Reply with QuoteA 3/4hp can deliver much more power for a short duration under load. If your VFD can deliver 2HP you can have short power requirements around that amount and not stall.
Your motor will also make more than 3/4HP at 75hz.
It will be fine.
G0704 - How much horsepower do you really need?
I'm looking into doing a VFD conversion and two of the best options seem to be the 3/4Hp Leeson 192047 and the 1 1/2Hp Leeson 192048.
I've noticed a lot of conversions use 1.5-3Hp motors, but they are very large and heavy which complicates the installation of a power drawbar. I'm also concerned about how that much weight interacts with rigidity when you are also doing a Y axis extension + head spacer.
The 3/4Hp motor has come up in threads but I haven't found an example of one in actual use. I ran some test cuts in g-wizard and I think I could get by with 0.75Hp and a couple of pulley ratios as long as I avoid heavy drilling (and use helical milling or multiple drill diameters instead). On the other hand, it would be a shame to go through the effort and expense of a conversion only to discover the motor cannot perform the jobs I'd like.
Any thoughts?
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Re: G0704 - How much horsepower do you really need?
A 3/4hp can deliver much more power for a short duration under load. If your VFD can deliver 2HP you can have short power requirements around that amount and not stall.
Your motor will also make more than 3/4HP at 75hz.
It will be fine.
youtube videos of the G0704 under the name arizonavideo99
Re: G0704 - How much horsepower do you really need?
No, it will not. A 3-phase motor run by a VFD will have, approximately, constant torque up to the motors rated base speed, and constant power above base speed. A 60Hz 3/4HP motor running at 75Hz will still produce only 3/4HP, unless you exceed the motors ratings. And, at 75Hz, torque will be reduced by 25%. You can force a motor to produce power above its rating only for short periods, at the risk of over-heating or other damage.Originally Posted by arizonavideo
Regards,
Ray L.
Re: G0704 - How much horsepower do you really need?
How much horsepower do you really need?
Do you drive a 600 HP Corvette?
Don
Re: G0704 - How much horsepower do you really need?
Nope....just a 500hp pickup....a 420hp sedan and 400hp SUV. No one "needs" hp but it's nice to have some to spare.
Re: G0704 - How much horsepower do you really need?
According to the Grizzly site that mill already comes with a 1HP motor:
Drill/Mill with Stand | Grizzly Industrial
The proper way to do it is to have a speed (RPM or Hz) vs power output (HP or kW) graph for the motor you want to use. Then input the gear ratio to see what kind of HP is available at different RPM. Then you can calculate your feeds and speeds based on the cutter and the material you're cutting. Then you can calculate your depth of cut or material removal rate based on available HP at that RPM.
You need the speed vs power graph to set the parameters on the VFD.
What assumptions did you make in order to run your test cuts in g-wizard if you did not already have a speed vs. power graph for the motor? What is the gear ratio of the mill / what are you thinking of changing it to?
The two motors in the links you provided are not, if I read it correctly, in leeson's variable speed range products. So how they will react at different speeds and what you will use as parameters for the vfd, I don't know.
http://www.leeson.com/Products/produ...anBlower65.pdf
Variable torque
motors have horsepower ratings that vary as the the square of the speed, while torque varies directly with the speed. These
motors are typically used on applications such as fans, blowers and centrifugal pumps.
Constant torque
motors are capable of developing the same torque for all speeds. Their horsepower ratings vary directly with the speed.
Constant torque motors are used on mixers, compressors, conveyors, printing presses, extractors, feeders and laundry machinery.
Constant horsepower
motors develop the same horsepower at all operating speeds, and the torque varies inversely with the speed. These motors are often used on machine tools, such as drills, lathes, punch presses and milling machines. Please contact LEESON with details for constant HP applications.
So two motors with the same HP rating, do not behave in the same way at different speeds. I would contact leeson and ask them for the info you're missing. You can't make a good decision without it. Or, you can copy exactly what someone else has done (same exact motor and VFD curve) if they have had good results.
Perhaps someone with more know how can give you better advice, but that's what I'd do.
Re: G0704 - How much horsepower do you really need?
I knew this would happen.
The question was how much power was needed. I said that for short duration you can exceed the rated HP. It will not hut the motor at all. I'm sure your a good engineer but unless you have tested a motor's thermal dissipation ability and efficiency you don't really know how much power a motor can give for less than a 100 % duty cycle. The standard rating is for 100% or 95% full load amps. If you hook a fan to a motor and run it 24/7 then you really need to watch the contentious rating. If you have a cutter run into a heavy cut for 30 seconds the motor will be fine at a slight over current load. Much of the time when you cutting your using vary little HP.
I know for a fact that at 70 to 75 HZ most motors will have better cooling because the fans is spinning faster. If you run the numbers of a 3.5A motor at 60 HZ and 3.5A at 75 Hz the motor can make much more HP at 75 Hz.
