts I’m still a little fuzzy on. It also took a long time to write the article so it would make sense.

      To expand your understanding you must have a lot of curiosity and a willingness to feed it. You must also exercise your common sense. If you find an old encyclopedia at a garage sale take it home and read it.

      Hope this explaination helps.

      • Yes, Papabear, this is helpful–thank you. I feel like I’m at the ‘learning vocabulary’ level, with a book I can tell is very useful but beyond my current level of comprehension.

        Thank you again for all the work you put into this article. You deserve the prize, in my book.

    • Lantana,
      In my case it was an early interest in science and a father who seemingly could do anything, from carpentry, plumbing, electrical, and auto repair. I remember when I was perhaps age 10, an electrician doing some wiring additions to my grandfather’s house (which was next door to ours) and me hanging out with the electrician and asking questions. Then there was electric shop in the 10th grade, and finally an EE degree. Throughout all of this the main thing was an interest in science and math, a curiosity, and the willingness to try out things, not really caring if I failed. Even failures can teach you something (as long as they don’t kill you, LOL). A Google search for “basic electricity 101” turns up over 2 million entries, so there’s bound to be useful of information out there if you’re interested.

      • OP, thanks for sharing your experiences.

        Your dad sounds a lot like my grandfather–he was his own contractor when he build his house, and worked alongside each tradesman as an assistant, watching and learning. His first job as a little boy was with a veterinarian; decades later, that veterinarian told my mom he was a hard worker and caught on fast but boy was he a buggy kid, asking questions all the time.

        He was always explaining things to us kids. And the one thing he drilled into us was how much you respect electricity, because it can kill you in an instant.

        Again, thanks for your insight and encouragement. There are so many things to learn in this world, but I’d at least like to become a better informed user of electricity–and not be the one who makes a situation worse by making a dumb mistake that burns down the house.

  22. Cal Hollis says:

    LOL, Papabear hit the nail on the head…. curiosity and many years of asking questions and trying to figure things out… It all sort of came together for me when I first got a ham license in the 60′s

  23. Great share.But they need fix to the power system as well.

  24. Great article. Very informative. I would have like to have pictures of the actual setup for us solar / battery bank newbies.

  25. I found a free app on android that might help some of us to learn the basic of electricity. Its called lessons in electronic circuits. Its pretty much a book and starts out with dc and then moves through ac, semiconducters and digital electronics. You dont even have to go through it all just the first couple chapters in dc have vastly improved my knowledge of electricity.