Thread: Interesting 3P motor

Originally Posted by RustyArc

Still curious to know whether you'd get away with running both motors off the one VFD...

I'm sure you could but at lower frequency the cooling effect of the auxiliary fan is much reduced.

The whole concept of this motor design is to maintain full cooling at reduced motor speed. This is important in some applications (constant torque loads). If you also slow down the cooling fan motor you may as well just use the standard shaft mounted fan.

John

I am damn happy I am licecncsed...

Originally Posted by GuzziJohn

I'm sure you could but at lower frequency the cooling effect of the auxiliary fan is much reduced.

The whole concept of this motor design is to maintain full cooling at reduced motor speed. This is important in some applications (constant torque loads). If you also slow down the cooling fan motor you may as well just use the standard shaft mounted fan.

Sure I appreciate that wired in parallel with the motor the fan will slow down when the motor is slowed down but it should still provide twice the cooling compared to if it was shaft mounted fan. From what I can see it is also a much better fan than a shaft mounted motor so it will be even more effective at low speed than the standard shaft mounted type.

My concern with using it in parallel is not so much at low speeds but rather at high end speeds e.g. if the motor is run up to say 100Hz the fan will be at 5700 rpm and I'm not sure it's designed to do this.

This is why I'm thinking of using it on my WW bandsaw because I am unlikely to run the motor higher than say 75 Hz and lower than say 25Hz.
With my current BS the 2HP motor is underpowered for the relatively long periods at higher loads associated with ripping/resawing and the motor does get quite hot. I'm hoping this higher capacity motor with better cooling will be a better option.

Anyway I will wire it 2up and test it out over the next couple of days and report back.

Originally Posted by BobL

Sure I appreciate that wired in parallel with the motor the fan will slow down when the motor is slowed down but it should still provide twice the cooling compared to if it was shaft mounted fan. From what I can see it is also a much better fan than a shaft mounted motor so it will be even more effective at low speed than the standard shaft mounted type.

My concern with using it in parallel is not so much at low speeds but rather at high end speeds e.g. if the motor is run up to say 100Hz the fan will be at 5700 rpm and I'm not sure it's designed to do this.

This is why I'm thinking of using it on my WW bandsaw because I am unlikely to run the motor higher than say 75 Hz and lower than say 25Hz.
With my current BS the 2HP motor is underpowered for the relatively long periods at higher loads associated with ripping/resawing and the motor does get quite hot. I'm hoping this higher capacity motor with better cooling will be a better option.

Anyway I will wire it 2up and test it out over the next couple of days and report back.

Bob, in my opinion you would be better off to remove that 3-phase fan. Replace it with either a single phase mains, or a low voltage DC fan. Something like an axial box fan (they also make them with round frame). You really want this to be a constant speed fan independent from the motor speed. And you certainly do not want the expense and extra complexity of a second VFD, just to drive a silly fan.

Originally Posted by DavidG

Rusty - A licensed trades person has a licence to do the work.

It was a licensed electrician who wired up those pumps with 3 red, 3 white 3 blue... just because the guy has a licence, doesn't mean he has a clue... I've worked with electricians for a lifetime. There's good and bad, like all trades, but it's a big mistake to assume that your house wiring type electrical contractor is going to know anything about 3 phase motor controls. Not that's it's all that hard, it's just stuff they might have done once years ago when doing an apprenticeship, and never touched since then.

So with that in mind I modify the disclaimer...

I strongly advise contacting an Electrician with Industrial Experience for all electrical work involving machine tools

Originally Posted by RayG

It was a licensed electrician who wired up those pumps with 3 red, 3 white 3 blue... just because the guy has a licence, doesn't mean he has a clue... I've worked with electricians for a lifetime. There's good and bad, like all trades, but it's a big mistake to assume that your house wiring type electrical contractor is going to know anything about 3 phase motor controls. Not that's it's all that hard, it's just stuff they might have done once years ago when doing an apprenticeship, and never touched since then.

So with that in mind I modify the disclaimer...

I strongly advise contacting an Electrician with Industrial Experience for all electrical work involving machine tools

Well said

Originally Posted by cba_melbourne

Bob, in my opinion you would be better off to remove that 3-phase fan. Replace it with either a single phase mains, or a low voltage DC fan. Something like an axial box fan (they also make them with round frame). You really want this to be a constant speed fan independent from the motor speed. And you certainly do not want the expense and extra complexity of a second VFD, just to drive a silly fan.

