Would a 110v to 220v transformer work?

[travis howe]

Was going to have my electrician run some new circuits into my garage for some 230v tools.

Is it just as cheap / safe to use transformers or not a good idea? Would like 3 or 4 230v outlets. Breaker box in basement but not far up into shop.

[Jamie Buxton]

Technically, you can use a transformer to make 230 volts in your shop, but it probably won't do what you want. The usual 115 volt outlet can provide 20 amps. When you transform it to 230 volts, you'll only be getting 10 amps. That is, the product of volts times current on the input side is the same as on the output side. You don't get any more power by running through a transformer. The usual 115 volt outlet can run a 1 1/2 horsepower machine, but is getting pretty marginal for a 2 hp machine, and doesn't work at all for a 3 hp machine. The transformer-supplied 230 would have the same problem. That's why folks bring 230 into their shops. It offers the ability to run 3 hp and even 5 hp machines.

[Mike Henderson]

Assuming you're going to pull some real current at 240V, the transformer would be iffy. The reason is that you'll have to pull twice as much current at 120V, plus some current to account for the inefficiencies of the transformer. That's really big wires for the 120V service, and those wires will have to be pulled anyway. Also, you'll have to pay for the transformer.

You're MUCH better to just run 240V from the distribution box.

Mike

[travis howe]

I figured there was a logical answer...thanks all!

[James Baker SD]

You are likely to already have 220V in the breaker box if it is the main box for the house (you need it for stoves, dryers etc). It is just two 110V lines out of phase. I wired my own 220V outlets in the shop just making sure each leg of the 220V was from a different 120V phase. My machines seem happy with my work.

James

[Scott T Smith]

Was going to have my electrician run some new circuits into my garage for some 230v tools.

Is it just as cheap / safe to use transformers or not a good idea? Would like 3 or 4 230v outlets. Breaker box in basement but not far up into shop.


NO it will not work. The transformers that you see advertised for 120 to 240V conversions are for operating non-US 240V equipment (240V single leg power).

US power is two legs of 120V that are 180 degrees out of phase, and 240V across the phases. I don't know of a transformer can provide you with two legs of 180 degree separated 240V power from a single 120V power input

If possible, consider running a 50A or 100A circuit from your main load center to a new sub-panel in the garage.

[Mike Henderson]

NO it will not work. The transformers that you see advertised for 120 to 240V conversions are for operating non-US 240V equipment (240V single leg power).

US power is two legs of 120V that are 180 degrees out of phase, and 240V across the phases. I don't know of a transformer can provide you with two legs of 180 degree separated 240V power from a single 120V power input

If possible, consider running a 50A or 100A circuit from your main load center to a new sub-panel in the garage.
As long as a transformer can provide 240V across 2 wires it will work to it's current limit. Note that in the US, when you use 240V, you don't use the center tap line - just the two outside lines. So whether the transformer is center tapped or not does not make any difference for 240V service.

Mike

[All power to the home is single phase. Many people think 240V is some kind of multi-phase power but it's just plain ole single phase. There are two wires supplying the power and there is a sinusoidal voltage across those two wires - a single sinusoid I might point out. That's EXACTLY the same as 120V power.]

[Rick Christopherson]

NO it will not work. The transformers that you see advertised for 120 to 240V conversions are for operating non-US 240V equipment (240V single leg power).

US power is two legs of 120V that are 180 degrees out of phase, and 240V across the phases.There is no such thing as a "single leg of power". All electricity takes two wires to flow. The terms "Hot" and "Neutral" are simply names we give to these wires, and have absolutely no bearing on how electricity flows through these wires.

[Scott T Smith]

Mike and Rick - I made a poor choice of words in my explanation - sorry for the confusion.

However, I was wrong on the key point... - it is indeed possible to transform 120 to 240. This is something that I was not aware of. Thanks for the education.

Scott

[Mike Henderson]

Sorry if I came on a bit strong, Scott. The idea that residential 240V is multi-phase is somewhat of a sore point with me. I've heard that error so many times that I over-react to it. Sorry.

