Vfd questions

[PNW_Guy]

Anyway, I do have a recurring problem with the VFD on my 5 hp air compressor, when it runs for an extended period of time it shuts down and gives an "over current" fault message. Letting the unit cool down corrects it. I have tried everything as far as setting parameters etc, and it is properly sized, installed, wire gauge, etc, but it still faults occasionally. I will be wiring the compressor to the RPC when time permits.

My understanding of compressors on VFDs is that they don't work that well. As the piston approaches TDC and the tank is at high pressure, the current draw goes way up. A RPC can handle the temporary overload, but the VFD has a hard time. An "overcurrent" error sounds like that's exactly what's happening.

 

[mksj]

If you size a VFD appropriately for the operating conditions and deratings, you should not get an overcurrent error. Piston compressors are a difficult starting load, but it all depends on the VFD used. It is pretty consistently reported that the generic/HY VFD's do poorly with difficult loads like compressors, and typically the VFD requires to be upsized at least 1 or 2 sizes (Hp) bigger to accommodate the higher starting loads.

Although a single VFD can operate multiple motors, it is in a V/Hz mode and each motor would need to have an overload protection device, so not really applicable to most hobby machinist or single machine applications. If one oversize's a VFD by a factor of 4-5X they have been used as a fixed frequency 60Hz power source in V/Hz mode, but at that point you are better off with an RPC or Phase Perfect fixed frequency digital phase converter. There are also issues of sub systems like transformers and contactors, that may not operate correctly when fed with PWM power. Most motors will operate with VFD power, it is not an age dependent factor, but performance of an inverter specific motor will be better over a wider speed range. With regard to motor insulation, it is a problem with motors as they get older, that there is some level of deterioration, but a failure of the insulation at the 240VAC voltage level is very uncommon using a PWM VFD. Most of these motors are dual voltage (230/460) and the motor cable are very short, which decreases overshoot peak voltages to the insulation. In some cases a dV/dT output filter can be used, but it needs to be matched to the output current as well as limited frequency range. See the attached white sheet on PWM and insulation issues.

I reviewed the Spedestar PC1 Series Drive manual, and have a few suggestions to try. First, the PC1-50, for 1-phase drives, the current rating of the breaker shall be 2 times maximum input current rating. This would indicate that you should have as a minimum a 50 or 60A breaker, and #6 wire gauge to the VFD. The startup current can be quite high and it depends on if you are displaying motor current vs. input current. That the VFD is not giving any error messages as to overcurrent or voltage issues, suggests that it is not reaching any threshold amounts.

I would do a factory reset of the VFD parameter's and then make a few programming changes as follows:
Pr0-02 Motor V/F selection = 10 (60Hz, 230VAC)
Pr0-12 Optimal Acceleration/Deceleration setting = 3 (Auto)
Pr1-10 Acceleration Time 1 = 3 seconds
Pr1-12 Deceleration Time = 3 seconds

Default motor parameter's Pr5 should be OK

I would start out with the factory carrier frequency of 10kHz, and not go above 12.
Pr0-14 = 10
Pr0-15 = 10

Run the motor Auto-tuning & control mode selection Pr5-05 = 1
I would run the motor in Sensorless Vector mode and see if that helps.

If all of the above does not improve the motor performance issues, then it is most likely a VFD issue, although if there is no fault codes, it could also be a motor issue. In that case, if possible try the VFD on another motor.

 

[knowitallyankee]

I sent the drive back to Polyspede, I should be able to touch base with them on friday. I'm assuming they're going to tell me there's nothing wrong with the drive which will put me back to looking at the motor. Would testing the motor with a megger tell me anything?

 

[mksj]

I sent the drive back to Polyspede, I should be able to touch base with them on friday. I'm assuming they're going to tell me there's nothing wrong with the drive which will put me back to looking at the motor. Would testing the motor with a megger tell me anything?

I would think that the drive would detect a motor issue fault, at least that has been my previous experience. Since the motor was running fine initially, the question is what changed? Once you get it back, I would load the parameters mentioned. I have had issues with motors running poorly prior to Auto-Tuning, and in some cases (Chinese 2 speed motors) I could never get them to run properly and ultimately replaced the motor which solved the issue. But this was a problem from the initial power up, since you are running at a fixed 60Hz it should work w/o any issues.

