Variacs

[BoldJava]

Couldn't roast this past weekend as the highest voltage was about 114.5.  Came down this morning and it was 114.1 and a water kettle dropped it down to 112.  Like I can roast with that?

Gotta deal with this as more hot weather is in the forecast and a/c's will be screaming.  I can build an SC/TO under Peter's tutelage and get tossed out of the house for smoke or get a variac and heat up the Behmor (thinking of moving to the RK drum next spring and calling it a ball game). 

So, variacs...15A or 20A? (Line is wired with 20A). 15A is the suggested minimum amperage, right?  Brands?  Vendors?  Dibs on Chris's?

B|Java

[bwilson]

I've been checking E-bay for a real cheap 15-20 amp variac that is in very good condition.     They don't seem to make them cheap and practically new at the same time.     So I patiently wait.   

[peter]

I should just do a search, and answer my own question, but here goes anyway...

How does a variac managae to take 114v and change it to 120v?  What is it taking out of the equation to add the volts in?  What are the practical limits of the variac's magic?

[ButtWhiskers]

I should just do a search, and answer my own question, but here goes anyway...

How does a variac managae to take 114v and change it to 120v?  What is it taking out of the equation to add the volts in?  What are the practical limits of the variac's magic?

Very tempted to give you the 'justf***inggoogleit.com' link...   

A variac is a variable transformer that allows you to control voltage through placement of brushes on a wire-wrapped magnet.  You actually get bonus voltage due to electromagnetic induction if you have the brushes set in the right place in relation to the copper coils and magnet.  Most of these variable transformers are effectively limited to 120% of the original voltage.

[peter]

Thanks for your kindness, O' Patient one.  I mean that, since I'm usually the short one w/ those who won't google.

Along those lines, since the power in the line has a limit, does boosting the voltage reduce the amperage, or something like that.  I wouldn't think that you can get something for nothing.

[cfsheridan]

Power is constant (or there's only a minor (5% or so loss with a good transformer).  So yes, upping the voltage reduces the available current in the circuit.  Since your circuit will be limited by the circuit rating (15A or 20A) or your variac fuse, it doesn't usually become a problem.

[ButtWhiskers]

Power is constant (or there's only a minor (5% or so loss with a good transformer).  So yes, upping the voltage reduces the available current in the circuit.  Since your circuit will be limited by the circuit rating (15A or 20A) or your variac fuse, it doesn't usually become a problem.

A good transformer is actually 99.75% efficient (about 0.25% power loss). 

 

[cfsheridan]

Spot on, BW.  Caught me doing radcon math again.

[paslug]

Along those lines, since the power in the line has a limit, does boosting the voltage reduce the amperage, or something like that.  I wouldn't think that you can get something for nothing.

I guess another way to say the same thing, If you feed the Behmor 120 Volts, the power consumption will be a little over 1600 Watts when it is on high power.

Volts Times Amps = power.  You will see the same 1600 watts both on the input and the output of the variac. On the input you will be pulling a higher current to provide the 1600 watts at the lower voltage.

I think you will find that the higher the current rating of the variac, the less you will have to play with it to maintain a constant output voltage. Mine is rated at 20A, and I still see my voltage vary about 4 Volts or so when the Behmor kicks in to high power. I believe a lower rated variac will give you more variation.

I watch the roast anyhow, so it is no problem to turn the variac up a little to maintain the voltage that I want.

[PaulM]

This may sound off the wall, but if your interior wiring is reasonably modern, the problem may be with power distribution on your street. Low voltages like that kill refrigerators, etc., all the time. I once lived on an older street with very, very variable power. So I called the power company. They came out to investigate, and lo and behold they concluded that the problem was THEIRS to fix! Then they installed a new transformer for my street, and my power was wonderful after that.

So hey, before buying a variac, maybe see what a phone call to the utility accomplishes, you might be surprised. I mean I couldn't believe I got satisfaction like that, and for free. In fact I was so surprised that I would guess that you won't have a similar experience. But then again you might... And if you do it will add years to the life of your refrigerator.

[BoldJava]

This may sound off the wall, but if your interior wiring is reasonably modern, the problem may be with power distribution on your street. Low voltages like that kill refrigerators, etc., all the time. I once lived on an older street with very, very variable power. So I called the power company.
...

Thanks, good suggestion and I will begin there.  There is nothing to lose and everything to learn.

B|Java

[BoldJava]

This may sound off the wall, but if your interior wiring is reasonably modern, the problem may be with power distribution on your street. Low voltages like that kill refrigerators, etc., all the time. I once lived on an older street with very, very variable power...

Mr PoleMan just left, scratching his head.

^  All the amperage is being drawn on one of the two outside lines (yet is balanced in the basement).
^  Replaced connectors on each of the 120 and neutral lines
^  Observered that the neighborhood has clearly had issues as he pointed out transformers on two of the poles near the house
^  Is requesting totally new service lines from pole to house
^  Is requesting "charting," to monitor the voltage for a period of time.
^  The transformer ("2200," an old POS according to him) is quite distant (42nd and FDL<?>, LakeCheddar boys) ... like I was supposed to know a 2200.

Stay tuned.  He said that they need to do all their stuff first before looking at the issue of one line drawing all the amperage (something at my box --) before calling an interior electrician or buying a Variac.

"Yeah, I will wait on that," in my best Dan Akroyd voice.

B|Java

[BoldJava]

When is Father's Day? 

Best price I have found on 20amp Variac, right in Ray's backyard:

http://www.circuitspecialists.com/prod.itml/icOid/7673

$105.  Group buy?  <wide grin>  I do think I with have BtR, my brother-in-law pick one up the next time he is down in Phoenix as we are flying out to visit non-Czarinita in Albuquerque and BtR and family in Northern Az at Thanksgiving.

Nah, just ship it.

B|Java

[kelppaddy]

That is an excellant price compared to the same thing on eBay for $165.

http://cgi.ebay.com/20-Amp-Variac-Variable-Transformer-NEW-8302_W0QQitemZ220262746554QQcmdZViewItem?hash=item220262746554&_trkparms=72%3A552%7C39%3A1%7C66%3A2%7C65%3A12&_trksid=p3286.c0.m14.l1318

They are made in China.

kelppaddy

[BoldJava]

When is Father's Day? 

Best price I have found on 20amp Variac, right in Ray's backyard:

http://www.circuitspecialists.com/prod.itml/icOid/7673

$105.  Group buy?  <wide grin>....

Nah, just ship it.

B|Java

B|Java