'Dimmer switch' for a 2.4 kw load

[Crumbling Nick]

I need something to control the rate of boiling in my brewing 'copper'. The vessel (recently bought) already has a thermostatic controller, but it doesn't work well enough for boiling. It's a lot worse than its predecessor which fell apart, but was still a compromise with the real requirement.

It doesn't need to be continuously variable. However I don't yet know how low the power needs to be, nor even whether a 'one size fits all' approach will work well enough.

The environment is inevitably somewhat steamy though locating relatively remotely is an option. I wouldn't expect to attach a device onto the boiler, so it doesn't need to be waterproof to the level of spillage or immersion tolerance.

Ideally I'd like an off-the-shelf solution. I'm not totally against a partial diy approach, but am certainly not competent to produce a device with electronics & mains in the same package for this envronment.

Any suggestions?

[Kim]

Theatrical dimmer.  They're usually 10A, sometimes 5A.  You can get self-contained one-channel units intended for followspots and the like.  Remotely controlled dimmers tend to speak either DMX512 (a serial bus) or a simple 0-10V analogue proportional control, which is eminently suitable for interfacing to homebrew (pun intended) control electronics.

Or a BFO variac.

Or roll your own thermostatic control with a microcontroller and a solid state relay.  Expect lots of tweaking of time intervals and hysteresis to get it to have the desired effect.

[aidan.f]

Really you should  use a burst fire mode for this, switching a proportion of full mains cycles to avoid harmomic interferemce . But I did not bother, just used a bfo diode for a simmer mode. Note - don't turn the heat down too much a rolling boil is required to achieve your hot break.

[Poly Hive]

On the brewing forums the oft suggested unit is this one: https://www.youtube.com/watch?v=30TvX1Zz1-Y

I use one for warming honey and it works very well.

PH

[Crumbling Nick]

Thanks for the reponses. My apologies for a very slow reply, partly due to my miscalculation of available internet time before 2 grandchildren arrived. However I've spent a lot more time than I had anticipated researching your suggestions, without finding a solution.

Meanwhile, I've retrieved the thermostatic controller & heating element from the defunct boiler to get the brewery working again as a work-around. I shall discuss the new one's inadequacy with the shop, to see whether it's faulty.

Problems, one at a time...

Theatrical dimmer looks like a good solution. Thanks Kim.

Single channel units seem to come only for rack mounting. I think I can cope with wiring & a suitable enclosure, but haven't yet found a supplier that sells them singly. I don't yet know how much one would cost. More research needed.

I've researched variacs, BFO variacs & BFO diodes, albeit not very thoroughly. Variacs seem prohibitively expensive. I've not found time enough to grasp the concepts behind the BFO stuff, but suspect that it's deeper water than my 4-decades-out-of-date electronic skills can cope with safely.

Neverthless, thanks aidan.f for the 'rolling boil' understanding of what I'm trying to achieve. I have problems with low alpha acid yield of hops & have resorted to pre-boiling on the hob of the gas cooker. It's primarily a way of capturing the aromatics, but has also increased the bitterness. I'm still "boiling" a brew for 2 hrs & the hot break happens well before then. It  would be nice to have a gas fired boiler - 3 kw on the hob is better than the electrical solutions - but gas firing is impractical for domestic brewing.

As you may have guessed, I don't think that any sort of thermostatic control is satisfactory. Physics of the temperature at which liquids boil...

I'm veering towards the idea of a simple cheap(2.4kw!?) step-down transformer that will provide a suitably low voltage for a good boiling rate. I doubt that 110v will be enough, but lots of thermal insulation around the boiler might make it it work. Any suggestions for finding out experimentally with domestically available kit? Starting point is 24x100w light bulbs in parallel, wired in series with the boiler. But 24xBC sockets are not cheap, and what would I do with 24 obselete incandescent lamps?

[Diver300]

You probably don't want to put resistance in series with the heating element as you end up with a lot of heat in the resistance.

The other solutions, variac or dimmer, are not inherently inefficient.

A heater is a pure resistance, so the current it takes is proportional to the load. If you think that 1/4 power will be enough to keep the boil going, then you only have to allow for 1/2 the voltage and 1/2 the current if you use a reduced voltage from a transformer.

(With a dimmer it is full power for 1/4 of the time, which is a bit different)

So if you get a 110 V transformer, it as to be rated to around 5 A, so 550 VA or more.

If you want to adjust the power, you can add and subtract transformer outputs but putting them in series, a bit like batteries. You can subtract voltages, with a winding that is reversed, which is something that you can't do with batteries. As transformers are AC, you can't test the polarity, but you measure the voltage once they are connected. You can be clever and look at the dots that mark one end of the windings, but that also means the primary has to be connected the right way round. The primaries of all the transformers are connected to the mains as normal.

So, if you have 110 V transformer, like a yellow site transformer, and a transformer with two 12 V outputs, rated at 5 A or more per winding, you could add 12 or 24 V to the 110V, or subtract 12 or 24 V, so you would get powers of  308 W, 400 W, 504W, 620 W or 750 W

A suitable transformer with two 12 V outputs is:-

http://www.ebay.co.uk/itm/Wall-mount-mounted-1Kva-110v-24V-site-engineering-workshop-twin-transformer-/331640003450?hash=item4d3748db7a

Ebay has lots of site transformers.

You might even be able to get most of what you want in one box, at a good price here:-

http://www.ebay.co.uk/itm/Wall-mount-mounted-1Kva-110v-24V-site-engineering-workshop-twin-transformer-/331640003450?hash=item4d3748db7a