Mike

[Rick Christopherson]

The idea that residential 240V is multi-phase is somewhat of a sore point with me. I've heard that error so many times that I over-react to it. Yes, there are definitely quite a few people that get confused, but I don't believe it stems from them thinking it is multi-phase power. Mathematically there is nothing wrong with referring to the 3-wire system as being 180 degrees out of phase, just so long as you don't believe they actually are 180 degrees out of phase. It is only your chosen point of reference that makes them appear that way.

I had a huge battle with a bullheaded electrician on an electrical forum over this issue, because he was stating that the two halves of the system were literally 180 degrees, not just that his point of reference (at the neutral) made them "appear" to be 180 degrees.

Sorry, I digressed.

What I believe to be the root of confusion for many people is the belief that a "hot" is a "supply" and the "neutral" is the "return". The telltale sign of this confusion is when someone suggests that with 240 volts, you have half the power coming from one phase and half the power coming from the other phase, or some statement suggesting that there are two "supply" lines. This comes up most frequently during discussions of dual voltage motors, where people assume that because the current is cut in half, it is because half of it is coming from each line.
=======================

By the way, there is nothing wrong with referring to each non-grounded conductor (aka Hot) as a phase, such as A-phase and B-phase. "Phase" and "hot" are synonymous terms, just so long as you do not refer to the system as being "2-phase" as a result. As used, these terms do not signify a time-shift (phase angle or phase shift) between conductors.

Phase is a single word with two meanings, such as "A bandage wound around a wound." One meaning of phase is any ungrounded conductor, while the other meaning of phase is referring to a time shift between signals.

[Chris Padilla]

I like to think of our single-phase system in our residential homes as being:

(1) Split-phase or

(2) 3-wire Single Phase

[Jamie Buxton]

I can't stand it. I'll tell you how I think it works....

At the shop, I have 3-phase 208 volts. That is, there are three hots. Each measures 115 volts with respect to ground. The phases are 120 degrees apart, so between any two hots you see 208 volts.

In the house I grew up in, there was just a true single-phase supply. It was 115 volts with respect to ground.

In more modern houses, there are two phases. Each one measures 115 volts with respect to ground. The two phases are 180 degrees apart, so you see 230 volts between them.

That is, the supply at my shop is 3-phase. The supply at my house should be called 2-phase (although it generally isn't). The supply at my parents' home was single-phase. Simple.

[Mike Henderson]

I can't stand it. I'll tell you how I think it works....

At the shop, I have 3-phase 208 volts. That is, there are three hots. Each measures 115 volts with respect to ground. The phases are 120 degrees apart, so between any two hots you see 208 volts.

In the house I grew up in, there was just a true single-phase supply. It was 115 volts with respect to ground.

In more modern houses, there are two phases. Each one measures 115 volts with respect to ground. The two phases are 180 degrees apart, so you see 230 volts between them.

That is, the supply at my shop is 3-phase. The supply at my house should be called 2-phase (although it generally isn't). The supply at my parents' home was single-phase. Simple.
If we're going to communicate effectively, we need to be precise about the definition of "phase". Rick C. has made a case for multiple meanings of the word "phase" but I only have one definition, and that's "signals of the same frequency which are not aligned in time". As Jamie points out, he gets true three phase power in his shop, supplied with three wires. The voltage across each two wires is displaced 120* from the voltages across the other two sets of two wires.

But residential service is supplied with a transformer to step the voltage down. The supply to that transformer is almost always one hot wire from a three phase supply with ground as the other side (the "other side" is not really ground but is a wire that is at ground potential). So the supply to that transformer is single phase.

The secondary of that transformer is center tapped, with 240V across the two ends, and 120V from either end to the center tap.

An ordinary transformer (like the one on the power pole supplying your house) cannot convert single phase to anything other than single phase. That is, it is impossible to get "two phase" from an ordinary transformer with a single phase supply.

