How can 6 HP motor be 120V?

[Russ Filtz]

Been looking for compressors and Porter Cable lists some of their 6 HP 20-25 gal. compressors for 120V @ 15 amp! The 6 is a "peak" rating, but still how is this possible? I thought for something that big you'd need 220?

[Bill Lewis]

Marketing!

It is a theoretical peak, no load, HP rating that is worthless. Same thing they do for shop vacs.

[Bill Arnold]

A 15A rating means the motor is actually 2.4HP.

120V x 15A = 1800Watts

1800W / 746(Watts per HP) = 2.4

[scott spencer]

When successfully used as a lightning rod I would guess the HP rating could go even higher ;) .....so essentially that rating is bunk. To add to Bill's rule of thumb formula there's also losses for efficiency and power factors that reduce the HP even further from the calculation.

[Jim Becker]

A 15A rating means the motor is actually 2.4HP.

120V x 15A = 1800Watts

1800W / 746(Watts per HP) = 2.4

Less any derating for efficiency...

[Tom McDermott]

Automobiles have a similar rating system. My 1974 Ford Pinto was easily capable of achieving over 350 miles per hour! Of course, you had to lift it to 35,000 feet, point it straight down and drop it.

[Richard Gillespie]

Automobiles have a similar rating system. My 1974 Ford Pinto was easily capable of achieving over 350 miles per hour! Of course, you had to lift it to 35,000 feet, point it straight down and drop it.
You have to understand that that is theoretical. As you approach 100 mpg parts on a Ford product will come loose and start to peel off. That will act as an air brake. By the way, I don't think any other major auto manufacture would do much better. ;)

[Ray Bersch]

How did we go from Porter Cable bashing to Ford bashing in only seven posts??:rolleyes:

(Ok, I know, no one was Porter Cable bashing, it was just an honest question.)

[Jim Becker]

My 1974 (small automobile) was easily capable of achieving over 350 miles per hour! Of course, you had to lift it to 35,000 feet, point it straight down and drop it.

Unless you put a rocket motor in it's butt and fired it off :p ...thats more than 100 MPH over terminal velocity! ;)

[Gary Max]

My luck the Pinto would run out of gas half way down.

[Richard Blaine]

Less any derating for efficiency...

And a smaller motor like that will have a 50% efficiency at best. So in reality, the motor is only giving you 1.2 hp. A far cry from the pie in the sky 6hp they are claiming.

Now who wants to talk about the inflated wattage attributed to car stereos. :eek:

[Dale Thompson]

Russ,
You are looking at a HP rating which is known as "Brake" horsepower. Correct me if I'm wrong but for "brake" HP you spin a motor at its maximum RPM, clamp it instantly to a stop and measure the torque. The torque is then coverted to HP. There is a technical validity to this but it is also used as a marketing scam. Relative amp draw is your best measure of POWER in todays competitive sales environment. :)

The auto industry also uses the "brake" HP thing. If you have a lot of money to lose, I'll make a bet with you. I will attach a cable from my 50 HP electric motor to your 17 Zillion HP, off-road, indestructible Hummer and see who pulls the other across the "line"! In fact, if you have three or four Hummers, I'll still give you "irresistable" odds! ;) ;) :)

Dale T.

[Michael Perata]

Russ,
I will attach a cable from my 50 HP electric motor to your 17 Zillion HP, off-road, indestructible Hummer and see who pulls the other across the "line"! In fact, if you have three or four Hummers, I'll still give you "irresistable" odds! ;) ;) :)

Dale T.
Dale

Since the thread started off talking about 120V motors, you'll be limited to 120V also, but you can use a separate circuit if you want. :D

[Ken Fitzgerald]

Michael.....I have a hard time imagining Dale being constrained by 120 v or anything other than what HE desires! :eek: :D :D :D

[Russ Filtz]

Dale, I think the analogy to BHP in autos is flawed! BHP is the real "actual" HP you should look at. I believe it's the HP the engine generates minus all the friction/mechanical losses from the crank or engine back to the wheels (hence, how much braking force the engine can overcome, or just on the edge)

Dictionary "The actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or dynamometer connected to the drive shaft."

