I have a 230 volt cabinet saw that seems woefully underpowered. I think the motor is smaller than the 3 hp motor which is supposed to be installed at the factory. What is the best way tio determine the output of my motor?
I’m familiar with the amps x volts divided by 746 formula and know that you don’t get 100% efficiency out of any mechanical process, but is their any way to measure the output with a multimeter?
The name plate does not list HP or amps, but it does say KW 2.2. The motor is a Leroy Somer. I’m calling their St Louis office as soon as I can get the time. Meanwhile any ideas or familiarity with this brand of motor?
Replies
A 3 horsepower 240 volt motor will be about 13-16 amps.
2.2 kW is about 3 HP. I'd suspect something else is wrong. For example, what kind and how much wire do you have between the outlet and the machine? When you say it's woefully underpowered, what happens? does the blade bind and burn?
Is this a new saw or used?
Pete
Edited 1/2/2007 10:58 pm ET by PeteBradley
Pete:
I have about 6' of wire running to the outlet, can't think of the gauge off hand, but remember using what was factory rec'd when I set it up. The blade doesn't bind or burn, I just have to feed the wood slowly to maintain motor speed.
Jim,There are several factors here. A 3 hp motor SHOULD be enough power for a 12" blade under most circumstances. BUT, it's easier for any motor to power a 10" blade through wood than a 12" blade. Your friend's Unisaw is a 10", isn't it? If he has a 3 hp motor, his saw will feel "more powerful" because the 10" blade has less of a "lever arm" from arbor to tooth tip to resist the motor's torque than does a 12" blade. That's the mechanical part of the equation. Put a 10" blade on your saw and you will suddenly be able to push wood through that brought the 12"-equipped machine to a stall.Still, your saw DOES sound like the motor is not giving you all the torque it should.Now the electrical part.You have measured the "no load" voltage at the outlet. It's good. That's a start. You also need to measure the voltage, at the outlet, or, ideally where the power cord is wired to the motor in the motor's junction box, while the saw is running, and while it's cutting wood. If the voltage drops under load (cutting wood), that indicates there is a serious resistance in the supply lines. The voltage should not drop more than a volt under load. It is very unlikely that the wiring is undersize, although if it is, that's the source of the voltage drop. It is possible that there is a loose connection somewhere along the wiring path back to the supply box, or a partial break (a deep nick) in one of the wires.Do you have another 230 volt circuit you could plug into?You can also measure the current the motor is drawing, especially under load. To do that, you need an AC ammeter as I described earlier.I got mine at Radio Shack. The AC ammeter is a separate part (comes with the multimeter in the box) that has its own battery. The module plugs into the top of the multimeter and converts the multimeter to an AC current device. An AC ammeter has a "hook" that opens to loop over one of the wires (red or black) of the supply line (in your case, the 230 supply line). You can't just hook it over the intact power cord. You have to open up the outlet box and pull the outlet out to get at the wiring. Be careful! The outlet will be hanging out of the wall while the saw's power cord is plugged in and running.Or you can measure the current at the breaker box if you can identify the wires going out to the saw. You'll need to pull one (red or black) partly out of the box to get the ammeter's hook around it.Obviously, you'll need someone to help, because the saw needs to be run by one person while the other is doing the measuring, and risking his life with live circuits (just kidding about the risk to life part).Take my advice. You do NOT want your wife to be helping in any of this. In fact, you might want to send her shopping while you have an electrician give you a hand with this project!If you can measure the voltage under load or the saw's current draw, let us know the result(s).Rich
Edited 1/3/2007 11:26 pm ET by Rich14
These discussions about measuring the current aren’t going to tell you much of anything in most cases, and putting the motor under load isn’t going to help. You already know the motor is 3 hp from the name plate, so you need to look for other problems. Checking the current is the last step.The very first place I would start is with the belts. A loose belt will give you the same symptoms as an underpowered motor. Also look for glazing on the belts.The fact that the motor nameplate is rated in KW tends to indicate that it might be a European motor. I didn’t look very far, but a quick internet search tends to indicate this too. Given that it may be a European motor, it is very likely to be a 240/480 dual voltage motor. You should check to make sure the motor is not configured for 480 volts.Since you have a volt meter, the next thing to check is the voltage of the outlet with the motor off, then on. As Rich suggested, this will indicate if you have a poor connection resulting in a voltage drop.The last option is to check the current draw of the motor. The main thing this will tell you is if you have a bearing problem or other unusual load. An idling motor will draw about 1/2 of its full load rating. You should be seeing about 7-9 amps at no load. If the current draw is much higher than this, then look for any type of mechanical drag on the drivetrain.Also, if the motor uses run caps, I believe that it will be underpowered and show a high idle current.The reason why there is no point in measuring the current draw under load is because you have no way of knowing when you are loading the motor to its rated output.