Early in power distribution history, there was a two phase system, with one phase 90* displaced from the other phase. The early power station at Niagara Falls was a two phase generating system. If I recall correctly, this was a four wire system, with each phase across two wires.

But the power brought into your home is single phase. No amount of wordsmithing will change that. Calling it "two phase" is simply incorrect.

The people who buy three phase motors and want to generate three phase from their residential single phase WISH the residential power was two phase. It would make their job a lot easier and cheaper.

Mike

[Mike Henderson]

Let me add a thought experiment for you. Let's label the wires from the secondary of the transformer as 1, 2, and 3, with 2 being the center tap.

Now, let's take an oscilloscope with three inputs. Connect input one to {1,2}. Connect input two to {2,3} and connect input three to {1,3}. What will you see on the screen?

Input 1 will be a sinusoid with an RMS voltage of about 120V. Input two will be the same AND THEY WILL BE ALIGNED IN TIME. Input three will be a sinusoid of RMS 240V and it will be aligned with the other two signals.

They are all different views of a single phase power source. The only reason you see the two 120V signals as being 180* out of phase is because you're inverting one of the signals in your mind.

Mike

[More on that - the other side of any two wire single phase AC power source is 180* out of phase with the first side.]

[travis howe]

Okay okay... I've got someone lined up to run new wire from my panel!!:D

[Leigh Betsch]

Some of the best entertainment on the web is when the electrical experts try to explain to one another how the stuff works. :rolleyes: Quite frankly I'm never sure who is right but it sure can get to be fun looking in. And if it ever gets dull just toss in a question like "What about wye, high leg delta? or split phase is another good one" Pretty much guaranteed to keep'em stirred up for a while longer. Just poke'n a little fun at ya, I doubt I'll ever truly understand what you're saying.

[Scott T Smith]

Mike and Rick - VERY informative - thanks for taking the time to share your knowledge and increase mine.

Regards,

Scott

[Jamie Buxton]

... I only have one definition, and that's "signals of the same frequency which are not aligned in time". ...


We agree about the definition of phase. In my example of a three-phase system, the three phases are separated by 120 degrees. In my house the two phases are separated by 180 degrees. So by your definition, my house should be called a two-phase system.

[Rick Christopherson]

.... my house should be called a two-phase system.You're barking up a tree that won't hunt....err....something like that.

The four nodes of a 3-phase 120/208 volt system are not collinear, and actually form the shape of a "Y", hence the name 3-phase wye system.

The three nodes of your 120/240 volt system are collinear, and that is why they do not constitute a multi-phase system.

Moreover, a 2-phase system does exist and it is fully defined in the electrical industry as one with a 90 degree shift. Just because you want to think of your system as being 2-phase does not make it 2-phase. I want to think of my pickup truck as a Ferrari, but that doesn't mean it will automatically become a chick magnet and go really fast.

[Mike Henderson]

We agree about the definition of phase. In my example of a three-phase system, the three phases are separated by 120 degrees. In my house the two phases are separated by 180 degrees. So by your definition, my house should be called a two-phase system.
The voltages across the two sections of the center tapped transformer are NOT separated by 180*.

Let me convert the example to DC and see if I can explain it to your satisfaction. Suppose we put a battery in place of the transformer section {1,2} and a different battery in place of the transformer section {2,3}.

Let's suppose those batteries are 120V DC each. To add, the polarities of the batteries must be aligned. Example: 2 must be positive in relation to 1, and 3 must be positive in relation to 2. If that's true, the voltage across {1,3} will be the sum of the two batteries.

Now, suppose those batteries were 60V. The voltage across {1,3} will be 120V. You can do all the voltages of one cycle of AC to show yourself that the voltages are in phase and add up. If they were 180* out of phase, the voltages would cancel and the voltage across {1,3} would be a constant zero.

I think what's confusing you is that (using my battery example) you're looking at one wire (wire 1) which is one pole of the battery (say the negative pole) and the other wire (wire 3) which is the positive pole of the battery. You see one is negative and the other positive which leads you to think that the voltages are out of phase. But if you look deeper, you see that the two batteries must be "in phase" for the voltages to add.