BHP can be exaggerated, as it might only be an "instant" measure and not something you can maintain without damage (maybe similar to locked rotor amps in a motor?). "Rated" HP ratings though, should be something it should handle continuously, but then again we're dealing with marketers in the ads!

[Dennis McDonaugh]

Automobiles have a similar rating system. My 1974 Ford Pinto was easily capable of achieving over 350 miles per hour! Of course, you had to lift it to 35,000 feet, point it straight down and drop it.

I don't know about 350 mph Tom, but I had to turn the air conditioner off on mine to pass anyone.

[Dale Thompson]

Why do you all get such pleasure from picking on moi? :confused: Being stupid ain't a crime - it's just inconvenient sometimes. :(

Michael: All electric motors, regardless of their rating, run on 120v. when all the electrons are counted. That's the reason for the multiples of 120v that we commonly see such as 240v, 480v, etc. Give me some #4 wire and about two thousand fuses and I'll get my 50 HP motor to run on 120v. If I get electrocuted in the process, you would normally be blamed. However, my doctor declared me "brain-dead" many years ago so you are off the hook.

Ken: What does 120v have to do with anything? We have to think outside of the box sometimes. I know because I LIVE in a box! :D Some folks would call it a cell? :eek:

Russ: "Friction brake and dynamometer" are the key here. Those refer to "brake" HP. "REAL" HP uses stuff like amps, voltage and/or resistance.
For example, I can pull 4000 lb for a distance of 50 ft in a period of 20 sec using only about 18 "real" HP! :) Guess who wins if I hook my 6 HP Sears shop vac up to my 3 HP PM 66? :eek: ;)

I'm still looking for the big Hummer to hook up to my 50HP bicycle. Of course, my bicycle will be tied to a 24" Oak tree! :cool:

Anyway, is there ANYTHING I can do to keep you bullies from picking on me? :confused:

Dale T.

[Dave Harker]

I have a PC "6 hp" compressor, it's a nice compressor - mine is converted to 220v (does that make it 12hp? - JUST KIDDING! :-)

It's converted to 220v since it kept blowing my 20amp circuit-breaker on 120v. This was a brand-new Square D "QO" subpanel and breaker, installed by pro electrician and inspected, with nothing else on the circuit. The circuit has never blown before, or since, on any other "15 amp" tool. So, it is a honkin' big "15 amp" motor.

I got a 220v conversion kit made by Coleman and sold in the compressor section at Menards - a cord w/ 220v / 20amp plug and ring-terminals on the bare wire ends (to attach to compressor motor). I followed the directions on the motor's sticker, and it works like a charm.

It's a great compressor, very quiet. CPL6025, I think. Made by DeVilbiss, for PC.

[Dale Thompson]

I have a PC "6 hp" compressor, it's a nice compressor - mine is converted to 220v (does that make it 12hp? - JUST KIDDING! :-)

It's converted to 220v since it kept blowing my 20amp circuit-breaker on 120v. This was a brand-new Square D "QO" subpanel and breaker, installed by pro electrician and inspected, with nothing else on the circuit. The circuit has never blown before, or since, on any other "15 amp" tool. So, it is a honkin' big "15 amp" motor.

Dave,
Congrats on the new 12 HP Compressor!! :) Your "15 Amp" motor must be a real honker. What you did by going to 220v is divide the amps going through each "hot" wire by two. If your "15 amp" motor was drawing 22 amps, for example, converting to 220 v cut the amps through each wire to 11 amps. If the compressor was brand new, your problem may have been temporary until the brearings, bushings, etc. were properly seated. In any event, the only savings that you get from 220v conversion is that you can use smaller wire.

Dave, I'm sorry about throwing a "wet blanket" on your new "12 HP Compressor"! ;) :D If it's any consolation, my compressor is only 1 person-power. I have a hand bicycle pump to run my framing nailer! :eek: :( ;)

Dale T.

[Dev Emch]

Holly Cow Guys, so far no one has really touched on this issue:rolleyes:

The short of the story is... well, I cannot say that or the module-later Dude will take out his cattle prod and poke me with it.

As I recall, somewhere in the last two issues of FWW, there was a blurp that the compressor industry was going to get its act together and stop this "deceptive advertising" and follow the rules everyone else has to. And it is very deceptive.

