Hello!
Given you have a jointer, band saw, and radial arm saw which could run on either 110 or 220 what are the advantages/disadvantages of running the tools on 220. I realize some re-wiring is required.
Thanks for your input – MSD
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Replies
There's not enough difference in the amount of electricty that is used to be concerned with but the one good reason to switch to 220 is that your motors will last longer.
Clem
There are two main advantages to wireing your motors for 220v.
1. Output from the motor is quicker (like putting a high octane gasoline in your car)
2. Costs less to operate. Less wear and tear on the motor. You can check that by feeling the motor after hard use. A 110 volt motor will be hotter
Current (amperage) and voltage are inversely proportional. If you increase the voltage from 110 to 220, you reduce the amperage by half.
Amperage causes heat. If you reduce the amperage, you also reduce the heat generated in the motor, and heat is the motor's worst enemy.
You are right that some rewiring has to be done, but the plate on the motor housing usually gives you the correct wiring for low voltage (110) and high voltage (220). Make sure to follow it exactly, as motors are wound differently, depending on the use. If the wiring method is not on the motor, check with your service manual.
As this forum has taken a new direction, and some of those posting have doubted the qualification of those of us who post, let me assure those that I went through an electrical apprenticeship, and have been a member of the International Brotherhood of Electrical Workers for over thirty years.
Len (Len's Custom Woodworking)
Edited 6/27/2002 1:25:26 PM ET by LRUTHERFOR1
Hi, Len, I'm new to this site and to woodworking. I do have several power tools and a limited knowledge of electricity. Can I pick your brain about current in parrallel and series circuits. How is the total current figured in each type. If you want to tell me to go get a book, thats fine.
I'll be glad to help in any way I can.
Thanks Len, could you tell me the formulas to calculate current in parallel and series circuits. I can never remember if its cumulative or constant. I do remember that in a motor circuit current is rarely constant.
Thanks in advance.
I got this info from Microsoft Encarta. It might help to explain why a motor would run cooler on 220 rather than on 110.
A series circuit is one in which the devices or elements of the circuit are arranged in such a way that the entire current (I) passes through each element without division or branching into parallel circuits.When two or more resistances are in series in a circuit, the total resistance may be calculated by adding the values of such resistances. If the resistances are in parallel, the total value of the resistance in the circuit is given by the formula
In a parallel circuit, electrical devices, such as incandescent lamps or the cells of a battery, are arranged to allow all positive (+) poles, electrodes, and terminals to be joined to one conductor, and all negative (-) ones to another conductor, so that each unit is, in effect, on a parallel branch. The value of two equal resistances in parallel is equal to half the value of the component resistances, and in every case the value of resistances in parallel is less than the value of the smallest of the individual resistances involved. In AC circuits, or circuits with varying currents, circuit components other than resistance must be considered.If a circuit has a number of interconnected branches, two other laws are applied in order to find the current flowing in the various branches. These laws, discovered by the German physicist Gustav Robert Kirchhoff, are known as Kirchhoff's laws of networks. The first of Kirchhoff's laws states that at any junction in a circuit through which a steady current is flowing, the sum of the currents flowing to the point is equal to the sum of the currents flowing away from that point. The second law states that, starting at any point in a network and following any closed path back to the starting point, the net sum of the electromotive forces encountered will be equal to the net sum of the products of the resistances encountered and the currents flowing through them. This second law is simply an extension of Ohm's law.The application of Ohm's law to circuits in which there is an alternating current is complicated by the fact that capacity and inductance are always present. Inductance makes the peak value of an alternating current lag behind the peak value of voltage; capacitance makes the peak value of voltage lag behind the peak value of the current. Capacitance and inductance inhibit the flow of alternating current and must be taken into account in calculating current flow. The current in AC circuits can be determined graphically by means of vectors or by means of the algebraic equation
in which L is inductance, C is capacitance, and f is the frequency of the current. The quantity in the denominator of the fraction is called the impedance of the circuit to alternating current and is sometimes represented by the letter Z; then Ohm's law for AC circuits is expressed by the simple equation I = V/Z.
Bernie, remembering my EE courses from 40 years ago, I agree with your dissertation. However, in certain regards, it is not really relevant to the way a dual voltage motor works.
A dual voltage motor has two separate but equal field coils. When wired for 120 volt, the two coils are in series and 120 volts runs through each coil. Each coil contributes equally to the amperage draw, so, if each coil has an amperage of 6 amps, the total is 12 amps when wired for 120 volts.
When wired for 240 volts, each of the two 120 volt legs is wired to a separate coil so one leg feeds one coil 120 volts and the other leg feeds the second coil 120 volts. The 6 amp in each coil is each on a separate leg of the 120 volts, not really in parallel as the formula you show.
