LOW VOLTAGE WARNING

[Lektrk]

The resistance of the motor may necessarily NOT stay constant.  You have impedance to play with too, CEMF, other issues, but probably diving deeper than most care to understand or even can.  Go ahead and plug your 115 appliance into 220 volts.  Ill stand by with the camera because yer gonna let the magic smoke out.

Aaron

I'm not saying you can run a 115V appliance on 230V, they have to be made to run on either and then generally there is a switch to change it or it has to be wired differently. I was commenting on kwksilvers comment that 110 and 220 were the same and also his comment that you can't have a 110V 30A circuit.

[kwksilver]

let's say it stays constant for this purpose. consider it a theoretical exercise. ohm's law V=IR
or the way you stated it:  I=E (orV)/ R  notice the difference in the formula?

I know that for AC it is V=IZ but lets pretend we are DC the motor is a constant resistor and not some inductor style thingy in AC. because I need simple and dumb. undergrad physics was a looong time ago for me.
I think V= I x R no?
I know that the motor is not a perfect ohmic device and that the relationship is not linear when you go far along and that the heat changes the resistor and that the motor isn't a linear reistor anyways.

But should  this resistor not have a direct relationship between current and potential rather than an inverse?
(i.e. if i double voltage from 110 to 220 I expect to have increased current runnign across this resistor NOT decreased it.)

Please feel free to correct me on this. I am no expert at all here, but if I did this wrong then I need to be corrected because I do want to be able to have a clear and correct understanding of basic things like ohm's law.

Felix

[BoldJava]

 I do want to be able to have a clear and correct understanding of basic things like ohm's law.

Felix...

Ohm's law means a Buddhist choir is near by.

B|Java, non-science major

[kwksilver]

quote of the day made by BJ!!!!!!

[paslug]

let's say it stays constant for this purpose. consider it a theoretical exercise. ohm's law V=IR
or the way you stated it:  I=E (orV)/ R  notice the difference in the formula?

But should  this resistor not have a direct relationship between current and potential rather than an inverse?
(i.e. if i double voltage from 110 to 220 I expect to have increased current runnign across this resistor NOT decreased it.)

Yes Felix, your ohms law is absolutely correct. However, a 110v motor would not be run on 220v. It would be able to be configured for either 110v or 220v. In the 220v configuration, it would draw half the current that it would draw in the 110v configuration.

If you visualize 2 windings, at 110v the windings would be run in parallel, and at 220v the windings would be run in series.

When you first look at that, it seems like you are doubling the resistance, and doubling the voltage, so should have the same amps. But, a motor is not a resistor, and works differently.

assume that the motor is rated for 2200 watts (for simple math). 2200w/220v = 10 amps.  2200w/110v = 20 amps

Hope this helps,
Ray

[Ascholten]

the problem here is. we are not worried about the motor... how did that take the lead in this topic.... the worry was the heating element not putting out enough heat to do the job.  the motor was working fine unless i missed a post somewhere....

Yes you would think that 110 v  220 v current halves, .. if you have the correct elements yes, but if you put 220 through a 110 element you double the current, and double the watts, and the element goes poof.

Due to the way they are constructed etc... the actual heat / temperature output of most heating elements is NOT linear with voltage... or to put it another way, they have a pretty tight 'band of operation' volt wise where you wont cook them..

we are talking about line drop issues though...... yes if you wiring is good, but you are having voltage drop problems causing you heat transfer issues,  220 volts might solve the problem for you, but it's a pretty expensive fix to a variac if your wiring.. again is good... or just roasting 14 ounces instead of 16 ounces... as an example..

Aaron

[kwksilver]

I get your explanation regarding the motor. let us go back to a plain resistor with a constant resistance. I think that makes a heating element. it is justa  wire runnign hot on purpose.

[kwksilver]

I think your are absolutely correct regarding the variac as the best real world pragmatic fix to the problem we may face.
The whole 220V thing is my theory/ dreamcraft regarding the cause of such woes.
If one has 220V in the kitchen or where it is needed and one has the choice of purchasing the corresponding appliance. We have a no brainer.
We have a gene or a Behmor at home (me=gene). We immediately have your variac as the fastest most efficient way of addressing a direct issue.
Does this put as all in the same opinion pot? I hope i did not shove anything into your motuh that you did not say.



PS: regarding AC motors. There i quickly meet my end. I understand simple DC motor principle and I have read to try to understand AC principles for motors.This was a long time ago when i was worried about heat dump of a pump into a hydraulic circuit. in either case I quickly met my master there. So I am not fit to dissect the details of how resistance of motors behave with variations in AC or DC vs. AC.

[Chris]

Just for the record, a 110V/20A Variac costs about $125 shipped.

And it can be used on anything: Espresso Machine, Roaster 1, Roaster 2, etc., etc.

We all know you have spent a lot more on silly things like tampers, steaming pitchers, gloves, BBQs, and probably a flux capacitor (you know who you are).

While all this theoretical talk is very interesting, the fix for a home-grade electric roaster is easy (whether you have low voltage, or you just want consistency from roast to roast).  It is called a Variac.  And yes it has some limits (you could not provide 205 volts from a 110 line at the full 20 amps), yes we know that.

