diversion load wiring output

GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
The diversion load 12 gauge wiring to a heating element is taking only 3-7 volts and 30 amps. Is this due to the wiring size or the heating element itself? How do I get the voltage up higher?
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Comments

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    The diversion load 12 gauge wiring to a heating element is taking only 3-7 volts and 30 amps. Is this due to the wiring size or the heating element itself? How do I get the voltage up higher?

    What is the expected maximum power voltage and current from your source (which I assume is a wind turbine)?
    Where are you measuring the voltage? At the turbine or at the heater? To drop even 3 volts at 30 amps the wire resistance would have to be 1 ohm. Have you measured or calculated it?

    The most likely problem is that the resistance of the heater is not matched well to the turbine output. For example if the turbine can put out 250 watts, then you will not get anything more than 7 volts when drawing 30 amps. If you double the resistance of the heater (two in series, for example) then you might get something closer to 10 volts and 15 amps.
    SMA SB 3000, old BP panels.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output

    Two heating elements are in parallel from the charge controller. Both are 600 Watt non wind turbine fed. Solar.
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  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    Two heating elements are in parallel from the charge controller. Both are 600 Watt non wind turbine fed. Solar.

    OK, that makes it clearer. I like to use the word "opportunity load" for the solar case, and "dump load" for the wind case to keep the distinction clear. The term "diversion load" covers both.

    What is the rated Vmp of your panel string? If the Vmp is 18 volts, try disconnecting one of the heaters. If the Vmp is over 30 volts, put the two elements in series.
    Whatever you do, you will continue to get roughly 30A from the panels until the combined resistance of the heaters is too high and the voltage goes above Vmp toward Voc.

    You will have to do manually what an MPPT controller does automatically, namely set the load resistance to a value which extracts the most power from the panels.

    In this case since you said that you have a nominal 600 watts of panel and are getting what is in effect an Isc of 30 amps, the Vmp of the panels is probably somewhere around 20 volts. So you should try using one element only and then two elements in series to see which works best for you.
    SMA SB 3000, old BP panels.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output

    Wiring goes as follows: Morningstar TS-45 controller diversion load straight to ONE 600 watt DC heating element. 3-7 volts 20-30 amps output. Didn't know you could wire the heating elements in series to double the voltage. The diversion load has been updated since yesterday yet not tested: 55 gallon drum with 20 gallons of antifreeze solution, 3 - 600 watt heating elements (2 are now used for diversion load) and one 12v DC circulating pump just installed. The 3rd heating element is on the main battery bank diversion load, not used that much. Going to sound funny, yet trying to do some pex tube heated floor inside my chicken coop under a few inches of ag lime gravel. The pump comes on around 6 volts yet doesn't have the power to push much liquid. Should the pump be hooked up in series also for even more volts ????
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  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: diversion load wiring output

    I am not sure I understand "hooking the pump in series" means (two pumps in series on the fluid side or the electrical side, to two solar panels in series or what?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    Should the pump be hooked up in series also for even more volts ????

    Once you provide a higher resistance load (such as two heating elements in series) the voltage from the panels will be higher. Then all you have to do is put the pump in parallel with the other loads, and it will get that same higher voltage. (Assuming, of course, that the pump itself is not much of a load compared to the heaters.)


    Paradoxically, the other way to get more power out of the panels is to use a smaller heating element, one which is designed for the same nominal voltage, but half the power output. This will draw the same current from the panels, but at twice the voltage. The thing to keep firmly in mind through all of this is that whatever load you put on them, the panels will still deliver pretty much the same amount of current (proportional only to the amount of light hitting them.)
    SMA SB 3000, old BP panels.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output
    inetdog wrote: »
    Once you provide a higher resistance load (such as two heating elements in series) the voltage from the panels will be higher. Then all you have to do is put the pump in parallel with the other loads, and it will get that same higher voltage. (Assuming, of course, that the pump itself is not much of a load compared to the heaters.)


    Paradoxically, the other way to get more power out of the panels is to use a smaller heating element, one which is designed for the same nominal voltage, but half the power output. This will draw the same current from the panels, but at twice the voltage. The thing to keep firmly in mind through all of this is that whatever load you put on them, the panels will still deliver pretty much the same amount of current (proportional only to the amount of light hitting them.)

    Update: Diversion load is putting out 12-15v until it gets to the heater element, then 1-7 volts. Hooking them up in series or parallel doesn't matter, the voltage cuts in half. Just burned out my circulation pump hooking things up this way. The pump was hooked up in reverse. Trying to get things in series like told. Was this why it burned up ?
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  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: diversion load wiring output

    It sounds like the diversion loads are too big for the controller (basically shorting the output of the controller? Remember heaters draw more current/have lower resistance when first turned on--so they will draw more than their rated wattage at that time). That can ruin the controller.

    Regarding pumps... How are you connecting them in series?

    And remember, not everything can be successfully connected in series to "drop the voltage".

    Some loads have "negative" feedback with respect to current... A common light bulb or Nichrome heater element... Draws more current (lower resistance) when cold, and less current when hot. If one bulb/heater gets a bit hot, it draws less current--stable.

