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OT somewhat. Reality TV & Electrical generation

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  • OT somewhat. Reality TV & Electrical generation

    I don't watch much TV, but over the cold winter I caught an episode of National Geographic's "The Boonies". Essentially looks into people living off the grid.
    My question relates to an episode where a fellow uses a stream driven alternator to power lights in his cave.
    Can't give specifics, but the alternator is driven ~100 RPM, the output run 1,000 Ft. through what might be 12ga. stranded, to power maybe four 12v headlights. It works!
    Well, maybe. I sorta think not, but I'd be happy to be told why it does.

  • #2
    Originally posted by Carm View Post
    I don't watch much TV, but over the cold winter I caught an episode of National Geographic's "The Boonies". Essentially looks into people living off the grid.
    My question relates to an episode where a fellow uses a stream driven alternator to power lights in his cave.
    Can't give specifics, but the alternator is driven ~100 RPM, the output run 1,000 Ft. through what might be 12ga. stranded, to power maybe four 12v headlights. It works!
    Well, maybe. I sorta think not, but I'd be happy to be told why it does.
    Much better. you do the work and show why not!

    Phil

    Comment


    • #3
      Without specifics, it's hard to say exactly what they had going.

      You can run low speed generators. The output will depend on a lot of factors, including gearing and windings. What was the output of the generator?

      You can power headlights from many different sources. A 50 watt headlight will draw about 4 amps at 13.8 volts. My calculations say it's about 4 ohms. If the voltage drops to 10 volts it will be dimmer (about 38 watts) and draw less amps. Most folks can't tell the difference between the output of a 50 watt lamp and a 40 watt lamp.

      The 1000 foot run is long for a 12 ga cable. At 12 volts, the 1.6 ohms will eat up most of the power with a 20 amp load. ( http://www.bulkwire.com/wireresistance.asp ) In order for a 12 ga wire to work, the generator would have to provide about 36 volts in order to present about 10 volts to the headlights.

      A more modern set of lamps makes a drastic difference. A 4 watt LED will provide about the same light as the under powered headlight at a fraction of the power.

      Dan
      At the end of the project, there is a profound difference between spare parts and left over parts.

      Location: SF East Bay.

      Comment


      • #4
        1000 feet of 16 AWG = 4 Ohms (and some change). So two ways for the return path = 8 Ohms.

        Automotive head light: 12 V and about 30 to 60 Watts. So, lets assume about 4 Amps. That gives us a resistance of about 3 Ohms. You say he has four of them and they should be in parallel so the total resistance is about 3/4 (0.75) Ohms. The total circuit resistance will be 8.75 Ohms.

        If the alternator is putting out just 12 Volts, they are going to be very dim. 12 V / 8.75 Ohms = 0.585 Amps and that will be divided equally between the four lamps so each one will get only 0.146 Amps. Not much compared to their normal 4 Amps. This is clearly not the case.

        BUT, alternators can and do generate higher Voltages. So it may output a nominal 18 Volts. At 18 Volts, you have a total current of 2.057 A or about 0.514 A per lamp. Now I think you can at least see them glow.

        Automotive alternators have Voltage regulation built in to them so they don't destroy a battery that is rated for a nomimal 12 Volts. Let's say he diddled with the alternator and removed all Voltage regulation. Now it may be generating 50 Volts or more. And that would give us a total current of about 5.7 Amps or about 1.4 Amps per lamp. I am sure you will see them at that current level. But they will still be dim.

        OK, most cord has three wires. Some is even four wires, more expensive and not as common, but it does exist. So lets say he doubles up on one or both conductors.

        If he doubles up on one conductor, then that doubled conductor will have a resistance of 4 / 2 = 2 Ohms. And the total circuit resistance will be 2 + 0.75 + 4 = 6.75 Ohms. And at 50 Volts that gives us 7.4 Amps or about 1.85 Amps per lamp. Now you are talking.

        If he has four conductor, 16 gauge wire then, upon doubling up on both conductors, you have a total resistance of 2 + 0.75 + 2 = 4.75 Ohms. And at 50 Volts that gives us 10.5 Amps or about 2.6 Amps per lamp.

        Of course he may have 12 AWG cable. Or even 10 AWG and the size may not be too much different in a camera image. With 10 AWG, even without doubling up the current per lamp may be as much as 4.5 Amps. Sounds like too much and my simple calculation may be in error. But then the lamps will clearly be lit to a very useful level.

        Many other possible assumptions. But this is definitely a doable thing if you do not expect normal performance from the lamps.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there IS a penalty for trying!

        Comment


        • #5
          I forgot to mention...

          When I was looking into off the grid power, it quickly became apparent that it's more efficient to save a watt than it is to create a watt. Each time you convert power from one form to another, you lose some of it. That includes storage.

          I also found that people use power in fits and spurts, so you can use the power from a low grade power source if you can store it. Example: If you have a small 12 volt, 5 watt solar panel that charges a battery 5 hours a day, then you can use five 5 watt lamps for 1 hour per night. If you only light the area that you are in, you can use one 5 watt lamp (or five 1 watt lamps) at a time for 5 hours.



