Water Heater reverse engineering

[RonRN18]

I realize that this post is probably a little odd for a large majority of folks here but I'm hoping to find someone that shares my hobby and hopefully much more knowledgeable than I to collaborate.

I had the circuit board of my 2019 Highland Ridge/Mesa Ridge 2410RL's hot water heater go bad on me the weekend before last as I was camping. The hot water heater is made by Dometic/Atwood and is a gas & electric hot water heater. It appears this is one of the most prolific hot water heaters out there on the RV market. I didn't know much about my hot water heater at the moment and have since learned quite a bit more of how it works. I have already fixed the water heater but this morning, as I was driving in to work, I started brainstorming on how to make an after-market improvement in a replacement circuit board.

I am NOT an electronics engineer, although that was my major my first year in college (I ultimately became a Registered Nurse). I work on electronics projects as a hobby. As I was deducing how the circuit board works, I realized that while it was ingeniously built, it was ingeniously made stupid. I'm sure that the reason it was ingeniously made stupid was cost related and realizing most people just "want it to work." I'm not one that likes stupid solutions to problems and likes to complicate things for the better; maybe, in a way that is stupid too.

My biggest gripe with my hot water heater is that it was designed to be WAY too hot. I learned that it has a fixed thermostat to cut off the hot water heater to attempt to keep the water at about 140F. I have learned that Dometic/Atwood makes an adjustable thermostat, which I purchased and installed, but that doesn't really solve everything either. Both the OEM thermostat and the adjustable thermostat are still relatively dumb. They are mechanical devices that either open or close a circuit, using I presume some type of factory calibrated bi-metal strip. My assumption is that when the temperature of this bi-metal strip reaches a certain temperature, it breaks contact and opens the circuit. Again, my assumption is that this bi-metal strip must cool down to a point for the circuit to close again. My initial "lightbulb" moment came when I thought I would like to replace this control thermostat with an electronic thermistor and a micro-controller. When I thought of a micro-controller, my first thought was an ESP-32; this would allow for control/monitoring via WiFi and/or Bluetooth and could be made to work with a smartphone app. The ESP-32 is cheap and relatively easy to program, but there may be others.

At this point, my imagination started to take off with all the possibilities this would add, but then I came back to how to actually accomplish this. I would like to make the form-factor of my controller physically fit in the spot of the original circuit board and I would like to continue using the same wires (essentially) for the same purpose. This is important so that it would be an easy conversion for someone else interested or to replace it with the original if it were to fail. I would like to make this easy for someone with NO knowledge of how it all works to turn the hot water heater on via either the original gas or electric switches, but also allow (a trusted) someone to tweak the temperature settings. I have learned from building out IoT home automation stuff that you need to allow for the un-initiated to control basic functions.

I'm not sure if this idea will ever come to fruition but I'm hoping that someone out there with hopefully more knowledge than I, can either help or take off with the idea. At this moment, my idea is not particularly commercial in nature, but more as a hobbyist-driven platform. My thought is that just creating a physical prototype is the first step, and then let the software side of things expand as seen fit.

My expectation is that using a thermistor instead of a mechanical thermostat will allow for tighter control of the temperature of the water. Future improvements may include remote temperature probes to fine-tune the heating of the water. I know that high-end RVs may already have such features, but I would like to bring "the smarts" down to entry-level RVs and enthusiast without it being too expensive.

[Old-Biscuit]

Howdy Ron

An IRV2 member has done it..... BobJones
Check out ALL the discussion, information, testing, components, results

https://www.irv2.com/forums/f115/my-...on-523022.html

[Soppy]

It's a neat idea , but all you would be replacing is the snap disc thermostat. The circuit board is required to ignite and monitor the flame for use on propane.
I installed a RANCO electronic thermostat on my domestic HW tank in my house. It allows for easier adjustment of the temperature as well as the cut in /out differential .

[Mudfrog]

I agree, I definitely like having an adjustable thermostat. Ours didn't come with the electric heating option so I ended up installing one myself. It came with an adjustable stat (mechanical) that I set around 120°F. Not sure what the differential is but it maintains temperature just fine.

Imo, attempting to attain too tight a control of temperature is not needed and could likely lead to a short cycling situation. As far as bluetooth-ing or wifi-ing, I'm not interested.

[Old-Biscuit]

Reason for 140*F (Atwood) ---130*F (Suburban) is due to small size of RV Water Heaters

Hotter the initial water temp is the 'more' hot water availability for end user (mixes cold with hot)

Atwood has an Optional 130*F T-stat
And the Atwood adjustable can be set from 110*F - 150*F
*although that adjustable IMHO is junk...flimsy stand off bracket, exposed to elements/corrosion on contacts, not very precise temp settings etc

ME....I'll stick with the OEM 140*F
Turn water heater ON....use it and let it reheat when temp drops to 110*F
****Kinda like residential water heaters...turn them on and use the hot water. No fiddling with, tweaking, no micro processor etc

Simple......

[Fiesta48]

I've thought about using two 12v relays, one for gas, one for electric. Eliminate the OEM electronic circuit board, that went out after less than 2 years.
Then I found for the same price as the OEM board one that is made with better HD parts, Dinosaur Electriconics. 3 YEARS later it's still working fine.
I've also added a timer to have the heater come on twice a day for showers, washer, dishwasher. Into the control circuit at the switches.
I've eliminated the mixer valve in the back. Added HD water supply lines. Added LEDs at the switch so I know when they are ON.

[mbridinger]

I went the opposite direction....low tech. I now have a completely manual heater that has an adjustable thermostat.

[pasdad1]

This concept was done already in a residential water heater years ago with poor results. I remember seeing them for sale years ago, and my friend had one.

Essentially, like you said, it used an electronic circuit to control the heating elements, instead of mechanical thermostats. This additional control afforded some cool features, like anti-freeze protection (just energize the heat enough to prevent freezing in an unoccupied house).

The implementation was VERY problematic however. EVERY circuit board failed within a short time, so much so, that the manufacturer had to redesign it, and start giving people a “lifetime” warranty on the new circuit boards, where before they were just covered by the standard 2 year warranty.

If you go this route, make sure to “over design” it, with many redundancies, and a fall back back to mechanical thermostats, if the electronics fail.

[Old-Biscuit]

Originally Posted by Fiesta48

I've thought about using two 12v relays, one for gas, one for electric. Eliminate the OEM electronic circuit board, that went out after less than 2 years.
Then I found for the same price as the OEM board one that is made with better HD parts, Dinosaur Electriconics. 3 YEARS later it's still working fine.
I've also added a timer to have the heater come on twice a day for showers, washer, dishwasher. Into the control circuit at the switches.
I've eliminated the mixer valve in the back. Added HD water supply lines. Added LEDs at the switch so I know when they are ON.

Hopefully swapped out that 155*F T-stat to 140*F or even the 130*F T-stat so folks do not get scalded

[Fiesta48]

Yes 130F Thermostat. Saves energy too.

[Old-Biscuit]

Originally Posted by Old-Biscuit

Hopefully swapped out that 155*F T-stat to 140*F or even the 130*F T-stat so folks do not get scalded

Originally Posted by Fiesta48

Yes 130F Thermostat. Saves energy too.