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Discussions > Coffee > Home Roast > [SOLVED] Using a...  
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rsnidjik
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rsnidjik
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Posted Fri Sep 6, 2013, 6:46am
Subject: [SOLVED] Using a transformer as voltage regulator
 

For several years, I've been running my 220V Rancilio Silvia (bought when I was posted overseas) through a hefty transformer set for 110V input, 220V output. I've had no problems whatsoever.

This is the transformer I have:

Click Here (www.amazon.com)

This transformer is not a toy. It's not a travel accessory, as it weighs over 20 pounds.

Now I'm in the market for a used Hottop roaster. Since I'm now in the U.S., I'm going for a 110V Hottop. I've seen numerous references to the advantages of running a Hottop through a Variac or other voltage regulator. Here's my question:

Would it be advantageous to run the 110V Hottop through the transformer but set the transformer output to 110V (i.e., input 110V, output 110V). Would this not have the effect of regulating the voltage somewhat?

I don't have any voltage testing equipment, so I'm asking for an educated opinion.

Thanks!
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triodelover
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triodelover
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Posted Fri Sep 6, 2013, 7:22am
Subject: Re: Using a transformer as voltage regulator
 

All transformers are ratio devices. In other words, their output will be a ratio the input that depends on their windings and internal resistance.  For a step up/down transformer, it's important to know what the input (i.e. line) voltage is.  For  transformer spec'd with a 110V primary, if your line voltage is something like 125 VAC (higher than specified line voltage is not uncommon), the output will be approximately 1.136x the nominal output specification (i.e 220VAC x 1.136).  A similar calculation would exist if your line voltage was lower than spec but in the other direction.

I checked the website of your step-up tranny and it's not clear whether it includes any VR circuitry to mitigate this effect of your line voltage.  Even so this won't accomplish what you can do with a variac unless your only goal is to feed the roaster a constant defined voltage.  I haven't read all the threads on the Hottop, but I'm guessing that folks use a variac to control roast temperature more precisely  than the Hottop's controls permit.  In particular, it could be used to stretch out the roast by "starving" the heating elements.  Your step-up won't provide this level of control.

At any rate, if you're going down this road, get a good multimeter.  You'll want to know exactly what the VAC output of the variac at different rheostat settings.
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rsnidjik
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rsnidjik
Joined: 23 Oct 2003
Posts: 74
Location: Dislocated
Expertise: I love coffee

Espresso: PID'd Silvia 230v, 110°...
Grinder: Baratza Vario
Vac Pot: nope
Drip: nope
Roaster: West Bend Poppery 1500W; am...
Posted Fri Sep 6, 2013, 10:09am
Subject: Re: Using a transformer as voltage regulator
 

Thank you for your knowledgeable reply, triodelover. I had been thinking the reason for using a Variac with a Hottop was to maintain a steady voltage. It looks as if it's more complicated than that.

To get it straight, you're saying that any fluctuations in my household current's voltage would be reflected in the transformer's output.

I think I will pony up for a multimeter. Most of my friends have them, and maybe I'd come across less like the liberal arts ditz that I am if I owned one of these.
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JKalpin
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JKalpin
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Posted Fri Sep 6, 2013, 10:54am
Subject: Re: Using a transformer as voltage regulator
 

When my 1500W Behmor is drawing full power my line voltage varies from 116V to 119V.

If I had a Variac, I could adjust it up to fluctuate between 119V to 122V.  That might result in somewhat faster roasting and darker roasts with larger batch-size.  

I think you understand it right:  With a Variac you can move the whole range up or down …but you still will have the variation.

Voltage regulation would be more expensive.

If you were going to buy a multimeter, why don't you start off with a $20 Kill-a-Watt meter, which gives you voltage, current, watts and several other less-used variables, to a device plugged into it.  I have a Fluke multimeter but …the Kill-a-Watt meter is much more convenient.