When an electric motor starts up, it is slamed onto the 60 cycle grid with no mercy. So there is a huge inrush current that averages about 6 times the normal runtime current. This is called a diarc start pulse and it is down right nasty. I often see these on the order of 60 to 200 amps!

But they are short lived. Very short lived. As the motor springs to life and settles in at a comfortable speed, the current drops down and settles in at the idle current. The nasty start pulse lasts for less than 1/2 second. Actually its in miliseconds but considering that not everyone is an engineer, lets just say it lasts for less than 1/2 second. Its short enough that it does not pose a fire hazard to all the now under-rated electrical components and the breaker. This is a known fact and the NEC and local codes will allow for this exception in allowing overamp conditions to exist. In certain cases, you will also use time delay fuses to allow for this situation to occur. If your motor rotor were locked up however, then a start would expire the safe time limit and cause the fuses to burn out and the breakers to blow for sure.

Some breakers are time delay breakers for motor applications. I dont use them. The manfacturer of our phase converter told us to just add 25 to 30 percent ontop of the motors rated current output and size accordingly. This will prevent the start up spike from poping breakers.

If you have a condition where the breakers are being poped on a start up and you fix this by doubling your voltage, you should be aware that this works by also halving your current. Double Voltage ----> Divide Current in Half. There are no free lunches when it comes to power. One pony eats as much hay and oats as the next pony.

So what the heck did the compressor guys do? Well, power is made up of voltage and current. I paid a ton of good money to the state of colorado to learn this nursery rhyme... "Twinkle twinkle little star...... Power equals I squared R". Well, there was this other dude by the name of Ohm and his law allows us to convert this I*I*R into V*I. So by now you should see what these little devils have been doing! Yup! They are using the diarc start pulse to compute power output. Tisk Tisk Tisk Tisk. So for about 1 millisecond or so, your consuming 6 HP of energy. But, like every good invention of our times, nothing is perfect. Hardly from it! So some of this goes in the form of heat loses, some in the form of mechanical loses and the rest in the form of actual usable power. During this very small time period, the vast majority of your 6 HP is going up in the form of heat loses and whats left is beginning to turn the rotor. You actually get squat nada!

The fact that these guys have gotten away with this for so long is truely amazing. Fraud is the only word I have to describe it on this forum. That is why if a compressor does not have a real, air pressure controlled mag starter by someone like sqaure D or allen bradley and the motor is not a standard frame industrial by leeson, lincoln or baldor, I am outta here!:rolleyes:

[Mark Singer]

Plug it in 4 times and add the horespower...:D

[Dave Harker]

Dale, thanks for presenting the explanation. I failed to explain that myself (that doubling voltage halves the amp load). When I planned the electrical layout for my shop, I put in a dedicated 220v circuit for my (then future) compressor - converting the compressor to 220v was going to happen anyway, even if it didn't blow a 120v breaker. I made sure the compressor I got could be converted to 220v, and was only trying it out on the 120v circuit - so your theory about it not being broken in yet is probably correct.

[frank678]

Starting torque (inrush current or diarc start pulse ) for motors with across the line starters are typically 6-7 times the full load amps, hence lights dimming, etc. when you start large motors.

If you really want to know what you're buying pay attention to the amp draw of the motor and not the advertised horsepower...

Locked rotor amps is the terminology used for the current draw of an electric motor with the shaft stopped and in a locked in position. This is the current you draw when a tool stalls out.

I too can't believe they can get away with this false advertising...

[Dev Emch]

Frank678....

Amen Brother! And its usually the borg compressors and craftsman compressors who are the worst at doing this. You would think they know better. Any person with even a miligram of common sense will ask when they have to get help to pick up a 5 HP baldor saw motor and then turn around and pick up these 6 HP compressor motors with one hand!

This makes buying compressors and air tools very hard for average folks. An olde timer will sell you a jitterbug auto body sander and ask you how many HP your compressor has. "Uhhh, 6 I believe. Ya, no worries, it will work just fine." You bring home your new toy only to find that it eats 12 CFM at 90 PSI regulated continuous and your compressor can only put out 6 CFM continous at 80 PSI. NOW WHAT????

So the best thing to do is always shop by "CONTINOUS CFM" numbers. Sure a big compressor can put out more instantaneous CFM but its using the blowdown from the receiver tank. Your better off by just matching continous CFM as that will guarentee you that you can run your new air tool continously.

