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What type of battery is good for emergency power for blackouts?

Discussion in 'Power Electronics' started by Ghost314, Sep 27, 2018.

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  1. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    That's what this forum is all about. A used bicycle and a used alternator pulled from a wrecked car should put you in business. Maybe get a tandem bicycle built for two riders, so you can sell the excess power generated.:p
     
  2. primuspaul

    primuspaul

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    Feb 7, 2018
    As I've found out from personal mistakes, alternators are NOT a good way to produce power in an emergency. First because they require power to generate power (spinning an ordinary alternator will not, on its own, produce any energy at all) and second because they are tuned to produce power at the speed of the serpentine belt, which is a hell of a lot faster than any normal human can spin it without implementing a complex (and expensive) set of gears.

    You'd have better luck buying a wind turbine, AKA permanent magnet alternator. I've seen videos on DIY making these yourself from an old car alternator, but the process still requires costly magnets and more importantly the use of a hydraulic press which defeats the entire purpose (you'll spend more money doing it yourself than just buying an often superior product).

    That said, for small power requirements, you'd be better off keeping some Alkaline cells in storage. They are very cheap so you won't get hit in the wallet as hard when you have to rotate them and they have very good shelf life.
     
  3. Ghost314

    Ghost314

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    Sep 27, 2018
    From the research I've been doing it looks like the alternator is not even necessary, a DC motor will output DC when spun. Then you just need to run it through something like a charge controller and into a battery. There are a bunch of videos on YouTube where DIYers have built this kind of set-up.

    Alkalines have been in the back of my mind from the start as a fallback option. It just seems like a shame to resort to such a cheap solution when I wouldn't mind spending more for a somewhat better solution. Which is why I was curious if I could take a heftier AGM battery and follow the recommended maintenance procedure of charging it to capacity with low current every few months, and have a lot more power available.

    Another option I considered for a fair bit of time was a portable fold-out solar panel. I may live in an apartment, but I could take one of those out to a park and read a book or something while charging. Downsides are, you still need a battery to charge, or you need to bring your electronic devices that need charging outside and pray that the weather cooperates.

    Overall I'm kind of liking the bicycle generator idea, mostly because it sounds the coolest :p. It also doesn't tie me to the weather conditions, and is completely sustainable over the long-term. I'm probably still going to research a little more before I make any decisions though. I also have a feeling I may get some alkalines as well anyway, just because they're so cheap.
     
  4. primuspaul

    primuspaul

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    Feb 7, 2018
    Maybe I missed it, but what exactly do you want to power in case of a blackout?
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Go back and read posts #10 and #12.

    Alternators are not "tuned" AFAIK. Their output voltage is a relatively simple function of shaft speed and rotor (exciter) current. You might ask yourself why alternators replaced generators in automobiles in the 1950s. The engine speeds didn't change, and the first alternators were driven from the same v-belt and pulley arrangement as the generators they replaced, so shaft rpm was not much different. What did change was efficiency.

    Alternators use a rotating magnetic field, created by excitation current in the rotor winding, to create voltage in three surrounding stator coils. The rotor current is supplied through a pair of slip rings which need carry only a few amperes of direct current. The fixed stator coils are arranged around the axis of the rotor to produce three-phase alternating current at a frequency determined by shaft speed. An integral set of six power diodes rectifies the three-phase AC into DC. Except for a small but significant voltage drop across the diodes, there are almost no losses (high efficiency) and, more significantly, no sparking and subsequent wear caused by the commutator and brushes necessary to get DC from a conventional generator.

    The biggest advantage of the alternator over the DC generator is the ability of the alternator to produce significant amounts of current at low shaft speeds, which normally occurs when an automobile is stationary with its engine idling. This is important in northern city climates in the winter where stop-and-go driving is the norm and the automobile electrical system is under heavy load from headlights and the heater/window defroster fan. DC generators simply failed to provide sufficient current under these conditions to keep the battery charged. It was not uncommon for drivers "in the know" to park their car inside a garage and connect a "trickle charger" to "top off" the car battery overnight.

    But you are right about alternators requiring some electrical power before they will produce any output. So what? Alternators are always used with a battery anyway, so electrical power is available to excite the rotor winding. And once the alternator is producing electricity, rotor excitation is derived from the alternator output, part of which current is used to keep the battery charged and the rotor excited at the desired level necessary to produce the total current required.

    For simplicity of construction, some alternators are made with permanent magnet rotors. However, without some means to control the strength of the rotor magnetic field, i.e., by adjusting the current in a rotor winding, the alternator has NO capability to adjust its output to accommodate variable load and variable shaft speed conditions.

