dummy load..for a dummy..new to this

new to all of this....I'd like to create a diversion load to manage wind and full batteries....I have a 160 watt charge controller.....do my loads need to be DC? or can I connect/splice to AC.(fan or heater) do I need an inverter for my dummy load?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: dummy load..for a dummy..new to this

    Generally, charge controllers are rated on battery voltage and current--not Watts...

    Which leads to the next question, what is the size (amps or volts/watts) of diversion load you need for your system?

    And a diversion controller is just an On/Off switch which connects the battery bank to the load. So, if you have a 24 volt battery and need a 10 amp load to prevent the wind/water turbine from over charging the battery bank--then you need a load that can run at 24 volts and 10 amps.

    Typically, it is some sort of resistance heater. You could, in theory, connect an inverter to the diversion output to run an 120 VAC heater, motor, lights, etc... But, that may be easier said than done.

    Inverters typically need a very low resistance/impedance path from the battery bus to the inverter's DC input. The wiring and the diversion controller may cause too much voltage drop for the inverter to operate correctly/reliably.

    I believe that the NEC may actually require two diversion controllers+loads for reliability (if one fails, you could damage/cause a fire with your battery bank--depending on lots of stuff).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NewYorkManNewYorkMan Registered Users Posts: 19
    Re: dummy load..for a dummy..new to this

    I use these dump loads for my wind turbine:

    http://www.windynation.com/products/accessories/dump-loads/300-watt-dump-load-24-volt-systems

    http://www.windynation.com/manuals/300-watt-dump-load-24-volt-technical-specifications

    If you only need a 160 Watt dump load and you have a 12V battery, I think you can use the dump loads I linked to. Someone will tell me if I am incorrect.

    2.9 ohm resistor and say about 14V when the battery dumps:

    I=V/R
    I= 14V/2.9ohm = 4.8amp

    P=IV=14V x 4.8 amp=67 Watts

    Use one for a 67 Watt dump. Wire two of these DL's in parallel for a 134 Watt dump load and if you wire three in parallel it is a 201 Watt DL.

    I hope another person can confirm my math is right :D
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: dummy load..for a dummy..new to this

    Yep, you got it right!

    Other ways to calculate power (little bit of rounding error):
    • Power = V^2 / R = (14v)^2 / 2.9 Ohms = 67.6 Watts
    • Power = I^2 * R = (4.8a)^2 * 2.9 Ohms = 66.8 Watts
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • openskyopensky Registered Users Posts: 13
    Re: dummy load..for a dummy..new to this

    I had the exact question, so this thread was really helpful. The guy who had installed the system originally told me that a dump load was $350. Looking at the links provided in this thread, I can get a kit to provide 1500 watts of diversion/dump load for $120! I would rather be able to direct wire to a 24v DC Heater and/or Air Conditioner but these dump loads will be cheaper and easier.

    Question #1 - How quickly and how much heat do these things put off? Since I'm considering mounting it in my battery shed, do I need to worry about cooking my batteries during the summer? I'm going to do all I can to use up the power so I don't need to dump any but if I'm away for a day or two of sunshine and wind, I'm worried that the temp in the battery shed will get hot in a hurry during the summer. At 1500 watts, it probably won't need to dump for more than an hour or two max in a 24 hour period. But I just added 1200 watts of solar to the existing 1000 watts of wind so I'm not sure just how much excess power I will have this summer.

    Question #2 - How well do these things hold up outdoors? I didn't see an option for an "outdoor" enclosure but I assume I would need something more than the mesh enclosures for an outdoor installation.? I thought, worst case scenario, I could put it inside during the winter and outside during the summer...
  • silvertopsilvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: dummy load..for a dummy..new to this

    I use the resistance dump loads also, and they can get too hot to touch, but if you're only dumping for an hour or two, it's not going to produce that much heat in an outdoor shed. If you can open a small window, you will be fine. I would treat these like I would treat any electrical device, and protect them from the elements. Mine are mounted on a raised aluminum plate indoors; kind of a heat sink. I don't produce enough dump to overheat a 12 X12 room. These came from Windy Nation but there quit a few listed on Ebay and also the internet; just google. Be sure to use the correct voltage for your system.:cool:
  • openskyopensky Registered Users Posts: 13
    Re: dummy load..for a dummy..new to this

    Thanks, that helps a lot!
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: dummy load..for a dummy..new to this

    In theory there is a lot of junk you could use as a load dump.
    I was considering using old electric cooling fans from a car or possibly a small bank of old used car head lights if I wanted to go the ultra cheap or free rought.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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