Mike

[If, after all that explanation, you still think the two voltages are out of phase, you need to explain how they're out of phase.]

[Rick Christopherson]

Mike, maybe this will help. Surprisingly, this is a graphic I used over a year ago making the very same argument on Mike Holt's forum. The red text is indicating the polarity reversal you were describing in your posting, which coincidentally was what I also needed to explain a year ago.

http://www.rts-engineering.com/tempgraphics/Batteries.jpg

[Mike Henderson]

Thanks for the pix. You're going to confuse people by putting in the negative voltage. You're correct but it just adds a level of confusion. It would be best at this stage of the discussion to leave that off.

Mike

[Jamie Buxton]

Here's a drawing.

[Rick Christopherson]

Thanks for the pix. You're going to confuse people by putting in the negative voltage. Yes, it is confusing, but that is exactly what people are doing when they state the voltages are 180 degrees out of phase, or the drawing that Jamie just showed. They are using a negative-of-a-negative, and that is what the red text signifies. A negative of a negative is still a positive.

Also keep in mind that I did not create the graphic for your discussion, but had it on-hand when I read your discussion. I created this over a heated battle with a dinosaur of an electrician that was claiming the right-hand image was correct.:D

[Mike Henderson]

Here's a drawing.
The problem is you're showing the voltage to ground on each side of the transformer. As I pointed out earlier, that's an incorrect way to view the system - it's just an inversion of reality. It's like using the negative pole of the battery for one signal and using the positive pole for the other signal.

On any single phase two wire line, one wire will be going negative (in reference to the other) while the other will be going positive in reference to the first. That's true whether you have a center tap transformer or not. It's true on a 120V line, as well as on a 240V line. It's true on a 4KV line. That's just the way electricity works. It does not mean you have two phases.

Take a 120V line. Look at the voltage on the hot in reference to the neutral. When the hot is positive, the neutral is negative. Now plot the opposite. Look at the voltage on the neutral in reference to the hot. The two sine waves will be 180* out of phase BECAUSE THAT'S THE WAY ELECTRICITY WORKS. It does not indicate two phases.

Look at a DC circuit. Measure one line in reference to the other. One will be positive referenced to the other, while the other will be negative in reference to the first. Again, that's the way electricity works.

Mike

[Jamie Buxton]

On any single phase two wire line, one wire will be going negative (in reference to the other) while the other will be going positive in reference to the first.


Nope. The usual convention in house wiring is to represent voltages with respect to ground. Ground and the neutral wire are zero volts all the time. The voltage on a hot goes postive and negative from that reference, as I drew in that diagram.

[Mark Norman]

. Ground and the neutral wire are zero volts all the time. .
Not true! the neutral wire is considered a current carrying conductor and does so. the ground is a safety consideration. Check the IBC for confirmation

I came across a unique set up just today, a three phase chiller with three fan motors. 440v and each fan motor was single phase, one on each leg.

[Mike Henderson]

Nope. The usual convention in house wiring is to represent voltages with respect to ground. Ground and the neutral wire are zero volts all the time. The voltage on a hot goes postive and negative from that reference, as I drew in that diagram.
You may use that convention but it will not give you an accurate view of what's happening in the system. And I think that's why you (and others) hold this incorrect view.

Again, looking at the system as consisting of two batteries, with the center grounded (which you will use for a reference), you'll see one battery as positive and the other battery as negative. But in reality, they are "in phase" and add to produce the sum of the two batteries which you measure when you measure across both batteries. (note that you change your reference when you measure the 240V compared to when you measure the 120V. If you measure from either side of a 240V circuit to ground you'll get 120V.)

Your incorrect view comes from using ground as a reference, without understanding what the reality of the circuit is. It's like the blind men who each touched a part of the elephant. They were all wrong because they couldn't see the whole animal.

