Another one for the electricians...

dennisdk2000 · Sep 20, 2012

Would it be possible to modify a tea urn by replacing its built-in thermostat with a PID unit with a temperature probe so that one could set a given temperature and the urn would then switch on and off to maintain this temperature? Would use it as a mash tun and boiler...

Don't worry - I won't start messing myself, but was wondering if could be done.

Dennis

simonranson · Sep 20, 2012

I cant see why not. A small little control box with a PID and a solid state relay (SSR) would to the trick. Only possible hic-up could be if the tea urn is double skinned. Not a show-stopper, but cutting holes in, and sealing could take a little more time.

Simon

dennisdk2000 · Sep 20, 2012

Cheers for that! I saw this the other day, and it got me thinking:

http://www.aldi.co.uk/uk/html/offers/sp ... _26570.htm

Looks like all the gubbings are in the plastic part. It's the perfect size for me, as I only do small brew due to space restrictions, so usual boilers are too big.

Dennis

Baldbrewer · Sep 21, 2012

It would be possible Dennis but don't forget SSR's (Solid State Relay's)

do generate heat, you can buy some with heatsinks prefitted but you will need to consider this when planning your PID control box. You don't want a plastic box melting off the wall.

Things to consider with this boiler:

Any mods you do will invalidate warranty. (porbably not bothered about that though given your plan!)
Where and how will you install PT100 temp probe?
Will this element maintain a rolling boil?

Do you need a PID? can the current control system ( probably a rotary temp setting knob!)
be friggged?

Looks a nice little boiler though for low volume brews.

Goodluck

Kevin Wood · Sep 21, 2012

I would say a PID controller built stand-alone would be more flexible, although increasing the number of trailing wires a bit.

A stand alone device can control the HLT, then be moved to control a HERMS / RIMS setup should you move on to that in future. Once fermenting, mine is pressed into service controlling the temperature of the FV.

In addition, if you decide to move on to a bigger or more shiny setup in future, it's easier to re-use. Ditto if an element fails during a brew and you have to transfer to another pot.

The ALDI boiler might well need modifying to work. Most urns like that have a second, lower power setting that they switch to once they boil, which just keeps the water up to 80 or 90 degrees. Hot enough for a cuppa but some way off the boil. It could be that this is triggered by steam as is the cutoff on most kettles, in which case it probably won't switch over if the lid is open. Alternatively, there might be a thermal switch you need to bypass.

Has potential, though. 950W should give a reasonable boil with 7L of wort, especially as the sides of the pot are probably quite well insulated.

dennisdk2000 · Sep 21, 2012

Baldbrewer - don't think there is any way of selecting temperature on the urn as it is, hence I was thinking about modifying it, especially as I'd want to mash in it and therefore want to be able to operate it at several temperatures.

I should imagine the boiler would provide a rolling boil - might need a little additional insulation, but that would be a big problem.

Where and how will I mount the PT100 temperature probe? To be honest, I'd not even considered it...

this might pose the biggest problem. I have no clue where the probe would be best positioned, and as I think the urn is double skinned, I have no idea how to fit it!!! And good point about the SSRs!

Kevin Wood - I agree that the stand-alone PID unit would probably be better - and easier to make. Yes, a couple more trailing wires, but with a bit of planning, they could be minimised.

I hadn't considered the "keep warm" function - and looking at the urn, it does appear to have this function.

Hmmm, I think I might have to abandon the idea. Too many things I don't know enough about, and I don't want to kill myself!

Cheers, though, to everyone for their input!

Dennis