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wildcat
11-26-2006, 03:47 AM
I am piecing together information for a VFD purchase. Single phase 220V power is available and the motor will be a Leeson 2HP 3phase. The VFDs that I am considering include the Hitachi L200 and SJ200. My main question concerns the derating that many have mentioned in this forum. At least one sales rep says that Hitachi says that derating is no long necessary when running their drives from single phase power. Does that match the experience of those here or should I go with a more expensive 3HP VFD?

My main reason for replacing the motor on my mill is to double the upper speed. I am curious though what the reasonable range of VFD increased and decreased motor speed. Can a person expect to alter the speed range +/-5%, 10%, more? Is there potential damage to the motor? Are there any other negatives to be aware of?

Thanks

HuFlungDung
11-26-2006, 08:39 AM
If you buy a new motor, get one that is rated to be suitable for VFD service. I think this implies that the motor can handle 120Hz, which would make a 1725 rpm motor run at 3450. Running at a higher rpm than that may require more accurate rotor balancing and a modified cooling fan that won't explode. Quite often a 1725 rpm motor has a quite beefy fan, with large fins, and it gets quite noisy at high rpm. Centrifugal force on those large fins may cause them to break off after fatigue occurs.

At the lower end of rpm, if the motor is working hard, it will not be properly cooled at very low rpm if run there for extended periods. This may not seem to be an immediate problem in your search for more speed. However, the motor can be used down to quite low frequencies, until it starts to power out. This might be down around 5 to 10Hz or so, if using a vectorless VFD.

If you are trying to get more spindle rpm than 3450, you might be as far ahead to use a mechanical speed increase, via belts and pulleys, to get the spindle rpm up in the range where you want it. This will allow you to cycle your VFD in a reasonable range to preempt the purchase of an ultra spec motor.

SuperChuck
11-26-2006, 10:56 AM
Wildcat,

Motors have a typical 1.15 service factor, this means they are generally rated to allow for up to 15% over the stamps on the motor. Its not carte blanche to overrun the motor, but it can be used inside that SF range frequently without any expected problems. If you redesign the pulleys to allow the motor to run at 66-72Hz(110-120%) while giving you the final speed you wanted, then all could work out well.

The only issue with increasing the speed, mechanically or with the VFD is the loss of torque at your tool(at the final drive point). To compensate for this, you may need more than a 2 HP motor with 1.15 SF.

If you detect a problem with the tool stalling thoughout the speed ranges, or just the upper limits, you may need to invest in a more powerful motor. To allow for that contingency, I'd recommend you go ahead and purchase the 3 HP VFD, that way if you do experience problems, its ready to run a replacement 2.5 or 3 HP inverter duty motor.

SC

Al_The_Man
11-26-2006, 11:10 AM
I have fitted a few VFD's to Vector and non-vector rated motors, and this has been my personal experiences and practice.
I would not run a standard non-vector motor above 3600rpm, this means if you have a 2 pole motor you cannot run much over 60hz, if you have a 4 pole motor , I run these at 120hz ( I double the rpm).
For Vector rated motors, I follow the manufactures rated top RPM, for example some Baldor vector motors are rated at a base speed at 60hz but can be run from 0-133hz, almost 4000rpm.
I have not yet lost a non-vector rated motor using these prcatices.
Usually the Vector rated motor may have better bearings, be better balanced and are wound with high insulation wire to prevent damage due to the High switching pulses they are subject to.
Al.

unterhaus
11-26-2006, 12:46 PM
I thought that the recommended derating was very conservative, the manufacturer could easily get rid of the need for it. That being said, I'm always worried about listening to salesmen.

wildcat
11-26-2006, 02:01 PM
The motor that I plan to get is the Leeson 192074 which you can see the details of at http://www.leeson.com/findaproduct/ after entering the this number in the first field. This motor has a native speed of 3470, SF of 1.15, draws 5.2A at 230V under full load, and has marked in the inverter type field PWM. Oh, in the speed range field they have 3-60Hz. So, should one stay only within this range? Would the addition of a cooling fan help with lower speeds? Do the Hitachi VFDs do breaking without the need for a breaking resister? Can one switch from forward to reverse quickly across the speed range (for tapping)? Again, thanks for the help - VFDs are a completely foreign item to me.

