HomeRoast Digest


Topic: Variac - More questions (4 msgs / 165 lines)
1) From:
I have read quite a bit about the use of variacs with iRoast roasters.  =
I have a variac and an iRoast but I still have some questions.   I =
understand (I think) that a variac will even out the voltage so one can =
obtain more consistent results (from say a kitchen, garage w/ extension =
cord, or right next to the circuit board).   Here are my specific =
questions...
1.   Why do I blow fuses with my Variac (only tried it once).
2.   Logic behind being able to do multiple roast with the use of the =
variac.
3.  Where the heck does one set the variac knob???   Or does it not =
matter as long as it is in the same place.
4.  Other advantages to using a variac.
Thanks
 
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4/1/2007 8:49 PM

2) From: miKe mcKoffee
Since no one else has answered I'll jump in.
Re 1) Can be various causes for blown fuse. Most commonly over load. What is
the rating of your variac, more specifically what is the fuse rated? While
you said "blow fuses" (plural) you also said "only tried it once". Also
possible simply had a bad fuse.
Re 2) Don't understand question as stated. If you meant multiple back to
back roasts variac would have zero impact.
Re 3) You set the knob where ever is needed to yield the desired output
voltage. For a given point on the knob output voltage will vary depending on
the input voltage. The only way to know for sure is to measure the voltage
with a meter.
Re 4) Advantages to using a variac? Varies depending on roaster,
implementation, imagination... And understanding (at least rudimentary) of
the principles applied.
Kona Kurmudgeon miKe mcKoffee
URL to Rosto mods, FrankenFormer, some recipes etc:http://mdmint.home.comcast.net/coffee/Rosto_mod.htmUltimately the quest for Koffee Nirvana is a solitary path. To know I must
first not know. And in knowing know I know not. Each Personal enlightenment
found exploring the many divergent foot steps of Those who have gone before.
Sweet Maria's List - Searchable Archiveshttp://themeyers.org/HomeRoast/
<Snip>

3) From: Dean
A variac can be used to readjust the voltage due to extension cord 
losses or normal power line voltage drift (I'm assuming you have the 
sort that can boost the voltage by 15% or so).  You can also use it to 
change the voltage-dependent performance of a resistive heating element 
to speed up or slow down the roasting.  It won't (can't) compensate for 
the voltage changes  by itself--that's a whole different gadget.
1. I don't know, you have not provided any information for 
troubleshooting this.  Mine doesn't, but I use 2 Rosto.
2. If you're asking about doing multiple back-to-back roasts and the 
influence this has on variac sizing, then:
you can get away with overloading a variac for a while, depending on the 
overload, so if you want to run several batches at a time, you should 
probably use a variac with a  rating close to the current demand of the 
load, if not a smaller (cheaper) one would probably work if you're careful.
2. If you're just asking if this means you can do more back-to-back 
roasts, prob'ly not.
3. If the variac has a dial scale, there is sometimes a mark at 100%--go 
up or down from there for tweaking
3. If the variac has a voltmeter, set it at 120 no load and tweak
3. If neither, plug in your voltmeter to the outlet & measure at no 
load--mark @ 120, tweak
3. None of the above--you're just guessing, variac will only confuse 
you.  Buy a voltmeter, use it carefully. 120 Volt AC can kill you.
4. 3-syllable word starting with a V--how cool is that.
4. You can use it to control the unloaded speed of a universal motor.
4. The only thing it does it raise or lower the voltage without messing 
up the waveform.  That's it. Power =(E^2)/R-->for a resistive load, more 
volts=more power, less=less, it's a control thing.
jay wrote:
<Snip>

4) From: Ross
Hi Jay,
Fuses?  Not a good sign, do you have a voltage meter on the Variac?  If so 
start with 110Volts that seems to be what my IR2 expects.  If you have some 
old rusted out Variac that is blowing fuses (of the correct size) use it for 
a fishing weight/boat anchor.
The advantage of a working Variac is two fold.  You can stabalize the 
voltage at a value that will make your machine logic happy and to some 
extent you can modify your programs on the fly by giving the machine a 
little adjustment up or down, usually under 10 volts up or down to slow or 
speed up the program.  Although this voltage adjustment sounds like total 
control it has some limitations because the IR2 fan will also adjust with 
the voltage so it works against you and limits what you can do, bottom line 
you can't save a bad program but you can make small adjustments that do have 
an effect of a tweek on an otherwise good program.  That's why others have 
seperate controls for their heating elements and fans in other roasters. 
The big advantage is number one, it will correct a voltage source that makes 
your IRoast not work well at all.
Regards,
Ross


HomeRoast Digest