Using existing thermostat for diversion water heating

northernsunnorthernsun Registered Users Posts: 1
I'll be installing a 20 gallon hot water tank in my off grid cottage this summer. My plan is to replace the existing element with a 900w 24v dc element connected to the DC side via a SSR. Pretty standard setup so far. My plan is to run the aux 1 output from the Midnite classic through the stock AC thermostat on the hot water tank in series with the SSR. My thinking is that since its just 12v at very low amps coming out of the aux there should be little to no chance of arcing or pitting. Has anyone done this or can anyone see a problem with this setup?

Thanks in advance,

6x Hanwha Solar G4 305watts
Midnight Solar Classic 150 w wizbang jr
4x 6v crowm 395 ah
Xantrex SW4024
location - Southern Quebec


  • mike95490mike95490 Solar Expert Posts: 8,030 ✭✭✭✭
    You may need some snubber circuit, to absorb any inductive kick from the cables.
     is Aux 1 a voltage source, or dry relay contacts ?  if dry relay contacts, you need a 12VDC source too, to trigger the SSR
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  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    SSR's generally need a good sized heat sink (they can get hot and fail).

    You need a thermal/pressure relief valve (normal for most water heaters--If the thermostat or SSR fails, you don't want the tank to over heat/over pressure).

    A tempering valve is generally used to take the extra hot (scalding) water and mix it with cold water for safe temperature at the sink.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,135 ✭✭✭✭
    Since you are using much lower voltage (240V->12V)  and much much lower current (whatever the SSR input draws), using these AC rated contacts for DC should be fine.  
  • westbranchwestbranch Solar Expert Posts: 5,114 ✭✭✭✭
    Don't know if you have been there , but the Midnite Forum has had a lot of recent discussion about using Aux 1 and 2 for DHW heating

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