As you can see, the motor doesn't care or even know that the total input voltage is 240. Each coil sees only 120 volts and 6 amps no matter how it is wired. Same power, same heat.
Hi Howie, I cant take credit for the disertation, it is copied directly from Microsoft Encarta.
Anyhow, I think what I'm hearing you say is that the circuits for 110 and 220 are both serial and 220 is not parrallel at all. Would that be correct?
For some reason, since there is a common ground, when I get back to the panel, I see a single service feeding it. If the breakers are simple switches and the motor coils are tied to a common ground then for some reason I think I'm seeing a parrallel circuit when the motor is wired for 110V.
Maybe I'm going to have to rip one apart and see it in action before I'll be able to get it through my thick head.
Edited 6/28/2002 1:31:02 PM ET by Bernie
Bernie, go to: http://theoak.com/rick/Electricity_in_the_Shop.html
Then click on "Motors" and then scroll to section 6.5.1. There is a little diagram there that shows how thing work inside a dual voltage motor. See if that helps.
The key is that 240 volts is produced in the home by having two legs of 120volts 180 degrees out of phase. If you tap one of the hot lines in the wire and measure it to ground you will find 120 volts. If you measure across both hot wires, you will find 240 volts.
Howie is correct. Technically speaking, you have no 240 VAC coming into your house or shop. What you have is two 120 lines. Like putting two 6V batteries in series to get 12V, that's how you get 240.
240 gives you more available amperage because it's connected to two separate lines (a 240 breaker is always dual pole) and so at peak loads you'll experience less voltage drop due to high amperage draw because you have more available amps to begin with. Another benefit is that you don't overload the rest of your 120 system, so when you start the table saw, the lights don't go dim. 240 motors generally last longer for a variety of reasons. The biggest killer of electric motors is low voltage which causes severe heat generation.
Howie, Thanks. I checked out the website. Very informative. You mentioned that inorder to get 240, I would need to have two 120v circuits 180 degrees out of phase. Wouldn't that mean that I would need a three phase circuit in my shop and then use only two of the legs? My electrical service is only a single phase 120v feed with a common ground.
Talk to your electrical company Bernie. They will tell you what you have and what you need to do if you don't have 240 volt service. I'd be surprised if you don't have 240V but, it's possible if you have and older home and haven't upgraded your service.
Howie, I just went and looked at the panel. You are correct, I do have 3 wires comming in from the street. 2 Black and one White. A little bit of research indicates that the white wire is the neutral and connected to the center tap on the transformer while the two blacks are 120V and are 180 deg's out of phase.
I just found this little tid bit of information out on the internet.. Here's a link to the site..
http://www.team.net/www/shop-talk/wirefaq1.html
"Theoretically, it doesn't make any difference. However, there is a difference is the amount of power lost in the supply wiring. All things being equal, a 110V motor will lose 4 times more power in the house wiring than a 220V motor. This also means that the startup surge loss will be less, and the motor will get to speed quicker with 220V. And in some circumstances, the smaller power loss will lead to longer motor life. This is usually irrelevant unless the supply wires are more than 50 feet long."
Edited 6/28/2002 12:59:38 PM ET by Bernie
Bernie,
All very true, but length of the supply is not enough; they're just giving a general guideline. Any standard electrical wiring book will give you a chart of recommended wire sizes for different loads. If the wire resistance causes too much of a voltage drop in any situation, you can either move to 220v or increase the wire size, and gain the same effect. Most often, it's easier (and cheaper) to move to 220v.
Gerry
Thanks Gerry, my little shop has 120V, 20 amp home run circuits all wired with 12/2 NV in 3/4" EMT along the walls. I have three separate circuits all with dual gang outlets. All of these are less than 50' from the panel and I don't use extension cords. From all of this great information and advice I've been getting I think I've decided that there is actually nothing to gain from changing to 240 so I'm gonna leave em all just like they are.
Thanks to everyone for the wonderful help.
Bernie
Bernie,
I just got a used 10" Craftsman Radial Arm Saw.
Both the 15amp and 20amp breakers are tripping
after 20-30 seconds. The saw was the only thing running
each time. I was using extension cord to reach the outlet.
Got any advice for a rookie???
Rick [email protected]
Length and wire size for the extension cord? If it's too small and/or too long your voltage loss will cause the saw to draw excessive current.
Did they trip with the saw just running free, or cutting wood? Does the saw seem to run okay until the breaker trips? Does it seem to come up to speed quickly?
Are these two separate circuits you tried (15 and 20 amp)?
