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Old 12-11-2009, 06:29 PM   #1
mikeal
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Default Another electric kettle question

First, I'd like to introduce myself.

Hi. I'm Mike. I brewed for awhile, then stopped. Now I'm back!

On to the questions! I read through all the electric brew kettle threads that I could find but did not see these addressed anywhere.

Question 1.

If it is true that:
A) A 5500W or 4500W element will cause a boilover on most kettles if it is not regulated.
B) You can run a 240V heating element at 120V and get half the heat output.

Than can you simply use a SPDT switch to switch the second 120V leg to neutral, resulting in a 120V circuit to the heating element?

My concerns with this are that there is no GCFI protection on the resulting 120V circuit and that I really don't know what I am talking about and might burn down the house and/or kill myself.


Question 2.

If, as in the case above, you are controlling one 120V leg of a 240V line with a 120V 20A SPDT switch, could you use a 120V 20A SPST switch on the other leg? What would happen if you energized the 120V / neutral SPDT switch without the other switch being on?


Question 3.

Is it necessary to have GCFI protection on a 240V line?


Question 4.

From what I understand, the PID / SSR combo does not really monitor the temperature. You set it to a ON/OFF ratio that keeps the kettle at the desired temperature, but you have to know the ratio beforehand. Is this correct? If so, how do you build a control on which you can just dial in the desired temperature?

Thanks. From what I have seen while lurking, the members of this forum are among the friendliest and most helpful that I have ever seen.

Mike

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Old 12-11-2009, 06:38 PM   #2
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If you run a 240V element at 120V you will output 1/4 the 240V power of the heating element. If you half the voltage and the resistance is the same, you half the current, resulting in 1/4 the power.

GFI is not an absolute requirement, from what I have read, but I dont really want to chance that one.

The PID SSR combination will either control the temperature quite accurately based on a thermocouple, or you can set it to manual when you are boiling and it will output the heat you tell it to. If you did not have it on manual for the boil, it would cause some issues and not be easily controlled.

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Old 12-11-2009, 06:53 PM   #3
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Question 1: I imagine you could setup the 120v-240v switchover like that, but it would get complicated if you tried to control it. It you just want straight on/off function then sure. Maybe not the best way to be handling line voltage but I am sure it would work. An electrician might say something different on the safety side. Not sure.

Question 2: If I understand you right..... Nothing would happen. There would be no current flowing on either leg. 240v needs both legs energized to work. That leg would be live if you touched it and grounded yourself but the element would not be energized.

Question 3: No not necessary but advised. You are working around water.

Question 4: Like jfkriege said you can indeed control the temp with logic. The PID is reading the temp from a thermocoupler and adjusting the signal as necessary.

If you just want a simple dial to control the boil, you could use a PWM circuit like me and some others are using/building.

Not sure how that would work though if you plan on putting a switch to flip between 120v and 240v. That might get complicated.

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Old 12-12-2009, 12:46 PM   #4
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I was looking at an electric kettle thinking that it would be cheaper than a propane burner, but it looks like that is not the case. A GFCI breaker doubles the price for the setup...

The switch to flip between 120V and 240V would just change one leg of the circuit from 120V to neutral. It seems like it would work, but at 1/4 of the output I don't know if it will maintain the boil. Is 1375W enough?

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Old 12-12-2009, 02:10 PM   #5
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The really nice thing about electric is that you never need to run out and get another propane tank. It is also cheaper to have fine control over (PID vs automated flame control).

I would also think that over the long run it could be cheaper, but I have not done that math.

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