Diverting extra pv power to immersion

YerfYerf Posts: 65Registered Users ✭✭
Is there a practical way to switch on the immersion heater on a sunny day when battery bank soc is over 95%.

I am planning a setup of Victron venus gx which has a programmable relay, it also has a Modbus TCP gateway. Or perhaps off of the auxiliary on the mppt blue solar victron 150/70 charger.


  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Yes, it can be done. Midnite (another manufacturer) actually has a mode that controls the digital output to cycle a digital relay connected to a heating element ("waste not" mode?).

    I do not know anything about the Victron controllers--If they are programmable for this type of function, then it is possible. Use a digital relay (solid state relay) and also put another switch in series to turn off the heater when the tank is hot. Also, make sure you have a Temperature and Pressure safety valve on the heater. Typically, in the US, we have two element vertical water heaters. The top element is connected to 120/240 VAC, and the bottom element is sized and connected to your battery bus voltage (or, possibly an AC inverter to 120/240 VAC).

    Another method is to use an inexpensive dump mode controller (such as Schneider's Cx0 series PWM controllers). When the battery is "full", the Cx0 is configured to turn on and drive a heater (up to the rating of the controller). The MPPT controller is programmed to absorb charge at a higher battery voltage, while the Cx0 controller pulls the battery bus voltage down.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • YerfYerf Posts: 65Registered Users ✭✭
    Ok cool. See what I can do. My immersion is controlled through a panel that controls the solar hot water system. It's pretty smart it will heat the water with the sun and then top it off with the immersion if desired temperature is not achieved.

    I'm going to have to find a way of signaling this panel in order to start the immersion if there is excess solar power. You would think these things would be easier these days with all these smart gadgets around.
  • Spence_McCallieSpence_McCallie Posts: 9Registered Users ✭✭
    edited November 2017 #4
    Your Victron 150/70 Controller has a programmable relay that can engage the heater when the battery bank goes to "Float" or to a specified voltage level. 

     Manual: https://www.victronenergy.com/upload/documents/Manual-BlueSolar-charge-controller-MPPT-150-70-EN-NL-FR-DE-ES-SE.pdf

    Page 9 shows your options for turning the relay on, Page 15 shows the setup menu, and page 22 shows the wiring. You will have to use an appropriate relay to engage the heater, because I'll bet the controller can't handle any wattage (seems like an alarm contact). As BB says above, it will discharge your batteries while it is on. I would probably try the specified battery voltage level. I would worry that you would immediately kick the batteries out of float when the heater engages. I would also set a minimum relay closed time in the controller (Page 15). That way you won't cycle the relay too often. I also agree that BB is right on the temperature switch. You can wire in a rising temp switch (switch is open when temp is above set point, 120 degrees for example) that would kick the heater off if the temp is too high. Here's one:


    I would wire it so: Power source -> FUSE! -> Victron Relay -> Temperature Switch -> Relay on heater. You may have to land a DC common somewhere on the heater relay.

    Make sure that your voltage is in line with the switch/relay. Most of these industrial things won't operate above 32V.
    Denver Area
    Off Grid: 1.2kW, 48V, Midnite Kid, Grundfos SQFlex
    Industrial design and automation.
  • YerfYerf Posts: 65Registered Users ✭✭
    solid state relay SSR-10DA SSR-25DA SSR-40DA 10A 25A 40A actually 3-32V DC TO 24-380V AC SSR 10DA 25DA 40DA high quality new
    (from AliExpress Android)

    Is this an appropriate relay?
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