Gerry
Gerry,
The extension cord was 16 Ga. and 25 feet long. The gauge is too small I have found out. I'm learning ! A 12 Ga. cord plugged into the 20 amp circuit allowed the saw run normal. It would still not run on the 15 amp circuit. Part of my problem is that the house is wired with aluminum wire, which does not carry the volts as well as copper (wire ga. being equal). One gauge heavier wire is required for aluminum to equal copper and it looks like that rule of thumb was not followed in our house. I never thought about the wiring when I bought the house. My mistake. A friend is going to help me run a new 20 amp line (copper !!!) into my garage. The 20 amp line I'm using is in the kitchen.
One thing I'm still trying to figure out. The saw motor is rated 11 amps and the saw is labeled as 2.5 HP Maximum. The 15 amp breaker is tripped even without an extension cord and running free. There must be a surge of amps? the aluminum wire is at fault? the breaker itself is faulty? or something else...?
Thanks for your reply...any more helpful comments are appreciated, Rick
Normally, I would say that the saw should operate fine on a clean 20 amp 120 volt circuit. I would check the breaker as it may have been weakened through long usage. Second, check the length of the run from the panel to the outlet. If it is over 50 feet and of aluminum wire, you may be getting a large enough voltage drop that the extra amperage drawn at startup trips the breaker particularly if the breaker is weak. Third, is this a dedicated line? If not, there may be other problems at other outlets.
Rick,
Yup, that extension is a bit small. For the saw, 11 amps is sorta small for 2.5hp, but they rarely make sense anyhow, so just go by the current. From that rating, I'd guess a 15A brief startup surge, but that by itself wouldn't trigger a standard 15A breaker, as they have thermal sensing to handle very brief startup loads. However, if you're losing too much voltage in the total wiring to that saw, the lower voltage could cause the motor to draw over 20A on startup.
You will always lose some amount of voltage from your wiring. For any given current load, wire type and guage, charts will show you the longest permissible run. The motor is designed to run within a certain voltage range. If the voltage drops below this range, most motors will start drawing more current to try and maintain speed. This is both at startup and when running. If the voltage continues to drop, the current continues to increase. In addition to tripped breakers, this current increase will cause the motor to become much hotter than normal, shortening its life.
For an 11A rating, you should be able to run that saw on a 15A line, assuming a short run and nothing else loading the circuit. You could trip the breaker if you jam it while cutting thick wood, but that's not so bad.
Gerry
Just out of curiosity, do you know anyone with a clamp-type current meter, like an Amprobe or Fluke. This would answer a lot of questions and either confirm and/or disprove a lot of speculation concerning the motor current. What bothers me is the rating you posted...11 amps...ignoring the fact that you have a motor with a continuous H.P. rating less than 2.5 (closer to 1.5 or 1.75)...the current rating you read from the motor nameplate is FLA (Full Load Amps) This means that under normal full load (the saw being used to rip a board of moderate thickness with a sharp blade), the motor would draw 11 amps of current. Yes, during startup, the inrush current is going to be substantially more, but after 2-3 seconds the current should lower to around 8 or 9 amps with no load...maybe even less. I design automation equipment for industrial customers, and when I get a report of a motor running at full load amps when there is no load on it, then I get concerned, recalculate the mechanical load, have the wiring megged, check for faulty motor, etc.
What I'm trying to say is that even though you may be able to prevent the symptom (tripping breaker) by providing a higher ampacity circuit and feed, you my not be isolating and correcting the real problem, which may be a bearing going bad, a bad motor, low voltage supply in the house due to something external (you may actually have 105 VAC at you house due to other problems down the road at a transformer), etc. I'm not saying that the circuit/breaker/extension cord/copper feed was not the problem, but it would be best to check the current draw and voltage of your saw after you have the new circuit installed. It my save a spun bearing or damaged equipment later on due to brown-out conditions.
Wow, that was more than 2 cents, probably closer to a dime!
-Del
Del,
I'd ignore the HP rating here, as we know the stories that make up on that. I agree with you on the rest, with lower numbers (have taken measurements on typical shop equipment). Probably 4-6A no load, under 1 sec for most of the startup surge, given the motor size and load. Between the Alum wiring and the extension cord, I'd guess he went down to well under 90v. Given the situation, he really needs to have that system checked out, and I'll further emphasize your warning, as he may end up with most of his powered equipment having a rather short lifetime, and won't realize that until it's too late.
Gerry
One gauge heavier wire is required for aluminum to equal copper and it looks like that rule of thumb was not followed in our house. It's more than a rule of thumb. NEC Table 310-16 requires overcurrent protection no greater than 15A using 12ga aluminum, and 20A with 10ga (mostly), so if your wiring does not meet this, you have a much larger problem than a sluggish saw. Call an electrician specializing in aluminum wiring in older houses, and have him or her look at the wiring, breakers, and device connections. Don't wait for a house fire to force the issue.
Be seeing you...
you need to be real careful with ALuminum wiring in your house.