    Of course it will, just not very efficiently but conveniently. The "add on" market for bicycle road lights that are energized by a generator, driven by one of the bicycle wheels through a friction contact with the tire casing near the outer rim, is a good example. With LEDs replacing incandescent lamps for road lights, the need for a bicycle-mounted generator appears to have decreased in favor of using throw-away alkaline batteries, so it might be a bit difficult to find a bicycle-mounted generator today that isn't made in Asia.

    [​IMG]
     
  6. Ghost314

    Ghost314

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    Sep 27, 2018
    As a matter of fact, when I started investigating bike powered generators, I discovered that those are not only still around, but the technology has actually improved. Modern bike 'dynamo' generators are actually magneto generators, and have been incorporated straight into the hub. This helps eliminate loss of energy from friction and general tire wear:
    [​IMG]
    [​IMG]
    They are apparently still used by touring cyclists, and bikepackers, who like to travel very long distances without necessarily having easy access to grid power. However since they're designed to be used while the bike is actually travelling somewhere, they try not to sap too much of the riders energy. They produce somewhere around 1.5 to 3 watts, which is a far cry from what I've seen from stationary generators.
     
  7. primuspaul

    primuspaul

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    Feb 7, 2018
    Call it whatever you want. Tuned, designed, etc... You cannot spin it fast enough by hand to produce any usable amount of power.
    That and alternators are apparently cheaper to make, which was likely the #1 consideration when designing something that's going to be thrown out with the car when it breaks.
    The bottom line is he's never going to be able to spin it fast enough to get any usable power. He'll need some sort of bike connected to a pulley/belt system to do it. And it's not just as easy as getting a used bicycle. You need to build at least some sort of wooden platform to hold the entire assembly. You will need something like a large serpentine belt to connect the wheel to the alternator. Overall, he's looking at a bunch of money and a lot of work for something that "may" work.

    Also, the entire assembly will use up a LOT of space even when not in use.

    Or he can just get a PMA for $50. With China selling stuff for next to nothing, the DIY solution is often more expensive than just buying something.

    Still, the best solution is probably a cheap flooded battery from Walmart (which he can throw out every few years when it goes bad), a cheap charge controller, and a $100 solar panel, which he can install outside of his apartment window.
     
  8. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The best power is always the most 'compact' power (bang for your buck) and in that sense it will always be a fossil fuel of some sort. If you have a LIMITED application for energy then you can look for 'worse' solutions but only the person in need can make the right decision.
     
  9. primuspaul

    primuspaul

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    Feb 7, 2018
    Gasoline comes to mind, but it can't be stored for long, so it's not good for emergencies unless he has a car and "rotates" it. Too much of a hassle IMO.
     
  10. Ghost314

    Ghost314

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    Sep 27, 2018
    Don't forget that I don't have good ventilation either, so fumes are an issue. The concerns I had regarding solar panels are that they need solar rays to hit their surface at a perpendicular angle to produce the power that they advertise. To get the right angle I couldn't just hang it out the window, I would need to build some sort of platform for it. I'm also a bit concerned about how much sun it would get, since there comes a time of day where neighboring apartment buildings, not to mention my own, will start to cast shadows and cut off the sunlight. Then of course there is the issue of lousy weather.

    I did manage to find a pre-built bike powered generator at a price I was willing to pay $259 (US), but the company only ships to the States (booo). Most of the other generators seem way overpriced and geared towards public demonstrations rather than practical usage. Depending on how high the DIY price is, I may still pick up a solar panel and cross my fingers.
     
  11. primuspaul

    primuspaul

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    Feb 7, 2018
    You're never going to get the "rated" power except when the panels are directly facing the sun around noon in clear weather, but so what? You're still getting some power into your battery during the day and for a phone/flashlight/laptop, it may be enough.
    Don't forget that your bike will be subject to the same maintenance issues as a normal bike, save for maintaining the tires, brakes, and maybe the wheels. The chain can still stretch, the pedals can still break, you'll still need to oil it, etc...

    I read a bike generator typically generates 100W. I imagine that's from pedaling full power for a regular unfit adult. Let's say you can do that for an hour (and I'm being generous). That's 100wH per day. Let's say your solar panel gets direct sunlight for an hour a day. There's your 100wH. But it's still generating some power throughout the rest of the day.

    Do you own a car? Might be worth it to just charge your electronics there during the day.
     
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