Question for VFD guys

[Shoreline_]

Hey why would a company program a drive for 69 hz and 2048 rpm for nameplate parameters when nameplate is 60hz and 1750 rpm? It works fine, they progam all their machines like that. They all work fine that way. Inside joke?

 

[American Locomotive]

Because they need more speed, there's really no mystery here.

 

[jar944]

I run one of my direct drive machines at 70hz to get the cutterhead speed where I want it.

 

[larry_g]

Hey why would a company program a drive for 69 hz and 2048 rpm when nameplate is 60hz and 1750 rpm? It works fine, they progam all their machines like that. They all work fine that way. Inside joke?

Because that is the speed that they want the machine to run at. The 60hz/1750rpm is just the rating on the motor. That is one feature of a VFD drive control, you can spin the motor at whatever the speed is needed within the operating parameters of the motor. Dig into all the ratings of the motor beyond what is on the motor plate.

lg
no neat sig line

 

[Shoreline_]

Haha no no. I mean in the parameters for nameplate rating, they don't enter the name plate rating. They enter 69 hz and the async speed of 2048. Im wondering what is the reasoning behind this.

 

[PCustoms]

Haha no no. I mean in the parameters for nameplate rating, they don't enter the name plate rating. They enter 69 hz and the async speed of 2048. Im wondering what is the reasoning behind this.

Because they want to run at 2048 rpm?

 

[Shoreline_]

Okay so far no one who has replied is a VFD guy lol.

 

[Shoreline_]

Because they want to run at 2048 rpm?

If you enter 60 hz on the drive it will run at 1750 rpm, so why didn't they just set it to that? The machine runs from 25hz to 80hz depending on the load, its runs all over the place. I'm not talking about the setpoint.

60hz 1750 (or 1735 whichever) is the same as 69hz 2048.

 

[PCustoms]

Okay so far no one who has replied is a VFD guy lol.

It's been a few years since I've had to program one, but without any context or additional information you haven't given us much to go on.

If you enter 60 hz on the drive it will run at 1750 rpm, so why didn't they just set it to that? The machine runs from 25hz to 80hz depending on the load, its runs all over the place. I'm not talking about the setpoint.

60hz 1750 (or 1735 whichever) is the same as 69hz 2048.

I doubt it.

If you're so confident, go set it to 60/1750

 

[American Locomotive]

If you enter 60 hz on the drive it will run at 1750 rpm, so why didn't they just set it to that? The machine runs from 25hz to 80hz depending on the load, its runs all over the place. I'm not talking about the setpoint.

60hz 1750 (or 1735 whichever) is the same as 69hz 2048.

I see what you are saying now.

The only two reasons I can think of are that they either wanted 69Hz to be the "default" speed (100%), or they're using simple V/Hz control, and setting the name plate to 69Hz shifted to the V/Hz curve to a point where they wanted it.

 

[loganb]

What is the machine? Sample size of 1 (assumingly) also means that could have just been something that wasn't reprogrammed correctly...mistakenly trusted default programming etc

 

[larry_g]

Okay so far no one who has replied is a VFD guy lol.

I don't know why you assume that. I spent a career working on VFD controlled machines and do know a bit about about them. I can only assume that your ignorance of the machine and processes it does gives basis to your vague question...

Give us specifics on the machine, exactly what parameters are set to 69hz and where this 69hz is specified and who specified it.

lg
no neat sig line

 

[timgunn1962]

Context is everything and the OP hasn't given us that. We are not even told what the machine is, whether it stands alone, or whether it is part of a larger machine or production line.

There could be a number of reasons for the "odd" values.

My best guess would be that it's been done that way for decades and is an "if it ain't broke, don't fix it" thing.

An old-school V/Hz VFD varies the Voltage and Frequency together below the Rated Frequency, giving Constant Torque. Once the motor is at rated Frequency, it is also at rated Voltage. It can continue to increase Frequency, but Voltage is at maximum safe level and can't be increased. Above the rated Frequency, the Frequency is increased, but the Voltage is constant, giving Constant Power. It may be that the values were chosen to match the motor power profile to the machine load profile.

Most likely, back in the mists of time, someone fairly bright, and with an understanding of the process, commissioned a machine, probably in consultation with the tech experts from the motor manufacturer and the VFD manufacturer.

I first used a VFD in 1989 and they've come on a long way since then. Motor efficiencies have increased, Mainstream VFDs have Sensorless Vector capability.

However, whenever we change one out, it almost invariably gets the same basic parameters as the one it replaced, simply because it's almost never worth the downtime associated with commissioning and optimizing from scratch. We have some plant out there with settings from three VFDs and 2 motors back.

 

[fitter30]

Can overclock a motor so long as it doesn't run over name plate amps.

 

[cvairwerks]

Another possibility is that the original machines were built with weird rpm motors that are no longer available. I have a shear that has a 550 rpm motor on it.....and it's not a geared motor.

