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I have a basic knowledge of electronics and an even better knowledge of film photography.

I'm looking to create my own heated water bath with a thermostat that will allow me to adjust the temperature of the water (Min 21c - max 38c temp) for different use cases in heating film developing chemicals within bottles in said bath.

I am looking at using a washing machine heat element (Specifically, a 230V 1300W Hoover/Candy Part number 41042459)

Example heat element

I have then sourced a thermostat that I will rewire to use the existing Temp sensor in the Washing machine element (Instead of the flimsy little one).

Thermostat

The thermostat is rated at 110 - 220vac.

My first question is:

If I wire the thermostat to use the same power supply as the element, will the 230V heating element burn out the thermostat because of the rating of the thermostat?

My second question is:

Would I run the earth from the mains directly to the Heat element as the thermostat does not have its own ground? or would I be required to source a thermostat that has a ground (If that is a thing). I want to be certain that if any electrical leakage is present from the element due to degradation or defect, I wont end up cooked if I place my hand in the water bath to retrieve the bottles.

Just to add, I don't intend on using anything that will likely kill me (Water, electricity and lack of knowledge) so my plan is to build this thing, and then ask for a professional electrician to look at it and confirm that it is safe to use before I entertain the idea.

Any help on making my idea become a reality would be greatly appreciated.

Update: I forgot to include the RCD in my initial post, and was looking to source a 10mA RCD RCD that will be fitted to the appliance as it would need to be portable. I was looking at the following. Although, the use of a sub-distribution (Which I'd pay a professional to do) for my lab would work really well in one of my basins and has given me something else to work on

nizzlebizzle
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  • Do you have an RCD circuit for this? – Spehro Pefhany Apr 05 '23 at 14:08
  • @SpehroPefhany Apologies, I forgot to include the RCD in my initial post, and was looking to source a 10mA RCD that will be fitted to the appliance as it would need to be portable. [Link](https://www.ebay.co.uk/itm/403517700022?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=6cadgfw7qp2&sssrc=2047675&ssuid=CIX6NqoDRMi&widget_ver=artemis&media=COPY) – nizzlebizzle Apr 05 '23 at 15:07
  • Just how much water will be in your heated bath? How quickly do you need to bring it to the target temperature (and from what starting temperature)? It seems like you could get away with something designed for a smaller volume than a washing machine. I suggest doing the thermal calculation before worrying about the electrical design. – Theodore Apr 05 '23 at 15:36
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    A side note: the market is flooded with cheap and readily available water heaters for sous vide cooking. This is a reliable, safe and affordable solution for all the non-tinkerers out there. – Vladimir Cravero Apr 05 '23 at 16:02
  • @Theodore Good question. I had calculated that to heat 9Ltrs of Water at a starting Temp of 16c to reach a maximum end temp of 38c with a 1300w element would take 11 minutes. I moved onto the washing machine element as it meets the requirements nicely (includes earth and temp sensor within the same fitting, and something like a 2 or 3 kw element for an immersion heater would be overkill for the volume I'm looking to heat. – nizzlebizzle Apr 05 '23 at 16:03
  • @VladimirCravero Thank you for the suggestion. for home developing, a sous vide would be great, but this is required for a more permanent and frequently used solution, and would have more reliability and be more cost effective in the long run. – nizzlebizzle Apr 05 '23 at 16:05

2 Answers2

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Answer 1: The Temperature controller has a 10A relay inside and if you use the heating element at ~230V, then the current will be 1300W/230V = 5.65A and it will work. The relay will not burn through.

Answer 2: For the heating element the ground is necessary, but not for the thermostat, because this has a insulated housing.

The power line of the heating element must have an RCD, you must be sure that this exist!

I use separate 10mA RCD (HAGER ACS916D) for my bath. You can also install a separate sub-distribution in your photo lab and install an Fi there.

Hint: You can paint the circuit so how you want to connect the part with each other and we can help you with it. In Germany it is right now not easy to get an electrician, because many people want to use PV-modules right now and have to change the electrical system, so the people will not find someone, only for next year are free places. If you can prepare 50% or if you can 90% of the work, then the bill would be lower too.

MikroPower
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  • Thank you for your reply. Apologies, I forgot to include the RCD in my initial post, and was looking to source a 10mA RCD [Link](https://www.ebay.co.uk/itm/403517700022?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=6cadgfw7qp2&sssrc=2047675&ssuid=CIX6NqoDRMi&widget_ver=artemis&media=COPY) that will be fitted to the appliance as it would need to be portable. I was looking at the following. Although, the use of a sub-distribution (Which I'd pay a professional to do) for my lab would work really well in one of my basins and has given me something else to work on. – nizzlebizzle Apr 05 '23 at 15:03
  • @jsotola Apologies, I have updated the Question. Thank you. – nizzlebizzle Apr 05 '23 at 15:57
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The element will draw about 6A and the temperature controller relay is (apparently) rated at 10A so it shouldn’t immediately burn out. It might not last longer than a few weeks of 24/7 operation though, depending on the quality of the relay they used. It would be better to have the internal relay work as pilot duty for a larger relay, contactor or SSR (selection of such is outside the scope of this answer).

You need a solid earth to the heater shell. I can’t speak to the electrical or fire safety of the controller. The heater is pretty much orthogonal to the controller in terms of shock safety since it receives full mains voltage. A (valid) UL or CSA file number on the controller would give one some confidence that (say) the front panel is safe to handle. If the heater is a genuine OEM component it should have valid approvals. Since you’re coming into contact with the water a RCD (GFCI) should be used.

Incidentally, from a system pov, you should protect against the possibility of the controller, sensor or output relay failing and maintaining heat on. Make sure that cannot cause unacceptable property damage or injury to any living thing.

Spehro Pefhany
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  • One way to protect against that is by adding another thermal cutout into the circuit, to break the circuit if the temperature is way too high (say, 50 degrees). Is this a suitable form of protection? – user253751 Apr 05 '23 at 16:29
  • Yes, a mechanical thermal cutout or one-time thermal fuse would be suitable as it’s a completely independent safety device. – Spehro Pefhany Apr 05 '23 at 17:27