    A typical motor is the opposite--When the voltage is high, the motor draws less current. When the voltage is low (and there is significant torque on the motor) it draws more current. Put two motors in series--If one has a bit "low" of voltage or needs to supply more torque, it will draw more current, which will drop the voltage across the motor, which draws more current (and can over voltage the other motor). Not stable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    BB. wrote: »
    Remember heaters draw more current/have lower resistance when first turned on--so they will draw more than their rated wattage at that time.
    -Bill

    Some well instrumented tests (results at this link) have shown that although the typical tungsten light bulb filament does have a massively lower resistance when cold than when at incandescent temperatures, the typical (e.g. Nichrome) heating element does not. A heating element, whether stove, furnace, heat tape, etc. will not have any significant current surge at turn on.
    (Yes, the resistance does vary with temperature, so does the resistance of copper wire, just not enough to worry about for heating elements.)

    One lesson from this, however, is not to try to use light bulbs as diversion loads. :-)
    SMA SB 3000, old BP panels.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    BB. wrote: »
    It sounds like the diversion loads are too big for the controller (basically shorting the output of the controller? That can ruin the controller.
    -Bill

    Good point Bill, I was assuming that the 30 amp current number was the limit of the output current from the panel. If the controller is also actively limiting the current, then the controller will be under a lot of stress, while the panels themselves would not be damaged by short circuiting.
    We need to know more about the "diversion outlet" of the controller.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: diversion load wiring output

    I thought Nichrome heaters would draw about 5-30% more current when cold (not a huge amount)--But I certainly can be wrong.

    http://en.wikipedia.org/wiki/Nichrome#Current_Temperature_Characteristics_of_Nichrome_.28straight_wire.29

    Increase in resistance with temperature



    [TH]DEG.F[/TH]
    [TH]DEG.C[/TH]
    [TH]NiCrA[/TH]
    [TH]NiCrC[/TH]


    68
    20
    0
    0


    600
    315
    3.3%
    5.2%


    1000
    538
    6.3%
    8.6%


    2000
    1093
    6.0%
    10.5%



    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    BB. wrote: »
    I thought Nichrome heaters would draw about 5-30% more current when cold (not a huge amount)--But I certainly can be wrong.

    http://en.wikipedia.org/wiki/Nichrome#Current_Temperature_Characteristics_of_Nichrome_.28straight_wire.29

    Increase in resistance with temperature



    [TH]DEG.F[/TH]
    [TH]DEG.C[/TH]
    [TH]NiCrA[/TH]
    [TH]NiCrC[/TH]


    68
    20
    0
    0


    600
    315
    3.3%
    5.2%


    1000
    538
    6.3%
    8.6%


    2000
    1093
    6.0%
    10.5%



    -Bill

    You are absolutely right about the numbers! But let's look at the practical effects:
    1. If the heating elements are used to heat water, the highest element temperature will be far less than 600 degrees. It will be higher than the water temperature, but not enormously.
    2. Compared to a tungsten filament, the 3-6% variation in a nichrome heating element is unlikely to cause overload problems unless the system is poorly designed to start with.

    PS: If you are dealing with a constant voltage source, the current will be inversely proportional to the resistance. There will be no factors of two in the percentage as there would be for the dependence of power on voltage, so I am not sure where your 30% top end is coming from.
    SMA SB 3000, old BP panels.
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output

    How did we get off the subject of my issues ?

    Curious to find out that I replaced one of the 12v DC heating elements with an AC element. Voltage is fine now around 12-16v and about 1-2 amps.

    The other unanswered question is if reversing the pump caused it to burn out or too many amps from the 12v heating elements ???
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  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: diversion load wiring output
    How did we get off the subject of my issues ?

    Curious to find out that I replaced one of the 12v DC heating elements with an AC element. Voltage is fine now around 12-16v and about 1-2 amps.

    The other unanswered question is if reversing the pump caused it to burn out or too many amps from the 12v heating elements ???

    The AC element has a higher resistance. But it has such a high resistance that you are now only using 15-30 watts. You have gone too far increasing the resistance.

    If the pump motor is designed for DC only and is polarity sensitive (not quite sure why it would be unless it has control electronics built in) then hooking it up in reverse might damage it.

    If the CC output is 15 volts and the motor is only rated for 12 or less, that might also damage it. There are too many unknowns in your description of how you wired it and how the pump motor is built to be more specific.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: diversion load wiring output
    How did we get off the subject of my issues ?

    Trying to show that some loads are not appropriate to connect to a constant voltage source...

    As Inetdog says--Even with the "numbers", the application specifics still matter (heating air vs water, etc.)...

    And, yes, I was just relating the 30% from another appliance site I had read years ago about heating element surge current--don't remember the site or the application (I think it was a drier--Assuming it was some form of Nichrome wire).

    LED lamps are another--That is why LEDs have a ballast device of some sort (resistors, constant current source, etc.) to control the current flow through them.
    The other unanswered question is if reversing the pump caused it to burn out or too many amps from the 12v heating elements ???

    Still lost--Are you using the heating elements to drop voltage to your pump motor(s)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output

    I've ordered two more AC elements to replace the total of 3 elements. The motor burned up likely due to low voltage and overheated the coils, melting it. Hooking up in reverse may make the impeller run in reverse which there was still water in the discharge line indicating the low voltage likely the culprit. $55 mistake that was overlooked. When I get the 3 heating coils and pump hooked up in series, should produce some better results, theoretically.

    Bill, just trying to make the most of a cheap floor heating system run by mother nature to help heat the chicken coop.
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  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: diversion load wiring output

    Found the reason for the pump burning out. Low voltage/high amps from the heating elements. Now with 240v AC elements and a new pump, doing fine together. May not get much heat from the elements, yet the system voltage maintains around 13-14 when dumped from the diversion load and the pump runs too. May have to get some 120v heating elements for less resistance/more heat, yet would that lower the voltage again and raise the amps like before or would it balance the volts/amps better suited for the system ?????
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