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Home Brew Forums > Home Brewing Beer > Electric Brewing > 4500w Element on two 110 outlets
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Old 11-11-2012, 08:53 PM   #31
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So I think I've decided I'm going to go with two 1500 or 2000 watt 120 v elements and two ssr. Just like the diagram I posted on page 1 which i think was from P-J.
Next question I have is can I use the 30 amp 120v circuit and run both elements or should I still use two separate circuit breakers? The 30 amp breaker I have has one outlet and doesn't have anything else installed on it. And thanks for the input this is really helping me decide what system I'm going to go with.


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Old 11-11-2012, 09:12 PM   #32
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Quote:
Originally Posted by ajdelange View Post
As phase is so confusing think of two AA batteries connected in series. You can get several voltages from that connection simultaneously
1) + 1.5 V between common point and + terminal on one battery
2) - 1.5 V between common point and - terminal on the other.
3) + 3 V between - terminal one battery and + terminal on the other.

I'm glad you posted that because it illustrates exactly why saying the legs are 180 out of phase is flawed.

Sure, measuring from an improper point of reference gives that appearance, but if you actually put the batteries 180 out of phase, negative to negative or positive to positive, (or if the two power legs were 180 out of phase) you still get 1.5V (or 120V) across each one, but you don't get 3V (or 240V) because they cancel.


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Old 11-11-2012, 10:10 PM   #33
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Originally Posted by ddahl84 View Post
So I think I've decided I'm going to go with two 1500 or 2000 watt 120 v elements and two ssr. Just like the diagram I posted on page 1 which i think was from P-J.
Next question I have is can I use the 30 amp 120v circuit and run both elements or should I still use two separate circuit breakers? The 30 amp breaker I have has one outlet and doesn't have anything else installed on it. And thanks for the input this is really helping me decide what system I'm going to go with.
2x 1500 would work on a 120V-30A circuit with a little cushion.

2x 2000 wouldn't be a good plan because that's 4000W and is greater than the 3600W a 120V-30A circuit should be called on to provide at max nominal load.
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Old 11-11-2012, 10:34 PM   #34
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Originally Posted by whoaru99

2x 1500 would work on a 120V-30A circuit with a little cushion.
Would that little cushion be enough to also run a pump? Or should that be separate
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Old 11-11-2012, 10:46 PM   #35
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Originally Posted by whoaru99 View Post
It is not two phase power and the legs are not 180 out of phase.
It is indeed as we shall see in a moment.

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Originally Posted by whoaru99 View Post
The explaination with the oscilloscope is a common one, albeit flawed, because both leads have to be moved, not just one.
No. That's not true. Reread what I wrote. The low side of the scope is connected to the common point between the two phases. If the probe is connected to one phase of the system you will see a wave form in phase with the primary. If you then move only the probe lead, leaving the low lead in place, to the other phase you will see a waveform 180 out of phase with the primary.

But a picture is worth a thousand words. You'll have to look closely to pick up some of the details but they are all there. The yellow cable is connected to a 4 prong 120/240 biphase system (right of the panel in the brewery). This cable makes both phases available in, respectively, cable marked with a black stripe and unmarked. There is a plug in a striped (but the stripe is barely visible at the right edge) and another in an un striped line. As you can see, though again you have to look closely, a red aligator clip is hooked to the gold (hot) terminal in one phase and a red one to the gold terminal on the plug connected to the other phase. You will also see a white wire connected to the silver (neutral) plug on the striped phase. No need to run this wire again from the unstriped as the neutral is common to both - it is the neutral of every circuit connected to this panel. It is connected to the center tap of the transformer on the pole.The white wire runs to the low wire of oscilloscope channel B (gray probe) and is jumpered (yellow) to the low wire of the other (A, red) oscilloscope channel. Thus both oscilloscope channels are measuring relative to the neutral. The oscilloscope shows two waveforms of identical amplitude but opposite (180 ) phase.


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Originally Posted by whoaru99 View Post
Using the center tap as reference is the reason that oscilloscope example is flawed.
You now have solid visual evidence that the oscilloscope example is not flawed. If you have an oscilloscope you can repeat what I did (just in case you think I photoshopped this - and I did, I used unsharp mask to make the picture a little clearer) and you will get exactly the same result which is, very plainly, two phases in a 180 relationship to one another.

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Originally Posted by whoaru99 View Post
This is akin to putting the black lead of a multimeter on the positive battery post and the red lead on the negative post, the proclaiming the battery polarity has miraculously reversed because the multimeter shows negative voltage.
No, it is akin to connecting two batteries in series and hooking the black lead of a voltmeter to the common point then measuring the two voltages at the other ends of the two batteries. You would get, with 1.5 volt batteries, + 1.5 and - 1.5 and, of course 3 across the outside.

So you've now had detailed theoretical explanations from an electrical engineer, multiple examples and visual evidence. Plus the 'step back from the trees to see the forest' concept which is that if you are right electrical engineers, the professors that taught them, GE, Westinghouse and Siemens and all the textbooks have all been wrong from the days of Steinmetz and Tesla (who invented 3 phase power) to the present.

If you can't take in what your eyes show you then I fear there isn't much else I can do for you.
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Old 11-11-2012, 10:58 PM   #36
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It is not two phase power with two legs 180 degrees out of phase.

That connection of the o-scope doesn't hold water for this purpose. Neutral isn't the correct reference in this regard. Use the waveform math on that scope and add those two together. Do you get 240V or zero?

You have to use an end point for reference because it's the only place you can get 120 AND 240, and as you see below they are in phase and that the voltage on CH B is 2x that of CH A because it's taken at the correct reference for a 120/240V circuit (disclaimer, I'm using a small step down transformer from the line but net result is the same, just lower voltage).

I do like your newer ScopeMeter though, but for my uses this old dog still hunts.
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Old 11-11-2012, 11:42 PM   #37
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Originally Posted by ddahl84 View Post
Would that little cushion be enough to also run a pump? Or should that be separate

IDK. What's the draw on the pump?
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Old 11-11-2012, 11:51 PM   #38
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I believe it's 1.4 amps.
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Old 11-12-2012, 01:09 AM   #39
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The heating elements and the pump would still be a few amps less than 30.
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Old 11-12-2012, 01:20 AM   #40
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Quote:
Originally Posted by sudbuster

Are you stupid, or just ignorant?
I guess stupid. This will teach me not ask questions. Thank you for your informative response.


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