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limiting a heating element in a water heater?

eddie_meltzer

Mar 21, 2021
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hey.
i really need to limit the power to a heating element for a water heater. its running on mains 230v,50 Hz. northern europe.
i need it to not quite boil, tho its not very exact.
i already have some 2w-33k and some .5w-1M resistors. is that something i can use after connecting them in series or something?
i know little about this but i promise to be very careful. please help me.

thanks,
 
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Alec_t

Jul 7, 2015
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i know little about this
Enough to be dangerous, it seems. :) Don't mess with mains voltage unless you are aware of and accept the risks, especially in view of this being for a water heater.
Unless your heater is very low wattage those resistors are unlikely to be useful for this project.
A thermostat is what you need. Various types are commercially available and the type will depend on the shape/characteristics of the heater.
 

Minder

Apr 24, 2015
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What type of water heater is it? All the ones I have been involved in has a thermostat fitted for safety reasons, if nothing else.
 

Externet

Aug 24, 2009
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A way to limit the heating current is to connect an incandescent 230V light bulb in series. The higher the wattage of the light bulb, the more heating your element will provide.
If the wattage of the heating element is around 500 watts or less; a dimmer rated for that is your most convenient option.
1674589909006.png
 

Bluejets

Oct 5, 2014
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A way to limit the heating current is to connect an incandescent 230V light bulb in series.

It might be "a way" but as mentioned above it is not "the way" .

"The way" is a thermostat, usually set below 70 degrees AND an over temp cut out (both in the same unit)
As an added precaution against the possibility of "all fail", an over temp/over pressure relief valve must be fitted to at least the top end of the tank itself.

https://ringhotwater.com.au/product/electric-hot-water-thermostat-st12-70k/

https://www.reece.com.au/search/val...-temperature-relief-valves-c235/?pageNumber=1
 

ivak245

Jun 11, 2021
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"Not quite boil" means it would be operating at over 90C. Domestic water heater thermostats have an over-temp of around 75-80C. How much water do you need? You can buy stainless steel urns which will give you a lot of boiling water, and these have a variable thermostat already fitted, so you will be able to vary the temp below boiling.
 

davenn

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Sep 5, 2009
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Domestic water heater thermostats have an over-temp of around 75-80C.

Exactly ... they are set at a temp that will not produce scalding to skin. For Australia. 75 - 80C is higher than legally allowed
it's more around the 65C mark
 

eddie_meltzer

Mar 21, 2021
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Enough to be dangerous, it seems. :) Don't mess with mains voltage unless you are aware of and accept the risks, especially in view of this being for a water heater.
Unless your heater is very low wattage those resistors are unlikely to be useful for this project.
A thermostat is what you need. Various types are commercially available and the type will depend on the shape/characteristics of the heater.
thanks.
its just a steel pot im making my self. no pressure involved. its about 750w. its like the elements in the waterboiler things for tea. but brazed onto another pot.
what do i need to control temp digitally? these things cost so little thses days that i might as well...
any ideas?
 

Externet

Aug 24, 2009
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The knob on the side will limit the temperature :
1674665026968.png
1674665205825.png

Plenty of coffee makers with adjustable thermostat, even in used stores or dumpsters.

The thermostat controls are very inexpensive :
-
--> https://www.aliexpress.us/item/3256804495707246.html?spm=a2g0o.productlist.main.17.5202CZtACZtAlj&algo_pvid=51173271-abe2-431e-9c8f-404e7813f283&algo_exp_id=51173271-abe2-431e-9c8f-404e7813f283-8&pdp_ext_f={"sku_id":"12000030083661048"}&[email protected][email protected]!12000030083661048!sea&curPageLogUid=wFysMNzDYr6K

Edited. By some reason the link split in two sections. I was unable to fix.
 

eddie_meltzer

Mar 21, 2021
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The knob on the side will limit the temperature :
View attachment 57765
View attachment 57766

Plenty of coffee makers with adjustable thermostat, even in used stores or dumpsters.

The thermostat controls are very inexpensive :
-
--> https://www.aliexpress.us/item/3256804495707246.html?spm=a2g0o.productlist.main.17.5202CZtACZtAlj&algo_pvid=51173271-abe2-431e-9c8f-404e7813f283&algo_exp_id=51173271-abe2-431e-9c8f-404e7813f283-8&pdp_ext_f={"sku_id":"12000030083661048"}&[email protected][email protected]!12000030083661048!sea&curPageLogUid=wFysMNzDYr6K

Edited. By some reason the link split in two sections. I was unable to fix.
??? i dont get it. is there a reason why i cant do what i want to?
 

Minder

Apr 24, 2015
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What type of heating element is it? Rod immersion type?
It may have been more economical to obtain a immersion style with the thermostat pocket fitted.
Fitting a separate one afterwards can be costly.
 

ivak245

Jun 11, 2021
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If it is not a sealed container or system, you could get one of the cheap electronic temperature controllers from Ebay, and attach the sensor inside the vessel. Just make sure the relay on the controller can handle the current, otherwise use the relay to control a contactor.
 

Bluejets

Oct 5, 2014
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For Australia. 75 - 80C is higher than legally allowed
it's more around the 65C mark

That depends on purpose...if for comnmercial dishwasher, also other special purposes, then high temp remains.
If for hand washing etc. same place, then there , as in domestic, outlet temp is regulated down by a mixing valve introducing cold water to a set constant lower temperature. Heated temperature remains the same, around 70 degrees C.

Check the adjuster maximum setting on the thermostat in the picture in #5 above.
 
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kellys_eye

Jun 25, 2010
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Get a thermostatically controlled regulator - as per the advice above, they are cheap and readily available. You cannot just 'lower' the input power as this would only mean the water taking longer to reach boiling point - which it will always do if there is nothing to switch the power off when it's reached the desired operating temperature.

Some water heaters (tank) have a thermostat mounted on the outside - measuring the water temperature through the body of the tank. These are the simplest types and a wired in series with the heating element and you simply 'dial' the required water temperature on the front face of the controller.

An 'open vessel' is the safest way or, as above, some for of safety cut-out for over temperature/pressure is ESSENTIAL.
 
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