JRaef
11-26-2006, 09:41 PM
So many questions... Responses in order of when I think of them;

Your motor selections is TEFC, Totally Enclosed Fan Cooled. There is no method of adding an external fan anyway. That is why they give you the low speed rating of 3Hz. Any lower than that and your rotor will overheat, and fans etc. have no effect on that.

Since you have chosen a 3470RPM motor, was your old design using 1725RPM? If so, then you have already doubled your speed and will not need to go over 60Hz with the VFD. If on the other hand, your machine has already been designed around 3450RPM and you want to take it to ~7000RPM, you must consider more than just the motor consequences anyway. Please clarify this issue if you want more advice.

Of those 2 Hitachi drives, the L200 is intended for LIGHT DUTY loads, i.e. pumps and fans. I would not use that on a machine tool unless I bought a larger one and derated it. Just use the SJ200, it's a better drive for the money.

If you want to do fast reverses for tapping, you need Dynamic Braking which takes the kinetic energy of the motor and load to a resistor bank to be burned off as heat. The Dynamic Braking issue is that in the SJ200, the braking control (transistor) is built-in, but you still need the resistor externally. On the L200 the control is not included, so you need an additional Braking Unit, which is the resistor plus the transistor in a package, which of course costs more than just the resistor alone.

Most 230V VFDs 3HP and under do not need derating for 1 phase input, that capability is inherent. Starting at 5HP 230V, and ALL 460V drives however must be derated by 50% for 1 phase input (with one exceptions at 5HP 230V). So even if you bump your HP size to 3HP in order to compensate for the torque loss at higher frequencies, you should still be OK.

wildcat
11-27-2006, 03:35 AM
JRaef - Yes, my current motor is 1725RPM. I thought perhaps it may be possible to go slightly faster but I guess you are alluding to possible consequence mechanically of driving the gear head faster than 3600 RPM.

Within the 3-60Hz range motor spec. will there be torque lost?

Sounds I should get a 3HP SJ200 plus the resister bank for this 2HP motor and go outside the 3-60Hz range. Is that correct?

Thanks

JRaef
11-27-2006, 03:07 PM
... I guess you are alluding to possible consequence mechanically of driving the gear head faster than 3600 RPM.

Yes I am.

Within the 3-60Hz range motor spec. will there be torque lost?

No. You lose torque using a VFD only when you go over the motor's base design speed. In order to maintain torque, you must keep the Voltage and Frequency ratio (V/Hz ratio) constant with respect to the motor's design. Once you get to 60Hz, you are at full voltage. When you go above 60Hz, you have no more voltage to give, so the torque begins to drop rapidly. Within the design frequency range however, that VFD will allow the motor to provide full torque. Just keep in mind that this is radically different than changing speed with pulleys or gears. When you lower speed mechanically, you are INCREASING torque. When you lower speed electronically, you can at best, MAINTAIN torque.

Sounds I should get a 3HP SJ200 plus the resister bank for this 2HP motor and go outside the 3-60Hz range. Is that correct?

I would, as long as what I just said above is not a problem for you. What I usually recommend is that if you have a pulley system now, leave it in place with the sheaves that give you the speed you will do most of your work at when the motor is at full speed. Use the VFD to trim speed for accuracy and convenience, but if you need high torque at low speeds, change the sheaves.

wildcat
11-28-2006, 06:43 PM
Thanks for all the help everyone. I ordered a 2HP motor and 3HP SJ200 today (the sales people were not sure about the resister and the Hitachi tech said to give the VFD a try without the resister first). Should be fun to hook it up.