On an aside, I love air tools, esp. the japanese made, auto service tools marketed by Ingersoll Rand. They make a disc sander and 3/8 inch drill that are just out of this world. All polished cast aluminium bodies and no frilly things attached. Been on the market since the mid '70s. Overall, air tools are smaller, denser and better made than the electron burner counterparts. In some cases, vastly better. For example, I bought a cheapo CH air powered roto zip tool from home depot for less than 30 bucks. How much does Dewalt and Roto Zip want for the electrical versions? Lots More! But, the electrical version needs to suck air into the motor to cool it. The air powered version needs to expel air as air is used to drive it. When cutting holes in concrete and dry wall gypsum, this abrasive dust is being sucked into the motor of the electric versions thus beginning to compromise your bearings. NUFF SAID!

Also, air motors tend to suck lots of air but given the same volume, are much more powerful than corresponding universal electric motors. If you have ever used an air powered 3/8 inch drill, you will know this. Also, the drill can deliever full torque almost instantly.

[Dave Wright #2]

Worth noting that the only machines that get inflated ratings are ones whose motors will never experience that horsepower demand. For example, the only way you can get the motor circuit in a 6 HP shop vac to attempt to draw that much current is to pop a framing nail through the housing into the impeller before turning it on. In normal use it might draw 6 amps. Plug up the hose and you hear the impeller RPM rise, which means it's seeing less resistance and pulling fewer amps. Remove the hose completely and the RPMs drop. That's as loaded as the motor will get, and it's still way short of 6 HP.

[Kelly C. Hanna]

All horsepower numbers are 'arrived at'. HP cannot be measured and therefore is not a really good indicator of power. I prefer torque and amps to HP. The HP ratings are peak on these compressors and as Dale pointed out, they are useless in determining real power. I pay very little attention to the ratings they spew out for tools, cars, etc. The tell tale of power if performance in the real world. For compressors, that's the SCFM numbers. Paying attention to what the tool will do is more important than the power rating to me.

[Steve Cox]

Dev that "twinkle twinkle...." bit is interesting. I learned it as PIE. P (power, in watts) equals I (current, amps) times E (electromotive force, volts). I recently received a new air ratchet as my part of a class action lawsuit against Campbell-Hausfeld (who makes most of these compressors) for false advertising about their horsepower ratings.

One mis-understanding I keep seeing in threads like this is that switching to 220V will halve your current usage. It is true that doubling volts will halve the current running down that leg but when you switch to 220V you are adding another hot leg also with half the original 115V current so you use exactly the same amount of current. Voltage has almost nothing to do with the power of a motor. I have seen 24VDC motors that were the size of medium size trashcans but the wire to supply them was the size of a water hose. The only reason to run a motor on 220V vs 115V is so we don't have to run #4 wire or something similarly sized to our outlets. 12/2 is bad enough.

[mike malone]

can somebody help, a pinto just hit our henhouse!!...and there's a picture of Jim Becker on the side of it!!!!!!!!!

[Dev Emch]

Steve and others interested in a bit of lec-ga-getty for the shop.

I really need to beg your forgiveness and disagree. The only reason you boost your voltage is to cut your current. Power is voltage and current and only power is conserved. Change voltage and you change current and vice versa. If you look on dual voltage motors, you will find a nameplate. Look on that name plate. You will see a notation like 220/110 volts and 7/14 amps. For normal single phase use, you have 110 volts from your positive lead to your neutral. When you go to 220 volts, you are actually taking a second pole of 110 volts to neutral and using these two to supply not one but two breakers with a common bar. On a single device breaker, there are two output screws. One is positive and the other is neutral. Measuring across these two with a volt meter will yield 110 volts. In my case, its 120 volts. But a double slot breaker or 220 volt breaker is not the same. Here, each breaker has its own positive output lead. So if I were to measure each of these leads to my neutral bar, I would get 110 volts. If I measure between these two leads or terminal screws, I get 220 volts. That is a differential voltage and why its so important to make sure your ground lead is installed correctly! The absence of a traditional neutral can redo your hair do in a hurry if that green wire is not correctly used.

