Using existing thermostat for diversion water heating

northernsun · March 2018

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,

mike95490 · March 2018

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

BB. · March 2018

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.

https://www.homedepot.com/p/Honeywell-Thermostatic-Mixing-Valve-AM101C-US-1/202264710

-Bill

jonr · March 2018

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.

westbranch · March 2018

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 http://midniteftp.com/forum/index.php?action=unread

Using existing thermostat for diversion water heating

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