First, All the sockets and switchs and light fixtures must be the right kind. They are now rare and cost $3-5 apiece. Another alternative is to use copper fixtures and a special jelly. Using the copper style fixtures/swicthws/outlets by them selves with alum wire may result in intermittent operation and overheated possible fire hazard since the aluminum changes size when heated and works loose.
Next, if you add circuits then you must make sure you have the right interface between the copper wire and the junction box which should be one for ALum wire which will lead to the same problem i mentioned before.
I think the ALuminum wire heyday was in the mid 70s and not that many people in hardware stores are aware of the problems. The problems are why they stopped using it.
Good luck, be careful and be safe.
Loring
Rick, the extension cord is the only undetermined variable. Can you plug it in without it and see what happens. That saw shouldn't blow the 20amp breaker so there maybe something wrong with it.Steve - in Northern California
Steve...please read my reply to Gerry and any advice will be appreciated.
Thanks for replying, Rick.
Rick, I hate houses with aluminum wiring. I would start right from the get go with a sub panel in the shop. This should allow you to keep all of your runs to less than 50ft. You will need an electrician to install the subpanel since it will have to be properly sized and your incoming power requirements may need to be upgraded. Only a licensed electrician will be able to get the correct permits, etc so that your job goes smoothly and your homeowners insurance remains effective.
Having a friend do it for you is O.K. and a great way to save money. Just make sure he is qualified to do the work and knows how to figure the load at the panel. If he can't do that then don't let him do the work. There's a little more to it than just pulling some wire and slammin a new breaker into your box.Steve - in Northern California
Bernie,
These discussions of voltage drop are focusing on the inrush current of a motor during startup. While this current is extremely high, it only lasts for a fraction of a second. It is true that a motor will start faster at 240 volts, but once started, the difference is negligible.
The power losses in the wire are extremely small, so four times a small number is still a small number. Regardless, the power loss in the wire is of no concern. What is a concern is the voltage drop that the motor will see. This number is proportional to the current, and the 4-times factor becomes a 2-times factor.
If the wiring is up to code, and the run is not very long, this voltage drop will be no different than the normal voltage fluctuations you would see in the power lines (utility service) throughout the day.
================
Also, while I didn't fully read the Encarta quote, I don't think anyone answered your question regarding series versus parallel circuits. The equations are not that complex.
In a series circuit, the current will be the same through each device, and the voltage will be divided among the devices (proportionally by their resistance). This is like a freeway that travels through several towns; every car must pass through the same set of towns. So each town will count the same number of cars per day (the current), but the number of cars in a single town at one time will depend on how big their road is (the voltage)
In a parallel circuit, the voltage will be the same at each device, and the total current will be divided proportionally. This would be like having several small freeways (each with the same number of drivers) going to each town. Even though one freeway may be smaller than another, they all must still pass the same number of cars per day.
The resistance in any of these towns is equivalent to the number of lanes of traffic, and this will determine how fast you can drive against the gridlock.
Thanks Rick. I've been getting well schooled on the subject and think I have a pretty good grasp on whats happening. Now, I just have one more little tid bit to throw into to the pile and I'll call it quits.
What if any effect do you and others think the fact that in 240v mode the voltages on the two fields are 180 degrees out of phase. I've been looking at some motor physics information that indicate there might be less induced physical resistance in the motor since one field is following the other in a push pull type action.
If that is true, then this might be why so many folks seem to feel they have more power and why the motors would run cooler.
Bernie,
I didn't comment on the encarta quote, as it had items you really didn't need for this issue. Rick's explanation of series vs. parallel covers the useful part of it pretty clearly.
So, what motor physics info is this? Physical resistance is not induced. What you're looking for here is ampere-turns, which relate to the magnetic field intensity, and that's what runs the motor. It doesn't really matter how you get them, nor how many phases you supply.
From another point of view, the motor can't tell the difference. You said that, with 240v, the two voltages are 180 degrees out of phase. That's true, but you won't see that unless using ground for a reference. If you were to use an oscilloscope to look at a picture of that sine wave, and you measured across (between) the two feed lines for 240v, you would see a single sine wave, and that's what the motor sees.
Push-pull circuits have some advantages, but nothing that I can see applying here. With large motor-generators they reduce ground current problems, but that's not here either.
The power supplied is the voltage times the current, and as long as that product is the same, going between 110v and 220v doesn't matter (with constant power factor, of course).
Now, if you keep reading, look for different types of motors and how they behieve when you reduce the operating voltage. See what happens to the current drain, why, and the effect it has. That will give you a better idea why some people see motors getting too warm with 110v.
Gerry
Bernie;
That was an interesting concept and it made me stop for a second. What you are referring to is the "Inductive Reactance" of a coil of wire. This is why you can't run an induction motor on DC power: There would be almost no resistance, and the wires would melt from high current.
