Variacs

[jspain]

Variacs and Kill-A-Watts.  Thank you Milo.

I couldn't get any reading off my Kill a Watt voltage meter when running power thru my Variac.  Enter the EE Milo from the Left Coast (no phone booth in which to change clothing; cell phones are cramping his style).

I had read that the dial on the variac should be at "0" and then take up to appropriate level.  Wrong Wroger.  I could never get any reading thru the KAW, regardless of how high I turned the dial.

Milo, thru trial and error demonstrated that the dial on the variac must be set at "85" when plugged in which corresponds with about 120, 85% of the variac's voltage potential.  Something about the KAW needing a minimum amount of power to transcirculate the microcuitry thru the transitory tunnel which parallels the rabbit hole.  Or something like that.

Just have the variac at '85' when you plug it in.


B|Java, business major

When I got mine a year or so ago I didn't have mine set low enough when I plugged it in and popped the breaker. Learned my lesson.....! I use mine exclusively with the Behmor for samples. I have not manipulated mine much to alter roast profiles but use it to maintain constant voltage. I will try at some point to manipulte the roast, but always concerned I ruin SOMETHING!  Jim

[Richdel]

I have some questions about the use of a variac with a Gene Cafe. I have read through this thread, not sure I have found the answer.  First a little background.  I am using an outlet that reads anywhere from 120v to 123v by my Harbor Freight Kill-A-Watt (KAW) knock-off device prior to turn my Gene on.  While my Gene is in heating mode, the voltage often will drop to 116v, and to as low as 114v.  This is to low to roast.  I was able to borrow an older variac to try.  The person who lent me this believes it to be 0-130v. and 22a.  The variac came off a piece of Process control equipment.  He has added an external on/off switch and an external duplex outlet.

So this morning I began my testing.  My outlet is reading 121v prior to turning on the variac or roaster. 
I connect the variac to the house outlet, then out of the variac outlet the KAW device, then the Gene. 
I start the Gene on a 10 minute preheat to 482dgf.  The variac was set to deliver an even 120volts.  When the heater on the Gene kicks ON, the voltage reading on the KAW drops to 111v.   I dial the variac up to a voltage at 118v (this has worked OK for me in the past), and it appears that the Gene is normally preheating.  When the Gene reaches temp and the heater turns OFF, the voltage reading on the KAW is 127v. 

This is the problem I am trying to resolve.  Does the Gene input voltage requirements allow for a voltage that high (127v), or will this damage the circuitry of the Gene?  When others are using their variacs, are you constantly dialing voltages up and down depending on the whether the heater is on or off?  Is the variac even working correctly?  I can not roast properly with the Gene unless I am getting 117v (or higher) with the heater running, and ideally 118-120volts.  But there seems to be about 10volts difference when the the heater on the Gene switches from one state to another when using the variac. 

Any help would be greatly appreciated.  Thank you.

[Richdel]

I just finished 3 roasts using the variac I mentioned in the above post.
On one of the roast, after adding the beans, I set the temp on the Gene to 465dgf.
The KAW showed the volatge dropped to 111v.  I adjusted the variac to get a reading of 119v.
This produced a wattage reading on the KAW to above 1300watts.  Everything was fine until
the Gene reached 465 and began turning the heater on and off trying to maintain the 465dgf.
The KAW showed valtages as high as 136v (heater on and a watt reading of over 1500watts) and
as low as 111 when the heater was off (wattage reading of 5 watts).  I spent a lot of time
during the roast adjust the variac to keep voltages between 116v and 126v.  I read somewhere
that most AC appliances will not be harmed by voltages +/- 5% of the appliance rated voltage.
Since the Gene back panel lists the Gene as a 120v appliance, +/- 6 volts from 120v was the basis
for this decision. 

Is this how others are using their variac?  Constantly adjusting voltages to keep an even 120v. 
The only advantage I see right now is the ability to use outlets that I was not previously able to use
due to low vaoltage. 

Any Gene users with variacs who can help me?

