Dirt-Cheap Uninterruptible AC Backup Systems for Preppers

by Prepper Doc

power homemadeWhen the grid goes down, it is not a happy feeling if you have no backup power at all. Even a LITTLE electricity goes a long way. For most people I know, their first priorities are to have just a few electric lights, and then keeping the refrigerator from spoiling the food is next on their list. After that comes luxury items like A/C.

In a true end-of-the-world, where fuel becomes unobtainable, only solar power, hyroelectric power or other renewable electricity source will remain. Until you have that squared away (and a simple system isn’t that hard), having a generator or a battery-based uninterruptible AC power source (UPS) will get you through several hours. This article will focus on the battery-based system. They are especially helpful if you really didn’t want to run that generator all night long!

You can easily put together an uninterruptible power supply (UPS) that lasts far longer than the familiar computer UPS’s that run your computer for 15 minutes….just long enough to shut it down, basically. All of those system involve three components: a built-in inverter that can provide AC; a battery to run that inverter (automatically turned on when it senses the grid power disappeared) and a built-in charger that keeps the battery always ready to go.

If you have such a UPS, and if the battery inside of it happens to be 12 volts (which they often are) that certainly makes it easier– all you need is to add more battery staying power. Get a car battery – the Group 24 is often the cheapest per watt-hour – and simply connect it in parallel with the existing battery in the UPS, or even replace the UPS battery with the car battery. Use wire that is commensurate with the power level of your UPS– a 250 watt UPS can pull 20A from a 12 volt battery, so use 10- or 12-gauge wire. A 500 watt unit can pull 40 amps, so move to 6- or 8- gauge. Of course, if you pull that much power, you are going to exhaust your battery pretty quick….a typical fresh, fully charged Group 24 battery is about 75 Ahr, or roughly 800 watt-hours (at best)….and you really only want to pull half of that from it. So a few LED or CFL lamps would be fine (20 watts could be powered for 20-30 hours). You are NOT likely to be able to run your refrigerator from this computer type UPS – fridges pull 20+ amps of AC for a very brief startup interval…..which your UPS can’t provide.

You need a beefier charger to keep that car battery charged up than what is in the UPS. But you also want it not to boil away all the water in that precious battery. A modest-sized car charger that automatically slows to a trickle charger (most do that) when you aren’t using any AC power will do the job. If you basically never use that AC source, you could even us a timer to charge it only an hour a day. If you can get a cheap VOM from Harbor Freight, measure the voltage on your battery while your trickle charger is running – it needs to be around 12.8-13.5 volts for best life.

What if you don’t have a UPS? Not a problem. There are plenty of cheap 12-volt inverters that can produce anywhere from 75-400 watts of wall-plug type AC output. The inverters I’m talking about are NOT the $2000 solar-power-pure-sine-wave inverters; they are the simple quasi-sine-wave inverters that really put out a stepped square wave, and can be bought at the auto parts store or chain retail store for $30-$70. Connect one of these to your battery using appropriate wire. If you use one that is cigarette lighter-based, remember the center conductor is positive, and the side connector is negative. Or just purchase a socket, which will usually come with red (+) and black (-) wires.

If you want to simply USE that inverter to power the lights in one room of your house, no problem, just choose a charger that can put out some watts—there are usually ones about the size of a loaf of bread that can easily provide 60 watts worth of DC to your battery, where it will be immediately trans0ferred to the inverter and run the light in your room all the time. If the power goes out, you might not even know it! Of course, don’t waste electricity by using incandescent lights – get the far more efficient CFL or LED bulbs! Since the charger won’t really be CHARGING the battery (it will just be trickling it to keep it charged while most of the charger output really goes to the inverter), you won’t make any significant amount of hydrogen gas. I woudn’t lay a flame right on top of the battery, but other than that, no worries. You might put the battery inside a simple plastic tub in case any acid ever came out, however.

Trying to run the refrigerator is a much bigger deal. About the only want to really do that (in my experience) other than a generator, is to have about four car batteries wired in parallel, and use huge wire to go to a really capable 2000+ watt inverter….anything smaller is unlikely to be able to start the fridge. The “start” current (locked rotor amperes) can be 20 amps! The actual steady-state draw from a modern refrigerator once it starts is on the order of 150-200 watts, and they tend to run about 1/3 of the time unless your house is really hot. With four batteries, I could just barely get through a night in my experience.

I’m enclosing a photo of a very simple UPS built from a 75-watt cigarette lighter-type inverter, wired to a Group 24 battery, which is being continuously charged by a simple battery charter. You can see pretty much all of the wiring. Red on the charger goes to plus (+) on the battery, and plus (+) on the batttery goes to the red wire of a socket into which the inverter is plugged. From there it is just simple AC wiring.


