Alternative suggestions for a Dump Load

2Guido
2Guido Solar Expert Posts: 62 ✭✭
in Solar Beginners Corner #1
Came home today after very sunny skies and found my inverters all shut down from over-voltage (33.5 v) The dump load light was on the controller (Coleman 440) but I had disconnected the dump load weeks ago figuring I would never generate enough power to use it. So I would like some alternative ideas for loads to dump into instead of wasting the current into resistive banks. My thought was to relay it to a hot water heater element. Any other suggestions would certainly be welcome. Is there a problem using a 110 volt water heater element for dumping the 30 volt load into ??? or is this a plain stupid idea ??
Thanks Guys !!!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Alternative suggestions for a Dump Load

    Nope--Not a problem at all... You can use 120 or 240 VAC water heater elements of different wattages. For example, a 240 VAC 6000 watt element:
    • P=V2/R; R=V2/P
    • R= 240v2 / 6,000 watts = 9.6 ohms (approximately--Resistance can vary with temperature)
    • P=V2/R= 12v2/9.6 ohms = 15 Watts
    • P=V2/R= 30v2/9.6 ohms = 94 Watts
    • P=V2/R= 48v2/9.6 ohms = 240 Watts

    So, while an electric water heater element is a handy off the shelf solution--You may have difficulties in finding one that will pass enough current at low voltages to be much use.

    You could, for example, get a cheap MSW inverter and get a 1,500 watt ~ 120 VAC element... That would work.

    But, as you can see, things "happen", so with a dump load controller, the NEC would require two independent controllers to prevent over voltage/dangerous battery failures (i.e., boiling dry, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2Guido
    2Guido Solar Expert Posts: 62 ✭✭
    #3
    Re: Alternative suggestions for a Dump Load

    Ahhh...ingenius...run the dump load into an inverter powering a heavy load such as an AC unit to cool the small room housing the batteries and inverters...Good Idea....Are you familiar with an MSW inverter that would turn on from an off state without power so I would not have to physically power it up ???
    You're the best !!!

    Just had another thought..if the voltage is already overcurrent, then the inverter would not power up ???
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Alternative suggestions for a Dump Load

    I would have thought that most "inexpensive" MS Inverters would turn on if there was DC power (those with push button on/off/electronic switches may not).

    There are inverters with remote on/off external inputs... But they are probably more expensive versions (For example, the MorningStar 12 volt TSW 300 watt inverter has a remote on/off switch input).

    The mechanical relay in the Coleman may be heavy enough to cycle the input for an MSW inverter--But you would probably want to ensure that it could be set up for something like a 5 minute on/off cycle so that the system does not "chatter".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
    Re: Alternative suggestions for a Dump Load

    If you already have 3kW prosine inverters why not use those instead of buying another one? I.e. you connect the water heater to your normal load circuit and just turn it on when there's surplus power. Can the coleman be configured to just turn on a relay when it's meant to start dumping? Or do the prosines themselves have programmable relays?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #6
    Re: Alternative suggestions for a Dump Load

    I believe the Coleman can be configured as either a shunt or a series regulator--I am not sure about the details (on/off times, hysteresis, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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