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Thread: Dump load questions

  1. #11
    Junior Member
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    How would you make a "dump circuit"?

    I don't use much power from my system either and most of the time my cc indicates over current. I'm looking for a way to automatically divert power from the panel to a separate circuit to run a ventilation fan to cool down the house.
    My idea is for the fan to run only when my batteries are full. I would use the fan to circulate cool air from the basement without draining the batteries. If it's cloudy out the fan would not run but the house would not heat up as much either so it wouldn't be needed.

  2. #12
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    How would you make a "dump circuit"?
    You need a charge controller, that has relay or control outputs, so that when a preset voltage & time is reached, the relay activates and turns on your load.

    You can get voltage sensitive relays or switches, but you loose the absorb time sense.

  3. #13
    Solar Fanatic
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    Quote Originally Posted by TheAwkwardGuy View Post
    How would you make a "dump circuit"?
    You need two things. A controller that lets you do this (an old Trace C40 works well) and a dump load. Biggest warning: the dump load MUST be larger than your power source. If you have a 1500W wind turbine you need a >1500W dump load.

    I don't use much power from my system either and most of the time my cc indicates over current.
    Something doesn't make sense here. Overcurrent is not a problem you can solve with a dump load. Indeed, it makes it worse. Dump loads reduce the voltage in battery banks by INCREASING the current drawn from them. They only make sense for wind, hydro and other sources that cannot easily be disconnected without an overspeed.

  4. #14
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    Quote Originally Posted by billvon View Post
    Something doesn't make sense here. Overcurrent is not a problem....
    You're right. I meant to say the cc indicates Over Voltage meaning that the battery bank has reached full charge.
    I don't have Wind or Hydro, just Solar.
    If it's a sunny day, I reach full charge around mid-day. The cc allows ~1Amp to go to the batteries and should I get ~4Amp max output at that time of day.
    That means I have ~3Amps of energy available but not being used? I'm just looking for a way to use this extra energy.

    It looks like a voltage sensitive relay or battery isolator might be what I'm looking for.

  5. #15
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    Quote Originally Posted by TheAwkwardGuy View Post
    It looks like a voltage sensitive relay or battery isolator might be what I'm looking for.
    Sort of. Here's the problem:

    Batteries go through three stages of charging - bulk, absorption and float. Absorption is the highest voltage but the charge isn't "done" at that point, so if you used just voltage on the battery you won't get a full charge before you draw the battery back down.

    However if you use a PWM charge controller and you put the voltage sensitive relay on the panel side, then set the relay to higher than your max battery voltage, then you will get power only when the charge controller doesn't "need" the power. Note that your load will have to deal with full panel voltage (17-22V for a 12V system) for this to work.

  6. #16

    Default What I have done for dump loading

    I know this is an old thread but...
    For my RV, I installed a 220 watt solar panel on the roof. Designed a 2-stage microcontroller dump controller, which allows a preset user changeable window of operation.
    I set it for 12.9v and 13.4v window....it boots up on solar panel voltage, shuts off after sunset. The panel is default in parallel (NC contacts of a controlled relay) with the battery, charging. When the upper window limit is reached (13.4v) a first stage dump relay is thrown (a 12v diesel glow plug in the 6 gallon water heater drain plug thread). It dumps till the lower voltage is reached-i.e battery still full voltage) The dump heater is limit controlled by a surplus water heater thermostat tank mounted switch-no boiling over. There is a 2nd stage relay which is thrown if a 10 second timeout trips due to charging voltage still exceeding the upper 13.4v window voltage. This is wired across the existing 12v heater in the 3-way fridge. Gives priority to dumping. During the day, with just the fantastic overhead fan on low speed as a load, the dump is operating almost 60% of the time to the water heater. On a really sunny day the fridge gets power too.

    This week I will revise the system....parallelling a solar panel with a 33v open circuit voltage, to a 12v battery bank loses lots of available power. Will insert a DC-DC converter in series to swap current for voltage, roughly doubling the output current.

  7. #17
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    Oct 2014
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    Cool

    My Newbie 2 cents.

    On some solar controllers there is an indicator light (full, charged, etc.) which you could tap into to activate a relay which would then transfer that "dump load" to a box fan heater with a thermostat or a separate water heater with a thermostat.

    If you don't have that indicator light as previously mentioned, why couldn't you have a 2 or 3 pole relay and think of it like a IF/THEN statement. If my battery bank reaches X volts then "toggle" and send "dump load" to secondary device.

    Heck you could even have it charge up your vacuum cleaning robot and come home to a clean house! Obviously, there are many other uses and I’m not getting into the details since there are SO MANY variables out there. Ultilizing a voltage sensor module from Arduino or a Raspberry Pi are super easy and in expensive. EXAMPLE: http://www.emartee.com/product/42082...o%20Compatible

    My moto “KISS”.

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