  1. Thank you Prepper Doc. I’m going to add a system like this. Question: Will an emp fry the battery that’s in a modern, computerized vehicle? & which parts in this system need to be protected in a faraday cage?

    • PrepperDoc says:

      Hi. Batteries for the most part are completely safe against EMP. Particularly car batteries!!! The computers in the car? The jury is still out of that, nobody knows. There is some chance that a significant percentage of cars will still work.. Then again, maybe they wont! There are plenty of cars however that don’t need those computers….

      The inverter is at risk if it has more than a foot or two of wire extending out….and any CFL that is in a fixture with wires extending out. You might get away with putting a surge protector (MOV) RIGHT ON THE INVERTER OUPUT and you might even be able to keep the fluorescent lights attached if you gathered up their cords so that they were physically close to the inverter…

      The car battery charger? Well, if you put a surge protector on it right at its plug, and gathered up the cords somewhat, it might be fine, especially if it IS connected to the battery…..with relatively short leads (emphasis on “short” to reduce antenna pickup of the EMP signal).

      So if you’re protecting against EMP there are two ways:
      1. Put the inverter, and the CFLs, or LEDs….in a faraday cage.

      2. Alternatively, put a surge protector on the battery charger plug, gather the cord up so the charger is close to the surge protector, keep the inverter physically close to the battery, with short wires (like in the photo) and put a surge protector right on the inverter, and then gather up the AC loads with short space between the inverter and the AC loads.

      And it never hurts to have spare….

      • Thanks Prepper Doc, our vehicles are new enough that I’m expecting their computers to be fried by an emp. If they’re not, it’ll be like icing on a cake. But my plan, at this pt, is to build a system like u’ve shown here, & then put it in storage w/ the key parts in a faraday. & may order a spare. I already have rechargeable batteries & small solar rechargers that can be used to recharge batteries.

        • in some ways the emp situation is not entirely bleak as is described. unless we get hit with multiple salvos from one border to another, there will be some things that will be protected and survive. we are a nation of steel buildings and what i call “emp shadow’ will occur. if the supposed emp blast is over omaha, anything on the south side of a steel building will be unaffected and inside the steel building too.
          as i understand emp, it is more line of sight, not really able to bounce around corners or reflect backwards. this opens the situation to more survival of systems than previous thought. the “faraday” cage can come in many unexpected forms which will protect circuits and power generation/control. your location will have a lot of effect on whether you get emp blast, the backside of a hill or mountain at a long distance from ground zero may protect you also.
          all is not lost

          • PrepperDoc says:

            Josh — good points. I can’t claim to have a PhD in this, but with 40 years ofHF ham radio experience, I think I have some grasp, as most of the EMP can be considered to be a huge RFI ranging from DC to 100MHz and then with some degradation up to 1 GHz and beyond.

            All is certainly not lost — I expect to have plenty of working equipment and systems afterwards, but remember that radio waves do refract and reflect;you get cell phone signal even inside your car, and behind buildings….so I wouldn’t completely count on it.

            There is the “waveguide beyond cutoff” idea….problem is that the EMP energy extends to 1 GHz and tht means it can go throughPRETTY SMALL openings…. Certainly between the metal beams of a metal building….. Of course, as you move to the center of the metal-framed building, the field strength is probably falling off rather dramatically. My hospital has underground portions– those should be fine; and cars that are underground have a far better chance of being unaffected.

            Plan for the worst, and hope for the best. Shielding where possible, surge arrestors where possible, filtering to reduce the exposure of circuits where possible….all adds up.

          • On what grounds can you say that an EMP could be directional?!

    • Hildegard says:

      The behemoth refrigerators Americans are used to use too much power for a battery-based system. Look into converting a small chest freezer into a fridge. You can get a plug-and-play thermostat from Amazon. At least get the stat now, as it will be difficult to order from Amazon during a nationwide crisis. The small chest freezer is much more easily obtained during an ‘event’, just don’t be too forthcoming about your reason for wanting it.

      • Hildegard

        I just received my thermostat! I have a chest freezer, now to buy another to convert to fridge. I am thrilled to do something so much more practical than corporations want. The onboard computers are junk.

  2. PrepperDoc says:

    I’m always intrigued when people are concerned about the vulnerability of 12 volt car batteries….

    A charged up 12 volt car battery, with some space around it to allow outgassing, is one of the tougher physical items on the face of the earth.

    Think about it. It gets rattled half to death the entire time it is is functioned by a swerving, pot-hole-jarring automobile. It gets assaulted by who knows how many high voltage attempts as transients from motors and spark plugs whiz around it….and they only fail after several years, or you leave the lights on several times to completely kill the battery.

    If you kick it, or drop it on your foot — it will break your toe.