 

[wyliesdiesels]

If you enter 60 hz on the drive it will run at 1750 rpm, so why didn't they just set it to that? The machine runs from 25hz to 80hz depending on the load, its runs all over the place. I'm not talking about the setpoint.

60hz 1750 (or 1735 whichever) is the same as 69hz 2048.

since i dont work with VFDs very much, can someone explain to me how they are the same?

 

[BrandonV]

since i dont work with VFDs very much, can someone explain to me how they are the same?

All a VFD does is change the input frequency provided to the motor. So if the motor has a nameplate RPM of 1750 RPM at 60 Hz (which is a 4 pole motor) if you were to bump the frequency up to 69 Hz the RPM would be around 2070 RPM. Ideal RPM for a 4 pole motor at 60 Hz is 1800 RPM.

NS = 120 * f / p

NS would be your RPM. f would be the input frequency and p would be the poles of the motor.

 

[BrandonV]

Give us specifics on the machine, exactly what parameters are set to 69hz and where this 69hz is specified and who specified it.

Yup... big missing piece of information.

 

[PCustoms]

All a VFD does is change the input frequency provided to the motor. So if the motor has a nameplate RPM of 1750 RPM at 60 Hz (which is a 4 pole motor) if you were to bump the frequency up to 69 Hz the RPM would be around 2070 RPM. Ideal RPM for a 4 pole motor at 60 Hz is 1800 RPM.

NS = 120 * f / p

NS would be your RPM. f would be the input frequency and p would be the poles of the motor.

So then it's not the same?

 

[BrandonV]

So then it's not the same?

I mean once you account for synchronous speed, full load speed, slip, various motor parameters, etc.

 

[BreeStephany]

The likely reason, depending on the drive used, is that the drives default speed is set to the motor default, so the parameter was changed to have to drive "default" on startup / after power loss to a set speed other than the nameplate rating of the motor., thus defaulting the output of the drive to adjust output frequency upon startup.

 

[Shoreline_]

The likely reason, depending on the drive used, is that the drives default speed is set to the motor default, so the parameter was changed to have to drive "default" on startup / after power loss to a set speed other than the nameplate rating of the motor., thus defaulting the output of the drive to adjust output frequency upon startup.

No the frequency changes if it's blowing down, or near the set point. On restart the frequency can be whatever the demand is.

 

[Shoreline_]

Most likely, back in the mists of time, someone fairly bright, and with an understanding of the process, commissioned a machine, probably in consultation with the tech experts from the motor manufacturer and the VFD manufacturer.

This is exactly what I'm looking for. Why did the engineer at Eaton set up the drive for 69 hz 2048 rpm in the nameplate parameters.

Knowing what equipment it is doesn't matter. These arent parameters for the process.

 

[mm08822]

Doesn't make sense to me.

I'm guessing a few too many cooks in the kitchen and somebody didn't know what they were doing.

How is the setpoint adjusted....via parameter change, hard-wired pre-set speed inputs or potentiometer to a fixed dial setting?

Do you have multiple machines with same parameter settings AND same motor np values?

Does this machine have to speed synch to another?

Is this machine running open loop or encoder feedback?

 

[manwithtools]

I'm guessing a few too many cooks in the kitchen and somebody didn't know what they were doing.

This is likely the case. Could be an artifact of another machines settings even.

Knowing what equipment it is doesn't matter. These arent parameters for the process.

Frankly, knowing the equipment and the controls architecture does matter. Being obtuse about that fact will not help get you the answer you are looking for. Also what voltage is this drive / motor combination?

 

[American Locomotive]

This is exactly what I'm looking for. Why did the engineer at Eaton set up the drive for 69 hz 2048 rpm in the nameplate parameters.

Knowing what equipment it is doesn't matter. These arent parameters for the process.

It absolutely does matter. Setting the nameplate frequency higher than it actually is on the VFD has the effect of shifting the V/Hz curve. It will reduce the voltage the motor sees at all frequencies below 69Hz. This reduces the maximum torque at a given RPM and will increase part-load efficiency.

They might have done it to create a torque/power curve better tailored to the specific application. They may have done it to reduce motor heating/losses if the process runs partially/lightly loaded often. So know what specifically this motor is doing may help clue in why they did this.

It should also be noted that 2048 RPM is 2^11 - a power of 2, or the maximum value that can be represented by an 11-bit binary number. Binary of course is how computers operate, so using numbers that are power of 2s is very common way to make math simpler. I don't know how the drive is controlled, but that base/nameplate frequency may have also been chosen if it resulted in making some kind of RPM calculation easier.

 

[mm08822]

I noticed the 2048 as exactly that too, but w/o knowing how the vfd is interfaced to, makes this question no better than an easter egg hunt w/o any hidden eggs.