I know that this topic gets talked about a lot in here, so I’m sorry if you’ve heard this before:
I just picked up a used motor (3/4 hp, 1725 rpm, 110/220 V) for an old bandsaw (a recent Craigslist score).
I have a 220 line in my shop. All other things being equal, what will make the motor happier: 110 volts? 220 volts? Doesn’t matter?
I have heard people say that it will run cooler on 220. I have heard others say that that is not true, and that the real advantage of 220 is that you can run a lighter gauge of wire in the shop, as each hot leg draws half the amps.
This weekend, I will retire to the shop with tools, WD-40, and the requisite malt beverage, and try to get the bandsaw fired up. So any input would be helpful.
Thanks a lot.
Outside of a dog, a book is a man’s best friend. Inside of a dog, it’s too dark to read.
-Groucho Marx
-Groucho Marx
Replies
If you have the 220 by all means use it half the current half the heat
The heat comes from the amount of current (Amps) going through your wires (both the cord and the motor windings).
Your motor will always draw the same power if kept under a constant load (watts/hp) therefore if you use the formula for Power:
Power = Volts * Amps
If your volts goes up then your amps have to go down. If you have fewer amps, then you will have less heat.
Always go with 220V if possible.
Edited 5/16/2008 7:55 pm ET by rblondeau
Point understood, and taken. I'll raise a malt beverage to the both of you.
AlexOutside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
yes but doesn't that current get combined again in the motor? half the heat for the wires, yes, but not convinced half the heat for the motor. and I don't know a lot about electric motors so if i'm wrong maybe you could explain why.Brian
No. There are two windings in the motor. When the motor is wired for 120V, the two windings are in parallel. When the motor is wired for 240V, the two windings are in series. Each winding sees 120V at 7A (for example). With the two windings in parallel, the total is 120V at 14A. With the two windings in series, the total is 240V at 7A. In either case, the individual windings see exactly the same voltage and current; it's only the combined voltage/current that differs.
-Steve
I know this is an older topic, but FWW takes threads off the main board so quickly if there are no new messages . . . It sounds like you are agreeing with me that motors wired for 240v will not run cooler than 120v wired. I guess it's my wording that you disagree with, but thank you for the gimpse inside motors anyway. Do all electric motors have two windings, or only those capable of 240v wiring? Brian
"I guess it's my wording that you disagree with..."
You said, "...doesn't that current get combined again...," and that was what I was trying to clarify, that it doesn't get combined per se.
Multi-voltage operation is the principal reason for having multiple main windings in a single-phase motor. The kind of induction motor typically used in woodworking equipment (say, 1/2 HP and above) also has a separate starter winding, but this winding is typically smaller and is wired in such a way that you can't hijack it for dual-voltage operation. There exist other kinds of induction motor that don't have the extra winding, but they're normally used only in low-torque applications.
Motors that run more slowly than the "natural" 3450 RPM of a 60Hz motor (e.g., 1725 RPM or 1150 RPM) also have additional physical windings, although these are connected together internally and are technically separate poles rather than separate windings.
-Steve
Thanks, Dude.Brian
It's been a really long time since I did my motor theory, so I can't comment on that. I do know that 1hp = 746 watts, so if your motor is 2 hp, then it will always use 1492 watts regardless of how it's wired. This translates into 6.8A at 220V or 12.4A at 120V. This means that your wiring from the motor to your outlet will run cooler at 220V because there is less current running through it.
"I do know that 1 HP = 746 watts." Very true, but your statement that a 2 HP motor will use 1492 watts is not quite accurate. A given motor will use amperage according to the amount of power it is delivering. Also a motor is never 100% efficient so that it always uses more wattage that that formula would indicate.
If everything else in your system is wired properly, 110 or 220 won't make a difference.
The typical 110/220 induction motor has 2 sets of windings. To run at 220 volt, you connect the windings in series - tie B & C together, input to A & D.
For 110, connect the windings in parallel - tie A to C, B to D, input to AC & BD.
