Help Sally with a generator

Energy & Sustainability
Help Sally with a generator

Make 1119
Sally writes in –

Hi- I wondered if you might be able to help me find a way (if there is one) to construct a backup battery power system for keeping household appliances (fridge), lights, etc running for some time in the event of an emergency (I live in L.A.). Any suggestions? To purchase these things already made is quite expensive. Thanks, Sally.

Here’s a start! – Link.

34 thoughts on “Help Sally with a generator

  1. Stokes says:

    How long do blackouts last? Getting a more efficient fridge might be better; unpowered, one could stay cool for hours.

  2. RonNelsonII says:

    While the idea of using an old alternator is a good one, I doubt that any (inexpensive) inverter would be able to handle something as juice-hungry as a fridge.

    I lived in Puerto Rico for a while, and the power seems to always go out in the campo. The fridge (left CLOSED) would stay at reasonable temps for about 8 hours. (“Reasonable” meaning less than 50 degrees fridge, and 40 degrees freezer. It’s not ideal from a food safety standpoint, but not horrible.)

    We’d turn on a generator if the power was out for longer than that. The generator would only be used for the fridge and the pressure pump (water supply). Flashlights and candles for lighting.

  3. wsuverkropp says:

    Definitely, it’s best to use the most energy efficient applicances. A dollar spent on conservation saves three dollars on generation (or something like that).
    Your best solution would be to have a battery charger with ‘float’ mode, a bunch of batteries, and an inverter. the charger keeps your batteries topped up, and when the power goes out, you can run your applicance off the inverter. You will have to either plug the appliance into the inverter, or install a transfer switch, so you don’t feed power back into the grid, and potentially kill some poor lineman.

    Another home-built genny is here:
    Just hook up a batter and inverter and you’re in business. Generators are loud and not very ‘green’.

    Food will keep in a good quality fridge for at least a whole day, typically longer.

  4. danielj says:

    LA is so wasteful all around: cars, cars, cars, and now a generator for everyone?

    Waste waste waste. We should maybe start to look at these DIY articles in that frame: for example, if everyone gets a two-stroke gas powered generator going, isn’t that kind of a bad idea, environmentally? Let’s not forget where that oil is coming from and what it costs to protect the supply!

    Yes DIY is good, but let’s not forget that a lot of times it’s just another way to be a consumer.

  5. tikitime says:

    from the original question:

    construct a backup battery power system

    not make a homemade generator. :)

    Golf cart batteries, a charger, and an inverter is what she needs to construct a high capacity UPS.

    I’m interested to see if anyone has implemented one using a recycled APC unit as a controller?

  6. inkyblue2 says:

    a typical fridge is so power-hungry that there’s really no good solution other than having a gas-powered generator on hand or spending a lot of money on some serious battery and inverter overkill.

    a cheaper and far more efficient option would be to wire up a 12VDC emergency circuit to run a low-power 12V top-loading fridge or icebox along with some LED lights. this circuit could be set up to run off of a couple of lead acid/AGM batteries which are topped off by a charger attached to the 110VAC line. when the 110 goes out, your wall sockets will go dead, but your emergency lights and fridge will keep running as long as the batteries last. you could use a regular old car inverter sparingly to run 110V gadgets off of the 12V line if you needed to.

    converting 110VAC power to 12VDC is a lot easier, cheaper, and more efficient than going the other way. plus, there are already a lot of 12V products out there that have been designed for power efficiency in RVs, boats, and off-grid houses.

  7. tikitime says:

    600$ 12V Norcold Fridge (like on my boat)
    much smaller than your regular fridge.. virtually worthless uif you are trying to save the whole fridge
    168$ deep cycle group 27 batteries
    (walmart -Yellow two @ 84$)
    200$ smart charger for trolling batteries
    @ boaters world

    uggh. That could buy a lot of groceries.

    Or, you could buy (or make) a superinsulated fridge that should keep things cold through the blackout for at least 24 hours

    949$ 5 cu ft Sundanzer (
    + batteries & charger as above.

    Do you have medicine you need to keep cold.. or?
    how long do you anticipate your outages to last?

  8. Dave1959 says:

    It will take a rather huge inverter to power a refrigerator. Plus, there’s some doubt about whether a 65 Amp automotive alternator could provide enough power to run one continuously without the battery being depleted. 65 Amps at 14 Volts is only 910 Watts. At 120 Volts, that would represent 7.5 Amps. Since most refrigerators require their own 15 Amp circuit, there may be a problem (even if you discount the fact that most of the current is used for the starting surge). Additionally, by the time you factor in the inefficiencies of the inverter, you may have a real power problem.

    Of course, one approach would be to simply increase the size of everything. Let’s see, we could go up to a 100 Amp alternator, which would be 1400 Watts. That’s a bit under 2 horsepower, so the existing 3 to 3.5 HP engine should still turn it (assuming not too many losses in the mechanical system). But, that still leaves the inefficiencies in the inverter.