The " constant power" is not really true either. when hooked to a 60 Hz line the torque curve is not perfectly flat and when using a VFD that has torque compensation it can increase voltage to the motor to prevent RPM loss.
A VFD can deliver more voltage to a motor than the standard 60hz AC line. They can deliver a shaped wave up to the peak input line voltage with a wave form with a higher power transfer function. Peak voltage of a 220v line is about 308V. A modified square wave at 75Hz will make more power. For a short duration you can make a LOT more power.
Some day with a spare VFD I have I will do a little video of over HP cuts with a standard 3 phase motor.
youtube videos of the G0704 under the name arizonavideo99
Re: G0704 - How much horsepower do you really need?
I've been doing most of the math with the motor running at its rated speed (3600) or faster. For example 3/8" Endmill slotting 0.4" deep in aluminum at 6000RPM/12IPM calculates to 0.4HP, which is probably about as aggressive as I would get when milling.
At a 1.5:1 pulley ratio I hit maximum power at 3600/1.5 or 2400 RPM which is about where I would be running a facemill.
Drilling is where this motor would run into trouble since they tend to want ~0.2HP at 1000-1500 RPM. If I can maintain that kind of output for say 30 seconds then the motor can probably do everything I need. Otherwise I'll helically interpolate or step drill the hole.
Its good to know that the VFD will go over peak power for short periods when necessary, since CAM tends to include the occasional entry or corner which requires much more power than the rest of the cut. I plan on using a Huanyang GT series inverter which has sensorless vector control.
Re: G0704 - How much horsepower do you really need?
I assume that was a typo? 0.04" deep for 0.4HP.
Are you going to have a high and low gear? 6000 x 1.5 = 9000 RPM. The two motors you linked two list an RPM of 3600 continuous. Are the bearings in the motor good for it?
So you're just looking at what HP you need at this point. OK. There are the three types of motors I previously mentioned. You need to find out what kind of motors they are, what the power vs speed graph is through the RPM range you want to use, what short term power you can get in addition, and what max speed you can drive them to. I'd send Leeson an email. I can't answer those questions. Any reputable motor manufacturer should have that data compiled.
You original question was how much HP is necessary. My best answer is that it depends on the motor curve, the gear ratio, and what kind of HP you need at different RPM. So essentially what I am saying is that two different 1HP motors will perform differently at different speeds and that the real question is, what motor should I use for my project, I'd like to keep it as small as possible?
Of course arizonavideo has actually done this with good results. I checked out your youtube channel arizona. nice. I wonder what he used?
If you look at the power vs speed curve of an HSD spindle, for example, there is a very large difference in available power output continuous and short term. They show this right on the graph. I looked at some made in China HSD clones on EBay, and they actually list the power output of the spindle at the short term output if you look at the graph. So the two are not comparable, the HSD one is far more powerful for the same listed power of spindle.
I have to assume that the amount you can overdrive a motor in the short term is dependent on the manufacturer. Perhaps there is a standard that I am unaware of. I'll let other people discuss what that might be. I don't know.
I've never heard this before. How do I input parameters on a 220V VFD to drive up to 308V? Are you saying that I can input a V/f curve and set 308V at the top end on a VFD that has 0...Vin listed on the sticker as the output and is made for 220-240V normal a/c power? Like a single phase to three phase VFD running on house power, it will actually let me input a value of 308V for the output for use on my v/f curve?
Or are you saying that this only happens on specialized VFDs that are being run in constant torque mode? The kind used for pumps, and not for CNC machines?
I'm not disagreeing or trying to be argumentative, I honestly would like to know if this is possible for my own project.
Re: G0704 - How much horsepower do you really need?
The short answer is no it is not possible, NA single phase is 240v, when powering your VFD with 240v Input the output is 240v 3 phase and in some cases can be a little less than the input voltage, there is no way to change any parameters to increase the output voltage, it also would serve no purposes what's so ever, just as Ray said it's not going to happenI assume that was a typo? 0.04" deep for 0.4HP.
Are you going to have a high and low gear? 6000 x 1.5 = 9000 RPM. The two motors you linked two list an RPM of 3600 continuous. Are the bearings in the motor good for it?
So you're just looking at what HP you need at this point. OK. There are the three types of motors I previously mentioned. You need to find out what kind of motors they are, what the power vs speed graph is through the RPM range you want to use, what short term power you can get in addition, and what max speed you can drive them to. I'd send Leeson an email. I can't answer those questions. Any reputable motor manufacturer should have that data compiled.
You original question was how much HP is necessary. My best answer is that it depends on the motor curve, the gear ratio, and what kind of HP you need at different RPM. So essentially what I am saying is that two different 1HP motors will perform differently at different speeds and that the real question is, what motor should I use for my project, I'd like to keep it as small as possible?
Of course arizonavideo has actually done this with good results. I checked out your youtube channel arizona. nice. I wonder what he used?
