Adding A Resistor To (Schuko) Mains Plug.

[Hamzaan]

HI,

I'm trying to modify an electric Moka pot imported from Germany, so it is fitted with a schuko plug and has a complimentary uk adaptor, to boil slower and therefore produce better espresso. (FYI: with standard, i.e. stove top, Moka pots the recommendation is to lower the heat and have the coffee boil through slowly or quick boiling new coffee smothers the crema)

I thought by adding in a resistor I could lower the power of the heating element, which should slow the boil hopefully. I'm not sure how schuko plugs are wired, but if they have the same wires as we would find in a standard UK plug I was thinking I could strip it back to wire it into a normal uk plug and solder in a resistor just before the neutral terminal. Could that work?

Any ideas welcome, cheers

Hamzaan

 

[Hamzaan]

Additional relevant info:

Power rating: 330-400W

Voltage: 220-240V

So the maths would work out to give a circuit resistance around 144Ohms, so I am thinking either adding in aroudn 50 ohms to get 3/4 power output or another 144Ohms to get half power.

Cheers,

Hamzaan

 

[Hamzaan]

Did some more maths and some looking around, unless I can get a 400+W resistor the idea above will just burn the resistor. WIth a 1k ohm resistor it should be okay to use 100W resistor (taking into account the fact that mains is RMS) it could work. it would lower the power to 1/8th so it will take quite a while to boil though.

Also I think I'm being daft but I can't see an edit button...

Hamzaan

 

[ProDave]

forget resistors. Put a diode in series instead.

That will conduct on one half cycle and not conduct on the other.

So you will get half power into the pot, with virtually no wastage and nothing getting particularly hot to worry about.

you are looking for a 400V 2A or more diode.

 

[apprentice87]

Hi there,

Really love the thinking and you definitely seem to know your way around ohms law.... but unfortunately it will not work....

You obviously have figured out the current flowing in the circuit. Now, if you add up the various volt drops around a circuit [hopefully caused in the main by loads] you find they add up to the supply voltage..

So... Lets say you added a resistor of half the resistance of the heating element in the electric pot, you will then have split the voltage between them, which is what you wanted.. BUT current squared X resistance = power, so you would need a huge resistor, as it would be dissipating the same power as the pot itself.... You obviously have the knowledge to understand what i mean..

I wonder if you could use a 110v transformer and feed the pot through that??? Some of the MUCH more knowledgeable forum members will be able to advise you on that...

Still VERY good question.....

john...

Hi again Hamzaan, You posted as i was writing mine!!!!! I KNEW you had the knowledge to work this out!!!!

john..

Great Idea by ProDave.....

john

 

[Bruspark]

Even if you could get the 100W resistor in the plug it will burn up immediately.    I would suggest the best approach would be a 400W (NOT 250!) insulated dimmer switch mounted onto an insulated enclosure with a UK Plug (3A fuse) on input and a (UK or Shucko if possible) socket for output.  This will give you fine control of power input, be less disturbing to any on-board electronics than the half-wave- diode - and anyway suspect youll only need a 10 - 20% power reduction to have the sort of effect you describe.

If you are not an experienced electrician / electrical engineer you might want to get someone who is to make or at the very least look at your finished product over before testing it with particular attention to proper wiring, ventilation, insulation, splashproofing, Earthing + Earth Continuity through the device to name just a few !!

 

[NozSpark]

I was just thinking of thyristor control......

 

[Hamzaan]

Even if you could get the 100W resistor in the plug it will burn up immediately.    I would suggest the best approach would be a 400W (NOT 250!) insulated dimmer switch mounted onto an insulated enclosure with a UK Plug (3A fuse) on input and a (UK or Shucko if possible) socket for output.  This will give you fine control of power input, be less disturbing to any on-board electronics than the half-wave- diode - and anyway suspect youll only need a 10 - 20% power reduction to have the sort of effect you describe.

What range of power reduction would these dimmer switches allow? I don't hugely know how the reduction in power will effect rates of boiling in all honesty so would like to try a large reduction to start. Do you think the heating element will survive varying the resistance during operation?

If you are not an experienced electrician / electrical engineer you might want to get someone who is to make or at the very least look at your finished product over before testing it with particular attention to proper wiring, ventilation, insulation, splashproofing, Earthing + Earth Continuity through the device to name just a few !!

I'm a complete amatuer so out of curiosity what is the relevance o fall of this for a kitchen appliance? Is a lot of it regulation/safety standards?

In other news, none of you guys sell something along these lines do you?

Cheers,

Hamzaan

 

[Hamzaan]

Would the follwing be a possible commercial work around if a DIY job is too difficult and/or expensive?:

Everspring Plug-in Dimmer (sorry no link, I'm too new to the forum!)

 

[Hamzaan]

Turns out philips do a 1000w remote control dimmer plug for most household appliances:

Philips SBCSP370For about £8 for each plug, £12 for the remote.....

Guess I'll try commercial route seeing as parts for a DIY job are not that cheap. Thanks for the help everyone!

Cheers,

Hamzaan

Admins:

I'll mark the thread as solved after testing the dimmer plug as it might not work!

 

[Manator]

I worked in Italy some ten years ago and all the Italians had these coffee 'kettles' , they just used gas burners or used them on open fires. The coffee always tasted good. I do not think the electric ones are as good as the old fashioned ones, but that's what age does to you.

I have three at home, all different sizes, but none are electric.

 

[Marvo]

If you run the entire appliance through a dimmer it will play havoc if there's any electronics for indicator lights or water-level sensing etc. I'd just wire a 600watt 2-wire dimmer module in series with the element only.

 

[Hamzaan]

I worked in Italy some ten years ago and all the Italians had these coffee 'kettles' , they just used gas burners or used them on open fires. The coffee always tasted good. I do not think the electric ones are as good as the old fashioned ones, but that's what age does to you.

I have three at home, all different sizes, but none are electric.

From what I hear the stove top ones are really good. They are also 1/10th the price of the electric one! Problem is the only really good electric espresso machines are £500 to £3000! So getting a £40 electric moka pot and trying to fiddle with the electrics is much cheaper. You could get the wierd mechanical ones (the espresso presses) but they are slow

If you run the entire appliance through a dimmer it will play havoc if there's any electronics for indicator lights or water-level sensing etc. I'd just wire a 600watt 2-wire dimmer module in series with the element only.

Thanks for the advice! As far as I can see the actual electrics are just a heating element, switch with light and probably a heat sensor that switches it off instead of a water level sensor as it is a pressurised system. I'm currently trying to avoid opening the product itself but if putting the whole thing through a dimmer doesn't work I'll have to find some way to open it up to wire in the dimmers as you advise.

On that note, anyone know how to open screws that have a triangle shape instead of the normal flat head/crosshead/torx shape?

 

[ProDave]

On that note, anyone know how to open screws that have a triangle shape instead of the normal flat head/crosshead/torx shape?

Yes.

Go to ebay and buy a 3 point screwdriver.