So if you use 5 amps @ 220 volt, the 5 amps of current goes through winding 1, then winding 2, both seeing the same 5 amps. The voltage is divided evenly between the windings, 1/2 the input. The same motor @ 110 volt will use 10 amps, but the current is evenly split among the two windings, giving you 5 amps per winding, with the voltage to each the same as the input, 110.
In either case, each winding sees 5 amps @ 110 volts. Thats how the total wattage for the motor at either input voltage is the same.
-Toby
Edited 5/16/2008 9:09 pm ET by tkb
Then why is a 220 option even offered? If it is the same either way, what is the point of a dual voltage motor? I could see why someone would choose 110 over 220 (110 voltage is everywhere, not so 220), but if it truly is "six of one and half a dozen of another", why would someone opt for 220 over 110?
Thanks,
Alex
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
Like you said in your first post - you can use lighter gauge wiring.
Commercial or industrial shops may have longer wiring runs causing more voltage drop at higher current.
Probably easier for a motor manufacturer to use similar design with higher hp motors.
Lower current is easier on contacts, switches and such.My table saw motor draws 26 amps at 110. It's not very common to have a 30 amp 110 volt circuit, so I set it up for 220. My 1hp jointer was already plugged & wired for 110, so I left it that way. Band saw was 220 only, had no choice.For a 3/4 hp motor, I'd say do what's convenient.-Toby
Edited 5/16/2008 10:14 pm ET by tkb
Thanks for the reply.
I am not in front of the motor now, but I think the ampere rating was 7/14.
If I am running 110v, pulling 14 amps, is the startup amperage likely to trip a 20 amp breaker? Or is that already taken into consideration when they give the amp rating?
AlexOutside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
There's a fudge factor in the ratings, so you should be okay. I've never had a problem running 15 amp motors on a 20 amp circuit. I've tripped the breaker with my old tablesaw while trying to cut thick stock, but that's one reason why I upgraded.-Toby
Thank you - the first message in the last 5 or so that I can actually understand!Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
I concur with tinker, the same formula the same result. I admit I as wrong on this account
"The electric company charges you for watt-hours, not volts. To figure volts you use the fomula Volts x Amps = Watts. A device that runs on 240V will use half as many amps as an identical device that runs at 120V, so the wattage will be the same -- and so will the cost"
MY BAD.
However in AZ we have a peak demand system and it gets complicated quick. They measure the peak demand you use in AMPS during every hour and bill you an extra amount every month for each amp you use... So we always try to keep our average amp usage down and have systems to regulate which devices will run on a priority basis. Check out APS.com if you really really care.
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AZMO,
Yes in Texas a commercial or industrial customer might pay a peak demand charge. Then load balancing is important.
Do they have demand charges for residences in AZ? If so, it might be worth the investment to "soft start" your AC and other "large" motors.
Yes, they do and both of my AC units on my house have soft start features. Plus solar hot water, and if you hang your clothes on the line, by the time you get to the last sock the first one is dry.... It is hot enough in the summer that I won't be in my garage much during peak hours 9 AM to 9PM <!----><!----><!---->
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Yes, here outside of Houston it's getting to be 96 degrees and 98 % humidity. When we hang clothes on the line they just mildew...
I'm not lucky enough to have an air conditioned shop so my work takes place before 11 and after 6.
I did find one thing about working in the heat of the afternoon, though. Sweat drops on quartersawn white oak leave an almost impossible to remove blue/black stain. Why, in just a few minutes I can stain an entire project...
You're just shutting things off completely, which will reduce your power usage. If you were going over your power limit and could instantaneously switch your 1650w motor from 110v to 220v, it wouldn't matter. It's still using 1650w and would be over the limit.If you use 1650w in any fashion, the utility will be delivering it to you through the 130KV high tension lines at .0127 amps. Do they charge for the .0127 amps at their end or the 7.5 amps at your end?-Toby
Edited 5/17/2008 12:11 am ET by tkb
I'm going to butt in because it seems that you are outnumbered at this point. I'm with you 100% on this one. There seems to be a lot of misunderstanding on electrical functions. Using the following designations
P = power (watts)
I = current (amperes)
E = pressure (voltage)
P = I X E.
