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fabricator

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I will be looking for a VFD, I thimk, soon, so can anyone direct me to low priced but quality VFDs?
I get all mine from automation direct now they are about $100 more than the amazon units but the quality is much much better and you get phone support from the US office and the manual is written in plain English and easy to understand.
 

fabricator

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Hi all, Just spotted this thread, and haven't really studied what it is all about - and it sounds like "the horse has bolted" so please excuse me while I "shut the stable door". Putting it simply, a 2HP motor will give 2HP at optimum load/torque/speed: If driving (say) a lathe through lots of speed reduction pulleys, then you get the Mechanical advantage of the pulleys to increase the torque - but not the power - at the spindle. Which is great for machining! Or you can use the pulleys for higher speed than the motor, but the torque (not the power) at the spindle will reduce accordingly.
Then again, a Variable Speed Drive is current limited - usually designed so max. power rating is at "Optimum" speed.... not necessarily maximum speed, but it may be. So when you fit a VFD speed control to your lathe (or whatever) and try and take a decent cut at a very low speed - or in your case just overcome the starting friction of the 3HP motor? - the VFD will give it's rated current to the motor, but as the power is speed dependant there will be hardly anything coming out of the shaft.... The torque is constant on this VFD set-up, irrespective of speed - as it is current limited. But the power is gnat's elbow at start going up to the rating at the rated speed. Your simple solution (as I read what you have done already?) is to buy a bigger VFD, that gives more current to overcome the initial starting friction. Then it will give you whatever it can at whatever speed you use it at.
Example: My 1.5kW motor on my lathe will stall when tapping anything over 3/8" when at 80 rpm.... and cutting cast iron large (3" and above) at such slow speeds needs small cuts. But There is plenty of torque and power for anything I need when it is running upwards of 300rpm... Yes, I can hear (and read) the speed drop a tad when applying a hefty cut at speed - The small angle of phase slip is what motors have to do to develop the torque... or so I understand? - but nothing overheats (touch wood!) and the Chinese electrics are still good after more than 10 years abuse from me. The stop-start push-buttons did burn out though and have been replaced for about £2.50! Just "Bunce"!
ALSO: a 3-phase motor on the appropriate single phase voltage only gives around 80% of the power rating... and torque is much lower as well. (I think it is sq.root 3 over 2? - But my "electric theory" is 50 years old and memory plays tricks... I'm sure someone will correct me!).
Enjoy! - and remember, Ratings are always "Laboratory conditions on a "perfect" example of the product... Caveat Emptor!
K
Everything you say is correct, but on my mill I can always use the low range at higher speed. My 15" lathe has a 7hp motor and a 10 hp drive and it will take .250 cuts at higher speeds with no problem.
 

OrangeAlpine

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I do not know who sells them, but they are made by XinShuang. 3 hp units cost about $75 apiece. Instructions were not a problem. In fact, instructions were barely needed. I cannot comment on sizing, other than to say an oversized unit has no drawbacks other than cost, which is extremely reasonable. I bought two 3hp units. One for a 2hp mill and the other for a 1hp lathe.

No regrets. They are simply wonderful. Want a slightly slower spindle speed? Simply dial it down a bit. No noticeable loss of power. The soft starts are addictive. I do wish I could install a remote control panel, the speed control knob is sort of small and I wonder about its durability. But that sort of stuff is way out of my league.
Bill
 

ignator

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When you say "reasonably priced", what range of prices, please? and do you have a link to this place?
Richard, if you buy off eBay, make sure it is the 200volt class, as that will run on 240VAC input, the 400volt class which are common, require the 440VAC input power. Also, they typically do not come with the manual, so take the part number and brand, and find the manual online. If you can't, don't look further. There are brands like Rockwell Automation (Allen Bradley) that I've found don't keep old pdf's of their products available.
For brand new, I have purchased from:

They have typically had the lowest prices I've found on the web. You DO want a VFD that has sensorless vector, in its design, as this allows large torque at low operating speeds (I can drive a tap or die without backgear and very low speed on my belt driven lathe left in the middle speed setting). You do not need to oversize a VFD that accepts single phase input, unless exceeding 3HP. Down load the manual and see what the installation requires. Just in case you don't know, NEVER switch the output of the drive between the VFD and motor, this must be hard wired. This is what will damage the output transistors in a VFD. Also for connections less then 10 feet between the motor and VFD, you do not need any filters. And really this only starts being a problem in large HP motors.
 

