I have a resistance (~3800 watts) to boil water. The idea is to control the power supplied to regulate the output water temperature. The voltage supplied is 230v.
What is the best way to regulate power in order to get always the same water temperature?

Any help will be much appreciated. Thanks.

 

First - optoisolator in order to live in the safe side. Second, best algorythm of driving would be here for certain a zero-cross driving. Some optos have an in-built thyristor (or symisthor aka triac) driver, thus just make what datasheet demands. Querry at Octopart may stand "triac optocoupler zero-cross". Of course, the search engines habitually (except my beloved Tor) are indexing Your seach history, thus with this querry phrase YOU probably shall have another count of results, but at my screen it gave out the 230 options. Enough, huh!? If too much, add the output current, voltage, speed or whatever. Ah ya, for T sensing in this large-innerce case where no any linearity is demanded, nothing is better than thermo-resisor - at least it is sensitive enough, thus You may escape the need to use any operational.

 

Great, thank you so much for your reply!
I am not experienced in power electronics, still have to research about the triac optocoupler zero-cross, but could you draw a diagram or circuit? Is possible to control the power by a microcontroller or analogue electronics then?
Thank you again.

 

The circuit stays in the datasheet. Datasheet stays at Octopart. Some ideas how it may look one may find as (for example) with ARM
http://www.bristolwatch.com/ele2/zcnew.htm
or
https://forum.arduino.cc/index.php?topic=314773.0
without, I mean the the basic version
https://electronics.stackexchange.com/questions/304366/zero-crossing-detection-and-light-dimmer
and some "dummy" lead-in tutorial at
https://www.electronics-tutorials.ws/blog/optocoupler.html

The thermistor part may look like in this picture
or being built like a bridge/halfbridge in no-ARM version straight to the Optos input. Logically, then resistor will have far less ohms.

http://www.giangrandi.ch/electronics/ntc/ntc-voltage-divider.png

 

The type of control you need depends upon how accurately you need to control the water temperature.
But if you are boiling the water, then how will controlling the temperature help?

 

Thank you Janis59, I think it will be very useful.

Crutschow, the temperature doesn't need to be very accurate, just to get ~100 degrees for 10 seconds approximately. The best way to do it, means to me, simple and efficient.

 

wow, wow, wow, what the 100C in 10 seconds? It means You must have a through-flow system but not a boiler. At least at my location boiler means a giant bundle never less than 40 liters but sometimes even so much as 240 liters. And those fast systems like Checzh-made Through-Flow Water Warm-up devices within half-price of boiler or even a third-price. Why it seems touchy for me? Just some 20 years ago everyone electrician was teached-in, that such system for douche application is plainly suicidal. And sad, but it was truth. Nowadays DIFFERENTIAL CURRENT FUSE (Differential safety Relay, Differential Automat) are at last invented and became a mass-product for some minor 20 Eur with small tail at 20-32Amps. Last week I got one to buy for my sister throught-flow device, 20A. I had choices or 16 Eur for China out-of-ass pulled automat or well recognized EU producer ETI made one for 24 Eur. I choosed the last-one. So, this is device what ABSOLUTELY MUST MUST and one more time MUST be installed before You ever touch to the water made by this method, or even just think about to touch it. Please, keep Your soul alive!
Example of fuse looks like (sorry, one of most expensive in markets, but trustable) https://sg.rs-online.com/web/p/residential-rccbs/5401622/
And this is how those Chezch wunderwaffe looks like http://santehnikasparadize.lv/veikals/lv/?route=product/product&product_id=1507231882

 

Yes, I forgot mentioning safety, that is the most important! Even more, if I don't have much experience with power electronics...
I think you are right, through-flow system.
About safety, If I understand you, do I have to install a differential current fuse in my prototype, apart from the differential that new buildings already have installed?

Thanks!

 

What are the water use conditions? Do you use a specific amount of water each time?
Is there an addition, or a change in the primary volume of water ... that is being used, this includes change in temperature?
If usage conditions are reasonably constant, the electrical power requirement could possibly be constrained to turning on the resistance heater for a specific time interval, when boiling water is required.

 

We could say that the amount of water each time is constant, what can change is the water temperature before heating it

 

The link referred to below is a calculator that tells how many watt-hours of energy are necessary to heat a substance (choose liquid water) from one temperature to another. It might be described as slightly 'touchy', but does seem to produce numbers of some reasonable magnitude. Maybe it can provide an estimate of how long your heater will need to be turned on, in a static situation.
https://www.omnicalculator.com/physics/specific-heat