    If you try and short it out — it will turn whatever wire you used into a Roman Candle for a second or two. If you use a piece of steel — it will weld it. If you connect up a high voltage power supply to it — the odds are that the incredibly low internal impedance (measured in thousandths of an ohm) will fry the powersupply within seconds. If you boil it with too much charging current — with a bit of luck, it will blow you up in revenge with emitted hydrogen gas! If you try and freeeze a fully charged battery, you will probably freeze first.

    ANYTHING connected by very short wires to a 12 volt battery is not going to even know an EMP happened if it has no other antennas connected to it.

    • tommy2rs says:

      If you take a piece of standard electrical wire, wind it around a the metal shaft on a screwdriver then touch one end of the wire to one terminal of the car battery and the other end to the other terminal of the battery you create a magnetic screwdriver. The longer you hold it the stronger the magnet, up to a point. Induce a voltage you induce a magnetic field, induce a magnetic field you induce a voltage. Or use the battery to charge up a condenser/capacitor then toss it to your buddy and watch him squawk when he catches it. Filed under: Things Bored Mechanics Do.

  3. I would not use car battery’s. Use Deep Cycle RV or Golf cart Battery’s. 2 six volt golf cart battery’s will give you many hours more power. You can learn a lot more about this type of set up on the RV forums.

    • PrepperDoc says:

      Yep….if you have the cash, your advice is certainly correct!!! Howver, this is a UPS — which is not likely to be used often, so it might be cheaper for poeple to just use a deep cycle marine battery from Walmart. I don’t know the current price, but they used to have a Group 27 130 A-hr for only $110. I think that’s a pretty good deal.

  4. Use 6 volt deep cycle batteries, wired for 12 volts, so you need two of them. Better yet, get 4, that’s what I have.
    Don’t get a cheap inverter. You need a pure sine wave inverter. Tiger Claw makes one for about $199 on Amazon. And that charger won’t do you any good when the grid is down. Get a couple of hundred watts of panels and a charge controller. If you can’t charge those batteries, it’s a false sense of security.

    • PrepperDoc says:

      Joe, that is a fascinating inverter!!!! I have never seen a pure sine wave that inexpensive. Almost down into the modified-sine-wave category!!! I would definitely consider that one….I read the reviews, and it performed well; the only difficulty was the fans wore out (but that is easily replaceable by someone with a bit of tinkering ability). This is the first time I’ve EVER seen a sine wave inverter of that power class for that kind of $$$. Thanks for pointing it out!

  5. CountryGirl says:

    Most RV’s have 12VDC systems for when they are not connected to AC. Some have inverters built in and many have inverters added on. Some RVs have solar panels on the roof AND all (or almost all) systems inside are 12VDC (as opposed to a 12VDC and a 110VAC separate systems). The Ideal system is one with a solar panel(s), 2 or more deep cycle batteries and mostly 12VDC appliances/devices with an inverter only for special cases. This system when used with LED lights allows lighting in the evening and TV/radio/laptops/phone charging/etc. Most RVs (probably excluding the $100k plus models) have these simple funtional off grid systems that work and work day after day, year after year. I would not reinvent the wheel. Improve on some things, sure. Even cut corners here and there to save dollars. But in the end what you have in most RVs is a time tested working off grid system that has provided campers with years of satisfaction and dependability. Having said that, I have camped next to big Winnebagos with four huge deep cycle batteries and multiple large solar panels that have to run their generators for hours each day. These systems can be overwhelmed if you insist on having 60″ TVs or you allow teenagers free will with the entertainment systems.

    One last point. It can be problematic to connect two very different batteries in parallel. If you want two or more batteries in parallel buy them at the same time, same brand and same size. When one goes bad, replace them both. Batteries connected to chargers and electric systems are constantly active and current can flow even while everything seems to be shut off. Two unbalanced batteries in parallel will drain the system over time.

    • PrepperDoc says:

      That’s good advice. If people are willing to buy a few LED automotive lamps, or other 12 volt LEDs and run them directly off the battery….they can increase efficiency.

  6. believer says:

    Check Wikipedia for VRLA batteries. Basic information on AGM and Gel cell batteries. Considered maintenance free they won’t require periodic checking and adding distilled water. Generally speaking they have a longer useful life than the basic lead acid battery. If there was a great reset I would expect to see cottage industries producing lead acid batteries as they are very simple in construction.

    • PrepperDoc says:

      Hi, thanks for your input! I would just caution that I have a friend who went with AGM batteries……and had to replace them after 5 years…..I chose Rolls Surrett 6V flooded lead-acid batteries, which according to our calculations offer TWICE the lifetime dishcarge cycles (watt for watt) and are half the price…… my friend switched to flooded lead cells for his replacement set.