And yes, we know now that 220V is superior to 110V, and in the US 110 is the defacto standard.  So you pay an electrician or buy a Variac.

Or do what I am going to do: Put a 880V/100A system in every outlet, and then step down as necessary.  Does anyone know where I can get a Blu-Ray player that will accept 880V without blowing up?
 

[Ascholten]

If you do get a variac, make sure you get one big enough to handle your equipment.  It may cost a few bucks more but if you are running say 950 watts in your roaster,  don't go with a variac that has a 1000 watt rating.  Yes... technically it can take it, but running it at that close to 100 percent of its capacity is not the best method. Also as you boost the volts you will boost the watts you are using as well and can find yourself AT capacity or slightly over,  again it can take a little overload but not the best way to do it.

Id get a 1200 watt or 1500 watt as a minimum...in this instance.  Besides we all tend to end up upgrading eventually, let your machine grow into your variac and use the extra money youd have to spend on yet another bigger variac for your new rig ---pay for that new rig.

For the DC motor thing, I wont go there,  there are actually many different ways to wind DC motors to make them behave differently as well.  Series / shunt field/rotor  etc etc.  Don't feel bad that you don't have the savvy of knowing all this crap, those of us who do, didnt learn it overnight, we have worked with this stuff for years and years.  Wasn't trying to insult you or anything, just point out that unfortunately, it's not just a simple thing .. that'd be too easy for us then 

Heating elements yes, are technically just resistors, but once you start heating something to the point it is turning colors, it can start getting tempermental at that point about many things.  Too much voltage.. not by much, they go pop .... too little... not by much and they are just 'warmers' instead of heaters... touch the thing somewhere and cause a 'cold spot' and it goes crack, followed by pop.... you get the idea..

Heat essentially is caused by current flow,  voltage pushes that current, yet higher voltage means less current needed to make that heat.... all this flows through wires... heat is a bad thing with wires.... current flow through wires, in a sense is a bad thing too... the less we can get away with, the better, less voltage drop... due to heating etc etc..so yes 220 would be better on that mindview because it's using less current however in the usa where we live in a 115 world.. this can be problematic. 

Our main problems are not necessarily the current the device needs, but dragging that current through the wires to get it from your fuse box TO the coffee cooker...the wires are the problem. so unless you were there when they built your house and demanded 12 gauge or even 10 gauge wiring to all your receptacles.. they probably used 14... because its cheaper, and code let them do it.

Ill shut up and go lay over by my dish now.

Aaron

[J.Jirehs Roaster]

Our main problems are not necessarily the current the device needs, but dragging that current through the wires to get it from your fuse box TO the coffee cooker...the wires are the problem. so unless you were there when they built your house and demanded 12 gauge or even 10 gauge wiring to all your receptacles.. they probably used 14... because its cheaper, and code let them do it.

Ill shut up and go lay over by my dish now.

Aaron

I hope I didn't cause some of this 110v 220v debate with my post earlier....

Aaron, correct me if I am wrong.. The 220v 60Amp outlet in my Garage for the ceramic kiln is two 110v lines and one neutral line.. If I were to wire a 110v outlet to each of those 110v lines and the neutral (this is a dramatization, do not try this at home) then plug in my coffee roasting omnibus wont it only draw the amps it needs? and wont that big 60amp line mean I have plenty of headroom even if my line voltage is a little low at the moment?  I know it is not as sure as a variac but I presume it would be closer than the 20 amp kitchen outlet that runs everything in the kitchen 

[Ascholten]

Well, technically yes.

Every house is wired for 220....  through a center tapped transformer.... ie its split in two, so if you take one hot leg and the middle leg you get 110...half the entire 220 being sent to you.

The 110 volt loads, by far the most common in any household should ideally be split between both legs... in other words  dont drag too much energy off one of the hot legs and ignore the other, it could cause problems.....  another common nomenclature for the centertap /halfway point is called the neutral line, which again technically is supposed to be at ground (ie zero)potential... don't depend on tghat, a fault in your wiring will set you on your ass in a second if you automatically assume neutral = ground.

If you have a 60 amp breaker for your kiln and you want to take a bite off one leg, and the other through the neutral / ground  and run your coffee pot,  well that will work very well.  Being 60 amps that wire is very thick  probably 6 gauge or thicker, that will easily handle what your roaster / brewer will need any day.  You can even hook another one up and tap off the other side of the 220 line into neutral .... and thensome.

What you are saying is pretty much what happens in any house... the 220, they take one line, and return it to the neutral for 115 volts... your setup will work fine.   

As for your voltage, you should not have a voltage drop over that setup with your coffee pot, if you do, there is a serious wiring fault, which to be honest, your kiln should have started the fire in your walls long ago with its probably 40 to 50 amp draw...   If the power company is giving you low voltage, there is nothing you can do to change that except a variac, which will allow you to boost it.... if your low voltage under load is caused by the wiring, then bigger wiring, as in your 60 amp rating will help..... or again a variac....

also, yes you are absolutely correct,  your cooker will only draw what it needs....  the 60 amp rating is pertaining to the MAX amount that wire can safely handle,  you can draw UP to 60 amps, and your roaster  will draw whatever amps  .. the thing you have plugged in needs.  if it draws over 60, the circuit breaker will eventually trip.

Aaron