The important point to remember here is that this differtial voltage has but one big loop so current is not being branched. The true killer in all wire is current loading. AMPS. Not voltage. A 12 gage cupper wire made of THHN conductor can handle 20 amps. It does not matter how you get that 20 amps. Ohms law in its most basic form gives you a relationship between voltage, current and resistance. V=R*I. So if I want to see how current is changed, I can rewrite this as Current(I) = Volts/Load(ohms). So using the same wire, I can get a variety of combinations of resistance and voltage to produce the same current which is what limits that wire.

So it does not matter how much voltage I use or what the load is. If the current passing through that wire reaches 20 amps in the case of 12 gage copper, I am in trouble.

The stator windings of your motor have a limit as to how much current they can handle. Go above that, and the shellac like insulation burns out and the stator shorts out and the motor is junk. If I double my voltage, I cut the operational current in half. So now my motor runs cooler and a bit more efficiently. As temperature of copper goes up, so does is resistivity and hence resistance. So you get a bit more efficiency by running cooler at lower amperage. You still get the same power output as power is a combination of voltage and current and is conserved and is determined by the electromagnetic design restrictions of both the stator's magnetic fields and the interaction of the induction rotor.

So in short, you do see a halving of your current. Things get much wirder when you make the transition to three phase power. Now, you have three conductors running current and these tend to follow your argument. In three phase power, you dont have three separate systems.... rather, you have a relationship in phase betwee any two of the three wires at any time. They are normally known as L1, L2 and L3. The phase shift between L1 and L2, for eample is 120 degrees. Likewise between L2 and L3.

Most of us are running rotary phase converters to get three phase power. L1 and L2 of the L1, L2 and L3 combination are actually pass thru conductors from your single phase service center. In otherwords, a single phase unisaw running on 220 volts is actually tapping itself into L1 and L2. At this point, there is no 120 degree phase relation between L1 and L2. The phase converter is a single phase device that runs on a double pole breaker. It has two wires going in. It has one wire comming out. This third wire is the wild leg and it contains the 120 degree relationship between L1 and L3 and L2 and L3 and, by default, L1 and L2. But only when its running. The output is L3 or the wild leg.

If I measure voltage between L1 and L2, I get 220 volts. Nothing magic here as this is the incomming service being passed through. Now, if I measure voltage between L1 and L3, I may get something like 245 volts. Likewise between L2 and L3. The wild leg on a phase converter fluctuates and that is why is called wild. As I load up the system by turning on a saw or shaper or what not, this 245 voltage will tend to drop back down to the incomming service voltage. Nothing to worry about here. That is how it works.

Now, if I meaure voltage between L1 and neutral and L2 and neutral, I will get 110 volts. But if I measure L3 to neutral, I will get the square root of 3 times 110 or 190 volts! That is how I find the L3 wild leg.

But there no free lunches. Sooner or later, its time to pay the piper or in our case the power company and the inspector. So yes, I run most of all my machines on THHN 10 gage wire which can handle up to about a 10 HP motor on three phase. But that applies to everything downsteam of the phase converter. Everything upstream of the converter leading back to the single phase service center and eventually to the pole pig sees life from a single phase point of view. Here, the overall load of the shops three phase power is computed as follows:

I(single phase) = 2.6 * (Combined Horse Power Load) * (3) ^ 1/2

So if all I ever did was run a 3 hp, 3 phase unisaw and a 2 hp, 3 phase jointer at the same time, then I would have....

Isp = 2.6(3+2)*1.732 = 22.51 amps total.

Now I need to make the inspector dude happy and this means derating this value by 1.25 or 1.5. I forget the exact value and you need to check your local code for this figure. Taking the 1.5 derate, I get

Isp = 1.5 * 22.51 = 33.7 or 40 amps.

This would be the size of the single phase, 2 pole breaker that I need to install to feed my phase converter and all the toys downstream. It consists of two 40 amp breakers glued together with a common bar having 40 written on it. Somthing like you would see on your oven or stove circuit.