    Plus, another problem is that the battery used for such a system really needs to be a deep cycle battery, not an automotive starting battery. Automotive starting batteries are designed to produce a huge surge of current for a very limited amount of time, and then be immediately recharged. Deeply discharging a battery designed for engine starting service usually results in a rapidly diminished capacity and rapid failure. A battery designed for deep discharge use should last much longer. Unfortunately, these batteries tend to be a bit more expensive (as least, in the short term) than batteries designed for automotive starting service.

    We could, of course, skip the 12 Volt system altogether and go directly to a 120 Volt system. It may be possible, by removing the voltage regulator and diodes, to extract a higher, AC voltage from an automotive alternator (possibly as high as 70 to 100 Volts).

    Yet another option is to use a large induction motor as the electrical power producing device. These may be fairly inexpensive if salvaged from a discarded washing machine. There are several tricks to doing this, and it’s not necessarily for the feint of heart. But, it can be used to produce reasonable amounts of 120 Volt AC power (Search the web for “induction generator” or “induction alternator”.).


  9. Austringer says:

    For those thinking about waste and energy consumption think about how much effort and energy goes into producing a refrigerator load of food.

    If this is to support occasional incidental usage – once a year the lights are out for a day and you want to be able to cool the refrigerator back down every six hours or so you might be able to get away with a small bank of deep cycle batteries and a big inverter.

    I put an alternator on a bicycle training stand* and managed to charge a 12V deep cycle with it a couple times for low power usage (rechargeing hand tool batteries in the middle of nowhere) but even if your initials are Lance Armstrong you’re not going to keep up with a refrigerator. Hauling the batteries to some place that still has power and charging them with a conventional plug in charger might work, but at this point you might be looking at a situation where just putting your food into ice chests and calling all your friends looking for someone who still has power and room in their refrigerator might be the more efficient route.

    *Oddly enough, if you go out and buy a new alternator with price being your only concern what you want (at least as far as the nice lady at Advanced Auto Parts could find on their computer system) is one for a Chevy Corvette. Not exactly intuitive.

  10. Quatermass says:

    It may be painfully obvious but just in case some people are unaware, any time you use any generator, make sure it’s in a well-ventilated area outdoors away from open windows. Carbon Monoxide is colorless and odorless and can easily kill you, your pets, your children, etc.

  11. grouchaux says:

    Suggestion: put a couple of gallon or half-gallon milk jugs of water in the freezer. When the power goes out they will help maintain the temperature in both compartments. Don’t open the door unless you have to, though.
    A full freezer / fridge is more efficient than one that’s almost empty because the compressor doesn’t have to cycle on as much. If there’s more stuff that gets (stores) cold, the temperature won’t rise as fast as it does when the fridge is nearly empty.
    Even after you construct / source your generator, the frozen milk jugs help fill “inefficient” air space in the freezer.
    Growing up with hurricane seasons, you pick up on little tricks like this.

  12. mi-ke says:

    According to a Swedish consumer magazine you can get a 100 liter freezer with and additional 180 liter at +5 for vegetables etc drawing 336 kWh/year at 25degre celsius ambient temp. 336000/365/24 is somewhat below 40 watts on average.

    Now, it’ll probably draw a lot more for a short period, so you’ll need a hefty inverter. A conservative estimate lands you at 15 hours running time per 100Amp/hour you have on a 12V battery pack. This is with an estimated system efficiency of 50% for the inverter, which is on the low side for a good inverter. Not that a good inverter is cheap though. Some kind of sealed – preferably deep cycle – batteries is what’s needed, but you could probably get away with any sealed batteries, as long as you don’t run them down totally, and not have long power outages every week…
    If you find a lot of batteries you could go with a dc-motor + alternator or alternator/transformer approach instead of inverter. It’d could easily be less than 50% efficient unless you find good matched parts. You also have to have some kind of rpm regulation to get a steady 60 (? I’m not a local)Hz.

    Cheap is hard here i think, but a fridge is not _that_ energy hungry if you buy one that really is insulated, and keep the door closed as much as possible. Oh, and don’t take out cold stuff and let it warm before you put it back, that’s a sure fire way to use much more energy than you need to.

  13. Jim12311 says:

    Anyone who needs power for a refrigerator or medical device in an emergency can use an inverter instead of a generator. An inverter changes power from a car or truck to the type needed by your house. I hooked a 1500 watt inverter to my station wagon battery posts with heavy jumper cables to run a refrigerator several hours a day for several weeks during power outages. The car was in a garage that’s separate from the house and the garage door was open while car was running so the inverter was kept dry and fumes were not an issue.

    The vehicle generator or alternator must be big enough. Mine is 1200 amps which looks like a lot, but that is at 12 volts. When converted to 120 volts, you only get 12 amps. Your car’s generator/alternator amps can be found by an automotive parts store that can look up a replacement generator for your vehicle. The amps or amperage it produces will be listed. Some of these stores also sell inverters, as do boat stores and eBay. A 1500 watt inverter will cost about $300.