          Dan
          At the end of the project, there is a profound difference between spare parts and left over parts.

          Location: SF East Bay.

          Comment


          • #6
            Originally posted by Paul Alciatore View Post

            Many other possible assumptions. But this is definitely a doable thing if you do not expect normal performance from the lamps.
            That is the key. If you have no expectations, any lamp will be "about right" over a wide range of power supply conditions.

            BTW, that's nicely written up. About the same conclusions as I came to too.
            At the end of the project, there is a profound difference between spare parts and left over parts.

            Location: SF East Bay.

            Comment


            • #7
              Originally posted by danlb View Post
              I forgot to mention...

              When I was looking into off the grid power, it quickly became apparent that it's more efficient to save a watt than it is to create a watt. Each time you convert power from one form to another, you lose some of it. That includes storage.

              I also found that people use power in fits and spurts, so you can use the power from a low grade power source if you can store it. Example: If you have a small 12 volt, 5 watt solar panel that charges a battery 5 hours a day, then you can use five 5 watt lamps for 1 hour per night. If you only light the area that you are in, you can use one 5 watt lamp (or five 1 watt lamps) at a time for 5 hours.



              Dan
              Correction:

              You can use 3 and a fraction 5W lights...... One disappears in battery efficiency (~~80%), the other part of the fraction disappears in resistances etc.

              No 100% efficient process exists.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Thanks for the expositions. What gave me the greatest doubt was losses in such a long run of wire. No gearing, the alternator was driven by a belt directly driven from about 1" iron pipe. No pulley.
                Will an alternator put out rated voltage (12 in this case) at less than engine idle RPM?
                Unknown whether the alternator was hot rodded.
                All components were salvage, alternator and headlights 70's era.
                Hard to determine brightness... any light in a pitch black cave would be bright on film.

                Comment


                • #9
                  Originally posted by J Tiers View Post
                  Correction:

                  You can use 3 and a fraction 5W lights...... One disappears in battery efficiency (~~80%), the other part of the fraction disappears in resistances etc.

                  No 100% efficient process exists.
                  I was simplifying for those who did not care about the math. You are correct. There will be losses.


                  Dan
                  At the end of the project, there is a profound difference between spare parts and left over parts.

                  Location: SF East Bay.

                  Comment


                  • #10
                    Maybe he was using LED's. A one watter actually puts out a good bit of light.
                    John Titor, when are you.

                    Comment


                    • #11
                      He was using a car alternator and if it was turning 50 RPM I'm a monkeys uncle and he was using 4 car head lights and they were bright so where is the batteries/generator . Remember it's a reality program so they push the bounds hoping they don't get caught

                      Comment


                      • #12
                        I Saw that show. and his set up was total TV producers BS! Anyone that saw that, did you see how fast the paddle wheel in the stream was turning??? TV reality shows are just a bunch of BS entertainment, watched by people who have no idea. As posted, that paddle wheel was turning a maximum of 50 RPM!!! All BS, with him scrounging up the headlights, then finding that old alternator in the back of that scrapped pick up box. TOTAL BS!

                        Comment


                        • #13
                          An alternator needs the rotor to turn at least 1000 RPM for it to even charge. On cars and trucks, there is a larger pulley on the crankshaft to step up the speed so that it will charge at a dead idle. There is no way that it is putting anything out at 50 RPM.

                          Comment


                          • #14
                            There are any number of plans for hot-rodding alternators to put out 110V, so it's perfectly possible that the alternator is not stock. Also alternators are EXTREMELY unstable as to output voltage.... so they tend to put out lots more than you think when not loaded fully, and the voltage regulation is done manually.

                            Then also, could charge batteries, which would run the lights. Its surprising what a few amps 24/7 will do as far as charging. One thing is for certain.... those shows NEVER show you everything, and most often some of it is bare-faced lies. Much of the rest is merely inaccurate.....

                            Bottom line is that you have not got enough information to agree with it, or to call BS on it.
                            Last edited by J Tiers; 03-10-2016, 07:01 PM.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              You can estimate the power of a waterwheel to see how many watts the setup might produce. A five foot diameter waterwheel with 100 gallons/minute might give 0.1 HP or about 75 watts. If you have 10 x 1 gallon buckets with a shaft speed of 60 RPM you have 5 of those buckets supplying power so 300 gallons/minute and a little over 200 watts:

                              http://waterwheelfactory.com/hptable.htm

                              Here is an interesting discussion where someone wanted to make a low RPM 70-80 HP waterwheel generator:

                              http://www.permies.com/t/19874/hydro...eel-wheel-high

                              There was a reference in that discussion to the Laxey Wheel, in the Isle of Man, 72 feet diameter, 6 feet wide, turning at 3 RPM, and producing 200 HP of mechanical power transmitted through a connecting rod 600 feet long to drive a mine pump:

                              http://www.uh.edu/engines/epi2728.htm




                              Last edited by PStechPaul; 03-10-2016, 07:55 PM. Reason: Laxey wheel
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

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