      Now, it is true that every three months I go out and add distilled water. My cells stay fully charged ALL the time, so they don’t use much water. I run one discharge cycle per month as suggested by Rolls engineer. AGM is indeed less work….but comes at a price. There are only so many coulombs of electricity that are going to go in/come out of a battery during its useful lifespan, and that number is higher for a flooded cell from Rolls Surret than it is for the AGM my friend chose….

      • Elricky says:

        The problem with lead acid batteries of any kind is that they eventually get a coating of sulfates on the lead plates inside and that in turn lowers it’s ability to conduct and degrades solution. This occurs much more on a battery that is not charged up properly. A battery that gets discharged down hard and charged up a lot will get the build up on the plates much more thicker and sooner. To remedy that they add antimony to the lead mix in the battery plate. That is what a deep cycle battery is. The antimony alloyed lead plate does not build up the sulfur on the plates near as bad when undergoing the deep discharge and charge cycling. The trade off is AMPS. A regular lead car battery of same size to a deep cycle is going to provide more amps.
        Now to avoid getting the sulfate build up, charge the battery with a battery tender instead of a regular charger. A good tender is a must and made for the type of battery you have. Maintaining the battery at it’s ideal charge will increase it’s life more than charging alone. To know exactly why is too long to explain here. Just want you people to know that there is more to charging science than you are getting in any of these comments. Worth your study. And maybe the author here will do a study and write an article.
        I have seen home made battery banks in off grid conditions where the person is so distraught because they can’t keep batteries charged. That is because they have ruined them all by either overcharging or leaving them low charged too long. And all they had was a simple car charger hooked up to them to charge them. Do your self a favor. Insulate battery from the ground. Use a tender or a charger with a real built in tender. Use the battery type you really need. That is, if your really going to be draining down hard and charging many times then go deep cycle. If your building a back up that will more serve as emergency use that maybe gets turned on 2 times year, then a lead acid will be your best and longest lasting solution.
        BTW, AGM or glass mat batteries are no different in chemical composition than lead acid, they just have mat in between the plates. This in itself can lower it’s life causing no place for the sulfates that build up on the plates to fall off too. But you won’t normally have that problem if your battery is tended correctly. It’s when it is not treated accordingly to it’s type. It’s not some unknown magic. There are ways to get all types of batteries to last a long time. Each different battery type has it’s pros and cons. And each type suffers differently under different conditions. And each type have different ideal charge voltages. That is why many people have lost when trying to run AGM in a car. Those whose voltage regulators were set ideal for lead acid got less life from those sealed batteries. If you were lucky and your voltage regulator happened to be right for your AGM then you had little complaints. People, stop being ignorant about batteries and you won’t complain about your bad luck in having them.
        A high quality, properly stored, properly maintained and properly charged battery should last you over 10 years. I’ve seen them go 15. The mid range cheap battery I put in my truck lasts 4- 7 years. Besides water I cant really control it’s maintaining.

        • PrepperDoc says:

          WOW! LOADS of info there!
          On my very expensive solar batteries, the manufacturer specifies the exact voltages to charge to. I follow that schedule. Apparently (according to that manufacturer) at a certain (charge) voltage there is an optimal tradeoff between sulphation (if not charged enough) and corrosion (if kept at toohigh a voltage?) — I follow their specs, which have an exact charging plan (done automatically by my charge controller) and a final voltage to which the battery is KEPT.

          The manufacturer was uncormforable with me merely keeping the batteries in that charged state for years and recommended a discharge of 30-40% once a month. So that is what I do.

    • just pay the big bucks and get an Optima battery.Gel cel,spiral wound copper cells.I have one in my truck thats 12 yrs old and still great

  7. Great info Doc! I have a 100 watt solar panel and a recycled 900 CCA battery that runs a 12 volt pump for my outside sink and two very bright off road lights. I also have a 3500 watt inverter that I salvaged from an 18 wheeler before I sold it. I know it’s way more than I could ever use with one panel and one battery,but I plan on adding to the system as I can afford it. Solar is the next avenue of preparedness I plan on going down.

  8. I did miss something??? I see the wire from the charge going off the table then under it. So what did you plug the charge into???
    Is it self perpetuating – charger plugs into inverter batteries runs inverter and powers what ever .
    Science break through since electricity.
    Yes an emp will fry an inverter and charger.
    Get a stationary exercise bike HEAVY wheel and mount a 90-100 amp generator or alternator from a car, surpentine belt,get in shape, power inverter abtteries.

    • PrepperDoc says:

      Like #2 or bigger!

    • PrepperDoc says:

      No Mystery, charger was plugged into a wall outlet.

      Humans can’t put out much power for long…100 amp x12 volts > 1 horsepower…… Not happening with ME pedaling!