SuperChuck
11-30-2006, 10:57 PM
I may be on the wrong track here, but I'll give it a go. They were probably thinking that the inertial load of the drill is not enough to worry about. The more rotating mass/inertial load of the system(loaded belt conveyors, revolving mills) , the more significant the regeneration. If you can deal with a longer decelleration time, then the surge is manageable, but if you actually use the drive to control the slow down, then you'll see more current and need somewhere to send it, so it gets directed to the resistors to be converted into heat.

The really high end models are true regenerative models that actually convert the braking energy back into A/C and return it to your process.

Anyhow, good luck with the purchase and installation, we'll be glad to hear how the combination of parts work out for your purpose.

SC

wildcat
12-09-2006, 03:41 AM
Got the VFD and motor hooked up this evening. Wow! VFDs are really cool! Thanks everyone for the advice. The SJ200 was a really good choice. The smallest AWG wire I could get from the hardware store was 12/4 SOOW which has to be complete overkill for a 2HP motor but oh well. I am still not clear if the motor I used, a Leeson 192074, is a 4 or 8 pole motor though. Is there an easy way to know? There are nine wires coming out of the motor. Three are connected together, then each pair of remaining wires connects to each of the three lines from the VFD. Does that make sense?

Al_The_Man
12-09-2006, 11:40 AM
If it is 3470 rpm as you say, it is a 2 pole motor.
On 60hz it will be rpm=3600/pole pairs - slip frequency.
It has connections for 220/460 operation.
Al.

JRaef
12-11-2006, 03:54 PM
Just something to watch out for.

The output wires from any VFD should be run in metallic conduit or shielded cable. The output of a VFD is a "Modulated Frequency", and if you just swap those words around, you have "Frequency Modulat(ion)". Does that look familiar? As in FM radio? Those output wires will be transmitting a relatively strong FM radio transmission, which can result in interference with other electronic devices in the vicinity. If you notice other things starting to get squirrely on you, you may want to reconsider that SOOW cord.

Al_The_Man
12-11-2006, 04:02 PM
IRC Belden sell some very expensive cable, specifically designed for VFD's, I generally run TEW Twisted together, and a separate Ground conductor inside Metalic Flex conduit. T&B SuperFlex also has a small copper wire wound with the metallic sheath for ground continuity.
Al.

wildcat
12-19-2006, 08:51 AM
You guys were absolutely correct... once I actually started to use the mill for something after attaching the VFD I had tons of erroneous limit signals. I ran twisted 12 AWG wire down flex conduit (like Al said) with two grounds (two insulated and one bare copper - figured the bare Cu would ground the conduit real well). This helped... the mill would run for probably 10 mins or so. Additional grounding of the mill and shields, etc. has brought the expected time to failure to about 30-45mins. The encoder and limit switches have shielded wire but the servos do not. When the erroneous limit is encountered Mach3 shuts down but the motors wander slowly I guess due to noise. I am using the Sound Logic Combo board. I do not currently have the VFD controlled by the board (trying to limit what might be introducing the noise). Debounce is currently set to 14 in Mach3. What else can I try? Have I can troubleshoot these problems without having to do a cycle of try something and run a program until failure? I trust it is reasonable to be able to get this to work eventually :) Thanks

HuFlungDung
12-19-2006, 01:32 PM
Make an aluminum foil hat to put over top of your computer? ;)

Some m/b are sensitive to RF. I do not know if there is a surefire method to truly prove this out, other than try to shield the computer by moving it farther away, run it with the covers all on, or simply trying another make of computer.

JRaef
12-19-2006, 03:57 PM
EMI can knock you on your butt the first time you come up against it. Don't give up though, there is a solution.

http://home.freeuk.com/nedslider/image007.jpg

Seriously though, VFDs also create harmonics on the incoming line, and sometimes other sensitive equipment can be affected by them directly through the power source in common, or by the EMI on the incoming lines as a result of the harmonic currents. Go back to your Hitachi supplier and ask if they have an EMI/RFI filter, sometimes also called an EMC filter. It will go in-line or parallel (depending on their design) with the line side of the VFD. That may be all it takes.

