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Topic: Variac purchase (17 msgs / 371 lines)
1) From: Maureen Azcoitia
I am interested in buying a variac.  I know that our hosts have one
available, however I am currently being impatient and would like to
know what store I can walk into and buy one.  I searched lowes,
homedepot, and ace but with no luck.  Am I looking in the right place?
 What national store chain might have one?  In what kind of store
should I be looking for a variac?  Out of respect to our host, please
reply offlist.
Thanks,
Maureen

2) From: raymanowen
Maureen, what problem are you trying to solve?
Let me reply onlist, not with a source of Variacs, but with some insight
that might save some equipment from being run into the ground.
Put it this way: there are many electrical appliances available on the
market, and they're all designed to operate on a certain fixed supply
voltage, usually  10% of nominal. That is to be certain the device will
operate normally in spite of variations in electrical distribution.
If you want to force "more" out of a device by turning its power supply
higher, it's not likely to be successful unless the appliance is something
like an incandescent light bulb or other electrical heating device.
The Variac can supply anything from -100% (0) to + 20% (140v). Way outside
the UL (insurance) certification. They don't supply Variacs anywhere that
the man on the street can get one easily.
It's too easy to inadvertently destroy equipment or set fires with an
unattended Variac(r). If your supply voltage is too low, a Variac is not th=
e
solution, just an additional problem. Look up MiKe's fan voltage mod.
If that looks obscure to you, I humbly and respectfully suggest that a
Variac could cost you more than you expect.
Cheers and 73 -RayO, aka Opa!
On 8/25/06, Maureen Azcoitia  wrote:
<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Might=
y
Wichita (ex- NYC Paramount) WurliTzer- 1976

3) From: Maryann & Dave Schellenberg
raymanowen wrote:
<Snip>
Ray, I wonder if on second thought, you might agree that you have 
overstated things a bit here.
I don't know all the reasons why the particular power receptacle that 
Maureen has chosen to use for roasting might have too low a voltage for 
her purposes.
I do know that some devices (some have said a good example is a HotTop 
roaster) don't operate well at voltages below 120v.
A Variac may well be the best solution for that problem - certainly 
cheaper than rewiring the house, especially if it is a rented house.
I used a Variac very effectively to lower the voltage to my Poppery I 
heating element at certain stages of the roast, so that I could follow a 
recommended profile.
In fact, I would heartily recommend it over the use of a long extension 
cord for that purpose.
I can't answer Maureen's question as to where, other than Sweet Maria's, 
she should look to find a Variac, because I've never seen one in a store.
I think that's probably because there's very little demand for them from 
the average householder.
Dave S.

4) From: Maureen Azcoitia
I would like to do exactly what Dave S. is doing.  I roast using a
popper and would like to try some profiles.  I know very little about
voltage and such, so thank you RayO for that information.  I will most
likely end up getting the one SM offers, I was just trying to save on
shipping (time and cost).
On 8/25/06, Maryann & Dave Schellenberg  wrote:
<Snip>
.
<Snip>
ribes) go tohttp://sweetmarias.com/maillistinfo.html#personalsettings<Snip>

5) From: Floyd Lozano
I made the mistake of never  buying one for a reasonable price from
Sweet Maria's back when they sold them, and now I want one ;)  Anyone
know a good place to get a reasonably priced and well performing
variac?  I guess it needs to be 0-140v output, 15A (if not 20, though
I guess i should make sure my circuits at home can handle that).
-F
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6) From: Allon Stern
On Aug 20, 2008, at 12:32 PM, Floyd Lozano wrote:
<Snip>
Variacs are heavy.
I suggest buying locally, if at all possible.
Search on eBay, and sort by distance: nearest first
search on:
variac
variable transformer
powerstat
staco
pay attention to the voltage & frequency rating too.
Note that there's nothing wrong with putting a 20A variac on a 15A  
circuit - the variac is rated at up to 20A - you just can't draw that  
much from the circuit; it's the device on the output of the variac  
that is drawing the current, not the variac itself.
-
allon
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7) From: raymanowen
You could even use a single phase of a polyphase variable transformer. It
would work OK, if you disconnected the wye or delta wiring. They're just
very big and very heavy.
Say you have a 115v, 15a toaster/heat gun/coffee roaster ... powered through
an adequate *Variac*. When you have the *Variac* set to less than 115v
(stepdown), the heating device will draw proportionally lower current, and
the *Variac* will draw even lower current than the heater draws, by the
stepdown ratio.
The variable transformer is nearly 100% efficient, the heat loss is
miniscule. When set to the 115v example output, the heater is happy, *Variac
* is happy and Reddy Kilowatt (house wiring and devices) is happy.
If you set the transformer for 140v output, the heater will draw over 18a,
and the transformer will multiply that current to over 22a draw on the power
line. Your reward will be a blown breaker in the wiring panel, at best.
If weak wiring was the original problem, several others might become evident
at this point. The blue fire and smoke would be good places to check.
Cheers, Mabuhay -RayO, aka Opa!
Got Grinder?
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8) From: silascoelho
Another suggestion (I'm trying to do it now) instead of Variac you can buy a 
1500W (or more dimmer) there are some good ones at Ebay, for what I saw, 
cheaper then Variac's
regards
Silas