  9. If I am planning a small cabin of 400 sf should I bother with converting DC to AC? What if I ran it more like an RD with solar panels and DC fixtures? I don’t care about electric lights that much, but do want to run a chest freezer… which may only come in AC. Just wonderin.

    • Sorry, RV

      • PrepperDoc says:

        Hi — certainly you lose power at every step, so if you have a DC refrigerator, that would be better than going to AC! The problem is, the last time I looked for a DC fridge they were frightfully expensive…..but your search may be more successful.

        The real problem with running an AC fridge is the way the compressors are built, they require a TON of current to get the electric compressor started…..we’re talking 20 Amps. I even had a little dorm fridge that took 15+ amps….so you really just cannot start them unless you have either a very expensive pure sine wave 1 kw+ inverter, or a 2 kw “modified sine wave’. Thankfully, thelatter is only about $120. I have run typical fridge/freezer off such an inverter…..but be warned, I also had one compressor FAIL when the inverter couldn’t really get it going properly….so don’t scrimp here. If you really want a fridge the type advice folks above have been giving is warranged — something like 200-400 Ahr worth of 12V (or 6V in series) batteries, and a 2 kw modified sine wave is probably the cheapest…..

        The AVERAGE power used by a chest freezer is only going to be maybe 100 watt or less…maybe even as low as 60 in cold weather….so the watt-hrs consumed in a day isn’t that bad….but the batteries must be able to provide the surge current, and remember, at 12 volts they have to provide 10 times the surge current as come out the other end at 120 volts….so use huge wire also.

        It IS possible, just takes work.

        • PrepperDoc says:

          Take a look at the Tiger Claw inverter that Joe found (see other comments) — that might be helpful to you. Use BIG WIRES.

        • 123pieguy says:


          Thanks for the great article – hope it inspires some to throw a backup DC power supply together for When There Is No Power. We’ve had good luck with our rural electricity provider here in N. Virginia, with few losses of power in 20 years. Our longest was 24 hours when Sandy blew through a couple years ago. Fortunately, by then I had acquired a 2000 watt Generac generator, and ran it every 2 hours to keep our frig and two small freezers, so no food loss of any sort.

          My point in writing is to dig a little deeper into one aspect of DC to AC inverters that has been touched on here, but that can use a little more examination – on practical differences MSW (modified sine wave) and PSW (pure sine wave) inverters. MSW inverters kick out “dirty” sine waves, not the smooth sine waves that PSW inverters provide (that is also provided in our home outlets). A lot of things do run fine on MSW inverters (simple electrical appliances without electronic controls; look into this yourself to get a proper idea), but many things should run off of PSW inverters, especially when they have electronic control boards – e.g. many laptops, pellet stoves, medical equipment, even refrigerators.

          While running my frig/freezers during Sandy from my Generac’s MSW AC outlet, I wondered what wattage my frig was using. I plugged my Kill-a-Watt meter (very useful; get one) in then my frig and saw that my Kenmore frig was using about 850 watts, and seemed to run fine. After Sandy, when power had been restored, I plugged the frig and meter into a house outlet and saw the frig used only about 160 watts on clean AC.

          Two points – your appliance may run on dirty (MSW) AC, but many items like my frig may use only one-fifth the power (so 80% more efficient) when on clean AC. Secondly, many items may run on MSW AC but their electronics may be degraded over time, and may ultimately be destroyed by MSW AC. I needed a Plan B for winter, as I heat with a pellet stove, and no way would I run it straight from my MSW inverter. Right after Sandy I bought a fairly expensive PSW inverter that I can now power from a battery bank or from the DC output of my generator. I can now be confident in efficient and safe power to my pellet stove, frig, laptops, and other electronics.

          Fellow Wolfies – get on a few alt power/RV/generator/solar forums, and read the questions and comments. Some folks really know how to provide information in a way that makes it easy for others to understand. The article above (and some of the comments) are good examples thereof.

  10. After my wife and I built up our pantry solar backup was our next project. What I wanted was enough for lights, freezers and communications, I did this in two ways, I installed 1650 watts of solar panels and two rolls surrett batteries, if you go on craigslist requesting quotes for new solar panels you will be surprised how low the prices will go. Then I purchased landscaping 12 volt led lights and mounted them on bases for indoor lighting, there is so small of a draw on the batteries I could run for six months on lighting alone. The appliances, I purchased two small chest freezers which have a small draw so during a extended grid down I can alternate freezers on the inverter, then I found a old style refrigerator that is not frost free for my back porch. Frost free units run almost continuously so they draw a lot more power. Last what every body needs to remember is that the power inverters themselves draw a few amps, my 3000 watt unit draws 3.5 amps with no load, so down to ACE I went and bought a 400 watt unit which is for everyday use, this will run TV s etc. I did not mount the solar panels on my house, this gets the building dept and state elect inspectors involved plus can cause roof leaks.
    My every day motto is ” keep it simple”.