If Power is converted to heat, then the heat is a result of voltage times current - not current alone. And, for goodness sakes - the electric meter measures power, not current or voltage. It makes no difference to your electric bill whether all the electric comes from one leg or equally from both legs.
I remember when we first got electric power on June 23, 1941 that we just had one leg, the minimum was forty kilowatts for the total of $3.45 per month and even though we didn't use that much power we had to pay for it anyway because of the minimum. All we had in those days a light in every major room, not even a radio. And it was nice to have light! No one even dreamed of the use we would make of electric power of later years.
Edited 5/16/2008 11:36 pm ET by Tinkerer3
Edited 5/16/2008 11:37 pm ET by Tinkerer3
Edited 5/17/2008 11:00 pm ET by Tinkerer3
"I'm going to butt it because it seems that you are outnumbered at this point."Heh - thanks. It seemed like things were starting to spiral down for me.-Toby
Most electric services to our homes is 220/240. They measure the amount of electricty you use by the amps over time. We have two hot lines coming in, X and Y. If all of your 110 motors are connected to X instead of split up over both, your electric bill will be higher. Say you have two three 5 amp motors running, that is 15 amp total on X. If you wired that on 220 it would be 7.5 amps or half the electrical cost. So if you are trying to save costs, using 220 motors keeps the average as low as possible. If you want to check it out, take the same motor and wire it 220 and watch the meter run, then do it 110.
Industrial motors run on 3 phase for the same reason, it is the most cost effective.
AZMO
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Wouldn't that 15 amps be split up as 7.5 on X and 7.5 on Y, giving me the same electric bill?
AlexOutside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
No they measure the highest used as KW or volts X amps. <!----><!----><!---->
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That is utterly false. You pay your electric bill by the watt-hour( actually kw hr ), not amp-hour. Pull out your electric bill & look at it.-Toby
If you know that a KW is a 1000 watts and a watt = voltage x amp then you can figure this out. Yes they bill us by KW but just how do we use electricty, it comes with a set voltage, it is the amps they bill us for. Think about it...
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"If you know that a KW is a 1000 watts and a watt = voltage x amp then you can figure this out."What are you trying to figure out?"Yes they bill us by KW but just how do we use electricty, it comes with a set voltage, it is the amps they bill us for. Think about it..."You're contradicting yourself here & wrong on both. We're billed by KWH.-Toby
AZMO,
It's kilowatt, not kiloamp. Check the fine print on your PoCo bill.
-nazard
Please look at the posts above.
A kilo watt is 1000 watts
Watts = Volts X Amps
Since we have a standard voltage the only variable in the equation is amps.
The power companies bill us by KWH which is 1000 watts of power for one hour. We can change the amps by using a smaller motor, or use it for less time. GET it?
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AZMO,
Thanks! You just admitted to a factual error in your previous post and retracted said error. Its not often that you see anyone around these parts acknowledging that they made a mistake. Very refreshing, and my hat is off to you, sir!
Got a chuckle from your clothesline comment. We have family a good ways south of you in Patagonia and, in fact, are considering retirement there. Some of the most spectacular scenery in the world.
Stay cool!
-Jerry
"If you know that a KW is a 1000 watts and a watt = voltage x amp then you can figure this out."
This is true only for a non-reactive, purely resistive circuit. In a circuit that contains reactance (capacitance or inductance), the power consumption will always be less than the product of voltage and current.
In a residential setting, the difference is not significant, but for industrial users, especially those with lots of electrical motors, it can be. For a variety of reasons, the power company doesn't like large reactive loads, and will often penalize users that have them. The users can compensate by adding capacitance to their circuits to balance the inductance. However, this is a "don't try this at home" kind of thing: It's quite possible to set up a resonant loop that amplifies rather than reduces the amplitude of the voltage and current within the loop.