Inductive Reactance is a technical term for resistance that is dependant on magnetism (in very simple terms).
However, if the two fields cancelled each other out (in whole or in part) not only would there be an increase in current, but a reduction in motor power. That would make it a two-fold deficit.
=============
One extra point in this is that we don't call this a two-phase system because it is actually just one system, and we tap the neutral wire from the center. To keep the discussion simple, you are better off ignoring the 180 degrees. When you only have two points, it's always a straight line, and this is a similar concept.
=============
BTW, I later realized that you were not asking the question about series/parallel, but instead answering it. Because I addressed my response to you, a lesser man might have been insulted. I am very glad that you did not take my response negatively.
Thanks Rick, As a beginner, I don't have the option to react negatively. If I wish to learn this trade as well as I hope to, it will never be an option for me. Your information has helped me immensely. I'm going back to the books and try to undertand this subject even more. I'll be back with more questions soon. Thanks again.
Bernie
As deeply technical as this has become put to one side. My Table saw runs and performs much better wired and run on 240Volt. When it was on 120V it had a line to its self #10 twenty ft long. Within two days of owning this saw I "upgraded" it to 240V.
Ah the myths, the truths and the just plain silly facts.
Do motors run cooler on 240v then they do on 120v. I don't' know. Every time I stick the metal thermometer in there when its running it blows me across the room and by the time I recover, the breaker has blown and them motor has stopped.
However, In my opinion, it would be odd if they didn't. The electromotive force to move the free electrons through the conductors from the beginning of the circuit to the end of the circuit is now less so the time required to build the current needed for the circuit is less. Because of this the heat buildup period is shorter and therefore the motor should run cooler. I know, its a pretty lame way to explain it huh?
Now as for starting faster. I haven't figured out a way to modify the tach off my old Chevy to fit the motor shaft yet so I have no accurate way of measuring that either. But, for all the same reasons as running cooler, it should also start faster.
More power, sorry my dyno is down right now. But the reason people might think they have more power is because it might be easier for the circuit to maintain adequate amperage (current) to keep the motor running at speed when under load. The fact is that the motor can only develop the maximum amount of power that it is designed for either at 120v or 240v. How easily it can maintain it is the key.
Don't believe me? Thats O.K. I made it all up anyway... Not really, I've been doing some reading.... LOL Go figure.. me the studious type...
Steve - in Northern California
Edited 7/2/2002 6:00:42 PM ET by Steve Schefer
Steve,
You said, "However, In my opinion, it would be odd if they didn't. The electromotive force to move the free electrons through the conductors from the beginning of the circuit to the end of the circuit is now less so the time required to build the current needed for the circuit is less."
IOW, you say that it works better if The Force Is With You. As a Jedi Woodworker, I certainly can't argue with that one.
On your comment about the motor maintaining running speed, that's right on the money. As I mentioned earlier, some tools like the TS or RAS will draw a peak current that's several times higher than at idle. Even a cheap voltmeter lets you check the supply voltage while cutting a thick piece of hardwood, and that tells you if 220v will help. Few other tools will show a peak that rises so much. Your tach would work as well, except you'd have to measure it at both voltages, and that's hard to see through all the sawdust.
I could talk theory all day, but I'd rather measure something.
Gerry
Hmmm...sounds like we have some diverse opinions here:-)
Let's see now...
Clem - Care to state the reason why you claim the motor will last longer? With proper wiring and running voltages, I'm not aware of any basis for that. I suspect there's some other issue involved.
Al - The same field intensity and torque are generated, so the motor starts at the same rate. The only issue would be if the wiring were not sufficient for 110v so that the initial startup current caused enough of a voltage drop to starve the motor during that period. On larger motors, this is not uncommon, and is probably what you witnessed. If this were also the case while running, your 110v motor would be hotter as you described, and the increased voltage drop in the feed wiring would also consume more power. Finally, if in general you reduce the supply voltage to a motor (wire too small or too long), it may increase its current and power consumption, and get hotter. (Reasons for that get a bit more involved, and also depend somewhat on motor type.)
Len - Lrutherfor1 - Amperage doesn't cause heat. Heat is energy, and temperature rise is related to power which is energy over time. The same power consumption at 110v or 220v will result in the same heat generation. Suggest you check your branch wiring charts against motor loads, for wire sizes and lengths for permissible drops. That's your criteria for which voltage to use.
MSD - Other than individual motor size, the main concern is probably the peak load current for the tools. For instance, my 2hp DC doesn't see many current peaks, while the TS may see a 3-4 to 1 peak in current under load, and that's when you really want it working its best. For anything less 8" hardwood resawing, the band saw probably doesn't care. For my RAS, I measured the voltage at the machine while cutting a heavy load. If that had dropped more than a few percent, I would have switched to 220v. As the change was small (I have a short feed), there would be no advantage. If you take the motor current rating and the feed length from the branch box and wire size, Len can look this up in his tables and make a fairly accurate recommendation.