Mike

[Glenn Roberts]

Mike, I am just loving this thread. Here in Australia we use 50hz 240/415V. Where houses are generally wired in single phase, eg: one phase and neutral ( MEN Earthing). As you go down the street alternating houses use a different phase to balance the load etc.
Some houses (where their maximum demand dictates or large loads, ducted air con etc) are wired for either 2 phases or 3 phases.

For all too long I have been totally confused at your system when I see your equipment rated at either 110 or 220 etc. ( motors etc)

NOW I KNOW. THANKS!!!

How do you guys run large motors etc in a domestic situation? the current must be enormous.

Here we generally only run up to 3hp motors on single phase and then go 3 phase. Hence the potential problem for people wanting to run large dust extraction etc if they only have single phase ( 240v)

[Rick Christopherson]

Nope. The usual convention in house wiring is to represent voltages with respect to ground. While you are certainly free to use that convention, you must keep in mind the ramifications of misusing it, which you have in fact done. You have changed the polarity of the voltage source without acknowledging the double-negative sign that your measurements impose. The result is the circuit shown below.
http://www.rts-engineering.com/tempgraphics/MikeHolt/3-wire-scan2.jpg
If you solve this circuit for I2 you will discover that I2 opposes the voltage of the lower power supply, which by electrical definition makes the lower power "supply" actually a "load" which is consuming power instead of supplying power.

You can't have it both ways. Either the two power supplies are in-phase or out-of-phase. If they are out of phase, then one of them needs to be a load instead of a supply.

The bottom line is that you are misapplying your relative point of reference as being an absolute point of reference, and redefining the circuit based on this relative reference point. Doing so will result in erroneous circuit analysis, that without the application of some voodoo mathematics to correct the missing minus sign, will result in one power supply being a load.

If you acknowledge the missing minus sign, then the two sources are in-phase. If you don't acknowledge the missing minus sign, then one of them must be a load. That's the dilemma you face if you choose to make your reference point oppose the natural polarity of a system.

[Tom Veatch]

http://www.rts-engineering.com/tempgraphics/MikeHolt/3-wire-scan2.jpg
If you solve this circuit for I2 you will discover that I2 opposes the voltage of the lower power supply, which by electrical definition makes the lower power "supply" actually a "load" which is consuming power instead of supplying power.


I would agree the I2 opposed the voltage of the lower power supply if and only if the power supplies were connected + to + or - to - and the lower supply had a lower voltage that the upper supply.

Solving that circuit for I2 is simple. The voltage difference between A and B across the 100 ohm load is 230 volts RMS. The current I2 is simply 230/100 = 2.3 amps RMS. The current flows from top to bottom during the first half of the cycle when the topmost terminal is + and the bottom most is - and from bottom to top during the second half of the cycle.

If you replace those two power supply symbols with batteries, what would you say about them then. For two supplies in series with a load, the positive terminal of one of the supplies must be connected to the negative terminal of the other supply just like you've shown.

As shown, by convention, current flows from the positive terminal on the upper supply through the load to the negative terminal on the lower supply and from the positive of the lower to the negative of the upper. Assuming the supplies have the same voltage, that's the only way you are going to get any current through the load with the supplies connected in series as shown.

The only other way to connect them in that circuit is negative to negative or positive to positive. In the diagram, connecting + to + or - to -, and assuming the two batteries/power supplies are exactly matched, the load would see no current at all. If the two supplies weren't exactly matched, one having a higher voltage than the other, then you would indeed see the lower voltage supply acting as a load on the higher voltage supply. Under those conditions, the 100 ohm load would see a current given by the difference in the voltage of the two supplies divided by 100.

[Mike Henderson]

Mike, I am just loving this thread. Here in Australia we use 50hz 240/415V. Where houses are generally wired in single phase, eg: one phase and neutral ( MEN Earthing). As you go down the street alternating houses use a different phase to balance the load etc.
Some houses (where their maximum demand dictates or large loads, ducted air con etc) are wired for either 2 phases or 3 phases.