  11. j.r. guerra in s. tx. says:

    Many of us use CPAP machines to get a good night’s sleep. Having a unit that can be powered with such a setup would be great to have. Without a good night’s sleep – you lose a lot. Not having a working unit for even one night makes a huge difference the next day.

    • PrepperDoc says:

      I have a friend who feels the same way. Me, I’m trying to lose 1 lb a week……

    • JR, I have a new resperonics unit that runs on 12volts, but they draw 6 amps if you use the vaporizer unit in conjunction with the air pump.

      • WxNW, can u tell me the name of the company & model of that resperonics unit, & where I can find one. Thx.

        • Red c , I get my units thru the VA medical center here, they have to be prescribed by a doc.

          • WxNW, I know they require a presciption & am going to ask my dr to prescribe a 2nd cpap that I could use for camping w/out electricity. -Not my real reason, but I prefer that he not know my true intent. So what’s the make & model? Your VA has to get them from somewhere, right?

            • REDC the label has a UP22 on it,you should be able to go on their website. They are in Murrysville PA. Possibly they will have all there products there.

              • REDC, I just went on their web page, it is the REMSTAR AUTO, hope this helps.

                • j.r. guerra in s. tx. says:

                  Thanks for the information people, I believe my unit is eight years old now and is due to be replaced pretty soon. I was wondering if anyone had experience with off grid CPAP operation.

                  PrepperDoc, your advice on losing weight is good, but I’ve had this problem even when young and trim (snore like a freight train :^). I should lose some weight but I don’t think that will be a cure, only a bandaid.

                  Thanks again all.

  12. PrepperDoc says:

    I’d like to call attention to the $199 1500 watt “sine wave” inverter that Joe pointed out. This is almost too good to be true, but the reviews were pretty impressive…. I’ve never had that model but some people here might want to try it, if they need to start a compressor or such…..

    Amazon. Tiger Claw 1500 w pure sine wave.
    If anyone buys this, can you report back on YOUR experience with it?

    • Prepper Doc; in regards to any equipment related to solar power I always refer back to the engineers at Midnight Solar, they have a very good blog where just about any question will be answered.
      The engineer’s there have designed almost every charge controller or inverter that is on the market plus some well known stereo equipment.
      It goes back to you get what you pay for, I have in the last 5 yrs purchased economical and better inverters, the cheaper units have all went up in smoke eventually.(harbor freight)

      • PrepperDoc says:

        Can you get them to comment on this TigerClaw true sine wave for so incredibly CHEAP???? That would be very helpful information.

        • PREPPERDOC, I read every review on this inverter I could find, it seems like the real deal, it’s just a simple unit, no frills but good bang for the buck.
          I have a love affair going with solar but I must say your article was really good and I noticed invoked a lot of questions, good job.

  13. JP in MT says:


    Thanks I like it.

    • PrepperDoc says:

      Thrown together to illustrate the concept…. My solar panels are 8.9 kW & I have 38kWHr of Rolls Surret deep cycle batteries…. (I’m quite blessed!!!)

      • And I’m jealous.

        • PrepperDoc says:

          Yeah, sorry, that might have been a bit too braggy…..

          But these things MAKE MONEY — and have an effective return of about 5-6% —- far far better than Treasury Bonds; I count them as “bonds” in my mind for retirement investment purposes.

          • My DW loves our solar system, our payback is this, it runs our lighting yr round and now with longer days I will switch all electronics over to it, it keeps our power bill just about half of my neighbor across the way. And when every body else is out starting generators for a power outage we just sit here and say ,”ain’t this grand”.

  14. Buy an early Nissan Leaf, oldies ‘own’ the battery. The 24kw main battery tops up the 12v ancillary battery, so just tap this into a decent invertor and away you go.
    An alternative is a Prius, same scenario except the engine will cut in to top up the 12v battery.

    • Jasper, is it possible to find such a battery in those cars in a junk yard? Or are batteries one of the first things they remove to recycle or sell? Is it worthwhile to get a refurbished car battery from an auto parts store?

  15. How stable are solar collector systems that do net metering (ie are connected to the grid)? Will an EMP knock them out? Or maybe just the inverter?

    • PrepperDoc says:

      My exact situation!

      Here is what I have done, and I cannot guarantee it will be protected:

      Midnite solar makes special surge arrestors for both the DC andAC sides of solar systems. I have their arrestors (these are metal oxide varistors (MOV) on: the AC side of the inverter leading to the house, and leading to the electrical company; and also on the DC side coming in from the photvoltaics. Furthermore, I installed my own MOV’s out at the combiner box.