Gerry
Thanks for clearing up misconceptions and folklore!
Someone stated that the motors wired for 110 or 220 basically parallel or seies connect the windings. That is correct.
It also follows that there is substantially no difference in the performance or efficiency of the motor.
Furthermore the motor heats up because of losses of DC resistance in the windings and magnetic losses. The parallel/series wiring serves to make the actual current in each winding identical in the 110 and 220V configurations. Thus magnetic and DC resistance losses are identical.
The main advantage of 220V operation is that the line losses in the wire feeding the motor are reduced because overall the current is 1/2 in the 220V configuration even though the individual winding current is the same. Thus to get the same voltage at the motor, you need half the copper at 220V as you do at 110V.
Or to put it another way, going to 220V
you get more voltage at the motor with the same wire gauge
thus reducing motor heat (because the motor in trying to do the same work will draw more current and then DCR and magnetic losses increase, -if the line losses are too big this becomes a self-destructive cycle as the heat causes more DCR and more magnetic losses in turn causing more current and finally this is where a under-voltage supplied motor burns up.)
I guess the summation is that with a conventional motor and identical loads and means to get the proper input voltage AT THE MOTOR, then there will be no difference between 110 and 220V motor operation.
BUT, wiring requirements will be less copper with 220V - you can go longer with the same copper for identical performance or use less copper the the same distance.
Loring
(Electrical Engineer - BSEE, MEE)
Loring,
Nicely put, but you sent this to me? You're preaching to the choir here (read: complete agreement).
I'll just note (can any EE ever refrain from a "note"?) that low operating voltage is relative. A motor is designed to handle a certain load and duty cycle, within a range of input voltages. As the voltage drops below that range, more heat is generated than was allowed for in the design, and the motor life is shortened. If operated at this level for a time, the additional heat (actually resulting temperature) further increases the losses slightly, which is the cycle you referred to. Below a certain threshold, however, this cycle is self limiting. That threshold includes a stalled motor, tripped breaker, or melted winding insolation causing the motor to short out. This adds to, but in no way contradicts your statement.
Gerry (yet another EE)
Len,
Is there an easy way to tell if my system can support 220 ? I've got an electric stove and dryer in the house...but I'm not sure abut the service level..probably 200...
thanks, Randy
I agree with all the EE's said. The one thing they didn't tell you is to have a qualified individual check the amperage load at the service panel. That way you'll be able to tell if you have the room (amperage) to add another two pole curcuit. Even if you have extra blank slots in your service panel, you may, already, be at the upper limits of your service entrance conductors. It's best to check.
I can't believe that a Journeyman Wireman (electrician) just agreed with engineers!
:-) Len (Len's Custom Woodworking)
Hey, do you mean we're finally getting to the bottom of this. Hats off to the EE's. Thanks. Steve - in Northern California
Len,
The inversely proportional relationship of voltage to current must, I guess, only apply to AC? I know in direct current, Ohm's law applies ( I = E/R), which shows a direct voltage/current proportion. Could you elaborate a bit for my edification?
I'm not quiet sure what you're asking me to explain, but if you'll ask me a specific, I'll do my best to answer. I think that all who have posted in this thread have given the same answers, more of less. 1. If you increase the voltage, the amperage will decrease proportionally. 2. If you continue to have a problem after the feed to the equipment is replaced, it's probably not the electrical service, but the equipment. 3. Aluminum branch circuit wiring was bad enough when it was new, but is worse now. Most of the problems came from interaction between the copper screws in the receptacle and the aluminum. Very few were connected properly, with the proper type of receptacle with cu/al connections, and without a dialectic compound. 4. The longer the run of a branch circuit, the more "line loss" occurs, and the efficiency of the circuit is decreased. And, most importantly, #5. You need to have a qualified, licensed electrician check out your system.
Len (Len's Custom Woodworking) (And a licensed journeyman electrician)
Edited 7/16/2002 11:17:50 AM ET by LRUTHERFOR1
You are correct that if you increase voltage, your current will increase, as will your power disipation (watts). 1 Horsepower is 746 watts under 0% loss conditions. However, what may not have been explained is that the only constant in this thread is the power consuption of the motor, regardless of high or low voltage configuration the motor retains the same amount of horsepower. Thus, if P=I*E, then an increase in the voltage from 120 to 240 will decrease the current ONLY because the wiring configuration was changed from low(120) to high(240) voltage, effectively reducing the resistance(R) in the equation i=e/r. All things being equal, if you applied 240VAC to the motor while it was configured for 120 VAC, then you would see 2 things: 1) the current would double, and 2) sparks.
