Alternative dumpload?

Discussion in 'Dump Loads' started by mowindpower, Sep 2, 2011.

  1. Can't seem to find it right now, but I was reading about someone once making a dump load out of a spiral notebook binder coil. Could a typical small portable electric heater be used for a dump load? They are pre-rated to take a certain wattage. Basically, they are just metal coils designed to heat up repeatedly. Just wondering?
  2. TomT

    TomT WindyNation Engineer

    I was the one that did that. But would be for test purposes only.
    Have to work out the ohms to dump voltage. They sell 12 volt and 24 volt heaters. You could use them if you get enough for your wattage.
    Other wise you will have to hook jumpers in on a typical heater to use it at 12 or 24 volts. Which is beyond the scope and safety factor for most.
  3. I took a small 110 v heater apart (750 watt on low & 1500 watt on high) and it just had the cord coming in with one wire going to a dial switch, which I thought was on/off and a reostat, to adjust the temp., which you might have to bypass, and go straight to the rocker switch, and proceeded from there to the coils. I thought one might just cut the cord and wire it to 12 v, or wire a recepticle in to 12 v and just plug it in.
  4. TomT

    TomT WindyNation Engineer

    The resistance of the wire will roughly be 10 times too high. To get it to work you would need a jumper for testing till you find the right spot. Just glowing a little. Or ohm it out and place jumpers where needed. And I know someone is going to say it is unsafe and recommend buying a dump load resistor again. It is the safest way to go. But sometimes you have to go with what you got.
  5. Thanks TomT, I'm just trying to get it up and putting out power, get some meters on it, and figure out what I'm going to need before spending money on new parts that may be to small or to big for what I end up needing. I'm more of a shadetree mechanic, (use what I got), at least till I figure out exactly what I need to be spending money on. I don't see any reason to waste money to save money. Sometimes that works and sometimes it don't. But thanks again to all of you out there for the info.
  6. windyguru

    windyguru WindyNation Expert

    This will work just fine but you will need to de-rate the heater because it is designed to work off of 120 volts (120 VAC). If you want to use it as a dump load on a 12 volt battery system, then you will need to de-rate it significantly:

    Voltage = amps x resistance (let's say it is 120 volts and 12.5 amps which is about what it would be for 1500 Watts)

    120 volts = 12.5 amps x resistance (Then resistance = 9.6 ohms)

    Now, for a 12 volt system:

    12 volts = amps x 9.6 ohms (Then amps = 1.25)

    Power = volts x amps (which means this is now only a 15 Watt dump load)

    Wow, that seems low. I wonder if I made a math mistake. Can you take a multimeter to the coil and measure the resistance and let me know what you get?
  7. Minnesota

    Minnesota WindyNation Engineer

    10 times lower voltage and 10 times lower current is 100 times less watts. 15 is 100 times less than 1500, so the math is good is we ignore AC vs DC power aspects. Perhaps automotive 12V heaters could be looked into.
  8. TomT

    TomT WindyNation Engineer

    The other thing to look at is are you using this with batteries or just hooked after the rectifier? Because if you are hooking it up just after the rectifier with no batteries to test. It will present a small load to the turbine and as voltage climbs it will become a larger load as voltage climbs. Then you could use volt and amp gauge to see what you can expect out of it. Just to be safe I would only let it run while I was there watching it.
  9. I'm using a 2 1/2 hp treadmill motor as my generator. It's in the top of the 40' tower under covers right now. I can't remember what the data plate on it said, but on a 2 hp one just like it, it says(variable speed DC motor, 3210 rpm, V.arm 130, A.arm 15). I think from what I've been reading on here that I need to have some kind of load on it as soon as I put the drive prop assembly on and let it spin, to keep from burning the motor up from just freewheeling with nothing hooked to it. No batteries , just meters to tell what its going to put out. Just spinning the shaft on the 2 1/2hp motor by hand, it puts out about 6 to 8 volts and lights an auto test light bright. Do you think this motor will produce enough juice to be worth it? I'm thinking about hooking the 2hp motor to the shaft coming out the back end of the 2 1/2hp motor and driving them both. Could one wire them together at the top of the tower, possibly using blocking diodes, to keep from backfeeding each other, or would that even be needed? Or do you think I should scrap them and use something different to generate power? Hopefully my tower and drive assembly can be used to drive any other type of generator, just by changing the generator mount. The only limit would be how much the 8' windmill prop I'm using can turn efficiently.
  10. Minnesota

    Minnesota WindyNation Engineer

    An 8 foot flying rotor will run about 500 RPM at 25mph under load, so you need a PMA that can produce ~1000w (1.3hp) at that RPM to be comparible to others of that size. If your PMA does 2hp but needs 3210 rpm to get it, then at 500 rpm one might expect ~225w. :(
  11. Sorry, I forgot to mention that my drive gears the generator up 3 1/2 times to that of the prop. If interested, there are some pics of my setup in general questions, under (OK Engineers.....). I'm new to all of this, and I started this setup before finding any information at all on this subject. Looks like I should have researched it before starting.

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