Variacs

[rasqual]

I can control the speed of that motor with a $10 Radio Shack transformer + 600 watt dimmer switch that was household surplus.

Roger that for the II.

How much boost do you find the RS Xformer gives the blower output? I've always assumed it'll do something comparable to a boost to the AC on the pumper.

[rpn]

How much boost do you find the RS Xformer gives the blower output? I've always assumed it'll do something comparable to a boost to the AC on the pumper.

Tough for me to answer directly.  Here's the anecdotal:  Unmodified I was flying up to 450F in at most 5 minutes with only 75 grams of beans.  My first roast attempt after splitting the heater and fan I put a standard light switch on the fan.  So, with heater and fan full on it took almost 15 minutes to hit first crack and I barely got the beans up to 425-430F.  I could hear how much faster the fan was running and figured this was the problem.  I then swapped in the dimmer switch and now only run the fan at full speed for the first 3-4 minutes of the roast before I start to slow it/increase heat.  Now I can roast 125-130 grams and hit 435-440F in 12-14 minutes.

I do own a multimeter and know how to use it, but I'm a software guy with two little kids (you should have seen me trying to roast last weekend with the 4 month old strapped to my front  ) and a coffee jones.  I'm going about all this a bit frantically and lightly documented for now, but what I've got is working way beyond my expectations with a wide variety of beans including the decaf my wife requires.

[rasqual]

Sounds like you've dialed it in about perfect for boosted quantities to go with the boosted blower. Good show!

[headchange4u]

I have a question that I hope you guys might be able to answer.

Someone is selling a Variac @ CG and they said it had been rewired to 15 amps. I contacted the guy selling the unit and he told me it was a 5 amp unit and he replace the fuse with 20 amp and rewired it. Here is the response I got from him:

It's a 5 Amp KRM variac that has been upgraded with a 20 Amp fuse.  I've also rewired the place where you plug in the roaster using a big chord.  This is because the old plug is not set up for the heat generated from more than 5 Amps.
 

I am no electrician but me thinks it would take more than a fuse and heavier wiring to transform a 5 amp Variac into a 15-20 amp Variac. Thoughts?

[stradbash]

I am no electrician but me thinks it would take more than a fuse and heavier wiring to transform a 5 amp Variac into a 15-20 amp Variac. Thoughts?

I will heartily second that!  Sounds like smoke waiting to happen to me if much more than a 5 amp load is put on it.

[rpn]

I am no electrician but me thinks it would take more than a fuse and heavier wiring to transform a 5 amp Variac into a 15-20 amp Variac.

It depends on how you use it.  I believe the logic some of this is based on is that you don't run your roaster long enough to generate enough heat to melt down the entire circuit.  I know some people are just replacing the fuse, so with upgraded outlet wiring you may actually be in pretty good shape.  Then it's just a question of the materials used in the transformer wiring.  "Just" is probably the wrong word, but the point is that a significant portion of the circuit is now upgraded.

From what I've read this is a common hack on the cheaper variacs, but it's definitely got a risk to it.  Some might say, however, that as long as you've got an ABC fire extinguisher nearby and you monitor all your roasts, then the risk is fairly low.

My $.02.  Not a recommendation that you buy or use this.

[BoldJava]

Very good review of the Variac, at CG, written by Jim Schulman.  Clear, well written on the use of the variac to profile the roast.  I went for the 20V as electricity isn't my strong suit; not going to over ramp a smaller variac with a smaller fuse:

http://coffeegeek.com/reviews/accessories/variac/jim_schulman/1612

B|Java

[scott]

I've got the 20 amp as well, and have tried two different approaches (this is with the Behmor). One is to set the Variac initially to keep it at a stable 120-122V, and then not touch it again. The other is to do the same initially, then begin to ride it again before first crack, say to 125V, then back it off to 117V almost immediately and try to space out/delay second. Then ramp it again to 122V before hitting cool.

The second approach has given me good results w/ P2...but then again, I really don't know what I'm doing. The idea is to "help" P2 a bit.

Most importantly though, if I don't use the Variac, I frequently have initial line level at 115V or even lower and cannot get a decent roast.

[bwilson]

Hey Scott - When you're riding the voltage at 125 and 117, at what points in the roast profile are you generally at?  Do you hit first crack before getting to the 70% power point of the profile or does it go to 70% before 1st crack.  IOW, how do your voltage adjustments coincide with the P2 profile?

[scott]

Hey Scott - When you're riding the voltage at 125 and 117, at what points in the roast profile are you generally at?  Do you hit first crack before getting to the 70% power point of the profile or does it go to 70% before 1st crack.  IOW, how do your voltage adjustments coincide with the P2 profile?

If it's with a bean I am getting to know pretty well (for example, the Honduran COE from a recent distro here), it goes like this: I hear 1st crack begin; I go up to 125; within 30 seconds, it hits the 70% power point; I ride back down to about 117V...1st crack is continuing but is fairly...feeble, I guess...then in about 2.5 minutes I ramp back up to about 122V and a vigorous 2nd crack starts. Then I hit cool.

In a way I guess I'm augmenting P2. I should take better notes and see if I can replicate this say 10 times. Oh, and I hit + 4 times before starting. If I got a real good grip on where to hit + and - I probably wouldn't need to mess with the Variac!

[bwilson]

Is that 125 with the Behmor running at 100% or is it at rest.  Inquiring readers want to know. 

[scott]

Is that 125 with the Behmor running at 100% or is it at rest.  Inquiring readers want to know. 

Sorry if that wasn't clear. That's 125V w/ the Behmor at 100%...essentially right before it cycles down to the lower power.

I didn't roast yesterday, but will today, and take decent notes.

I wish someone w/ a decent video camera would make a short video of this process!

[BoldJava]

Variacs and Kill-A-Watts.  Thank you Milo.

I couldn't get any reading off my Kill a Watt voltage meter when running power thru my Variac.  Enter the EE Milo from the Left Coast (no phone booth in which to change clothing; cell phones are cramping his style).

I had read that the dial on the variac should be at "0" and then take up to appropriate level.  Wrong Wroger.  I could never get any reading thru the KAW, regardless of how high I turned the dial.

Milo, thru trial and error demonstrated that the dial on the variac must be set at "85" when plugged in which corresponds with about 120, 85% of the variac's voltage potential.  Something about the KAW needing a minimum amount of power to transcirculate the microcuitry thru the transitory tunnel which parallels the rabbit hole.  Or something like that.

Just have the variac at '85' when you plug it in.


B|Java, business major

[grover]

If you were buying a new Kill-A-Watt meter, which model would you get? I know it would depend on what you want to do with it.   But as a question to those who have one already which features have you felt a need for. Base model for $20 or ?? I want to check my SC/TO setup and compare it to a matching unit being used in an old building in a small town somewhere in Chedderville. Just to compare notes.

Thanks....

[peter]

The $20 model works fine for measuring everything in my house.