      Midnight solar has a VERY impressive video where you get to watch them throw THOUSANDS of volts onto their arrestor….which does a great job. That is the best that I can do….and I keep spares in closed garbage cans.

      By the way, I also have EMI low-pass filters coming from the inverters to my house (huge intereference problem with my ham radios) and those also offer significant protection against the RF of an EMP wave.

      • Interesting. Thanks.

        But it raises another question. These MOVs appear to protect the inverter.

        What about the solar array itself? Will it get fried so that it fails to harvest sunlight even though the inverter is functional?

        • PrepperDoc says:

          Not sure…movs on the combiner are to protect arrays. These are fairly low impedance panels & may survive.

          I have spares just in case….

  16. Interesting and informative thread
    Am looking into a scenario where power goes down for very long periods, we have panels already on our roof and the inverter.
    Was wondering if there is a way of using said panels in a down scenario with Batteries we have yet to buy and keep charged.
    Have been looking for a comprehensive manual on start to finish an off grid system, if there is a manual please let me know where to get it, we are in Western Australia, heaps of sunshine.
    All the info you and others have posted gives me some guidance and appreciate the info

  17. Don’t forget about wood gasifiers. Another renewable energy source.

    • PrepperDoc says:

      I read about those!! Fascinating. My problem is that although we have woods around us…..not THAT much wood. And I don’t really think that transportation is going to be my biggest need….

      You are certainly correct that they are renewable, however. I once looked at the “efficiency” of solar panels and compared it (in terms of calories, a unit of energy) to CORN….and was surprised to find the solar panels were extremely competitive to growing crops!

  18. PrepperDoc says:

    So….to recap — the main point of this little article is that it is SO EASY to have at least a tiny bit of uninterruptible electrical power. Anybody can do it. So….DO SOMETHING!!

    1. The tiniest, dumbest, homemade “uninterruptible power supply” will at least give you emergency lighting for a few hours.

    2 Add even a SMALL solar panel and simple charge controller and you have a renewable bit of emergency lighting.

    –ANYBODY– can do this. And you learn from having done it.

    3. Enlarge the size of your project with bigger / better batteries, better inverter, bigger solar panels and better charge controller — and now you have a solar power (renewable) system that just might keep a small freezer/fridge going, which is huge if you have medications that HAVE to be cold, or want to store other things short term. It also means you can easily keep comm gear going, which might be huge in terms of improving collaborative neighborhood defense teams.

    4. A generator is a great thing for short-pulse items like well pumps where you need to start a big motor, but don’t need to run it more than 3 minutes to get enough water for your family for days. By the way, propane generators are now readily available (Amazon) and an underground or above ground tank isn’t hard at all….learn a bit about propane piping NOW.

    5. I know it is EXPENSIVE but if you can put together enough solar to afford one of the inverters that can feed back into the grid (the Outback GTFX3648 is 4 kW and $1700) this becomes an INVESTMENT that pays a dividend somewhat better than bonds and not quite as good as the long term outocome of the stock market — but DEFINITELY a very reasonable portion of a diversified — and tangible — portfolio! All the little projects you did above give you knowledge and allow you save $$$$ when putting together a big solar system… and as one person pointed out, the folks at Wholesale Solar have helped thousands and thousands of people do-it-themselves.

  19. PrepperDoc says:

    One additional comment. Metal Oxide Varisters (MOV) are really cheap. You can buy them yourself if you know a tiny bit about electricity, enough not to get electrocuted. Digikey.com sells just about everything online. Remember, 120VAC is “RMS” volts….the peak voltage in either direction is 1.414 x 120 = 170 volts….and power lines aren’t perfect so they can have little blips even higher….and you don’t want your surge arrestors blowing every few hours….so you buy MOVs that are set to go at maybe 200 or 210 volts. They have tiny ones and big ones in physical size, obviously the bigger, the more joules of energy they can dissipate. They end up being less than $1 each, so buy a bunch and when you are building stuff, include them into the process and gradually all of your systems are more and more protected against the voltage spikes that come from EMP. They also make them in very small voltages — I bought a bunch at, say 20 volts, and put them across speaker terminals and audio lines in my ham shack as just another way to protect against EMP. My next goal is figuring out some sort of shielding box for a laptop that gives me still some way to see the screen and use the keyboard (at least occasionally) — maybe some sort of a grid of wires like chicken wire or something…. we’ll see. Anything is better than doing nothing. And you cannot “break the bank” and go broke with expensive solutions, you have to be creative.