 

[strantor]

Wow! That one generated some interest.
Get comfy, this turned into a novel.
Drive is a Polyspede (Drives Warehouse) Spedestar PC1-050 (5 hp motor).
Lathe original sell date (according to Clausing) was 1975, motor appears to be original.
FLA with 220 volts is 14.
Full load speed 1720.
Service factor 1.15
I originally set the machine up with the original 120 volt contactors to try to retain some of the original controls. With this setup the contactors were ALWAYS closed BEFORE the drive was turned on. After several discussions with Polyspede I also bypassed the contactors to run the motor directly and had exactly the same problem.
I purchased the machine in the fall of 2019 and purchased the drive shortly after that. I did not get the machine operational or hook up the drive until spring of 2022.
This machine is in my heated home shop and is only used occasionally, sometimes maybe only once or twice a week for short periods. Power to the drive was always turned off when the machine was not being used.
Machine operated perfectly for the first 6 months and then started intermittently acting up.
On the Colchester, the MOTOR is not stopped or started or reversed. Stopping, starting and reversing of the SPINDLE are all done with clutches in the headstock so the MOTOR runs at a continuous 60 hz the entire time the machine is running.
Drive was set for 2 sec. acceleration to 60 hz and 2 sec. deceleration (10 sec factory default for both).
I changed carrier frequency from 10 kHz to 15 to lower noise, all of these were later reset to defaults with no effect on the problem.
Amperage upper limit was left at the factory setting (I think 18.6. The tech from Polyspede gave me the menu parameter to check it, it's not in the manual and I already sent the drive back).

After about 6 months THE PROBLEM started at motor startup. LOUD high frequency squeal, acceleration to only about 6 or 7 hz and Amperage through the roof to a little over 36!
Drive was running on a 20a breaker (220v single phase) and even though it only went 5 to 6 seconds before I lost my nerve, it never tripped the breaker, shut itself down or displayed an error.

Cycling power to the drive would usually eventually get it working again but then THE PROBLEM started happening after the motor was running for a few minutes. During operation and with no warning I'd get the loud squeal and the motor would make a LOUD noise I can only describe as a garbage disposal full of walnuts! With the corresponding drop in speed and spike in amps.
My nerves are shot just thinking about it!

Once the drive was in "F!#k-UP MODE" I had to disconnect the outputs to even try anything (initially by opening the contactors and later by removing the leads from the outputs (no change in result)).
When start was pressed, hz went to 60 and amps stayed at 0 (naturally) but the acceleration time was slow. Eventually I did some checking. Keep in mind, nothing connected to the outputs.
Acceleration set to 1 sec became 3 sec.
Acceleration set to 3 sec became 9 sec.
Acceleration set to 5 sec became 15 sec!

That's how far I got over the course of about 2 months and four phone calls to Polyspede before I gave up. Also, as I stated this machine works perfectly fine on a rotary phase converter. The tech at Polyspede was not remotely interested in any of this information and only insisted that there was a problem with the motor.

Paw Paw Wine And Harvest Festival is still going strong, by the way, but I always try to avoid town that weekend because the main streets are closed for parades! I don't care much for people unless they make metal chips! HAHA

Congratulations if you made it this far, I'm looking forward to hearing what all y'all have to say.
Thanks, Mike.

The symptoms you described, sound like what happens when a 3ph motor only gets 1 phase power. Since you bypassed the contactors and since it works fine on a RPC, probably one or more of the VFD output transistors are failing.

Since it doesn't happen all the time, you're probably right, they'll say it isn't the drive, because when they test it, it will work just fine. That's how these things go 90% of the time.

 

[strantor]

Although a single VFD can operate multiple motors, it is in a V/Hz mode and each motor would need to have an overload protection device, so not really applicable to most hobby machinist or single machine applications.

Yep and most app notes on this topic also indicate the motors should be equal HP (ideally identical motors) and ideally all mechanically coupled to the same load (ex: long continuous chain conveyor). It's a pretty niche thing that isn't even common in industrial settings. For the purposes of this discussion, I think it is prudent to say simply "thou shalt not."

