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Old 06-13-2011, 04:16 PM   #1
skipper1953
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Default Is a pulsing electric boil really such a bad thing?

I have read in several threads that folks seem to be concerned about the pulsing nature of the boil in their electric systems.

I use an Auber Instruments 2352 PID to control a 3800 watt element in my system. I have my PID set to a 2 second cycle time. I bring my wort up to 200* in auto mode at which point an alarm sounds. I then switch to manual mode to bring the wort up to a boil and prevent a boil over. Once the 6.? gallons of wort is boiling and the foam has settled back, I dial the power level back to somewhere between 65% and 75%, set my timer and go about my other activities. The rolling boil in my kettle pulses in step with the 2 second cycle.

I guess I don't understand the concern about the pulsing. Is this a bad thing? Will it harm my beer? I don't see how it can. I have read a few posts about how to prevent the pulsing. I do not recall seeing anything explaining why one should go to the trouble to prevent pulsing much less care about it.

What am I missing?
Anybody?

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Old 06-13-2011, 04:25 PM   #2
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I guess the thought would be that you want to keep the boil rolling the whole time to maximize the extraction of alpha acids and boil off of DMS, etc.. At 65% I can't tell when my element is on or off, just a solid rolling boil the whole time. I suspect my cycle time is probably faster than 2 seconds, but I never paid much attention.

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Old 06-13-2011, 04:40 PM   #3
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My thoughts on the pulsing would be that it might shorten the life of electrical components. Don't know the stats on that however. Can't imagine it would effect the quality of the beer.

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Old 06-13-2011, 04:44 PM   #4
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Originally Posted by samc View Post
My thoughts on the pulsing would be that it might shorten the life of electrical components. Don't know the stats on that however. Can't imagine it would effect the quality of the beer.
These components were all designed specifically with this type of pulsing in mind. ie. A PID will switch much much faster than this 2 second cycle time if you let it. We use a SSR over a mechanical relay specifically because we want to be able to switch on and off frequently.
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Old 06-13-2011, 04:58 PM   #5
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So you are saying that 2 - 40 million hour lifetimes on these SSR's are enough. LOL, no worries, pulse on!

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Old 06-13-2011, 05:49 PM   #6
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Pulsing a resistor (element) wont damage it, and like already said SSR's are designed to be used like we are using them, just make sure to not get them hot, so buy over rated and heat sink and you'll have a long healthy SSR life span.


As far as pulsing... If my system doesnt pulse then no ones will. I have 11,000 watts in the kettle and I do 5 gallon batches. I put so much in because.... I hate waiting, it will boil 5 gallons from 130 deg F in under 5 minutes.

Once boil is achieved the PWM power output is set to 30%. This gives a nice rolling boil, no pulsing what so ever.

I will however warn you about your period. When talking PWM you have your duty cycle and your period. The period is how long the entire waveform is. If you have a 4 second period and a 25% duty cycle that means you're on for 1 second, off for 3. If you have a one second duty cycle and you're at 25% power you're on for .25 of a second off for .75.

So if you're running a long period you can get a pulsing boil, especially at high power. On my system I run a 1 second duty cycle, and with 11,000 watts (2x 5500 ULWD) elements it does not pulse.

The trick, just like any PWM controlled system, is to make sure that the system is enough of a low pass filter to make your square wave turn into an average DC output. And because water is a great low pass filter for heat we can run as slow as 1 second (I'm used to talking nano and mico seconds), but if you get too long, like say 10 seconds, you'll run into issues as the frequency is just too low for the water (your low pass filter) to turn it into something smooth and flat.

So if you ever have pulsing issues just reduce your period.

There's a second problem though, if you get much under 1 second in your period your SSR becomes a problem because it does not shut off until the zero crossing of the sine wave coming out of the wall. So if you turn it on, and then try to turn it off before the zero crossing it will not turn off until the zero crossing comes, and that's at 60 hz. At 60hz you have a zero crossing every 120th of a second, so that's the best resolution you can get. So you have to make sure that the smallest change in your output duty cycle represents greater than or equal to 1 120th of a second or else it will last longer than you wanted it too.

At 1 second you're slightly under this with 100 steps (1 - 100%) and so you're good, but you go much under 1 second and you cant switch fast enough with the SSR for a 1% duty cycle change.

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Old 06-13-2011, 06:20 PM   #7
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Quote:
Originally Posted by skipper1953 View Post
I have read in several threads that folks seem to be concerned about the pulsing nature of the boil in their electric systems.

I use an Auber Instruments 2352 PID to control a 3800 watt element in my system. I have my PID set to a 2 second cycle time. I bring my wort up to 200* in auto mode at which point an alarm sounds. I then switch to manual mode to bring the wort up to a boil and prevent a boil over. Once the 6.? gallons of wort is boiling and the foam has settled back, I dial the power level back to somewhere between 65% and 75%, set my timer and go about my other activities. The rolling boil in my kettle pulses in step with the 2 second cycle.

I guess I don't understand the concern about the pulsing. Is this a bad thing? Will it harm my beer? I don't see how it can. I have read a few posts about how to prevent the pulsing. I do not recall seeing anything explaining why one should go to the trouble to prevent pulsing much less care about it.

What am I missing?
Anybody?
Have you measured the cycle time? I had my PID set to t=2, yet the cycle time was over four seconds. Someone here on HBT showed me that the P setting impacts the minimum cycle time. Once I reduced P to 1 I had a two second cycle time.

The reason I want a constant rolling boil is that I can then control how hard it is boiling. I think a hard boil increases the maillard reaction, for example, which I would like to keep to a minimum in a pale beer. If the boil pulses then it is unavoidable to have a harder boil then intended for part of the time.
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Old 06-14-2011, 12:30 AM   #8
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At the risk of sounding overly technical, it's kind of creepy sounding.

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Old 06-14-2011, 12:34 AM   #9
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I guess I don't understand what is happening. Even with a PID, my boil never stops. It's still a rolling boil. You want to set it so that you maintain a rolling boil all the time. I can't even tell when my element is on or off- the boil is steady. I dial it down to maintain a rolling boil, usually 70% or so (it's a 4500w element).

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Old 06-14-2011, 01:19 AM   #10
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Quote:
Originally Posted by Yooper
I guess I don't understand what is happening. Even with a PID, my boil never stops. It's still a rolling boil. You want to set it so that you maintain a rolling boil all the time. I can't even tell when my element is on or off- the boil is steady. I dial it down to maintain a rolling boil, usually 70% or so (it's a 4500w element).
I get a very distinct on-off rhythm. Ferocious bubbling boil ... then calm and quiet. I would love to get it somewhere in the middle. I have a 5500 watt high density coil with 5 gallon batches.
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