-Steve
Back to the subject of the thread - how should you wire your motor? This is my 2 cents:
Wire it for 220V. Since this is a fairly large motor, it will have to be on a dedicated circuit if you run it at 110V. Moreover, though the in-rush current for a 1 HP motor can be relatively easily handled by household 20 amp circuit breakers, that's the in-rush in a low- or no-load condition.
On a bandsaw, it's a fairly common occurence to make a mistake and bind the blade. With a 110V 20amp circuit, that will likely trip the breaker, which is a pain. Presuming that you immediately shut off the saw when you accidentally bind the blade, there is really no danger in burning up the wiring, switches, or breaker - the breaker is designed to trip at about 110-120% of rated ampacity to prevent an over-current situation that lasts for 15 seconds or more, which could potentially start a fire.
Most household 220V circuits are rated at 30 amps or more, depending on the purpose of the circuit (an electric stove, circuit, for example, could be up to 60 amps). If you bind the blade on the bandsaw, it's unlikely to (immediately) trip the circuit. You can then shut off the saw, correct the situation that caused the bind, and resume work without having to go re-set the breaker.
WRONG, WRONG, WRONG, WRONG
Your electric meter is a POWER meter.
Power is Volts X Amps
I'll leave the arithmetic you you, you'll be surprised what you find.
Depending on the size of the tool, 220 may not offer much in the way of advantages ... and even introduce other problems. Let me explain....
Unlike 110, when you use 220 you need fuses on both lines. You disconnects need to open both lines. There's no "neutral" as it were - both lines are hot.
For stationery tools - and I include those you might have on wheels for storage - one advantage to 220 is that the tool is much more likely to come with some sort of magnetic starter. This provides the safety feature of requiring a deliberate effort to re-start, should there be a hiccup in the power supply. It's also much, much easier to wire in other controls if you have a starter - things like, say, automatically starting the dust collector.
In most cases, the efficiency and wire savings are not enough to worry about.
So, where's the cut-off? Well, I'd stay with 110 for anything that was under a 'real' 1hp, used a 30 amp breaker, and #10 wire. I'd definitely want 220 for over 3hp, 60 amp, and #6 wire. In between can go either way (IMO)
WOW! What a list of responses to a basic question.
Given the dichotomy of answers here and the potential for severe injury and loss of property if you choose to follow incorrect advice, hire a certified electrician to check things out for you. Phone the manufacturer of the motor and have this conversation with them. You cannot afford to follow bad advice.
I would not look at a power bill for your answer here. There is no difference in 1W of power at 120V or 1W of power at 240V from a cost perspective. Once your load demands exceed 20A, it is standard practice to utilize 240V to protect the wiring in the structure. In a 240V system, Current demand is essentially 1/2 so the same size wiring is used as in the 120V system, and the wires do not melt.
As to what would make the motor "happier", I'm assuming you mean "live longer". I'm certain the answer is "it doesn't really matter because it is designed to run on either voltage". You really need to check the efficiency curves if you are concerned about economy or heat build-up. There are many 3/4-3 HP machines running on 120V throughout most shops. Typically, anything over 3HP is 240V because the amp draw is approaching 20A — the limit of standard 120V wiring.
The distance from the power source /breaker box to the shop is another key factor here as voltage drops off with distance. Here's where you could be causing the motor to pull higher amperage and thus endanger it and your shop of burning up.
From a safety perspective: The advantage of 240V is that it tends to knock you back if you touch it; 120V tends to cause your muscles to clamp down and hold on. However, 240V will arc quicker than 120V.
Make sure you fully understand the advice you are getting over the internet. Talk with a certified electrician to confirm decisions especially related to electricity if you are not fully confident in your source.
The thing that concerns me the most here is WD40 and electricity mix well, but a malt beverage and electricity (or power tools) do not mix well. I am not trying to make a joke here or to impose my moral values on you. Leave the alcohol for after your work-time/playtime. You are making decisions that could endanger your life as well as anyone who walks into your shop. This is not a time to have even the slightest impairment. A slip may only damage a piece of equipment; but it may cost you the ability to enjoy woodworking or worse it may cost the injury of someone who comes into your shop at the wrong time.