One motor per VFD, folks. And always directly connected from motor to VFD, nothing in between (except reactor/filter, optional). No contactors, overloads, reversing switches, etc between motor and VFD.

 

[ltlvt]

If the lathe runs on the RPC,
Makes me think that there is a problem with the drive, how its hooked up, and/or programmed

I had a somewhat similar problem with my Clausing 5913 2hp 3 phase Reuland motor. It ran on the rotary but would not run on the VFD. I Megged it and it was in the yellow range. I took the motor to our local rewind shop, and they found one leg was bad. They did a bang-up job of rebuilding the motor and now it works on both the Rotary and the Same VFD that it would not work on. I am sure some of the problem was my lack of understanding the programing of the VFD. I am now using the same VFD that I thought was junk on a used 2hp 3 phase motor for my other lathe. And it works great on that motor also. Of course, the Used motor Megged out over 1000 mega ohms which is perfect. It all starts with the correct tools and understanding a few things about 3 phase motors. Which I am a 71-year-old electrical dummy. Perhaps the VFD could be tested on another motor.

 

[markba633csi]

So is the Polyspede unit coming back or did you return it for a refund? I'm curious how this all turns out
-M

 

[knowitallyankee]

I really appreciate everybody's input on this. There may still be a problem with the motor but for now I'll keep running it with the RPC unless that starts acting up. This has been a frustrating process to say the least but my conclusion is that the potential risks of using a vfd with an older motor far outweigh the benefits, especially since I don't need any of the control features that are built into a drive. Using a vfd in an application like this, especially a Chinese vfd, automatically means there is no warranty and no support. How could there be? Since when is there any warranty on an electronic component that's been installed? Any problem you have is YOUR problem. I think in the future my first choice will be to replace the motor with a single phase if the application permits.
The ending of this story is no refund, no credit. By sending back the drive all I was hoping for was a credit on a Hitachi Drive but they don't have any of those anyway.
I'll try to sum up the conversation I had with Polyspede on friday. The guy I talked to said he hooked my drive up to a 15 horsepower motor (three times what the drive was rated for) and got an over voltage trip and error code with a 2 second deceleration time and asked me if that's the problem I was having!?!? During that conversation I asked him what size breaker I should have been using, he said 50 to 60 amps. The entire time that drive was operational it was running on a 20 amp breaker which never tripped (no explanation for that). The 30 amps that I was showing on the output when it was malfunctioning was 12 amps over the factory preset limit (no explanation for that) and he said it would take 40 to 45 seconds before it would trip, then said that that part of the drive was working correctly. I didn't see anything in the manual about how long to hold an overload condition. I guess the fact that I shut it down before something caught on fire makes me a quitter. He also had no explanation for the discrepancy between the programmed acceleration and deceleration times and the actual times when the drive was acting up. Had absolutely no interest in any of that information.
He was big on asking me questions I couldn't answer like what was the incoming amperage with the rotary? I have no way of measuring that but he didn't bother to check that on his end. Etc etc.
Either they sold a bunch of junk drives and are doing damage control or he really doesn't know what the problem is or doesn't care or a combination.
I had no intention of trying to use the drive again and there's no way I'm going to try to sell it on eBay to get a couple hundred bucks for it just to have somebody complain and I have to eat it, so instead of paying return shipping I just told him to keep it. It's probably in a dumpster by now.
If anybody knows where I can find a Drives Warehouse/Polyspede customer satisfaction survey, I'm ready to take it. Thanks again for letting me vent, I appreciate all the help.
Mike.

 

[ltlvt]

My Fugi Mini was doing that on deceleration. 2 seconds was too fast . I changed the parameter to 10 seconds and it is running like a scalded dog. The real and often case is lack of knowledge when buying a VFD. I expected plug and play and they are not Plug and Play. I also expected clear and easy to understand English. Instead, I got Chinglesh Believe it or not after two years of thinking something was wrong with the 2 yes TWO VFD's I watched a video by Finno Ugric Machining on You Tube and posted in the electrical section of this forum. He was speaking in a language either Finnish German,Belgium , I do not know but I clicked on the Closed captions button and read his words in English. This forum and that You Tube video has been the greatest eye opener for me in the Realm of VFD's along with some very intelligent members of this forum. Thanks for asking the question because many others like me learn from others post.