  20. Hi PrepperDoc, I am from Southeast Asia and don’t know much about the technicalities of a solar set-up. Being reading up from various sources but its rather overwhelming. The solar service provider in my country is only interested in setting up a Feed In Tariff system which is not what I want as a prepper. My average electrical daily consumption is between 10-15Kwh according to the “smart” meter (which I doubt but thats another story). I wish to install a hybrid type system where I could tap into the grid or go full solar. What system configuration, equipment capacity and amount of batteries / specs I need to obtain the 10-15Kwh during a grid down situation. Appreciate your assistance. Thanks Mack

    • PrepperDoc says:

      To make 10 to 15 kWh per day, you probably need 3- 4 kW worth of DC panels, feeding thru an MPPT charge controller into about 15-20 kwrh worth of batteries, and then an inverter that is capable of supplying your power, I’m guessing 2 to 4 kW inverter would do your
      job. Where I live, people usually set up the batteries as a 48 volt pack

      • Thank you for your reply.
        What would 15 to 20Kwh of batteries comprise? E.g.
        1. How many deep cycle batteries would I need
        2. what sought of specs would each one be?
        3. Batteries labels tend to show the volts and the amp (I think). How do I work out the specs to Kwh so that I know how many I need.
        FYI I estimate sunlight to be about 3 to 4 hours per day. My front door is facing south but my roof is slanted to the west.
        What would you recommend? Thanks again for your insights. Mack

        • PrepperDoc says:

          Watts = volts * amps
          Kwhrs = kilowatts * hrs
          Use 6 volt rolls surett s-550 batteries, 400+ Amphrs each * 6 volts = 2.4 kwhrs each. 8 of them in series = 18 kwhrs @ 48 volts

          Google these issues , bone up a bit

  21. To Prepper Doc
    I’d appreciate if you could post the specific model(s) / part numbers of the EMI low pass filters you use on the power to your ham radios.
    I have that problem here, and the “workaround solution”, of shutting off the charger source (solar/inverter) when the transceiver is being used is far less than optimum.

    • PrepperDoc says:

      Finally, you must assure that your planned post-disaster power source will not create its own interference to radio communications! If you are planning a generator (even a 900 watt unit should suffice), this may not be a problem. However, we found that fancy inverters (you have one stored in a Faraday cage, don’t you?) generate wide-spectrum NOISE from their highly-efficient switching power supplies used to construct each point on the sine wave output, and “modified sine wave” inverters automatically create wide-ranging interference. We have successful experience dramatically reducing the radiated inverter-generated power line interference by placing a low-pass power-line-capable filter in series with the inverter output right at the output of the inverter. (An example of such a filter is the Chinese JR-1230-R 30A Alternating Current Power Line EMI Filter AC 115/250V.) Be certain to test your actual grid-down complete system to see if your communications radio actually works as intended in both transmit and receive conditions!

  22. It makes no difference what gauge wire you use, the plugs won’t accept more than 15 amps. so save your money on 10, 8, or 6 gauge wire.

  23. I am looking for a charge control that will take care of needs without costing me too much. I think I am looking for MPPT Charge Controller. Right now I have 3 – 100 watts Panels, running the batteries parallel to 12 volts. I am using a 2000/1500 watt power converter. The thing I have to watch is Temperature range (-20F to 80F). The question, does the power convertor connected to the Charge controller? Any ideas

    • 123pieguy says:

      I would recommend the Morningstar Tristar TS-45. I got this from Handy Bob’s super handy blog at:


      Read ALL of his 15 or so blog essays on panels, controllers, and monitors. Incomparable and irreplaceable. Copy his blogs as soon as you can so his wisdom and practical off grid advice does not get lost. Read them several times and you will be far ahead of so many out there giving advice. He lives what he advises.

  24. Texas Watchman says:

    What a fascinating article!
    The solution I came up with on a very limited budget, was I caught a harbor freight sale on their 12 volt battery/booster/jump start pack, believe it has a 17 Ah battery in it for <40 bucks, the smaller one without a air compressor in it, has also worked good for jumping off a dead car battery 3 times.(twice in very hot summer temps and once in deep winter).
    it comes with a a/c charger built in and can be charged from your car nearly full capacity as well. has a 12 volt plug outlet a meter and a lamp , I grabbed a 100 watt inverter, and waited and caught on sale the fold up 13 watt 12 volt solar panel they offer , looks like a brief case and comes with a lot of attachments as well.
    grabbed a cheap 30 watt solar charge controller off Amazon to round out this little set up. keep it in a faraday cage and top off the battery pack about every 6 months.
    this will give a few options if the power goes out,and give a few hours of use / day with lower current demands if able to recharge, all in cost under $200 , I dont know if this good for you YMMV but, its at least a option and its fairly portable. and on a tight budget, alltho there are probably much better options for solar panels, but this one was good for me for on the go.