packrat

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The VFD needs to put out same amps or more as the motor and have the KWs to run the motor HP I have a
Mitsubishi 2 HP 10 amps to run a milling machine not low priced at about $300.00
 

Stefan-K

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I can recommend Siemens or Danfoss. Both German engineered VFD's. They last a lifetime.
Stefan
 

Richard Hed

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Richard, if you buy off eBay, make sure it is the 200volt class, as that will run on 240VAC input, the 400volt class which are common, require the 440VAC input power. Also, they typically do not come with the manual, so take the part number and brand, and find the manual online. If you can't, don't look further. There are brands like Rockwell Automation (Allen Bradley) that I've found don't keep old pdf's of their products available.
For brand new, I have purchased from:

They have typically had the lowest prices I've found on the web. You DO want a VFD that has sensorless vector, in its design, as this allows large torque at low operating speeds (I can drive a tap or die without backgear and very low speed on my belt driven lathe left in the middle speed setting). You do not need to oversize a VFD that accepts single phase input, unless exceeding 3HP. Down load the manual and see what the installation requires. Just in case you don't know, NEVER switch the output of the drive between the VFD and motor, this must be hard wired. This is what will damage the output transistors in a VFD. Also for connections less then 10 feet between the motor and VFD, you do not need any filters. And really this only starts being a problem in large HP motors.
Can you explain what "Sensorless vector" is and how it works?
Are there other characteristics I should know about?
I have read about the VFDs in this forum and have thot to myself, 'I could use that, eventually' and "eventually" is getting much closer now so I have been trying to understand exactly what I will need. So far, however, I do not know the engine size--looks to be about 3-5 hp. I'll have to find out, but then, I do not have a firm price yet and these types of deals tend to fall apart when one cannot get a firm price. I did find out that the lathe has been in the weather for 5 years, that someone who workt at the same place had offered to buy it for scrap prices but was refused. Apparently, the lathe was (is) in fine condition, the reason it was replaced is because it is so old that there are no safety guards. That probably is a government regulation
 

ajoeiam

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snip

They have typically had the lowest prices I've found on the web. You DO want a VFD that has sensorless vector, in its design, as this allows large torque at low operating speeds (I can drive a tap or die without backgear and very low speed on my belt driven lathe left in the middle speed setting). You do not need to oversize a VFD that accepts single phase input, unless exceeding 3HP. Down load the manual and see what the installation requires. Just in case you don't know, NEVER switch the output of the drive between the VFD and motor, this must be hard wired. This is what will damage the output transistors in a VFD. Also for connections less then 10 feet between the motor and VFD, you do not need any filters. And really this only starts being a problem in large HP motors.
Hmmmmmm - - - you mention that "only starts being a problem in large HP motors" - - - - what is the definition of large HP motors - - please?
 

ignator

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Can you explain what "Sensorless vector" is and how it works?
Are there other characteristics I should know about?
It is additional software running on the microprocessor of the VFD, this runs a simulation of the vector currents in the motor, to properly drive the pulses driving the field windings. They used to be more expensive to the cost of the drive, but appear to becoming more standard now.
My original drives I purchased were TECO Flux-Master 100s. These are not vector drives, and would cog the motors at low RPMs. And the torque would drop off and the motor stalls out. I replaced the one on the lathe with the vector software, and as I indicated, leave the belts at the middle speed setting (low medium high range) and now can thread with a tap or die items up to 1/2"x13TPI, with no stall out.
Also, most motors on these machines are 4 pole, so they run at the 1725RPM (60Hz, minus the slip of phase operation), and the drive can be programed for a safe max output Hz of 120, as the rotors will support 3600RPM with no structural issues. This gives a very large RPM range on your lathe spindle. Also, the VFD of better quality allow the display to have a conversion constant programmed in, which in my case is the ratio of motor to spindle. So I display spindle RPM on the VFD front panel display. When you compute SF/M you now dial in the RPM to limit the cutting speed for the part diameter, and tooling (HSS or Carbide) your using. I do this on my milling machine as well so I don't burn up HSS endmills.
 