This may not be the most explanitory post you've read today, but the point is that the resistance changes when you reconfigure the motor, which changes the R your calculation.
Hope this helps.
-Del
P.S. For the EE's out there ready to flame me, I, also being an electrical engineer, understand that there is quite a bit more involved than this. However, I decided to make it short and sweet and decided to skip the watts vs. Volt-Amperes disertation, the phase shift differential between voltage and current, resistance vs. reactance, power consumption vs. load, etc, etc, etc. Please don't make me get out my college books, they were packed away for a reason.
Del,
An an EE with all the book right in front of me, prepare ye now for the worst...
You claim that applying 240vac with the wiring set for 120vac would cause sparks. From long experience, I'd instead expect, in sequence:
--Some bubbles in the coating on the winding.
--A dark colored but thin smoke.
--A small but intense spot of bright light.
--A few sparks
Other than that, your explanation sounded reasonable to me. Now, just to keep things going, shall we turn this thread into a discussion of power factor and explain imaginary power:-?
Gerry
Gerry, Sears does a real good job of explaining imaginary power. Just read the hp ratings on the motors they sell. LOL...Steve - in Northern California
They aren' the only ones.....2.5 H.P. with 11 amps at 120VAC....that must be the new math...
Kinda hard to get there isnt it.... LOL.. At least my Bosch CMS just says it has a 15amp motor. Steve - in Northern California
Steve, how true that is! I seem to recall that they measure HP with zero torque. IOW, with the blade jammed, which is not too useful of a technique on a saw, but there's no standard there. Now, does anybody happen to know the (UL I think) definition for the max operating current?
Gerry
well I just joined this forum and was excited to read the original post because I have the same situation. After reading the entire thread my head is spinning with information over-load (my mind breaker tripped).
here's my question: I am rewiring my shop. I have a new 80 amp subpanel installed and am running all new circuits. I bought a used craftsman 10" TS with a replaced motor. motor plate says 23.0 amps at 115 and 11.5 amps at 230. (saw would blow a 20 amp TD fuse at start up, yes I know that makes sense). Given that I am rewiring the shop should I wire a dedicated circuit for the TS at 230V and change the motor? Show of hands please aye or nay?
Thanks all,
Dave
Yes would be my vote.Steve - in Northern California
Yes, change the motor to 240 volt. To run your saw at 120 volts it would take a #10 dedicated circuit and a 30 amp 120 volt breaker (not sure there is one of those). With 240 operation, you can get by with #12 wire and a 20 amp 240 volt breaker.
Dave,
I really don't think there'll be any debate on this one...switch to 230v. (Hmmm...wonder, wonder, wonder how many HP that label claims?)
Gerry
label claims 2HP. it is a Dayton capacitor-start. Yes I meant changing the V configuration. Thanks again.
Dave
Dave,
When you say "and change the motor", do you mean change the motor voltage configuration? If so then going to 240VAC is going to be the best alternative. You COULD supply a 30 AMP 120 circuit, but this is not very common. Single pole circuits of higher ampacity are sort of looked down upon due to phase loading issues down the road, especially if your panel is rated at less than 100 Amps.
-Del
General purpose industrial induction motors, including fractional horsepower units, are built to the NEMA MG-1 standard. Required medium motor (nominally 1 hp to 500 hp) nameplate info includes:
a. Manufacturer's type and frame designation; b. Horsepower output; c. Time rating; .....f. Rpm at full load; ......i. Rated-load amperes; j. Voltage; k. Code letter for locked-rotor kVA or locked-rotor amperes; ......n. Service factor, if other than 1.0; o. Service factor amps when service factor exceeds 1.15; .... I've left out some of the requirements which are not germane. Small motor (fractional) nameplate requirements are similar. Universal motors (routers, vacuums, etc.) do not fall under this standard.
In a nutshell, for a motor to conform to NEMA MG-1, rated mechanical power output (torque x speed), speed at rated output, and current draw at rated output, along with voltage (115/230V for typical single-phase machines, but these and other voltages are also standardized in MG-1) must be reported on the nameplate. If the motor doesn't have horsepower nameplated, but instead says "special" or "sp" or nothing, it's because the motor doesn't conform to the standard, or the manufacturer of the machine wants to say things like "2.5 peak horsepower", even though the nameplate says 11A, and doesn't want the motor maker to contradict them. Sears and HD air compressors are good for this. Or the time rating is not continuous at that output and temperature rise. NEMA time ratings go as low as 15 minutes. There are lots of possible reasons.
