dump resistors

Discussion in 'Dump Loads' started by bluejay, Aug 31, 2010.

  1. bluejay

    bluejay WindyNation Engineer

    Could these be hooked directly to a battery and not start a fire? Could someone go turbine>battery>resistor and fan for heating capibility? :?:
  2. TomT

    TomT WindyNation Engineer


    That is what I will be trying this winter. I will be using an old mechanical thermostat from and old oil heater. To trip the relay when the temp drops. I just figured I did not want the dump to kick on and overheat the room before the battery got low enough to shutdown.

  3. bluejay

    bluejay WindyNation Engineer

    Thanks tom,but you still didnt answer my ?..What happened to windy guru,he has quit posting any info in a while..
    The info I am looking for is do you need the dump load controller for some voltage/amp regulation?

    Could a person set up a turbine just to rectify to dc then use a battery for voltage clamp then feed a fan blowing over the resistors.. It would only heat when the turbine was turning trying to charge that battery..you could even wire in a switch so you could charge a battery(or batteries) and turn it on to heat when it was full..

    Could you hook a resistor up directly to a battery and it draw only 300 watts and not melt anything? What regulates the amount of amps going into it?
  4. windyguru

    windyguru WindyNation Expert


    What you want to do will not work but the reason is different from what your concern is. The resistor pulls a specific amount of energy from your battery bank which is defined by the equation V=IR (volts = current x resistance). As an example, the internal resistance of our 300 Watt, 12 volt dump load is 0.73 ohms. If one of our 300 Watt, 12 volt dump loads is connected to a 12 volt battery bank which is at 14 volts (fully charged), how much power will the resistor suck from the battery bank? How much current will flow through the resistor?

    V= IR volts of battery bank = current through resistor x internal resistance of resistor

    14 volts = ? x 0.73 ohms

    If we solve for the ? (current through resistor), we get 19.2 amps of current flowing through the resistor. So, we have answered one of our questions. Now, how much power is the resistor consuming?

    Power = Volts x Amps Power = Volts of battery bank x Amps going through resistor

    Power = 14 volts x 19.2 amps and Power = 268.8 Watts

    So, as you can see if you use an appropriate dump load that is designed for the voltage of your system (i.e. battery bank), you do not have to worry about the dump load overheating or melting. If the dump load remains connected to the battery bank, it will continue to suck power from the battery bank. As it continues to suck power from the battery bank, the voltage of the battery bank will continue to drop. As the voltage of the battery bank drops, the power consumed by the resistor will drop because Power = Volts x Amps. According to this equation, if the voltage drops the power drops. So, over time the resistor will consume less and less power from the battery bank and the battery bank will get more and more drained.

    Now, you might be wondering what the problem with doing this is? Well, there is no real safety concern with doing this. But, draining your battery bank to zero by keeping a dump load on it will quickly destroy your batteries and they will eventually not be able to hold any type of charge.

    This is exactly why you need to use a charge controller. When your battery bank's voltage gets too low, the charge controller will automatically disconnect the dump load from the battery bank. Also, when your battery bank's voltage gets too high, the charge controller will automatically divert power to your dump load. This protects your battery bank from being overcharged which will also quickly destroy your battery bank. In short, a charge controller with dump load makes sure that your battery banks remains in its safe operating voltage range.

    The end result is that you SHOULD NOT do what you are proposing to do because your expensive batteries will not last long.
  5. TomT

    TomT WindyNation Engineer


    Windy is right on what he said. I will keep the charge controller hooked up so they don't over charge. The thermostat will trigger the relay when I need heat. I will only use the thermostat when I can be around to monitor the voltage and to make sure that it doesn't drop too far.

  6. bluejay

    bluejay WindyNation Engineer

    Thank you windy for taking the time and breaking it down to the technicals..I understand the concept now but I still have a ?
    What would happen if you wired ,say 3 300 watt dump resistors directly to a rectified turbine..I know the voltage peaks,I have seen 57 volts in moderate wind with this geared unit..

    Would there be a way to produce heat if you have a extra turbine to spare just for this cause. Would there be a way to clamp down the voltage(heavy diode?) and hook rectified dc to the loads for heat?
  7. windyguru

    windyguru WindyNation Expert

    You can do that but it is not so simple. The turbine can be connected directly to the dumpload but having all those dumploads connected directly to the turbine is basically a dead short on the turbine. The turbine would have a hell of a time starting to spin. The way it would have to be done is to the have the turbine start spinning with no load (no dump loads) connected to it. Then as the wind increased the dump loads would come on one by one. There are circuit boards people design and use to handle this but it is in no way simple.

    I think an easier way would be to have the dump loads you want to use as heaters, hooked up directly to your battery bank. Just put an on/off toggle switch in between the dump load and battery bank. When you want heat, turn the switch on and turn it off when you are done. Make sure the switch is rated for the amps going to the dump loads. It could be a lot of amps if you wire several dump loads in parallel.

    Also, I have access to low voltage sensors. This is a simple circuit which will disconnect the dump loads from your battery bank if the voltage of the battery bank hits a certain level. This will protect your battery bank from discharging too much in the event that you turn on your dump loads and leave them on for too long. As an example, you could turn your dump loads on and then fall asleep on the couch. The dump loads would stay until your battery was dead. But, if you had the voltage sensor, it would disconnect the dump loads from the battery bank at, say, 10.8 volts (assuming you are using a 12 volt battery bank).
  8. bluejay

    bluejay WindyNation Engineer

    thank you windy guru! You rock,let me know when you are in the market for a k9 member for your family.I will take care of you...[​IMG]
  9. BeachBum

    BeachBum WindyNation Engineer

    Cute pup. What breed is it?
  10. bluejay

    bluejay WindyNation Engineer

    American Bandogge Mastiff. (bully pitbull{bulldog x pitbull} x English or neo mastiff). :D
  11. windyguru

    windyguru WindyNation Expert

    That is nice looking puppy. How big will it be once it is fully grown?
  12. bluejay

    bluejay WindyNation Engineer

    she should be around 100-120lbs figuring the linage she is from. Alot of muscle....Can you tell me what you think on those long ac runs? I could rectify at the base and run one fat 0 gauge wire in and tie other mills into it. Otherwise I would have to have beefy runs for every ac run in. I never thought ac resistance would be a issue.. I also have a trailer snap disconnect inside befor rectifing..Its 16 gauge I believe so thats another bottle neck...

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