That is a sound option and is what I did with the 3kW Technomotori motor that had a missing independently powered fan.
On the TM motor I used a 240V SP mainframe computer fan which pumps out a lot of air.

I am still curious to see if it works and if it does, as I have all manner of TCs available that I can check temps along the way and decide what to do after that,

Originally Posted by Michael G

... there was only gland into the terminal box as pictured, so it was likely that only one supply was run to the motor. Looking at the terminal block photo again, it looks as if there are jumper cables between the two sets of terminals further supporting the idea.

Originally Posted by BobL

There was a couple of feet of old wiring still attached to the motor and there were definitely 2 sets of 3P power (one to the fan and one to the motor) in there

Looks like it was most likely 2 separate power sources, as Bob confirmed.

Finally got round to hooking up a VFD to this motor.

I have 2 spare 4kW HYs in the shed so I hooked one up (lets call that one A) and was immediately alerted to to an issue with higher than usual free running currents
The normal free running current for a 3P 3HP motor is usually about 1A at 50Hz but this one was drawing 2.5A, checked all the connections, all OK.

Then I checked other frequencies and dropping the frequency to 40Hz and the current increased (should decrease) and the motor also started to squeal.

The first thing I did was switched to the other VFD (B) - all good there, low currents, a bit of squeal but not more than I have heard on soother motors.

Then I switched to another motor (an ABB 3HP) and tested this one with VFD A and VFD B.

Here is a summary of all the results.

LSA = the Leroy Somer motor with VFD A
LSB = Leroy Somer motor with VFD B
ABBA = ABB motor with VFD A
ABBB = ABB motor with VFD B


It looks like the motors are fine running on VFD B but not as efficiently on VFD A and the ABB seems to be running better than the LS.
Anyone have ideas why this might be the case?

I have used VFD A as a testing VFD a lot more than VFD B, I wonder if it has undergone too many trips?

Hi Bob,

I assumed you checked all the parameters are the same.*
Were you using the current display on the VSD or your flash meter?

Neither of which would seem to be the full story

Stuart

* yes I feel a bit of a git asking lol

This is very interesting, perhaps more telling about VFDs...

Are all the settings the same on both VFD A & B Bob?

I could imagine current properties being different across motors, but (assuming all settings are the same) Id expect both VFDs to perform the same on each motor.

J

Time for a little basic physics, leaving aside any weird resonant tuned circuit effects, the current will be the same when the applied voltage is the same, and the motor slip ( or load if you prefer ) is the same. no matter what the brand of vfd or motor.

Since these are all V/F drives, not vector drives, then simply measuring the current with a clamp meter ( do a spot check to make sure all three phases are about the same )
and a simultaneous check on the voltage with an RMS reading meter will show up any differences in V/F curves for the different drive configurations.

So, given all that, what is the likely difference?, I'd guess that it's a fault in the current measurement circuitry is the most likely problem, second most likely would be that there is a phase imbalance and one drive is measuring the current in a different phase?

So, what does the clamp meter and the RMS voltmeter say?

Ray

If you look back at the origin of the word Licence, it means freedom and also permission. Interesting enough in Italian the same word is used to say a person is "Licensed" as in being allowed to go from a qualifying institution because he finished with the program and also letting go someone as in being fired from a job....so....please if you are in Italy, do not, and I say do not employ a Licensed electrician unless you are really sure what sort of Licence he or she was given ... hu hu

Originally Posted by Stustoys

Hi Bob,

I assumed you checked all the parameters are the same.*
Were you using the current display on the VSD or your flash meter?

Neither of which would seem to be the full story

Stuart

* yes I feel a bit of a git asking lol

I wouldn't feel any gittishness at all.

Both VFDs have had a LOT of mucking around done on their parameters.
What I need to do is a factory reset and take it from there.

None of the current measurements are done on the 3P side, they are all dome on the SP side of the VFD.

second most likely would be that there is a phase imbalance and one drive is measuring the current in a different phase?

Current is being done on the 1P side and while it may not be absolute it should be OK for comparing like for like
The last time this happened it was a dodgy connection on the 3P side but I have checked these already several times.