So to answer your question, if the motor is made to MG-1, the nameplate is complete and is the real thing, and I would believe what it says. Engineers and manufacturers rely on this information. That may be part of the reason people on this forum like Baldor motors as replacements; they're built and sold as stand-alone industrial units with complete nameplate data (as are Leeson, Marathon, Lincoln, and lots of others), and output horsepower is real. Contrast that with OEM motors (often made by the same manufacturers) which are just a component of the finished product. The product itself will have current or wattage data, and motor power output is left to the marketing department. In that case, I believe you are right that UL alone governs. But how in that case max operating current is determined I really don't know.
As far as how these "peak" horsepower numbers are arrived at, I suspect they use locked-rotor or breakdown VA or Watts converted to power, which is a worthless value. And, obviously, at zero output speed, output power is also zero, but let's not confuse the marketing department with facts.
Be seeing you...
Tdkpe,
Yes, I agree they probably use locked-rotor for their HP test. I did a (long) search on UL to see what's available. I finally tracked this down to _maybe_ UL 1004, then found out it would cost me $95 to get it. Probably easier to pull out the current probe and check some equipment, free running and typical load, and compare to the faceplate rating.
Maybe next time I'm waiting for some finish to dry.
Gerry
FWIW, this "developed" and "peak" horsepower rating stuff reminds me of mass-market audio equipment in the 70's. Radio Shack was the biggest offender, as I recall, with terms like "total instantaneous peak music power". They would report huge output power from glorified transistor radios with fuzzy terms like that. The dead giveaway is when the output power is greater than the nameplate input wattage. I was told it was the FCC that stopped that, requiring RMS values at fixed conditions (continuous output at defined distortion, frequency, load, etc.) to level the playing field somewhat. Perhaps some EE or Ham operator would know more about this, but my point is that it shows how marketing departments intentionally mislead the public, which in turn forces competitors to play along in order to stay in the game. This sort of thing is obviously a pet peeve of mine. I don't like companies intentionally misleading people in order to take their money.............
Be seeing you...
Tdkpe,
Oh yes, I remember that "total instantaneous peak" stuff well. At the time, I was doing hardware design on microwave comm, and we had all the equipment handy to measure all their specs on the audio equipment. Have you ever heard what one of their "peak outputs" really sounds like? If not, you haven't missed a thing! The FCC helped a bit. But what later happened was the high end customers learned what the specs really mean, and that forced some changes.
But in many other cases, the "mass market" is partly to blame. If we paid more attention (read: buying power) to accurate specs than to marketing hype, we'd know more about what we're buying. However, methinks too many people are too lazy for that to happen.
Gerry
Don't forget that gawdawful smell --
another EE.
The fact is that a dual voltage motor runs internally at 120 volts whether the input voltage is 120 or 240. All rewiring the motor does is change the two internal coils from parallel to series. No matter what, the individual coils always run at 120 volts and the amperage is the same. Same amperage, same heat produced.
Here is a good write up on the subject. Click on "Motors": http://theoak.com/rick/Electricity_in_the_Shop.html
If your motor is running hotter at 120 volts, then it means that there is a voltage drop in your 120 volt input line. The lesser voltage will cause more amperage which causes higher heat. Increase the 120 volt wiring size, and you should no longer have a hotter motor.
After reading through the entire thread, I may have a thought or two that was not covered.
1st penny) Any self-respecting woodworker will eventually replace their machines with LARGER ones - not smaller ones. The larger the machine, the less likely it is to have a motor capable of being run on 120VAC. So, with the future in mind, wire it for 240VAC and run a size or two larger wire, but your short-circuit overload device should not be up-sized. That way, all that needs to be done when you upgrade to a larger machine is increase the breaker size (unless you get a LOT larger machine). Increasing the wire size will also help prevent problems due to insufficient voltage.
2nd penny) You may not have space in your load center (breaker panel) for a double pole breaker, which is what is needed for a 240VAC circuit. If you have the space, then go for it.
Well, those were my 2 cents.
-Del
P.S. If you are not all that familiar with the electrical requirements, hazards, etc. of the task at hand, and you try it yourself, then you could very easily get blown to pieces and we will have one less woodworker in the forum. :(
MSD, hopefully by the time you get done reading all of this thread you will have made a decision.
In answer to your question.
1. Are there any disadvantages.... No
2. Are there any advantages... Not enough to justify spending the money re-wiring your shop.
However, if the subject line of this thread is correct and not a typo, then you gotta go 220/240 because 11VAC aint gonna run nuttin.
Steve - in Northern California
Edited 7/5/2002 2:29:33 AM ET by Steve Schefer
In Europe 240V single phase is common in every house. If you use mutch electricity e.g. for cooking or in my case: you have a small workshop you get two extra phases and 3x400V is within everybody's reach. Why is it so expensive in your country? (110V was common before the 2 worldwar in Amsterdam. In the 50th they swithed to 220)
Ruud Joling The Netherlands
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