    Most generators are basically a gas engine, generator and inverter. Anyone with a car already has the gas engine and generator. So you only need to add an inverter to convert the car’s 12 volt system to a 120 volt system. Portable generators need maintenance, while inverters need none and because your car is used frequently, it’s less likely to cause a problem when needed to power an inverter.

    Pay attention to overheating parts or cables when using an inverter. My car engine and generator did not overheat, worked fine at an idle speed and used a small amount of fuel. An inverter can be stored on a shelf and needs no maintenance. While not a perfect solution, it is another option to keep in mind.

    I have 2 refrigerators and was able to run both simultaneously, but felt they may not have operated well, sort of like equipment that runs during a brownout. Interestingly, this size inverter would not run my 700 watt microwave. However, the data plate says this microwave uses 1400 watts! Seems like a 2000 watt inverter would do the job. Perhaps the power loss over a 100 ft extension cord was the problem. Also, unless an inverter is a full-wave inverter it typically only produces 80 percent of available power and a full-wave inverter costs a couple times more than the 80 percent version. I don’t know if that means the 2000 watt device only provides 1600 watts, but if so, this would be added to the extension cord line loss.

    A last point: motors always need an an extra surge of power when they start. A rule of thumb is this surge is three times the running power. So a fridge that draws 10 amps needs 30 amps for a few seconds to start. The 1500 watt inverter, made by Cherokee, would handle the load but was slower to trip. I ran an electric chainsaw with a 13 amp motor from this inverter, but the inverter would trip half way through cutting an 8 inch limb. A 2000 watt Coleman bought later would trip 3 or 4 times doing the same task. The car battery also supplies some power and helps handle any start-up surge as long as the inverter is capable.

  14. nathan wright says:

    (From a UK perspective)when i went camping with my girlfriend and her family, in the caravan there was a refrigerator with the option to run on gas, i’m not sure how it worked but it was for when they went to campsites without proper power supplies. you might be able to get a version for your home, i dunno. or at least a replacement one

  15. codesuidae says:

    While many fridges consume tons of power, much of that power goes to the big heating elements that defrost the coils. In my fridge they are about 800W. If you were to add a switch to disconnect those you could run the fridge on a much smaller inverter and it would consume much less power.

    My Kill-a-Watt reports that my fridge consumes right at 1kWh per day. A good chunk of that is the defrost cycle.

    I’m currently building a lawnmower engine based generator using an alternator (’71 Chevy alternator, 30 bucks new). Fun project.

    My research on deep cycle batteries seems to indicate that the 6v golf cart batteries are the best deep cycle batteries you can get from the likes of Wal-mart. The group 27 marine batteries are a compromise between deep cycle and cranking amps. That’s what I’m using, but according to many battery sites the golf cart batteries have much more solid plates and so, while they don’t produce hundreds upon hundreds of amps, the plates also won’t fall apart as fast.

    I’ll be using an old APC UPC as the inverter. It has an atrocious output waveform, but it it’s free and so far everything I’ve tried to run on it is perfectly happy with it. I’m using a similar UPC to battery-back one of my house circuits, it’s working very nicely so far.

  16. Mark says:

    Wow. Never knew refrigerators used so much power. And that coil defrosting thing explains why our current one makes certain wierd noises that the old one didn’t… (much older design, probably less efficient and just didn’t need defrosting as it had waste heat knocking around)

    Still some of the figures sound pretty high – it’s not just because it’s a super large american model with icemakers etc being used in a warm climate, is it? Our fridges and freezers (UK) don’t need any kind of special circuit – they just plug straight into normal wall sockets. And they’re also fairly well insulated – my grandmother’s combination one had been broken down for about 24 hours (est. from the time she “noticed the light had stopped working”) before I noticed the milk wasn’t entirely chilled and the ice-cream was starting to soften during a visit.

    Also an idea that no-one seems to have picked up on – forget removing the voltage regulator on the car alternator… it’s an ALTERNATOR… can’t you just take off the diode then put a 10:1 transformer on it’s output? Maybe not the most efficient idea ever, but it’ll give you from ~100v upto 140v when running at optimal speed, from there you can hook up ten small 12v batteries or just use the power direct.
    (20:1 for use in UK/Europe)
    Also find one with a beefier amp rating, such as for a diesel van or something, for when that 900w just won’t cut it (also what I worked out my own one could provide, with the regulator still in place). Doubt even the crappiest fridge is going to average more than that, however. Just need a decent enough battery backing to cover the surges. Car batteries can hold a surprisingly good charge (65Ah typical, i think? With at least 30A sustainable for about an hour and >60A peak discharge (over at least 15s, for starter cranking – diesel car ones, even higher, as they have higher crank friction))

    How’s about, also, rigging it to e.g. an exercise bike and taking turns on it, a la Soylent Green? No emissions other than those natural to the human body, then, and it’ll help clear some of the food from the fridge without adding pounds to your waist. Chuck in some cheap PV panels and you’re golden.

    Or even if you want to be cheap and ghetto about it, and not too bothered about emissions to cover momentary crises, hooking up some jump leads and charging a secondary battery off an actual car. You won’t be able to run your appliances continually, but it should be enough to stave off complete spoilage.

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