I sort of hit search and got discouraged with the reading. I admit it. I will go back and hit it properly now as I would like to purchase one.

I roast and I am tired of wandering and low voltage being a variable (113-119). I would like to have some control over that. I am not an engineer, far from it, and would love it if someone could explain a VARIAC's functioning in layman's terms, make suggestions of models to purchase (pros and cons), and places to purchase them within canada.

Cheers!

I can't explain it -- I would merely embarass myself -- other than to say it is a mechanism to adjust voltage.

I bought one in Milwaukee as our voltage would fluctuate very low (111-116). I had the power company come out and he said, "You are stuck. Your transformer is about 3 miles away and the equipment is ancient." He checked everything at the house without solution.

I bought an old American model off ebay for ~$120 bucks after a Chinese $100 model burned up on me within 6 months. I bought the Chinese one despite Farm's fair warning. Don't buy one.

Mine is a 22 amp Powerstat (Superior Electric). I love it. With it, I can hold the voltage right at the 119.5-119.8V mark for a good even voltage for use with the Gene Cafe.

The VARIAC current and/or wattage rating must exceed the current or wattage rating of whatever you intend to plug into it. In very simple terms the variac is an adjustable transformer, it is not a voltage regulator though. A variac will allow setting the voltage to your roaster at a given value and you manually adjust from there.

First thing to do is look on the nameplate of whatever you want to power from the variac and see what the ratings are for that device. By the book the variac should be rated 5 to 10% above that device rating.

Variacs are quite heavy so if you are shipping one do not be surprised at the expense. Canadian eBay is probably going to be the lowest cost.

Boldjava wrote:I bought an old American model off ebay for ~$120 bucks after a Chinese $100 model burned up on me within 6 months. I bought the Chinese one despite Farm's fair warning. Don't buy one.

I've had the opposite experience. Bought the used American 22A variac & when that started acting up I bought the Chinese model. Been using it for about a year with no problems.

Variac is a brand name for a variable transformer.
A transformer will allow a linear boost or cut of voltage. It will not regulate voltage. So if the input voltage wanders, the output voltage will wander.

The way a transformer works is that you have a primary and secondary coil (inductor). AC (Alternating Current) swings from positive to negative and the flow of the current through the coils of the primary coil generates a magnetic field which is picked up by the secondary. You have a step up transformer if the secondary has more windings than the primary and a step down transformer if the secondary has less turns. So, basically, if your secondary has half the number of turns than the primary then your 120 VAC on the primary will result in 60 VAC on the secondary winding. There are losses, but as the voltage is dropped, the current available goes up, as P (Power in Watts) = I (Current in Amperes) * (Electromotive Force in Volts). Besides providing a step up or a step down, transformers can also be used for isolation. They are often wound around a metal core to work more efficiently. I should probably say that a current flowing through a wire will generate a magnetic field and that a magnetic field moving through a wire will generate current. This is how motors, generators, and transformers work.

Variacs, also known as auto-transformers allows you to move a slider up and down the secondary winding to tap off the voltage that you want, so if the tap is dialed all the way to one end you'll have 0 V, and if it's dialed all the way to the other end you'll have full voltage of the secondary. Many Variacs have secondarys that provide 120% or 140% of the primary voltage at full rotation which is where you can increase your dropping voltage to a higher voltage. Autotransformers/variacs often have one side of each coil bonded together instead of isolated.

That's the basics, but I did this from memory instead of consulting with a source so forgive me if I left anything out.

When I was in school, I had a transformer in a box that I'd connect to a nine volt battery to generate a higher voltage pulse that I could use to generate a nice jolt. It was a big hit on the playground.

yakster wrote:When I was in school, I had a transformer in a box that I'd connect to a nine volt battery to generate a higher voltage pulse that I could use to generate a nice jolt. It was a big hit on the playground.

This is the part that I understand best.... and it just made my day. Thanks for your description as it does edge me closer to understanding.

So I should think of it as a boost or a drop, but not a regulator? During a raost, my voltage will wander about 3 volts, most typicaly 115-117. The variation will not be more than that. My raoster would roast hotter if the voltage would be higher even if I was in the 117-120 range. So should I understand that a Variable Transformer (just using the proper lingo), will be able to boost it to that but it will not change the 3 volt wander, ex. you can set it to 119 and have it stay there if the input is wandering?

I really appreciate the help on this. So then I have to decide on American or Chinese eh! Other than Ebay, any other sellers to recommend?

With a Behmor, you'll want at least an 18 amp rating. I found an actual General Radio Variac on Ebay for 10 bucks (cost more to ship it than the item cost me). If you've got an active ham radio community near you, check ham swap meets for one.

One of the things I do with mine is drop voltage by 5-7% when 1st crack gets started and the beans go exothermic. It helps stretch first out for better bean development. The one thing you need to be careful of with the Behmor is that when the elements kick off, you'll get that voltage boost back, and you probably don't want to run the roaster at voltages substantially north of 121v for any length of time, so you need to kind of ride the Variac in that situation. But, since you shouldn't be walking away from a roast in progress anyway, it's not a particular problem.

Actual voltage regulation costs a lot more, especially with the current demands of a roaster.

Right, no voltage regulation with a Variac. Using a higher current rating on your Variac than your breaker can result in tripped breakers due to the temporary inrush current when you plug in / unplug your Variac. This can be a nuisance.

All right, I feel pretty well oriented to start my search. I'm not needing regulation, but being able to keep the voltage in a chosen range would be great for my roasts. If anyone hears of one available in canada then please let me know.