ignator

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It is additional software running on the microprocessor of the VFD, this runs a simulation of the vector currents in the motor, to properly drive the pulses driving the field windings. They used to be more expensive to the cost of the drive, but appear to becoming more standard now.
My original drives I purchased were TECO Flux-Master 100s. These are not vector drives, and would cog the motors at low RPMs. And the torque would drop off and the motor stalls out. I replaced the one on the lathe with the vector software, and as I indicated, leave the belts at the middle speed setting (low medium high range) and now can thread with a tap or die items up to 1/2"x13TPI, with no stall out.
Also, most motors on these machines are 4 pole, so they run at the 1725RPM (60Hz, minus the slip of phase operation), and the drive can be programed for a safe max output Hz of 120, as the rotors will support 3600RPM with no structural issues. This gives a very large RPM range on your lathe spindle. Also, the VFD of better quality allow the display to have a conversion constant programmed in, which in my case is the ratio of motor to spindle. So I display spindle RPM on the VFD front panel display. When you compute SF/M you now dial in the RPM to limit the cutting speed for the part diameter, and tooling (HSS or Carbide) your using. I do this on my milling machine as well so I don't burn up HSS endmills.
Richard, you don't have any detail as to this machine you're buying, if it is a geared head machine, you want to leave the max HZ at the 60 for the motor that is currently on it. The normal derating for a drive once you exceed 3HP of motor size is to double the drive capacity. This is mainly for the input rectifier diodes of the drive, so they don't burn out with single phase input power. But I'm running 2 machines that have 7.5HP motors, and using a 10HP VFD. I'm never going to push these machines at the maximum capacity of the motor. And most likely what would happen is the drive would trip out on the DC bus dropping below the drives monitor level.
 

fabricator

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It is additional software running on the microprocessor of the VFD, this runs a simulation of the vector currents in the motor, to properly drive the pulses driving the field windings. They used to be more expensive to the cost of the drive, but appear to becoming more standard now.
My original drives I purchased were TECO Flux-Master 100s. These are not vector drives, and would cog the motors at low RPMs. And the torque would drop off and the motor stalls out. I replaced the one on the lathe with the vector software, and as I indicated, leave the belts at the middle speed setting (low medium high range) and now can thread with a tap or die items up to 1/2"x13TPI, with no stall out.
Also, most motors on these machines are 4 pole, so they run at the 1725RPM (60Hz, minus the slip of phase operation), and the drive can be programed for a safe max output Hz of 120, as the rotors will support 3600RPM with no structural issues. This gives a very large RPM range on your lathe spindle. Also, the VFD of better quality allow the display to have a conversion constant programmed in, which in my case is the ratio of motor to spindle. So I display spindle RPM on the VFD front panel display. When you compute SF/M you now dial in the RPM to limit the cutting speed for the part diameter, and tooling (HSS or Carbide) your using. I do this on my milling machine as well so I don't burn up HSS endmills.
Tapping is one of the best features of vfd's you can have forward and reverse buttons for instantin and out of the tap. Also very handy if you want to just jog slowly with an indicator or jog a bit to get to the adjuster on a boring head that always ends up on the back side so you cand see it.
 

rmd55

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Before running your motors at higher than 60hZ, if not made for it, you need to look at the name plate and check the rating. A 1725 motor rotor may spin at 3600 rpm with no problem but the duty factor is the limiting unit to go by. My electrical engineering friend informed me that VFDs send voltage spikes that increase with hZ. 100% duty factor 60hZ 120% duty factor 72hZ. You can safely over drive by the same factor as the duty factor. The wiring is not made for the higher hz and voltage.
Richard
 

Noitoen

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I run 50 Hz 4 pole motors to 120 Hz all the time. 3~ 230 motors can be run with a 400 V VFD with the correct parameters. The power will increase linearly up to 86.6 Hz when the motor is supplied with 400 V and then stay constant until 120 Hz. Never had a problem this way with motors up to 2,2 Kw. A normal 1500 rpm motor's rotor and bearings can easily handle 3600 rpm.
 
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