Greg
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Edited 5/17/2008 5:35 am by Cincinnati
Thank you for your answer.
Yes, heat build-up in the motor is my concern, and it seems that there are two schools of thought on this. ("220 is better for the motor" vs. "220 allows lighter wiring").
As for safety: The 220 line is already run. The beer goes along with a rag, some wrenches, a can of WD, some good music, and the innards of my new (old) bandsaw.
Grant a man his simple pleasures! ;-)
Alex
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
In summary:
Understanding dual voltage 120/240 volt motors is prefaced by an understanding of how electricity is delivered to a house. Coming in from the pole are three wires consisting of two 120 wires and a common. Voltage measured across the two 120 volt wires will read 240 volts while the voltage read between either 120 volt wire and common will read 120 volts.
All convertible 120/240 motors run on 120 volts internally. There are two coils each running 120 volts and using 1/2 the 120 volt amperage (The coils act as a resistance and split the amperage). All you do when you re-wire the motor to run on 240V is change the wiring connecting of the coils from parallel to series. When wired for 240 volt operation, one 120 volt leg and its associated amperage is routed to each individual coil rather than a single 120 volt line providing 120 volts to both coils. The same voltage and amperage runs through the individual coils no matter how it it wired. It is amperage that creates heat, and because the amperage in each coil is the same for both wiring configurations, there is no difference in the heat produced by either wiring configuration. The motor is perfectly happy with either voltage and doesn't even know you made the change.
The only advantage to re-wiring for 240 is that it reduces the amperage in shop wiring running from the breaker to the wall outlet. This means that the voltage drop in the wiring is lessened. If your wiring is properly sized for the amperage and run length, voltage drop will be minimal and well within the operation range of any good motor. Voltage drop will be almost equal if the wire size is the required size for each different motor amperage. Only if your wiring is inadequate for the higher amperage of 120 volts will the motor run better when you convert it to 240. In this case, upgrading the 120 volt wiring one size and making it a dedicated circuit, will accomplish the same as installing a 240 volt circuit and wiring the motor for 240.
If a motor coming up to speed very slowly or is tripping a breaker during start up or when under normal load, you either have other loads on the circuit, or the circuit is undersized for the amperage or the run length. The fixes are: remove the other loads from the circuit or upgrade the circuit. To upgrade the circuit, either rewire with heavier wire and a larger 120 volt breaker, or convert the circuit to 240 volts which has the affect of lowering the wiring amperage draw. Either of these solutions will equally fix the problem. Again, the motor doesn't care and won't perform differently as long as it gets clean power.
Thank you for the clear and thorough explanation.
In my small basement shop, the wire runs are short enough, and everything is 12 gauge, so I guess 110 or 220 doesn't really matter. However, since I already have a dedicated 220 outlet, I will set it up for that.
Alex
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
"If a motor is .......tripping a breaker..."
Let me suggest one more cause. Sometimes those breakers just get old and tired and will trip much too soon. I had an electric range that would trip the breakers when only two burners were on. On the other hand, I have known a twenty amp breaker not to trip when there was a dead short! The 200 amp main tripped instead. Those breakers don't always work accurately.
Another thing you mentioned. It isn't current that creates heat. It is the current times the voltage that creates heat or (power). Have you see pictures of these big transmission lines that break down because of the ice load? They carry a huge current load yet don't produce enough heat to melt the ice.
Actually, it's the current through a resistance that creates heat. But you can't really isolate anything single electrical unit - they all interplay in a circuit.Transmission lines don't carry that high of a relative current load. 10MW on a 130kV line is only about 71 amps. Transmission lines can go much higher in voltage to carry more power and/or go longer distances. Russia has a 1200kV line.-Toby
Edited 5/17/2008 11:57 pm ET by tkb
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