 
Jerry
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rsnidjik
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rsnidjik
Joined: 23 Oct 2003
Posts: 74
Location: Dislocated
Expertise: I love coffee

Espresso: PID'd Silvia 230v, 110°...
Grinder: Baratza Vario
Vac Pot: nope
Drip: nope
Roaster: West Bend Poppery 1500W; am...
Posted Fri Sep 6, 2013, 11:05am
Subject: Re: Using a transformer as voltage regulator
 

Thanks, Jerry. I appreciate the explanation and the recommendation. I'll put a Kill-a-Watt meter on my wishlist. A toy -- er, I mean tool -- like this is a much better gift than socks or underwear.
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triodelover
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triodelover
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Location: Knoxville, Tennessee
Expertise: I love coffee

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Posted Fri Sep 6, 2013, 11:11am
Subject: Re: Using a transformer as voltage regulator
 

rsnidjik Said:

To get it straight, you're saying that any fluctuations in my household current's voltage would be reflected in the transformer's output.

Posted September 6, 2013 link

Yes.  This is  one reason to want well-designed power supplies with good isolation on all the things whose performance would be noticeably affected (computers, audio equipment, that big flat screeen, etc).

rsnidjik Said:

I think I will pony up for a multimeter. Most of my friends have them, and maybe I'd come across less like the liberal arts ditz that I am if I owned one of these.

Posted September 6, 2013 link

Hey, I  was trained as a scientist with my heart in the liberal arts.  I had a friend once who used to refer to me as a liberal artiste who does science.
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rsnidjik
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rsnidjik
Joined: 23 Oct 2003
Posts: 74
Location: Dislocated
Expertise: I love coffee

Espresso: PID'd Silvia 230v, 110°...
Grinder: Baratza Vario
Vac Pot: nope
Drip: nope
Roaster: West Bend Poppery 1500W; am...
Posted Fri Sep 6, 2013, 11:30am
Subject: Re: Using a transformer as voltage regulator
 

triodelover Said:

Hey, I  was trained as a scientist with my heart in the liberal arts.  I had a friend one who used to refer to me as a liberal artiste who does science.

Posted September 6, 2013 link

My twin from Reverso World (or is it Bizarro World?)! How about a coffee haiku contest?

Or not.

:)
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triodelover
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triodelover
Joined: 18 Sep 2004
Posts: 7
Location: Knoxville, Tennessee
Expertise: I love coffee

Espresso: Cremina, MCAL, Pavoni Pro,...
Grinder: HG One, Zass, Dienes and...
Drip: Technivorm Mokkamaster
Roaster: Quest M3
Posted Fri Sep 6, 2013, 2:57pm
Subject: Re: Using a transformer as voltage regulator
 

I'm terrible at haiku.  I never can remember the line count.  How about coffee limericks for adults? ;-)
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triodelover
Senior Member
triodelover
Joined: 18 Sep 2004
Posts: 7
Location: Knoxville, Tennessee
Expertise: I love coffee

Espresso: Cremina, MCAL, Pavoni Pro,...
Grinder: HG One, Zass, Dienes and...
Drip: Technivorm Mokkamaster
Roaster: Quest M3
Posted Fri Sep 6, 2013, 2:58pm
Subject: Re: Using a transformer as voltage regulator
 

triodelover Said:

Posted September 6, 2013 link

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rsnidjik
Senior Member
rsnidjik
Joined: 23 Oct 2003
Posts: 74
Location: Dislocated
Expertise: I love coffee

Espresso: PID'd Silvia 230v, 110°...
Grinder: Baratza Vario
Vac Pot: nope
Drip: nope
Roaster: West Bend Poppery 1500W; am...
Posted Fri Sep 6, 2013, 7:16pm
Subject: [SOLVED] Re: Using a transformer as voltage regulator
 

Welp, since I drove this thread OT, I should just link to this thread and leave it at that.

Oh, and there's also this.

Thanks for the technical info, guys. I'll mark this as SOLVED.
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