For all too long I have been totally confused at your system when I see your equipment rated at either 110 or 220 etc. ( motors etc)

NOW I KNOW. THANKS!!!

How do you guys run large motors etc in a domestic situation? the current must be enormous.

Here we generally only run up to 3hp motors on single phase and then go 3 phase. Hence the potential problem for people wanting to run large dust extraction etc if they only have single phase ( 240v)
You're really fortunate to be able to get three phase in a residential environment - I wish we could do so here in the US.

Load balancing across phases is done here in a more gross basis. In many cases, a whole neighborhood is supplied by one phase - that is, only one phase is brought into the neighborhood at high voltage. Then step down transformers are used to bring the voltage down to 240V center tapped, and each transformer supplies a few homes.

Of course, really big motors are not used in a residential environment. About the biggest I can think of might be a 5HP motor on a table saw, and yes, they do take a fair amount of current at 240V.

But there's a good reason why the US system is designed the way it is, and that reason is safety. In a residential setting, the highest voltage to ground is 120V. The only way you can receive a 240V shock is to put yourself across both wires of a 240V outlet. And while a 120V shock is dangerous, it's not nearly as bad as a 240V shock.

I haven't traveled in Australia, but in England they have (maybe "had" since I haven't been there in a while) some "unusual" code restrictions because of the 240V to ground system. For example, the switches for lights in a bathroom had to be outside the bathroom (I suppose so that you wouldn't be standing in water when you turn the light on or off).

Sidebar: I can imagine how that worked with kids, when one would turn the lights off while the other was taking a bath.

There are multiple ways to do power distribution and each has it's advantages and disadvantages.

One more sidenote: here in the US, people sometime ask for three phase in a residential setting. Most of the time the answer is simply "It's not available." But you can see the problem. Three phase is often not brought into residential areas. To supply it the power company would have to run additional wires, and of course, three transformers (or a special three phase transformer) would be needed to bring it into the premises.

Mike

[Chris Padilla]

While you are certainly free to use that convention, you must keep in mind the ramifications of misusing it, which you have in fact done. You have changed the polarity of the voltage source without acknowledging the double-negative sign that your measurements impose. The result is the circuit shown below.
http://www.rts-engineering.com/tempgraphics/MikeHolt/3-wire-scan2.jpg
If you solve this circuit for I2 you will discover that I2 opposes the voltage of the lower power supply, which by electrical definition makes the lower power "supply" actually a "load" which is consuming power instead of supplying power.

Well, if you take the voltage supplies out of phasor notation, you have simply 115 Vrms for the top voltage and -115 Vrms for the bottom voltage. The way you have them connected (+ to -) means they add and you get 0 volts and therefore no current flow, I2=0...as Rollie pointed out.

[Glenn Roberts]

Mike thanks for the description. It makes sense now. As a general rule, in most residential areas ( and our HV network) the 3 phases are run. So 3 phase is common place. At one stage in our local area all new houses where wired ( up to the box) in 3 phase ( in case it was needed in the future)

Yes 240v is potentially(pardon the pun) more dangerous and it has caused our large single phase motors to be of very limited availability and high cost. 3 phase motors (by comparison) are 'dime a dozen'. And they run slower than yours.(50hz etc)
That said not every one has 3 phase at their home even though it is in all streets.
Earth leakage CB's (RCD) are now wired on power and lighting circuits to help with the danger of 240v.

[Rick Christopherson]

Well, if you take the voltage supplies out of phasor notation, you have simply 115 Vrms for the top voltage and -115 Vrms for the bottom voltage. The way you have them connected (+ to -) means they add and you get 0 volts and therefore no current flow, I2=0...as Rollie pointed out.It was actually a rhetorical question, not one I was expecting anyone to solve. I also had a more complex version of this same circuit which included neutral currents and loads, but since this isn't an electrical forum, I wanted to keep it very simple.

In any event, you should see why confusing a relative reference with an absolute reference creates problems. It is OK to "think" of the voltages as being above and below neutral, just so long as you do not make the mistake of "defining" the system that way.