The next step would be enclosing the VFD in a metal box as well, some drives radiate EMI pretty bad.

HuFlungDung
12-19-2006, 04:25 PM
Jraef,

That's the way :D

LoL!

JRaef
12-19-2006, 10:33 PM
My motto;
Nothing is worth doing that isn't worth overdoing to make a point.

When I found that picture one day, I just had to bookmark it. When I worked in an office like that providing tech support for VFDs and PLCs, I was the one constantly spewing about EMI and RFI causing a lot of the problems we were seeing, but nobody listened. I almost think that had I stayed there someone would have eventually done that to my cubicle.

wildcat
12-19-2006, 11:15 PM
Do these VFD specific filters do something more than more common EMI line filters? Is the goal to remove noise from the line or to prevent noise from being introduced back into the line?

JRaef
12-21-2006, 08:03 PM
Prevent it from going back on the line. I doubt they are much different, but by buying them from the VFD supplier they are sized correctly (not to mention being able to point the finger at them if they don't work).

kimoyo
12-21-2006, 09:43 PM
Some m/b are sensitive to RF. I do not know if there is a surefire method to truly prove this out, other than try to shield the computer by moving it farther away, run it with the covers all on, or simply trying another make of computer.

Could the combo breakout board be having issues with the RF coming from the VFD?

Would there be any problems with using the 3HP SJ200 with the Leeson 3HP motor instead of the 2HP one? I know people get the 3HP VFD for the 2HP motor but the next step up, 5HP VFD, is only 3phase.

wildcat
12-21-2006, 11:13 PM
Well, tomorrow I start placing the electronics and VFD into their cabinet. All these electronics will be in the same metal cabinet but the VFD will be separated from the rest by two layers of sheet metal. Hopefully the VFD will not interfere even though the breakout board and VFD are in closer proximity. Is this only hopeful thinking?

wildcat
12-21-2006, 11:14 PM
Could the combo breakout board be having issues with the RF coming from the VFD?


Almost certainly... before the shielding the relays would really chatter.

LUCKY13
01-11-2007, 06:03 PM
Wow, is there any chance of causing someone close to you problems from this. Like I live next door to a Fire Station. Probably no where close to being that strong but just making sure.


Jess

JRaef
01-12-2007, 10:30 AM
No, not likely. EM field strength decreases at the square of the distance from the source, so by the time you are 2 feet away it is 1/4 the strength, 10 feet and it is 1/100th the strength. it would need to be one BIG farking drive to cause problems with a neighbor. If you do have a big drive (i.e.200+HP), you may cause problems on the power line that feeds you both, but that becomes a bigger problem for the utility. When you go to get a permit to install that, they usually will ask for a harmonics study first.

Al_The_Man
01-12-2007, 03:16 PM
Wow, is there any chance of causing someone close to you problems from this. Like I live next door to a Fire Station. Probably no where close to being that strong but just making sure.
Jess

Make a note of turn-out times when you have the machine running, if T.O's. double, you may be triggering an alarm:nono: :D
Al.

LUCKY13
01-12-2007, 04:30 PM
Make a note of turn-out times when you have the machine running, if T.O's. double, you may be triggering an alarm:nono: :D
Al.


LOL, I guess it is possible. My first thought was where they use FM radio equipment. We had a guy across the street running some "way to big radio equipment" and he was causing problems at the Fire Station. Which made me wander if I was to run a VFD if it was strong enough to cause such a thing. Sounds like it all can be shielded to eliminate any problems so in the end should be doable. I had run radio equipment in the past myself but I always went to them & worked with them to be sure no problems came out of it. I never had any problems that we had to fix either but it always pays to know what your working with. Then as ole Barney would say you can "Nip it in The Bud" before it becomes a problem.


Jess