For me, three phase with a converter is the way to go. Single phase motors are putz motors with issues when it comes to woodworking machines. For one thing, single phase motors cannot self start. You need special staring systems. You will find either repulsion/induction motors with commutators and brushes or capacitor start motors which are the more prevalent today. The orig. unisaw bullet motors were repulsion/induction motors. Today, the cap. start motor has a capacitor, a secondary stator start winding and a centrifical cutout switch inside the aft motor bell. Wood dust and motor grease combine to plug up this cutout switch. That is why it is so important to pull the aft motor bell and clean out that switch once a year! If that switch does not disconnect the secondary start winding from the motor after the motor comes up to speed, it will burn out the stator windings in a putrid cloud of electrical smoke. Every variation of a single phase motor is more often than not a new gimmick or scheme to start the motor. A three phase motor on the other hand has none of this. NADA. Three phase power provides its own rotating magnetic field which is what you need to start any motor. Single phase power in either single ended versions (110 volts) or differentially ended versions (220 volts) do not have rotating magnetic fields, thus they cannot self start a single phase motor.

Also, three phase motors are more reliable and cheaper once you get to about 3 HP and up. Single phase motors are still cheaper in the sub 1 HP range and the 1 and 2 HP ranges.

Hope this helps a bit. There is lot of info here and you may need to read it two or three or four times. But many gargage shops are quietly running heavy industrial iron on phase converters, many of which are home made, without any problems. Once you make the change, you will not go back. And its not a very big change either!

Regards

[mike lucas]

Russ,


The auto industry also uses the "brake" HP thing. If you have a lot of money to lose, I'll make a bet with you. I will attach a cable from my 50 HP electric motor to your 17 Zillion HP, off-road, indestructible Hummer and see who pulls the other across the "line"! In fact, if you have three or four Hummers, I'll still give you "irresistable" odds! ;) ;) :)

Dale T.
I'll take you up on that bet, but all I have is a 500 hp diesel truck. I also require you to meet me half way. :D and NO outside power source :eek: That`s the least you could do since I don't have 17 zillion hp nor do I have a Hummer :D

[mike lucas]

Why do you all get such pleasure from picking on moi? :confused: Being stupid ain't a crime - it's just inconvenient sometimes. :(

Michael: All electric motors, regardless of their rating, run on 120v. when all the electrons are counted. That's the reason for the multiples of 120v that we commonly see such as 240v, 480v, etc. Give me some #4 wire and about two thousand fuses and I'll get my 50 HP motor to run on 120v. If I get electrocuted in the process, you would normally be blamed. However, my doctor declared me "brain-dead" many years ago so you are off the hook.

Ken: What does 120v have to do with anything? We have to think outside of the box sometimes. I know because I LIVE in a box! :D Some folks would call it a cell? :eek:

Russ: "Friction brake and dynamometer" are the key here. Those refer to "brake" HP. "REAL" HP uses stuff like amps, voltage and/or resistance.
For example, I can pull 4000 lb for a distance of 50 ft in a period of 20 sec using only about 18 "real" HP! :) Guess who wins if I hook my 6 HP Sears shop vac up to my 3 HP PM 66? :eek: ;)

I'm still looking for the big Hummer to hook up to my 50HP bicycle. Of course, my bicycle will be tied to a 24" Oak tree! :cool:

Anyway, is there ANYTHING I can do to keep you bullies from picking on me? :confused:

Dale T.
Then why are there 440V and 550V? :D

[Phil Ordway]

Single phase electric motors operate atabout 65% efficiency. 12.3A at 110V is the benchmark for 1HP. Campbell Hausfield recently lost a class action suit for overstating horsepower. The manufacturers apparently assume 100% efficiency and the number of watts being consumed when the lights go out. Stick with Amps (half for 220V).

[Dale Thompson]

I'll take you up on that bet, but all I have is a 500 hp diesel truck. I also require you to meet me half way. :D and NO outside power source :eek: That`s the least you could do since I don't have 17 zillion hp nor do I have a Hummer :D

Mike,
HMMM?? OK, Mike, you WIN!! :) Since you are too timid to display your location, I can't say that I could afford the extension cord required to meet you half way anyway. ;) Also, since you are such an obvious "cheater", I'm surprised that you haven't taken Vegas for millions and can afford numerous Hummers. :eek: :eek: I suppose that YOUR rules would consider my mini nuclear reactor to be an "outside power source". Anyway, my reactor is still "under development" and I'm not sure that I would want to be around for its first start-up. :confused: I would probably send one of my kids or grandkids. ;) :)

Dale T.