so as not to hijack.....

Discussion in 'General Electronics Chat' started by PackratKing, Feb 16, 2011.

  1. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
    the cranked flashlight thread,
    I have been tilting at this windmill :rolleyes: : An "emergency light system" for the house based on white led's.

    The power source for it, would be either hand-cranked, or a small battery driven motor culled from a VCR or some such, belted to the little generator. If battery driven, a circuit could be built to make the motor run and recharge the caps when the voltage goes low, and leds begin to dim a little.

    This in turn would put the small generators' output - likely not much more than 4.5 useable volts, onto a bank of large scale capacitors, >> low volt 10K - 100K μF >> culled from wherever one can get them.

    Base this on the fact that if you hitch your bench supply to a 3v dc motor, and include a large [ 100k ] cap in the circuit, after you disconnect the power supply, the capacitor continues to run that little motor for a good long time.

    LED's draw far less current at the same voltage than a little hobby motor, so extrapolate this into a couple hundred K worth of capacitance, being drawn down by led's, properly hitched, led's shouldn't represent a dead short across the capacitors causing a catastrophic instant discharge when they are only charged to the limit of the generators output voltage.

    Far from being a setup to produce "perpetual light" :D it should work for quite awhile, depending on how many leds you wire into the circuit...........
  2. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    What is wrong with your electricity for it to frequently fail??

    A motor driving a generator wastes power by getting warm.

    The voltage of a discharging capacitor begins to drop immediately and drops for the entire discharge time. Then LEDs dim a lot.
    But the voltage of a rechargeable battery almost remains the same for most of the discharge time. Then LEDs do not dim much.
  3. someonesdad

    Senior Member

    Jul 7, 2009
    You folks who live in larger metropolitan areas don't understand what it's like to live where the power isn't terribly reliable. You can have power outages once or twice a month or even more often. Where I live, it has gotten better over the last decade or two, but when I moved here 30 years ago, it was pretty atrocious compared to where I came from (SF bay area).

    A hand-cranked thingy sounds like too much work to me. If I was going to put in an emergency light system with LEDs (something I've thought about a number of times, but never bothered), I'd just power the whole thing with a motorcycle lead-acid battery. I'd keep a trickle charger on the battery and a small relay that was powered from the AC line. The relay's NC contacts would be wired to power the string of LEDs. When the power failed, the relay's power would be shut off, causing the battery to power the LEDs. Dirt simple. And I wouldn't even bother with trying to make things not come on during the day if the power failed -- why add extra work? If you kept the current draw to less than, say, an amp, you'd probably have light as long as the power outage (I'm assuming power is typically only out for a few hours to 8 hours at most). If you run the LEDs at 10 mA and put three in series, then that means 10 strings of 3 LEDs, or 30 LEDs total. That should give you enough light to be able to see things around the house.

    I'd put such a thing in my house, but we have so much insulation in the attic that it would be a nightmare trying to locate everything and crawl around to do it (and it would be much easier if I was 30-40 years younger...).
  4. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    I can't remember when my electricity failed the last time. 5 years ago? 10 years ago? For a few minutes. It is inexpensive.

    But in some countries electricity is expensive and fails every day (load sharing).
  5. Wendy


    Mar 24, 2008
    Count yourself lucky, and understand it is luck. In the country the wires are a lot less maintained, as there simply aren't as many users and everything is trimmed down, including maintenance.

    In Texas there is going to be a big brew haha about the rolling blackouts, it is suspect there was attempted market manipulation that backfired.

    For an emergency lighting system I think I would prefer simple batterys, and a equally simple AC relay that makes contacts when power is removed. No recharging needed.

    I keep a small handful of the LED domes kicking around instead of candles for those times Garland Power and Light is working on the high tension lines. There is a lot of construction going on in the city, along with new commuter trains, that can be very disruptive of electrical service.
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    For us electricity is expensive.

    To reduce oil usage government planned on making a wind farm at a coral reef near Male'.

    The utility company who took upon the contract assigned a sub company. Now the both are under investigation by anti-corruption board for around 8.5 mil. the sub company guy has vanished. The utility guy cannot vanish as he happened to be a chairman or something.
  7. K7GUH


    Jan 28, 2011
    Battery backup can't be beat for reliability and economy. My principal concern is to keep an amateur radio station on the air under the worst possible conditions. When commercial power is up, the station runs from an AC supply, which also trickle charges a 12 volt storage battery. If power drops, an electronic switch transfers the load to the battery. 12 volt lighting (LED, fluorescent, and/or incandescent) can be switched on manually. If there is a prolonged outage, I can charge the battery with a putt-putt or my main (only) vehicle. The various components weren't cheap, but if I ruin one, at least I can afford to replace it.

    In addition, our local ARES club has a source of used but usable 7.5 Ah 12 volt batteries which can be carried to a dark room for emergency lighting. They get charged on a regular cycle with an ordinary auto battery charger. HD has stopped carrying 12 volt lamps and fixtures, but they are available from camping supply sources at a slight additional expense and inconvenience.

    If I had to buy one of the 7.5 Ah batteries, they seem to run about $25.00 at battery supply retailers. The overall system isn't perfect, but it keeps me on the air.