DC Generator / Steam Turbine

Discussion in 'The Projects Forum' started by dotkom, May 7, 2013.

  1. dotkom

    Thread Starter New Member

    May 7, 2013
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    I'm in the process of prototyping a steam turbine project. It will power a desk lamp. Designing and milling is not a problem but it's been about 13 years since my last electronics class. I need some help getting back on the horse.

    I am trying to power 3 banks of LED's. (2) 30 LED (1) 6 HPLED. The only specs I can get from where I purchased them from are that they are 12v. No resistance or wattage to speak of. Each set of 30 LEDs has (10) resistors marked 131 which I've found to be 130Ω. The HPLED's have no markings that I can see. I can't identify how the individual LEDS are connected. It appears to be a combination of series AND parallel.

    They all work fine when I hook them up to a breadboard with (2) 6V batteries hooked in series.

    The problem is that I'm going to be running them from a generator. I have a ton of motors ranging from 9v-50v. I'm looking at about 4-6000 rpm on the turbine which will drive the motor.

    My questions are:
    1. How do determine what the load of the circuit is without knowing exactly their resistance?
    2. If using a motor capable of 50V, how do I ensure that no more than 12V gets to the lighting?
    3. What else am I missing? What am I not thinking about?

    Any help/suggestions would be greatly appreciated.

    Useful Links to the components I'm using:
    http://www.tmart.com/1210-30-Led-Interior-Car-Light-Bulbs-White_p143161.html
    http://www.tmart.com/6-SMD-LED-Car-Interior-Dome-Door-Light-Lamp-White_p85819.html
     
  2. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Welcome to AAC.

    I can't say I've got much experience in power supplies, but hopefully I'll be able to help get you started.





    First, do you own a multimeter? The simplest thing to do is take a current measurement of each type of light to determine what the current draw is. This will help you determine how much power you'll need.

    Taking current measurements is straight-forward, but you have to be careful otherwise you'll blow a fuse, cook the meter, or damage your circuit. Since you've inferred you haven't played much with electronics in a while, let's step through it.

    1. Plug your red probe into the jack marked A (not mA, not V) on your meter. If A and mA are the same jack, no problem.
    2. Plug your black probe into GND, -, etc.
    3. Set your meter to A. This may be 20A, 10A, etc. - whatever is the largest A value setting on your meter.
    4. Connect the black lead on one of your LED assemblies to the negative terminal of your 12V (2x 6V) battery.
    5. Touch or connect the red probe from the meter to the positive terminal of your battery pack.
    6. Touch or connect the black probe to the red wire of your LED assembly.
    7. Read the meter to get the current requirement of said LED assembly.
    8. Repeat steps 4-7 for the other LED assembly.
    9. Turn your meter off and plug the red probe back into the jack marked V. This prevents you from accidentally blowing a fuse on the meter when you go to take a resistance or voltage measurement in the future. Note that when the red probe is connected to a jack marked mA or A, there is effectively a short between the red and black probes, so care must be taken to only take current measurements when connected as such.
    If unsure, let me know the make and model of your meter and I'll whip up some instructions with pictures.





    I'm assuming you're proposing to use a DC motor as a generator? If so, I *think* this will give you an AC voltage. You can check this by spinning the motor at a constant speed and setting your meter to measure DC then AC volts. Whichever appears steady is likely the type of voltage being produced.

    If it is AC, you'll need a bridge rectifier. You can buy them pre-made or make your own with four diodes. I'd suggest the former so you can be sure it will handle the current needed. Grant it, you can buy large diodes too, but I don't think you'll save much if anything and then there's less a chance of hooking something up wrong.

    Okay, not sure if there is a better way to do this, but I'd say use a 12VDC regulator. Assuming your total current requirement is less than 1.5A, a LM7812 should do it. This is used in electronics to step-down a high voltage to a steady 12VDC. From memory, these can only handle up to about 37VDC, so 50VDC would be a bit much, but you'll have to test the output of the generator to see if it gets that high. There are several regulators out there though, so finding one to meet your needs shouldn't be a problem.

    Someone may have a better take, this is just how I'd start it without knowing any better. :D





    You may want to add a diode in series with one of the output leads prior to going to the regulator to protect against reverse voltage to the circuit - say, in case, the motor is spun in another direction. Only a problem if the output is DC. No worries if the output is AC and you go through a bridge rectifier.

    You may also need to add a diode across the generator leads to help prevent back EMF. This is done for motors, not sure about generators. I'd suggest researching back EMF protection generators.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    This pretty well covers it. I'd probably add a nice big electrolytic capacitor after the rectifier bridge and before the regulator. This is optional, but may help reduce flicker of the LEDs at low rpm.

    Another thing to think about is whether the regulator is needed at all. It will cause inevitable power loss and it would be nice to eliminate it if's not contributing anything. If the load of the LEDs is high enough, you may not be able to exceed 12V from the generator.

    Another source of loss is the rectifier itself. It will be wasting 1.2V or about 10% of the power that the LEDs are using. If you could configure your LEDs differently (so that half are powered in one direction and half in the other), you might not even need the bridge. The LEDs are diodes, after all, and will perform the rectification all by themselves. Strings of holiday LED lights use this principal.
     