I think that the centrifugal start switch not opening would do this. Once the motor gets up to speed, if the start switch doesn't open the start windings stay energized and actually cause drag.
You might be right, but I am not entirely sure about this. First off, most of the motors in our tools do not have start windings, hence the capacitor. If the capacitor remains in the circuit after the motor is up to speed, the most noticeable effect is an increase in running current, but I am not sure it results in a loss of power.
This came from a webpage
sawdustmaking.com/ELECTRIC%20MOTORS/electricmotors.html - 28k
Capacitor Start
This motor has a capacitor in series with a starting winding and provides more than double the starting torque with one third less starting current than the split phase motor. Because of this improved starting ability, the capacitor start motor is used for loads which are hard to start. It has good efficiency and requires starting currents of approximately five times full load current. The capacitor and starting windings are disconnected from the circuit by an automatic switch when the motor reaches about 75% of its rated full load speed.
I've been to several classes on troubleshooting electric motors in pump applications, but most of what I was trained on was 3-phase, high voltage and horsepower stuff, run through motor control centers so the trouble shooting is a bit different.
Another few thoughts:
The run capacitor could be bad. IIRC that would also let a motor run at full speed but not develop full power.
I'd check the start switch first though, just because it's mechanical, and I own the screw driver it takes to get to it. To really test the motor, I'd need to buy a good ammeter, and then figure out how to safely isolate the wires while the motors running.
A third thought, but unlikely is one winding could have a short, which could be checked with a vom. Start by checking resistance between the wires in the box, and see if you get a low reading.
If the motor is dual voltage capable, check to be sure it is wired up correctly in the box. Again, I'm not sure, but I think if you misswired the motor, it would run, but not well.
"These discussions about measuring the current aren’t going to tell you much of anything in most cases, and putting the motor under load isn’t going to help."
"The last option is to check the current draw of the motor. The main thing this will tell you is if you have a bearing problem or other unusual load."
A bit of a contradiction, wouldn't you say?
TDF
No Tom, it is not a contradiction. Learn the English language before making presumptions. You have 4 posts in this thread and all are antogonistic. Do you have something of value to add to the discussion or do you just like being a jerk?Frequency does impact power, but the difference between 50 and 60 hertz is trivial. I noticed Joe's posting, but it wasn't worth commenting on, certainly not with your tone. But since you know so much, why don't you go to your shop and connect your tablesaw motor to DC power and tell us what happens.If you knew half as much about electricity as you think you do, you would know that the same equations apply regardless whether it is DC, 1 Hz, or 60 Hz; so explain to me why you would have smoked your motor without getting any usable power out of it.
Edited 1/4/2007 9:49 pm ET by RickChristopherson
"Frequency does impact power, but the difference between 50 and 60 hertz is trivial" A 20% increase from 50 Hz to 60 Hz is trivial? Rich
The difference in "power" between 50 and 60 hertz is trivial.
I don't have the formulas I need tonight for power. A motor designed for 50 Hz that is run at 60 Hz (same voltage) will experience a 20% increase in speed and and a 20% increase in torque. I seem to remember a power increase as a function of the square of the frequency ratio. 1.2^2=1.4. But as I said, I don't have the formulas tonight and there is a difference for single phase vs 3 phase. Normally the voltage needs to be decreased when frequency is increased to maintain constant torque and power for the frequency change.