9) From: Michael Wascher
I was able to find one at a good price, just the bare variac (well, it did
come with a knob). Mount it in a box, wire a cord & plug, and you're good to
go!
On Thu, Aug 21, 2008 at 1:35 AM,  wrote:
<Snip>
-- 
"Crime does not pay ... as well as politics." --Alfred E. Newman
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10) From: Robert Joslin
Floyd
    A unit which appears to be identical to the unit  once sold by Tom is
available at Marlin P. Jones & Assoc. Inc.  Web www.mpja.com
Page 6 of current catalog.  Specs look the same...output 0-130 V @ 2 KVA
(15A).  Price is about the same.  I'm posting this under the assumption that
our host no longer sells this item.          Josh
On Thu, Aug 21, 2008 at 9:18 AM, Michael Wascher  wrote:
<Snip>
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11) From: Justin Marquez
The beauty of a Variac is that it can correct low voltage issues, whereas
the dimmer dealie only lowers the voltage.
Safe Journeys and Sweet Music
Justin Marquez (CYPRESS, TX)
On Thu, Aug 21, 2008 at 6:05 AM, silascoelho wrote:
<Snip>
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12) From: Ira
At 04:05 AM 8/21/2008, you wrote:
<Snip>
Variacs can raise the voltage, Dimmers commonly only lower it.
Ira
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13) From: David Liguori
silascoelho wrote:
<Snip>
Dimmers are OK for heating elements, not good for electronics, like the 
control circuitry of a roaster.  You may luck out, but many power 
supplies for electronic devices expect to see something reasonably close 
to a sine wave.  Anything involving inductance like a motor or 
transformer could be a disaster.
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14) From: Dean
"Anything involving inductance like a motor or transformer could be a 
disaster. "
No argument with the first part (below), but of the motor is a universal 
(brush-type), it works just fine on a "dimmer".  Which is a problem 
because slowing the fan down is kinda at crossed purpose to controlling 
the heat.
I just last weekend  split wired my Rostos to get fan and heat 
control--been using a variac and a router speed control to turn the heat 
down but was not getting the control I was hoping for. 
As far as ratings go, if you use a varaic in batch mode rather than 
continuously you can get away with an "under-sized" one.  Check out the 
duty cycle ratings on the Superior Electric website and proceed 
accordingly.  There have been at least a couple of discussions regarding 
this in the past--check the archives for miKe or Dean.
Dean
In da weeds.
David Liguori wrote:
<Snip>
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15) From: raymanowen
"...the dimmer dealie only lowers the voltage."
The complete design using a Triac/diac dimmer would incorporate, say, a 24v
boost transformer with the 0-100% T/d dimmer control at the input.
With the fixed boost transformer, the dimmer gains a lot of utility with
high efficiency.
Cheers, Mabuhay -RayO, aka Opa!
Eschew Partial Designs
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16) From: raymanowen
" instead of Variac you can buy a 1500W (or more dimmer) there are some good
ones at Ebay, for what I saw, cheaper then Variac's"
"Dimmers are OK for heating elements, not good for electronics, like the
control circuitry of a roaster."
"You may luck out, but many power supplies for electronic devices expect to
see something reasonably close to a sine wave."
Then all of the Switch Mode power supplies are just so much junk? I doubt if
they care what is coming in, only the capacitor potential at the output. If
some sap design needed a sine wave input, a 1:1 input transformer, with a
tertiary winding at parallel resonance with a capacitor would do it.
Some have gone overboard and rectified any and all incoming garbage to
supply an HF power oscillator driving another resonant circuit at 10 - 100
khz. You can get all the perfect sine waves and power you want.
"Anything involving inductance like a motor or transformer could be a
disaster."
Does that mean all of the variable speed drill motors don't really work,
just an illusion? Mmmm- all these tools that only appear to work properly-
sure fooled me.
Don't believe everything you hear.
Cheers, Mabuhay -RayO, aka Opa!
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty
Wichita (ex- NYC Paramount) WurliTzer- 1976
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17) From: silascoelho
David
that is right, my intention is to use that with my Popper heater only (I 
have small trafo 12Vx1A for the dc motor) . Unless the electronic device 
that will be connect to the variac is isolated by a transformer + linear 
power supply, and doesn't use the line frequency as reference (zero cross 
detection and similar) the variac really cannot be used.
For heater, no issues at all
Silas


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