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  4. dotkom

    Thread Starter New Member

    May 7, 2013
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    0
    Thanks so much for the great explanations. So here is what I have. I took a picture of the setup just so you could see what I was doing. I guess I'm doing something wrong (on the LED's).

    http://jciproof.us/xi12/5hIqU3HN

    Also, on the motor, this one is a 24v motor, I have it spun up to about 6000rmp with a dremel (actually not sure what "6" means on a dremel, 6000 is my assumption but you know what that means). It appears as though it's outputting a DC voltage. I had thought about the AC thing but I read that was not the case with "brushed" DC motors. Not sure if that is the deal or not. Just what I saw online. Here is a pic of that.

    http://jciproof.us/ea3r/2bthnk9W

    If you could shed some light on the LED issue, I'd appreciate it.
     
  5. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Hmm, something is wrong with the current measurement. I see the meter is readings amps so I assume the dial is in the correct position, but I couldn't see where the red probe was connected to the meter. Assuming it is in the 20A jack, turn off the meter, remove the back and check the fuses.
     
  6. dotkom

    Thread Starter New Member

    May 7, 2013
    5
    0
    Hmm. That might explain it. No idea how to tell if the grey one is blown or not but the glass one appears to be. I don't see any filament in the middle.

    http://jciproof.us/Ck0E/2wsYEUUj

    Incidentally, if I just wire all of the LED's in parallel and turn the 24v motor at 6k RPM, the LED's light up 8V and are at peak brightness at 12v. At 6k RPM, I get a 12v reading with the load. If I run the same RPM with no load, I get high 23.x V. Once I add the load, it works just as it should but after a couple of minutes, the motor gets pretty hot. I just wonder if it could sustain 15 minutes of continuous operation. If I could figure out what amperage it's pushing out, I guess I could figure out if the load is too much for it.

    Just thinking out loud here, I apologize for being so ignorant on the subject.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    Spinning at high rpm with the Dremel is one thing, but I suspect you will have MUCH lower rpm with your turbine unless I'm way off on what that will be like. Your setting knob may say "6", but doesn't a Dremel run up to 10k or more rpm? The motor will probably be fine with your turbine if that's the case. I just hope you can get enough rpm to light the LEDs.

    I would say for now you can let any worries about the electrical components wait until you have more knowledge about the steam side.
     
  8. dotkom

    Thread Starter New Member

    May 7, 2013
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    The steam is the one part that I'm not worried about at all. The turbine blade is mounted on 2 full ceramic bearings so the only real resistance is to spin the generator. We'll easily get the turbine up to 3-6k rpm and could use any number of pulley sizes to pull down the generator rpm.
     
  9. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    These should be for the current measurement side only, in which case your meter will work without them, sans the current function. Thus, keep the fuses out, put the red probe back into the V jack on the right and set your meter to measure resistance. Touch the probes together - you should see close to 0Ω. Now touch the probes to the sides of one of the fuses. If you see close to 0Ω, the fuse is good. If you see nothing or a OL, the fuse is bad and needs replacing. Do the same for both fuses. If you're in the U.S., you can probably pick those up locally at RadioShack or simply order them online.

    Nice that it is putting out DC and appears to power your LEDs under load. You may want to add a diode in series with the positive lead to the LEDs to protect against reverse voltage in case the motor is spun in the opposite direction. LEDs are diodes and have some protection against reverse voltage, but there is a limit. If you're going to be extra careful and ensure the voltage going to the LEDs is never reversed, you'll be fine. Adding a diode will add ~0.7V voltage drop. Be sure the cathode side (marked by a line around the diode closest to the cathode lead) goes to the load - opposite (anode) side goes to the positive lead of the generator.

    Sounds like you're pulling more current than the motor can safely provide. You could probably use the motor's rating (if you have it) as a rough guideline on its limits. If, for example, the motor is designed to run on 12VDC at 100mA, then pulling 200mA is probably too much. Another thing to consider are motors and generators, while alike in many ways, have different designs to maximize their efficiency, so a motor designed to run on 100mA may only be able to provide 50mA when used as a generator.

    If the motor is getting hot after only a couple of minutes and you need 15 or more, I'd suggest looking for a bigger motor with a higher wattage rating. You'll need more torque to drive it, but it'll run cooler and you won't have to worry about burning up the windings.
     
  10. dotkom

    Thread Starter New Member

    May 7, 2013
    5
    0
    That's kind of what I'm trying to get to. If I could figure out what kind of load I have, then I can figure out what motor I need to get to drive it. I'll work on this some more this evening and post up. I really appreciate the insight.
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    Another way to measure your load current is to put a low ohms resistor (1Ω or less) in series with the load, then measure the voltage drop across it. You then calculate the current using ohms law. This is exactly what is happening inside your meter for the ammeter function, but you can make your own "external" shunt.
     
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  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    What a great fun project! :) Photos would be really cool.

    With first attempts at alternative energy type generators, a really good practice is to put two pulleys and a belt between the turbine and the DC generator.

    This lets you change pulley sizes (gearing) to easily optimise the most efficient operating power, as your turbine will have a speed where it is most efficient, likewise your DC generator.

    Even just a v-belt and some simple lathed v pulleys would be a good starting point.
     
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