I follow the speed increase but not the torque, the field strength isn't changing, just the rotational speed. I would by into the same torque, and more horsepower, as horse power can be calculated as a function of torque and rotational speed.
[Torque(ft-lbs) X RPM]/5250 = HP
Jigs,
OK, if that's the equation for the power, then power increases in the same ratio as the frequency change, which is what I thought was true in the first place.
Torque increases as the simple ratio of the frequency change if voltage is held constant. It's usual practice to decrease voltage in a motor that's used over a range of frequencies, (as in an AC variable frequency motor speed control) as frequency is increased. Normally in a speed control application, torque and therefor HP would stay constant over the control range as speed is changed. But a motor designed to be used at 50 Hz 220v, when used at 60 Hz 220v will experience a 20% increase in torque, and, according to your equation, a 20% increase in power.
All other opinions anticipated.
Rich
It's not that I serious doubt you on the torque increase, I just have a hard time picturing how, rotating the fields faster at the same voltage would increase their strength, and torque is proportional to field strength.
Unfortunately, all the books I have that might clear it up are still packed from the last move.
I'm a civil engineer who opted to take the third physics class (Electricity and Magnetism), instead of the third chemistry class (Organic), and spent some time around big motors, (they hooked them to my pumps), so I had to at least have a working knowledge of them.
I think it's related to the rotor velocity , relative to the field velocity. Just can't quite remember it. Anyone happen to have that equation handy?
This discussion is off-topic, so I am not willing to spend much time researching it, however, I will give you some food for thought.As I already stated, horsepower will drop with rpm, but I do not believe it is a linear relationship. This is why I said the difference between 50 and 60 hertz is trivial. While one of the many equations for horsepower is torque times rpm, you cannot assume the torque remains constant, so this equation will not help you answer this question. The more appropriate equation for motor power is current times voltage, but remember this needs the power factor component as well because of the real and reactive components of the current.As the frequency drops, so does the reactive component of the motor’s impedance, which causes an increase in current for the same voltage. The powerfactor also increases with a reduction in frequency until it reaches unity at DC power.If memory serves me, I believe that the power actually remains constant regardless of frequency in the theoretical area, but in reality, the current becomes so high (the same as locked rotor) that it cannot be achieved.As I said at the start of this posting, take this at face value because I have not researched it.
as you've correctly surmised, this post has gotten way off topic with the 60 v. 50 hz irrelevant side issue; it's a US motor from St Louis...my guess, as someone suggested, is simply tighten the belts- most likely the problem.
I emailed the OP this afternoon, and said that it appeared that we have hijacked his thread, and apologized.
If the belt was loose enough to cause a lack of power, wouldn't it have glazed enough to start squealing every time he loaded it up by now? I would expect that if the problem is drive belt tesnion, that he couldn't stall the motor by loading the blade, but would get that nasty squeal, and burning rubber smell instead.
Dear posters & Hijackers:
As the OP I've been amused and enlightened as well as confused as to the direction my inquiry has taken. Sorry I wasn't on top of this earlier when someone originally hypothesized the 50 Hz versus 60Hz dilemma. I could have, bad pun time, short circuited the whole discussion by telling you that the name plate claims it's 60 Hz, but hey the discussion and name calling were pretty funny. I never knew electrical engineer types could be so opinionated.
I'm planning on making some electrical measurements and double checking all the connections this weekend. I already tightened up the drive belt (singular) so maybe that will help. It doesn't appear glazed & I've never smelled burning rubber, but who knows?
Again thanks to all. Any break throughs on my end, I'll post 'em. Any brilliant ideas on your end, fire away.
One thing that has not been brought up. If the motor is a capacitive start, capacitive run motor, it has two capacitors (possibly two in one case with 3 or four wires connected to it) one for start and one for run. The values on the capacitors are usually very different. If the start cap is wired as the run cap and the run cap wired as the start cap or if the run cap is bad you could experience this problem.
