Immersion heater controller - Page 1
Forum section: electronics / general

author: oliver602
author_rank: Regular Contributor
timestamp: October 10, 2022, 12:07:59 am
content: I'm looking for an immersion heater controller that I can connect to some home automation software that allows you to control the power to the element.I have solar PV and excess energy is diverted to the immersion heater using a Solic 200. I have the immersion heater connected to that through a big relay and an energy monitor. The immersion heater doesn't do a good job of heating the whole tank, it just makes the top boiling hot. This is the problem I want to solve.Home assistant will turn the relay off after 3kw/h so the immersion does not heat the whole tank to scalding temperatures.I want to connect a temperature sensor to the pipe coming from the external immersion heater and control the power to keep the temperature in check. I considered using the relay on perhaps a 15 minute duty cycle to do this but that sounds like a bad idea.Is there something I can use to control the power, that's not an SCR dimmer?Or is there another way of solving this problem? besides replacing the water tank and immersion heater.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 10, 2022, 12:53:42 am
content: " it just makes the top boiling hot. This is the problem I want to solve."FYI domestic household hot water heaters in the US use two heating elements exactly for this reason. One about 1/3 of the way down from the top and the other about 1/3 of the way from the bottom.It's been so long since I worked on one that I don't remember if they use separate thermostats but I'll say that it's likely. I'm sure that someone will chime in that will will know the answer.

author: mikerj
author_rank: Super Contributor
timestamp: October 10, 2022, 08:35:35 pm
content: As Mr Electron says, you need a longer heating element. The short elements are designed to just heat the top of the tank for "boost" operation when you don't want the expense of heating the whole tank just for e.g. a quick shower. Dual heating elements were popular at one time, one for full tank heating, the other just for boost and each element would be paired with it's own (long or short) thermostat.If you can't change the element for some reason then you will need some way of circulating or stirring the water in the tank whilst it's being heated.

author: fourtytwo42
author_rank: Super Contributor
timestamp: October 11, 2022, 09:14:52 am
content: Quote from: oliver602 on October 10, 2022, 12:07:59 amWhy have you added this "big relay and energy monitor", they are not required in a Solic 200 installation ?Quote from: oliver602 on October 10, 2022, 12:07:59 amThen surely the solution to your problem is to adjust the immersion heater thermostat, or is it faulty ?As mikerj pointed out you may need to understand your immersion heater more, for example it's element length.

author: oliver602
author_rank: Regular Contributor
timestamp: October 11, 2022, 06:58:46 pm
content: Quote from: fourtytwo42 on October 11, 2022, 09:14:52 amI added the relay so I can turn on and off the immersion heater using home assistant. If the thermostat is adjustable, it is not accessible because of the way it has been installed. I have some understanding of immersion heaters. I can't fit a long element to my tank. Adjusting the power to the element would let me heat the top of the tank fast, or heat the whole tank to a more moderate temperature although a lot slower than with a long heater element. I don't want to spend the money to replace the water tank. Being able to control the power to the immersion heater isn't necessary, it's just a project I want to try.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 11, 2022, 09:59:34 pm
content: I'm a little confused. You say that you can't fit a long heating element but then say that the tank heats slower with a long element. Can you fit a longer element or not? Or do you just not want to?If you can't or won't fit a longer element then I suggest adding a pump and recirculating the water from the top of the tank to the bottom, or vice versa. Only having hot water in the top of the tank would not be acceptable to me. Regardless of where the heating power was generated or how it was controlled. It sounds to me like this is a more immediate problem than tinkering with the control circuitry.FWIW I accidentally burnt out one of the two heating elements in my WH one time and it's surprising how much the hot and cold water will not mix."If the thermostat is adjustable, it is not accessible because of the way it has been installed."What? The thermostat needs to be accessible! For a lot of reasons including safety. I don't know about where you are but I'm pretty certain that in the US that would be a building code violation. Maybe you should consider removing the tank and having it reinstalled correctly. While you're at it, put in a long heating element or a second element or whatever is needed to make the WH work as it should.

author: oliver602
author_rank: Regular Contributor
timestamp: October 12, 2022, 12:11:31 pm
content: Quote from: Stray Electron on October 11, 2022, 09:59:34 pmThe short element can heat the whole tank but it takes longer. Your right, a long element would be the best solution.QuoteThere is nowhere to fit a long element on the tank. There is only an external short element and it's fitted level with the bottom of the tank, that's why I can't access the thermostat. Maybe it was installed upside down?It was never a really a problem because we always heated the water with an oil burner. The immersion heater was never used until we had solar PV installed.A pump sounds like a good solution. Even though the immersion heater is at the bottom of the tank, the top can be 80C and half way down is cold. Still resisting getting plumbing done.

author: mikerj
author_rank: Super Contributor
timestamp: October 14, 2022, 01:56:08 pm
content: Quote from: oliver602 on October 12, 2022, 12:11:31 pmOk that's quite different to any hot water tank immersion heater I have seen, they are normally mounted in the top of the tank with the elements pointing down. If the element is at the bottom of the tank it's a bit surprising to me that that the water isn't being heated fairly evenly via convection, as the coldest water will be at the bottom.