[BoldJava]

No, I have nowhere near the huge swings you are reporting.  I use the Gene and the Variac.  It will stay within a few volts of 119 and I will tweek it if it drops below 117 to return it to 119.  Likewise, I never get spikes above 121.

I once discussed it with Tim at FreshRoast Inc.  He said high voltage 123 and above is problematic on the circuitry of the Gene.  I would suggest you call him and walk through what is occurring for you with your Gene.   He is a patient gent.

888-757-2326 or 435-940-1616, Tim Skaling

[Richdel]

No, I have nowhere near the huge swings you are reporting.  I use the Gene and the Variac.  It will stay within a few volts of 119 and I will tweek it if it drops below 117 to return it to 119.  Likewise, I never get spikes above 121.

I once discussed it with Tim at FreshRoast Inc.  He said high voltage 123 and above is problematic on the circuitry of the Gene.  I would suggest you call him and walk through what is occurring for you with your Gene.   He is a patient gent.

888-757-2326 or 435-940-1616, Tim Skaling

When you set the variac to 119v, is this as the heater is running and the Gene is ramping to a preset temperature?  If so, when the the Gene reaches that temperature or when the Gene goes to cooling mode (the heater is turned off), you are saying that the voltage reading is only increasing by a couple of volts upwards?

I wonder if the variac i have is faulty?  Not sure how to test it though.  I have used a multimeter on the outlet to verify what voltage i needed to set it at.  Maybe the variac is losing the ability to hold the voltage, just seems ironic that this happens as the heater turns off.

 Thanks for the insight.

[BoldJava]

When you set the variac to 119v, is this as the heater is running and the Gene is ramping to a preset temperature?  If so, when the the Gene reaches that temperature or when the Gene goes to cooling mode (the heater is turned off), you are saying that the voltage reading is only increasing by a couple of volts upwards?

Yes, just a 2-3 voltage jump when heater cycles on/off.  My main need for a Variac is that I often roast Sunday pms.  Folks are running air conditioning, doing the wash, etc.  That is when my home experiences lowest voltage and as you said, 114-116 doesn't cut it in the Gene.

I wonder if the variac i have is faulty?  Not sure how to test it though.  I have used a multimeter on the outlet to verify what voltage i needed to set it at.  Maybe the variac is losing the ability to hold the voltage, just seems ironic that this happens as the heater turns off.

 Thanks for the insight.

Haven't a clue.  A couple of the gents here are EEs and should be able to make suggestions.  I would compare the fluctuations without the variac and see if you get those swings (just spoil a batch, even at 114) and see how wide a spectrum of voltage readings you are getting.  That would help you troubleshoot in advance of calling Tim.

B|Java

[Gime2much]

[/quote]


I wonder if the variac i have is faulty?  Not sure how to test it though.  I have used a multimeter on the outlet to verify what voltage i needed to set it at.  Maybe the variac is losing the ability to hold the voltage, just seems ironic that this happens as the heater turns off.

 Thanks for the insight.
[/quote]

 The variac acts on percentage so it may be your voltage at that outlet fluctuating. If the source voltage is dropping and spiking, the output voltage of your variac will mirror that + or - the offset percentage selected. Only way to know for sure is to test the voltage coming out of the outlet under load. 

[Richdel]

I wonder if the variac i have is faulty?  Not sure how to test it though.  I have used a multimeter on the outlet to verify what voltage i needed to set it at.  Maybe the variac is losing the ability to hold the voltage, just seems ironic that this happens as the heater turns off.

 Thanks for the insight.
[/quote]

 The variac acts on percentage so it may be your voltage at that outlet fluctuating. If the source voltage is dropping and spiking, the output voltage of your variac will mirror that + or - the offset percentage selected. Only way to know for sure is to test the voltage coming out of the outlet under load. 
[/quote]

I agree with you, but how do you check circuit voltage while under load.  My understanding is the KAW is measuring the the volt/watt/amps of the appliance attached to it and what it is pulling.  I have used the KAW connected directly to the outlet on one side and the Gene on the other side.  When i have done this in the past, before starting the Gene (and Gene heater), the KAW reading was 121v-123v.  As soon as the Gene heater starts, the KAW reads 114-117.  This is what I was trying to rectify by using the variac.  I believe the circuit to be a 20amp circuit, with no other active objects pulling volts/amps on the circuit.  I have left the KAW connected (no Gene, just KAW connected directly to outlet) for several hours and checked the reading several times during those several hours, and have only seen an occasional 1v drop or 1v jump.  So why would 11amp device (KAW says this what the Gene is pulling when the heater is ON) on a 20 amp circuit drop the voltage by 7-8 volts?  Man I wish I had paid better attention when I took those electronics classes.