Jack
In addition to my earlier suggestion, leroy Somer has a huge website. Maybe they could provide you with some helpful information.
Loose drive belts cause a lack of power,but rarely do they squeal, like a car's drive belt...
But I'm a little mystified that this is a cabinet saw with only one drive belt- most have two or three for better power transmission...must a homegrown type of motor.
Yes, We're off-topic. What else is new. Are you the topic cop? As you may remember, I am waiting for my Hammer combo machine to arrive. In deciding which machine to buy, Hammer or Minimax, one or the other vendor (I can't remember which) told me that the machine came with a motor designed for 50 hz 230 volt service in Europe. The motor was rated at a higher HP here simply as a consequence of its being run on 60 Hz supply. I'm pretty sure the motor was called 3.5 HP in Europe, 4 HP here. Just say'n. Rich
"Take my advice. You do NOT want your wife to be helping in any of this. In fact, you might want to send her shopping while you have an electrician give you a hand with this project!"
This comment id very inappropriate and sexist!
TDF
I don't have firsthand with a 12" blade, but I'd expect it to want quite a bit of power. However, you still may have a problem. Assuming all the previous stuff is good, I wonder if you have a drivetrain problem of some kind. I'd see if the blade spins freely with the belts and power off, both cold and after use. Try the same thing with the motor shaft. Finally, make sure the belts fit and are not angled (in other words, the pulleys are in the same plane). There have been no changes to the pulley diameters, right?If it's possible to do safely, watch the belts while the motor is running and see if they vibrate (the part between the pulleys will look like a blur an inch or more wide rather than like a belt). This can eat a remarkable amount of horsepower and the solution is to simply tighten the belts.Taking one more run at power would be a good idea also. The volts at the outlet don't tell you whether the circuit and wires can deliver enough amps to the motor. If the outlet wasn't properly wired, or the cord to the motor is light gauge, or perhaps a problem with the way the motor is wired, this could be it. The fact that the previous motor burned out and had to be replaced may also be an indication that the wiring is amiss somehow.It would be interesting to know if a 10" blade works better. What brand of saw is this?Pete
Pete (and Rich)
Again thanks for the input. I have used a 10" blade, in fact a Forrest Woodworker II thin kerf, which cuts ok, better than the 12" but still.... The saw is an Inca 2200 (FWW cabinet saw best-pick in about year 2000 or so) which cost me $2500, hence my real disappointment at its performance.
Maybe I was unclear, but it has never burned up a motor, this one has just never cut like I expected it to.
I'll double check the pulley & belt, I do know that the blade spins freely when the saw is off, no binding or weird noises.
Jim: I have two other suggestions for you that may help with your analysis. Post your questions on the inca tool users group at yahoo. Another suggestion is to call Jesse at Eagle tools in LA. He knows more about the Inca tools than anyone around. I have this saw and have never had it bog down. But I haven't tried resawing with it and maybe haven't done any work that pushhed the motor to its limits.
2,200 ÷ 746 equals 2.95 HP at 100% efficiency as Pete says. He's pretty knowledgeable. Your problem is most likely somewhere else. You can get an ammeter which covers the wire without touching it at an electric shop but I doubt if it would be worth while for just this instance. Are you sure that 220 volts is supplied to the motor? You might double check the voltage.
Edited 1/2/2007 11:39 pm ET by tinkerer2
Jim, I have a small digital multimeter I recently bought from Radio Shack for $19.95. It has an AC ammeter hook module (that requires its own battery) that can measure up to 30 amps. Works well. You could measure the motor's draw and come to some conclusions (you have to place the hook around just one wire in the AC circuit). But the amount the motor draws just idling and at full load (FLA) will differ. Rich
Rich14 (& howard, Pete, Rich, Tinkerer & anyone else):
Thanks for your responses. Covering a couple of points that you all have raised. I've owned the saw since it was new , my 1st cabinet saw, and it has never seemed to have the "oomph" I expected. The real kicker came when a friend with a Delta Unisaw came by to resaw some wood on my machine (mine's a 12", my saw that is!). He was amazed at how little power it had. We went to his shop and ran the wood through his machine and there was a big difference it how easily it cut.
