Controlling the power of a 2.25kW heating element... NOOB

Hi people

I’ve got a little hobby project where I need to (quickly) heat up 15L of water(ish) then tune down the power of the heating element to control the vaporisation rate (steam) of the liquid.

I’ve bought a nice 2.25kW heating cartridge: http://www.jevi.dk/en-GB/Products/Heating-of-liquids/Immersion-Heaters/

First I thought of doing a simple on/off-regulation with a relay - but I’m affraid that this would result in vapor surges which would be bad for the application in mind.

How do I do it?

Please keep in mind that I’m a mech. eng. Therefore, my knowledge of electrical circuits and components is somewhat limited - so please use small words and big letters… :slight_smile:

Use a zero-crossing turn-on solid state relay (SSR) and burst-fire control, which is effectively PWM at a very low frequency (say 1Hz).

Could you use the 2.25kW element to rapid heat the water but then switch to a smaller element to maintain the steam. The size of the smaller element would depend on how well insulated the liquid is, how fast the steam is used and how/if the level is topped up during use.

DC42: I’ll look into that… Not quite sure what the zero-crossing and burst fire means (big words and all) but google is my friend. However, at such a low frequiency would’nt I get the same problem with steam surges? Thx for your reply.

Riva: Two problems with that solution. The heating elements are quite expensive ($150 or so). Secondly I have a limited space in my boiler. I’ve estimated the heat loss to around 400W based on boiler material and ambient temperature- but I’m unsure of how much steam I’ll be needing - so I would like to be able to regulate it when I run in my apparatus. At least in the range 400k-2000w. thx for your suggestion

Handberg: DC42: I'll look into that.. Not quite sure what the zero-crossing and burst fire means (big words and all) but google is my friend. However, at such a low frequiency would'nt I get the same problem with steam surges? Thx for your reply.

Unless your heating element is tiny (which it can't be if it is 2.25kW) then the thermal capacity and internal insulation of your heating element will smooth out the heating power if the burst frequency is 1Hz or so. If you boil an electric kettle and then turn it on and off, you will find that it takes several seconds to react. You can use a slightly higher PWM frequency if you don't need such precise control, e.g. using 50Hz mains then 1Hz burst frequency gives you 1% resolution, 2Hz gives you 2% resolution, usw.

DC42: Okay, I think I understood that. Good point about the capacity and insulation - It makes the project a lot easier (and cheaper). I think I’ll do it that way. Thx for the reply

Bear in mind that to carry 10A, your SSR may need a heatsink. Rapid has a good range of SSRs, see http://www.rapidonline.com/electronic-components/relays-solenoids/solid-state-relays/. You can also get cheap Chinese ones via ebay, e.g. SSR-25DA.

Thx for the links. One with a heatsink is on its way. :)

Though it is more advanced I would look at some PID software to control that element. Proportional Integral Derivative control is great at precision control of temperature. PID can be implemented with analog circuits or can be done digitally in software. There is some good info out there on PID control on the web. Check out http://en.wikipedia.org/wiki/PID_controller