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Diversion / Opportunistic usage - Point me in the right direction?

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  • Diversion / Opportunistic usage - Point me in the right direction?

    Can someone point me the right direction to research the feasibility / methods of only driving certain loads when the batteries are in float? IE water pump to the cistern, charge the battery in the hybrid car, electric water pre-heater, etc?

    Looks like possibly a relay controlled 240v subpanel driven off the aux output of the charge controller?

    Magnum MS4448PAE
    Outback Charge Controller

    Thanks,
    -Dwight
    Last edited by morgandc; 01-01-2018, 11:22 AM.

  • #2
    It looks like shedding load may be another option if I had a different inverter.

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    • #3
      I run a water pump during the day using cut in/out Voltage settings on the load terminal of the CC to a relay with 24V coil and 240V contacts, then to a 240V A/C Contactor

      From my inverter 240V supply i have a timer then through the contactor to my pump.

      The pump will run as long as the battery voltage has reached a preset level and cut out if the battery voltage drops to a preset level.

      If there is to much cloud it will cut out and not drain my batteries.

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      • #4
        There is not a lot out there for diversion and what is tends to be expensive. As said before a voltage sensing relay looking at battery voltage is a good indicator when to add a load. There are often more decisions that have to be made. There is a simple way to look at this. If you were in a room all day and could control everything with switches and meters, what criteria would you use. Pumps and compressors would need at least a minimum operating time and often prevention from hot starts. Heating space or water can be done proportionally so you use just that extra available. I n my system I use a cheap Arduino to make those decisions. If you are a junior sparky, the circuits and programming are fairly basic and can be learned quickly Programs can be written in fairly conversational English, if voltage is greater than and delay so many seconds. It has been interesting how many from different fields have been able to use this technology. It is an investment of less than $10 to find out. I run a pump a couple times a day. I check to see the battery voltage and what other loads are running. If suitable I run the pump for so many minutes. All my hot water is from excess solar. Panel voltage is constantly monitored. Under light loads the panel voltage rises. When it goes above the expected power point, energy is diverted directly from the panels to the heater. This avoids confusing the charge controller with an added load and saves inverter capacity for other uses. It is just a matter of figuring out what you would do if able to sit there all day and flip switches. It can be a lot of fun and greatly reduce the resources needed to be totally off grid. .

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        • #5
          You caused me to start looking for "smart breakers". Looks like we still aren't there, but lots of people working on them.

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          • #6
            Originally posted by morgandc View Post
            You caused me to start looking for "smart breakers". Looks like we still aren't there, but lots of people working on them.
            Square D makes a smart panel with circuit breakers that can be programed to shed load like lighting and receptacles in offices after everyone goes home. It isn't cheap but in the long run the company will save big $$ by using the load reduction feature.

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            • #7
              A little off topic, but look up Sonoff on ebay, amazon or whatever. These are wifi modules costing as little as $6 that can be controlled by your smart phone. There is a whole family of these including DC modules. They have a esp286 controller that is easily reprogrammed if you want to do something custom. A case, relay, controller, supply and shipped for that price. You can't afford to build stuff anymore. Great for turning stuff on stuff on before you get home and not wasting energy when gone.

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              • #8
                I heat the bottom 1/2 of my 40 gallon hot water heater with excess using my inverter an 120v to the lower element and stat. I run it off of the SOC Hi mode of my MidNite Classic 150 on Aux 1 using a SSR at the low voltage to hi voltage switch. Works pretty well as long as the suns is out. And when its not, I can flip over to AC and run the lower element long enough to heat the lower half of the tank. And I still have the top of the tank on 240v AC from the grid, so there is always some hot water.

                You can read what I did here. This was the end of a longer discussion and what I finally ended up doing.
                Last edited by Matrix; 01-02-2018, 03:14 PM.
                285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

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                • #9
                  A lot of good posts just tend to get lost in the volume. I think many people loose sight that 240V heater elements on 120V is a much better match in solar. The heating element is then one quarter of the rated output. Sure it has to run longer, but that matches up better with the time and amount there usually is to divert. And so much easier on the inverter. No need to get a bigger inverter just to heat water.

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                  • #10
                    Originally posted by PNPmacnab View Post
                    A lot of good posts just tend to get lost in the volume. I think many people loose sight that 240V heater elements on 120V is a much better match in solar. The heating element is then one quarter of the rated output. Sure it has to run longer, but that matches up better with the time and amount there usually is to divert. And so much easier on the inverter. No need to get a bigger inverter just to heat water.
                    Exactly why I did it the way I did with 120v. My 4500w 240v element runs at exactly 1045 watts on 117.5 ish volts and pulls about 9.5 amps. Perfect for my excess solar thru the inverter. You can buy DC elements at what ever DC volt (12/24/48) ... but why? If you have a large enough inverter, Just run it thru the inverter and buy an SSR for control and a 240v element to match your diversion needs.

                    Here is the conversion formula from 240v to 120v. Just insert any 240v element size you wish.
                    At 120v: 4500 (120v/240v) x (120v/240v) = 1125 w
                    The end watts will vary slightly due to voltage differences (mine is 117.2v) and resistance differences but it is really close.

                    Here is a list of common size over the counter 240v elements that can be used for 120v

                    2000 (120/240) x (120/240) = 500 w
                    3000 (120/240) x (120/240) = 750 w
                    3500 (120/240) x (120/240) = 875 w
                    3800 (120/240) x (120/240) = 950 w

                    It takes me about 4 hours to heat up the lower half of my 40 gallon tank to 160 degrees. I do it so hi so I have plenty of hot water at night. I have the upper element set to 138 degrees. So it never comes on as long as I get enough diversion to heat the lower (which actually heats the whole tank)
                    Last edited by Matrix; 01-02-2018, 04:07 PM.
                    285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

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                    • #11
                      Great thread! thanks for ideas!

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                      • #12
                        Originally posted by Matrix View Post
                        You can buy DC elements at what ever DC volt (12/24/48) ... but why?
                        Simple efficiency. Inverter ran at low levels can very inefficient. Even higher end models run around 90%. Improve efficiency, and you use less energy for the same amount of work.

                        MSEE, PE

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                        • #13
                          Originally posted by Sunking View Post
                          Simple efficiency. Inverter ran at low levels can very inefficient. Even higher end models run around 90%. Improve efficiency, and you use less energy for the same amount of work.
                          All very true. But for me the costs of the much larger copper for the 25 foot run and hi amps, the costs of the over sized SSR and (most imporrtantly) the concern about using a DC stat given the limited availability and even more the questionable origin, reliability and safty of DC stats, drove me to the AC inverter side. Just to many unknown variables for me.
                          285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

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