My blade is sharp. In addition I have a big, heavy (3/16) kerf, new Freud rip blade that I never use because it doesn't cut well, (another indication of insufficient power) so I know it's a dull blade problem.
I measured 236 volts at the outlet, it's not my shop wiring.
I am curious how I could measure the motor's output, in case there is a wiring problem inside the motor or switch. I didn't quite follow the instructions Rich 14 gave, maybe you could elaborate for a non-electrician.
The company told me today on the phone that the motor IS rated at 3hp. Maybe a 12" saw needs 5hp?
Edited 1/3/2007 10:55 pm ET by jimhamster
Edited 1/3/2007 10:56 pm ET by jimhamster
RichChristopherson's suggestion that the motor may be wired for 480 volts has merit. I ran a 240 volt motor on 120 volts for about a month before realizing that it was not wired for 120 volts. The only noticeable symptom was wimpy power. Have you ever thought that having it looked at by an electrician might find your problem? Wiring errors can produce unexpected results.Cadiddlehopper
Interesting.
I had always wondered what would happen under such conditions. So the motor ran at normal speed? Just didn't have enough torque?
Rich
If the saw is actually wired for 440, it should be drawing very low current, even at no load. I would guess, 4 amps. Less?
Rich
If it does have motor intended for Europe, remember that some of the countries there run 50 Hertz instead of 60 like in the U.S. That could be affecting the power output.
Joe,
60 Hz would give more power vs 50 Hz., everything else being equal.
Rich
"60 Hz would give more power vs 50 Hz., everything else being equal."
So give me the equation that relates power to frequency.
TDF
Are you incapable of looking it up?------------------------------------
The ultimate result of shielding men from the effects of folly is to fill the world with fools. -- Herbert Spencer (1891)
Yes. So give me the relationship.
Say please.
------------------------------------
The ultimate result of shielding men from the effects of folly is to fill the world with fools. -- Herbert Spencer (1891)
It would seem that it would have more power because it would turn 60/50 times as fast, but not increase the torque. Help me, some motor expert.
I know speed is a simple function of the ratio of the supply frequencies (within a rather broad set of other parameters). Torque is also a simple ratio of the supply frequency if voltage is unchanged. I don't have the formulas for the power ratio. Rich
I would guess the same.Cadiddlehopper
I have no way to measure rotational speed. It appeared very near normal to the eye. Torque was reduced -- considerably. Eventually, I required enough of the motor that it nearly stalled. That is when I did a thorough checkout of the situation. Interestingly, the motor came with a 120-volt plug (wired for 220) which plugged into a switch. The manual said it was wired for 220. Confused, I plugged it into 120. It started and ran just fine. Not wanting to damage the motor, I ran it on 120 until it stalled. I am not certain that the switch is legally wired as it is.Cadiddlehopper
Why do you think it's underpowered?? People often confuse cause and effect. Could be a wiring issue. Even a loose wire can affect things. Too many teeth on the blade. Less teeth requires less power.
Hi, Check the screw terminals at the breaker in your panel. Make sure they are TIGHT. It might measure 220v but not deliver under load.
Have fun, Paul
Hi jimhamster, Juat wondering if you checked your connections at your breaker? And your table saw switch and moter connections as well? I'm not an electricion but did run into a similar problem once. Turned out to be a loose wire at the breaker for that circuit. Might be worth a look.
Be careful though, Paul
Paul:
I tightened up everything, got a couple of turns on the screwdriver on one terminal in the box, wire wasn't "loose" but maybe that tightening helped a bit. I also took a bit of slack out of the drive belt and have hopes that was the problem. I'm in the middle of putting a new floor in my shop, so haven't given the saw the acid test with some 8/4 oak. I'll post next week after running the saw through its paces.
Thanks for your input.
Jim
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