Boiler power control

[Dr. Dextrin]

After all , I would suggest the most likely faults in our applications (assuming you got the ratings right to begin with) would either be open circuit (no problem) or something major like the element (or something else) failing and connecting live to earth or neutral - subtle overloads seem relatively less likely.

That's my thinking too. Plus, there'll be a standard 13A fuse in the mains plug that should protect against more subtle longer-term overloads - and of course protect the house wiring.

[Dr. Dextrin]

Thought I should point out that care may be needed in mounting these fuses. The one I linked to, for example, dissipates 3W of power at 16A according to the data sheet. That means something like 2W at 13A, so it's going to get pretty hot and maybe shouldn't go in a standard enclosed fuse holder.

[Graham]

Thought I should point out that care may be needed in mounting these fuses. The one I linked to, for example, dissipates 3W of power at 16A according to the data sheet. That means something like 2W at 13A, so it's going to get pretty hot and maybe shouldn't go in a standard enclosed fuse holder.

More importantly, these fuses are "underrated" by normal standards and they rely upon the sand filling inside them to conduct the heat away before the fuse melts. It is roughly how they work; they are maintained on the point of blowing at full rating, and the sand sinks the heat away, but when a surge occurs the heat cannot be sunk away fast enough and the fuse blows. These fuses are fussy about ambient temperature, and if they are in an enclosed fuseholder, the temperature could be high enough to cause premature blowing. These fuses fatigue much more rapidly than conventional fuses anyway, due to the narrow notches cut in the fuse element. Another point is that they are also fussy about power factor, and phase angle controllers mess up power factor in a big way.

These fuses are probably too much hassle, just on the off-chance that they might protect a triac worth £2.50; they very often don't.

[Hogarth]

These fuses are probably too much hassle

I've come to that conclusion too. And even in an integral unit like mine you could presumably replace the triac if it blew.

Anyway, I used my new controller for today's brew and it worked very well. I spent many happy minutes fine-tuning my 'rolling boil.' I've slapped a massive heatsink onto it, and it barely got warm: just enough to stop the steam from the boiler condensing on it. Definitely a good buy. Thanks for all the good advice, chaps.

[Kev888]

Thats excellent stuff - many thanks for letting us know!

Cheers
Kev

[Dr. Dextrin]

Good news there Hogarth. I'd be interested to know which heatsink you went for.

I doubt I'll get mine assembled till the new year now - bit short of circular tuits.

[Hogarth]

I had to google 'circular tuits' -- thought it might be a sort of potentiometer...

The heatsink came from Maplins. It wasn't on display, a chap had to find it in the stockroom. I can't see it on their website, however. Here's a piccie:



It's 150x95x14mm. I went for this split design because the triac and the pot are on the same surface. The triac was originally riveted to the inside of the unit, but I drilled out the rivet and substituted a bolt -- one of the two bolts you see beneath the knob. I used a bit of silicon grease too between the unit and the heatsink, so hopefully I'll get some decent thermal conductivity. I'll find out in August.

[barneey]

[quote="Hogarth"]I had to google 'circular tuits' -- thought it might be a sort of potentiometer...

Rounds

[Dr. Dextrin]

Thanks Hogarth, that gives me a rough idea of how much metal i might need.

[The_blue]

Ok, so i bought one of these and was just coming on here to tellyou about it when i found this thread..

I'm 30 mins through a test water boil and as said above have fiddled till it was just boiling.

The major differece for me is i havn't faffed about with it. No heatsink swap...


My build is is a 30 litre tea urn.I've pulled out all the old wireing and drilled a hole in the plastic base. I mounted the unit as it cam into the base and added live to one post and the element to the next. The neutral goes direct to the element and the earth to the metal body.

Thats it. my whole build.

The fuse listed above costs more than the unit so i'm not bothering. The urn had no internal fuse so i'm using the plug (and an RCD).



Fingers crossed!

[The_blue]

90 min boil went well. No issues

[Dr. Dextrin]

Which unit did you buy? We seem to have discussed several on this thread so far.

[The_blue]

post number 1.

http://www.ebay.co.uk/itm/150693732522? ... 1439.l2649

It's been relisted as a light dimmer

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0715811142

[Dr. Dextrin]

Interesting. I see they also do 2kW and 3kW versions now (the latter needing a heatsink adding) and the price has gone down a bit too.

Looks like you have the ideal mounting position there in the base of your boiler.

Have you noticed any problems with mains interference? When I tested mine, I could pick up interference from all the sockets in the house while it was running. I guess that may not matter, depending where/when you brew, but I think I'll need to do something to fix it.

[barneey]

Oh, wait, the one I linked to above does need a remote filter. This one doesn't.

Hogarth could you confirm that it is this One you bought and are using? UNITED AUTOMATION - QVR-TB-RFI - POWER REGULATOR

Cheers