So back to the question, how can I measure a circuit under load? 

[Gime2much]

I agree with you, but how do you check circuit voltage while under load.  My understanding is the KAW is measuring the the volt/watt/amps of the appliance attached to it and what it is pulling.  I have used the KAW connected directly to the outlet on one side and the Gene on the other side.  When i have done this in the past, before starting the Gene (and Gene heater), the KAW reading was 121v-123v.  As soon as the Gene heater starts, the KAW reads 114-117.  This is what I was trying to rectify by using the variac.  I believe the circuit to be a 20amp circuit, with no other active objects pulling volts/amps on the circuit.  I have left the KAW connected (no Gene, just KAW connected directly to outlet) for several hours and checked the reading several times during those several hours, and have only seen an occasional 1v drop or 1v jump.  So why would 11amp device (KAW says this what the Gene is pulling when the heater is ON) on a 20 amp circuit drop the voltage by 7-8 volts?  Man I wish I had paid better attention when I took those electronics classes.

So back to the question, how can I measure a circuit under load?  
[/quote]

 You are testing the cct under load. If it is dropping 7 volts under load, it will still drop that much thru the variac. It might be that the wire feeding this outlet is marginal or quite a distance from the breaker box. Even the breaker or outlet could be getting weak (no longer making good contact). All the variac is capable of doing is to increase or reduce the voltage feeding it and it is not self adjusting. As the feed  decreases in voltage so does the output of the variac and the same goes for increases. If you want to keep the voltage out of the variac constant as the roaster cycles you must be watching and adjusting manually.

[gt]

I agree with you, but how do you check circuit voltage while under load.  

Just remove the variac and plug in direct, then measure the voltage at the plug/socket while idling and while under load.  Then you can tell how much of your voltage drop is due to your wiring and how much is dropping across the variac.

 

[Richdel]

Thank you everyone for your insights. 

Gime2much - I believe your response validates what I did today.
I will have to manually adjust as the voltages change due to the heater cycling.
I just wasn't sure why the voltage difference was so much. 
But looking back at the roasting I did prior to the variace use, and the roasting
I did today, the drops are similar.  I was hoping the variac would keep the outgoing
line voltage steady.  I see now that this is a manual operation.

Still need to find out why I have such a big drop on the circuit when the Gene Heater
turns on.  House is relatively new, but wiring, breaker, or outlet could be bad.  Or maybe
there is something else on the circuit I am unaware of.  Anyway, thanks everyone for your help.

[rgrosz78]

I guess this is the week to show off our new variacs. I have no electronics / electrical hacking ability, so I bought a complete unit for $200.

Mine came packed in foam in a giant box. I checked to be sure that it can boost the volatage above 120 with my Kill-A-Watt.

I won't get to roast till the weekend.

[JHan816]

Rick and Chris, good find on those Variac units. Staco equipment is very well made and you shouldn't  have any trouble with it.

[BoldJava]

When I roasted on Sunday, I had between 111 and 113 at the outlet.  Thank goodness for the variac -- clipped right along between 119 and 122.

[BoldJava]

My variac is 22 amps.  Kept tripping the 20 amp, shared line I had it on. Electrician came out and put a dedicated line/circuit in the kitchen for me; 20 amps.  He said with new wire and this quality of breaker, it should support it.  He showed me how to put a 25 amp breaker in the box should it become problematic.  Code would call for a 20a amp though he assured me the line #12 was sufficient to handle the current.   He uses #10 wire for 30 amp and above.


So far, so good.