If you look at the power vs speed curve of an HSD spindle, for example, there is a very large difference in available power output continuous and short term. They show this right on the graph. I looked at some made in China HSD clones on EBay, and they actually list the power output of the spindle at the short term output if you look at the graph. So the two are not comparable, the HSD one is far more powerful for the same listed power of spindle.
I have to assume that the amount you can overdrive a motor in the short term is dependent on the manufacturer. Perhaps there is a standard that I am unaware of. I'll let other people discuss what that might be. I don't know.
I've never heard this before. How do I input parameters on a 220V VFD to drive up to 308V? Are you saying that I can input a V/f curve and set 308V at the top end on a VFD that has 0...Vin listed on the sticker as the output and is made for 220-240V normal a/c power? Like a single phase to three phase VFD running on house power, it will actually let me input a value of 308V for the output for use on my v/f curve?
Or are you saying that this only happens on specialized VFDs that are being run in constant torque mode? The kind used for pumps, and not for CNC machines?
I'm not disagreeing or trying to be argumentative, I honestly would like to know if this is possible for my own project.
With a VFD you can increases the output torque to match the higher frequency being used,( only with a good quality motor ) the voltage will not change
Mactec54
Re: G0704 - How much horsepower do you really need?
If you're using any of the high speed, or constant engagement, or adaptive clearing, or iMachining, or whatever, toolpath it should be able to "nibble away" at the corners instead of plunging into it. The best way to help avoid a large spike in tool engagement would be to use a tool whose radius is smaller than the corner radius, or simply drill or helix in a hole right at those corners before milling...
Re: G0704 - How much horsepower do you really need?
I would say anything less than 1.5hp is a waste of money when doing a 3phase motor conversion. If you need to offset the motor mounting to fit a PDB, that should be just fine. Also I believe it's been established that most pdb's will require a 2.25" spacer if you plan to mount it inline with the head casting and motor to have adequate clearance.
This gives you some decent y axis travel so that's a big plus!
The machine can handle a lot more than people give it credit for. More power from my experience has helped more than hurt.
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Last edited by lcvette; 05-15-2017 at 03:34 PM.
Re: G0704 - How much horsepower do you really need?
I've decided to go with the larger 1.5HP motor as it seems to have limited drawbacks. I'm fairly confident I could survive on 3/4HP, but if shedding 15lb has limited upside there is no point taking the risk.
It is theoretically possible for a VFD to output higher than line voltage, although in practice I'm not sure it would ever happen. The "average" RMS voltage of a sinusoid is much lower than its peak voltage: 220V RMS will have 308V peaks. If a VFD were to output a square or even trapozoidal wave peaking at 308V the average voltage would be greater than 220V without having to exceed the available input voltage.
Re: G0704 - How much horsepower do you really need?
Smart move, 1.5hp is an excellent power motor for this machine, it will allow much higher MMR!
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Re: G0704 - How much horsepower do you really need?
My VFD had a voltage output setting. It maxed out at 240V but if I had the 440V version I could set it higher than 240 because the PS in a VFD charges to peak value of the RMS 240 which is 308V.
At that voltage you could run a higher RPM and still develop the motors rated current.
None of this is necessary for your question. You will need the motor to be able to make enough torque for the tool selected. Large drills in steel and larger taps take all the power you have.
The numbers you see on all of the benchtop mills like 25 or 32 or 45 is the max drill diameter in mm the mill can do in steel. So a PM-25 should be able to drill a 25mm hole in steel.
For the 704 size mills using a 3/8" cutter you will be hard pressed to use over 1HP because of slow RPM and you cant take too deep of a cut.
I do wish I could find a nice 48 frame three phase for cheep but most are 56C.
Just get one of the lighter 1.5HP motors, 3/4 hp would still be OK with the right gearing.
youtube videos of the G0704 under the name arizonavideo99
Re: G0704 - How much horsepower do you really need?
Your information is not correct, 240v in you will have a max of 240v out no matter if you did use a 480v VFD that you some how manage to get to run on 240v, I know that there are some that don't have low voltage detection but they are very hard to find, it still would not make any difference what you set in the VFD it would only output the same as the input voltage, in relation to the DC Buss voltage, which can only be a max of 1.414 x the input voltage
You may be thinking of the VFD DC Buss voltage which is 1.414 times the input voltage ( 240V x 1.414=339 DC volts ), it then goes through the next stage and then the IGBT which regulates the output, you can't change this with any parameters
If you where measuring the output with a normal meter you would of got a false reading, as a normal multimeter can not be used to measure the output of a VFD Drive
Volts/Hertz ratio
The ratio of voltage to frequency, measured in hertz, determines the amount of torque produced by an AC induction motor. By keeping this ratio constant, the magnetic field inside the motor is kept at a constant level. This results in a constant torque.
Above the nominal frequency of 60 Hz, the voltage will not increase anymore, and the torque will decrease (see Figure 6).
Mactec54
