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Using Variac with Behmor P1 profile to create a P2 profile?
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Discussions > Coffee > Home Roast > Using Variac...  
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TeddyMac
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Posted Mon Jan 13, 2014, 7:55am
Subject: Using Variac with Behmor P1 profile to create a P2 profile?
 

Fellow 'Geeks,

There are some great discussions here about using a Variac with the Behmor, but none/few of them about practical ways you might create a specific roast profile with one. Since P1 is the most flat-out, the idea occurred to me to use the Variac with it to create a P2-ish (emphasis on the -ish) profile tailor-made to the batch size and beans being roasted (to a desired City+, in my case). This may be based on a complete misunderstanding of what the Variac does.

After a total re-wiring, the voltage in my house is a good and steady 120, so the Variac's use in this case would be to lower voltage, not boost it. What if using it could mimic something like the elusive heat drop at first crack of P2, but do so at the point desired. I realize the drum/fan speeds would drop as well with voltage reduction, but am hoping not so much as to promote either baking or charring...

So this is just a quick stab of an idea, but what if something like this happened? (By the way, I usually use 5-6oz of beans at the 1/2lb setting; but if having plenty of time to "steer" is desired, 1-P1 might make more sense.)

-2 minutes, Variac set at 116v to dry the beans.
-Up to 120v until browning and signs of first crack.
-When first crack begins, reduce to 90v, extending first crack.
-(Keep voltage low to avoid spike during Cool cycle.)

-An alternate additional step might be to lower to 115v after 4 minutes of 120v in order to slow the rise, thus increasing the effect of the heat drop at first crack.

So does this seem plausible to people, or is this a complete misunderstanding of how the Variac works? I beg mercy for a relative newbie who's only beginning to learn about the electrical bits of roasters!
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GVDub
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Posted Mon Jan 13, 2014, 7:39pm
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

I'd bet that the CPU in the Behmor wouldn't care for voltages that low.
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Frost
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Frost
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Posted Mon Jan 13, 2014, 8:13pm
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

I would never advise anyone to do such things..... but....
I would unplug the heater element from the controller and plug it directly into the Variac.
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JojoS
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Posted Tue Jan 14, 2014, 1:07am
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

Frost Said:

I would never advise anyone to do such things..... but....
I would unplug the heater element from the controller and plug it directly into the Variac.

Posted January 13, 2014 link

That's the surest way to control the heating elements to create a custom profile. How repeatable you can make it will be the next challenge.
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TeddyMac
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Joined: 28 Nov 2013
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Location: Boston MA
Expertise: I love coffee

Grinder: Capresso Infinity
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Roaster: Behmor 1600
Posted Wed Jan 15, 2014, 6:23am
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

Thanks to you all. I'm reminded by this that making a tweak in any roaster that's designed to control solely the heat takes more than something as simple as plugging it into a variac. I was hoping for it nevertheless since I don't trust myself with anything more than a screwdriver, and from the tips and descriptions of modifications I've read, those seem beyond my skills.

It never dawned on me that low voltage could have a bad effect on a Behmor, there's been such a focus on what too-high voltage would do. GVDub, when you mention that the CPU wouldn't care for that kind of voltage, I'm curious whether you mean damage could be done, or whether the roaster would simply give an error message and shut off, etc.
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GVDub
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Posted Wed Jan 15, 2014, 7:28am
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

TeddyMac Said:

It never dawned on me that low voltage could have a bad effect on a Behmor, there's been such a focus on what too-high voltage would do. GVDub, when you mention that the CPU wouldn't care for that kind of voltage, I'm curious whether you mean damage could be done, or whether the roaster would simply give an error message and shut off, etc.

Posted January 15, 2014 link

Don't know for sure in the Behmor's case, but low voltage can do permanent damage to a microprocessor. It can also just make it error outójust depends on the processor and how low the voltage is. My experience with complex CPUs and DSPs was that things started getting wonky when the sustained voltage dropped under 100, and most things would go south between 90 and 95.

Consider that a 20% voltage drop would be down to 96v (figuring a 120v base), and many profiles call for dropping to 60-70% of max power. That would certainly put an non-modified (i.e. heaters and controller on the same power supply) Behmor into total nervous breakdown, if not physical breakdown. Dropping voltage on an unmodified unit would also seriously affect fan speed and hence air flow, so you'd actually be screwing with multiple variables at once, without independent control, which is never the formula for successful, repeatable results.
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kboom1
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Posted Wed Jan 15, 2014, 10:07am
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

GVDub Said:

Don't know for sure in the Behmor's case, but low voltage can do permanent damage to a microprocessor. It can also just make it error outójust depends on the processor and how low the voltage is. My experience with complex CPUs and DSPs was that things started getting wonky when the sustained voltage dropped under 100, and most things would go south between 90 and 95.

Consider that a 20% voltage drop would be down to 96v (figuring a 120v base), and many profiles call for dropping to 60-70% of max power. That would certainly put an non-modified (i.e. heaters and controller on the same power supply) Behmor into total nervous breakdown, if not physical breakdown. Dropping voltage on an unmodified unit would also seriously affect fan speed and hence air flow, so you'd actually be screwing with multiple variables at once, without independent control, which is never the formula for successful, repeatable results.

Posted January 15, 2014 link

+1
prolonged low voltage will put undue stress on CPU's and microprocessors. You'd be much better off instead of messing with voltage, install a probe to measure Environment Temperature and control/graph your power ramps & drops  on P1 opening door to control your ET. Ajust your profiles off of your ET readings.
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TeddyMac
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Joined: 28 Nov 2013
Posts: 29
Location: Boston MA
Expertise: I love coffee

Grinder: Capresso Infinity
Vac Pot: Yama stovetop, Hario...
Drip: Hario woodneck, Bona-Vita...
Roaster: Behmor 1600
Posted Wed Jan 15, 2014, 12:23pm
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

This is very helpful. It's good to know I could inadvertently fry the CPU before trying my ill-advised experiment.

Just yesterday I did a P1 with the door trick, so your advice to put in a probe is a good one. I tried P1 multiple times early on, but was chicken about opening the door for long, and the beans tended to roll into second crack, getting the beans darker than I like. Not so yesterday. I discovered you can be quite bold with it. I've also been reading about using the P2 temperature readings trick, and am figuring out how to harness that information. I have a thermocouple which I can place in the very back, just under the heating element, as I've seen other so. I saw someone's posting who put the end of his thermocouple right in the afterburner's grill, saying that seemed to be as close to BMT as anything he's found so far. I'll give these a go.

Again, thanks for the warning. The last thing I want to do is fry the poor Behmor! It may have its quirks, but I sure do love it.
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kboom1
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kboom1
Joined: 31 Aug 2009
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Posted Wed Jan 15, 2014, 4:26pm
Subject: Re: Using Variac with Behmor P1 profile to create a P2 profile?
 

Closer to the drum would be better.Consistancy is the rule. even if temps arent true, once you can somewhat monitor ET temp no matter where probe is placed you will know how stable your temp is after drop so you don't stall, and even be able to monitor your ROR on your ramp. (: Happy Roasting :)
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