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12-15-2007, 09:52 PM #1
Over-rated VFD hp to motor hp bad?
Haven't found any info yet on this question. Looking for a VFD for a BP with 1.5 hp motor. Have a lead on a (used?) 3 hp VFD. Would this be a problem?
Also along this line, I see new 1.5 and 2hp VFD's advertised. Would using the 2hp be ok? (thinking of future upgrade or additions)
Any brands I should avoid? Has anyone listed best to worst brands of VFD's? Or just a Good-Bad ratings list?
12-16-2007, 01:15 AM #2
It will work OK.
My hitachi VFD is a 3hp, and it has my 2hp mill on it, and a 1.5hp surface grinder. You can tell the VFD how big the motor you have connected is. I say bigger is better when it comes to a VFD, if you ever get a more powerful machine, you're set with the VFD. That's part of the reason I went with a 3hp VFD, so if I ever find a 3hp vertical mill, I'm set. I don't have any experience with other brrand VFDs, but my hitachi (SJ200-022NFU) makes me happy. Either the L200, or SJ200 series should be good for you. I'd suggest getting the 3hp version so if you ever get a different motor, mill, or any kind of machine, you can use the same VFD. Another cool feature of hitachis is they have a motor profile function, and have 2 motor profiles you can select with an external switch. If you use a 4PDT drum switch, you can select which machine you want to control with the VFD. You have to select your machine before you turn the motor on, YOU CANNOT switch while the motor is spinning, or it will KILL your VFD! Simply wire up the 3 phase output to the common leads of the 4PDT switch, and the set terminal for selecting profile. Then connect each motor to each side of the switch, and the common terminal for the VFD's input terminals to one side. When you switch it, the output of the VFD is sent to the apropriate motor, and the 4th pole of the switch tells the VFD what motor it's controlling. You have to program the VFD to do this, which is the hard part, but it's not that difficult. I did it without knowing anything about VFDs before I started. The only bad thing about the hitachi VFDs is wiring them for single phase is confusing. You use terminals 1 & 3 for the hots, and the heatsink is ground. For some STUPID reason, they label terminal 3 "N" !!! Even a licensed industrial electrician (I asked one) would have connected the ground to terminal 3 if they didn't know better!!!! The 3hp VFD is the biggest of the SJ200, or L200s you can use for single phase power.
12-16-2007, 08:06 AM #3
The 3 HP or the 2 HP will drive your 1.5 HP motor just fine. The only snag I know of in modern VFDs with grossly oversizing the VFD is that your motor's FLA amperage rating may be so small that the programming entry on the VFD has no value small enough. I did this once; I needed a VFD quickly for a fractional HP motor (1/7 HP?) and the smallest VFD on the shelf was 3HP. I wired it up, and I believe it would have run, but basically I would have been running it without overcurrent protection because the smallest FLA it would let me enter was several times larger than the motor's FLA. It's a "real" problem, not just an annoying software entry thing: the VFD's current sensors (CTs or Hall Effect sensors) have to be scaled at the factory. The scaling that gives nice resolution for a drive that will be running between 0 and 100 amperes is going to resolve poorly if the drive runs between 0 and 1 ampere!
This issue should not come up with running a 3 HP VFD on a 1.5 HP motor. Buying a slightly oversized VFD is probably a good thing if you might upgrade the motor's HP in the future, or if you just like a little spare headroom.
You asked about drive recommendations. I have no interest in starting a flame war, and obviously everyone is welcome to chime in with their personal favorites. I know that the TECO Westinghouse drives are quite popular in this forum, as well as being formidable price competitors. My personal favorite is Allen Bradley. I've used their stuff for many years, and most of it is quite good. I am totally biased in favor of reliability, and the Allen Bradley equipment I've encountered or put in has generally been very reliable. It's also expensive; if you're footing the bill for this personally you may want to have a look on ebay rather than buying one new.
I welcome opposing viewpoints and criticism, but generally not floggings. :-)
12-16-2007, 08:54 AM #4
I know the hitachis can control very small motors.
You set the current in the hitachi VFDs with a decimal value, you can go down to .1a if I remember right. Look in the manual, it will tell you. I know it can be set for a fairly small motor, it's got a LOT of programable options, really a complex device.
12-17-2007, 01:46 AM #5
Finally got a look at those VFD's. Lenze brand. Look new, in box with documents. Mostly in German, with some translation. Model 8100. Not current production, it seems. Looking at both the factory site, and USA importer site, unable to find info. German site doesn't seem to list it, and the US site's library is not responding.
Was hoping to find info I could study before making a decision to buy. Looking at the manual by flashlite at night is not conducive to comprehension necessary to determine if it will do the job.
Minimal keyboard, hidden under the main cover. No pot for speed control. Seller wants about 1/2 cost of basic Hitachi. No warranty, of course.
Did a search, a previous thread on a machine with a Lenze VFD oem system was interesting. Enthusiastic support, but they eventually had to send another VFD to verify the problem.
Seller calculates it is actually rated for 2hp. I think it may be a single/3phase dual input. He's not sure if the 2 hp would be 3 phase, and lower with single phase. My B'port is 1.5hp.
Any thoughts on this VFD/deal?
12-17-2007, 02:32 AM #6
12-17-2007, 10:42 AM #7
The Lenze 8100 is way obsolete...while it may be new in the box its probably been sitting around for a number of years, which means the bus caps have deteriorated. You could reform the caps and give it a try, but I would see if you can find a newer generation VFD.
12-17-2007, 11:25 AM #8
+1 on the TECO FM-50. I am using a 2HP FM-50 on my 1 1/2HP Bridgeport and love it. I got mine at Factorymation for $145. Also you will find their customer support very helpful if you have any questions.
12-18-2007, 12:23 PM #9
Gentlemen, thank you for your responses to my query. Seems the FM50 is the best deal at this point. If the Lenze was really cheap, it might make an interesting project. However, I have enough projects to deal with. TECO it is.
12-18-2007, 03:16 PM #10
Oversizing the VFD by X2 won't hurt at all. As a matter of fact, if you plan on running single phase in and three phase out to the machine, you have to run a X2 drive . If your three phase motor is a 2hp, you would need atleast a 4hp VFD. There again, I prefer a slightly larger VFD from the stand point of maxing out the capacity of the VFD if you approach max hp and current for either long time or if you are ramping up and slowing down alot.
I perfer Yasakwa VFD, you can find them on ebay for cheap and they are a nice unit.
12-18-2007, 03:51 PM #11
There is no need to derate most current VFDs *IF* what you order is rated for single phase input, and most probably are in the size you are looking at. Just check the specs before you buy. The TECO FM50, FM100 and MA7200 up to and including 3HP all are equally happy with one or three phase 240VAC power. FM50s are also available up to 1HP that operate off of single phase 120VAC, a real convenience. There should be no problem with a larger capacity VFD, nor is it necessary. Hard to beat FactoryMation pricing.