Testing VFD with low HP motor

Jieve · Jul 26, 2015

Hello,

I have an older 3-phase (400V), 3hp Siemens Micromaster VFD that I want to test to make sure it still works. I have access to 400V 3-phase, but only access to 1 hp squirrel cage 3-phase motors. The drive manual says not to run any motor smaller than half the rated vfd power (1.5hp). They don't specify their reasoning, but i'm assuming the motor parameter settings wont go low enough to be set for the smaller 1hp motors. I was thinking i could either test it by running 2 motors in parallel in V/Hz mode, or run a single motor off of single phase 230V (or could even do single phase-phase 400V for that matter) since the vfd input current would be significantly increased. But still not sure if i can set the parameters that low in the single motor case (havent tested it yet). What would you guys recommend in this case? I have phase-neutral 230V, 3-phase 400V (phase to phase) available.

Also, this VFD was hardly used at all, i think it might have been used for educational purposes for a very short period but nothing more. Its probably been sitting around for 10 yrs but looks to be in outstanding shape. I know I need to condition the capacitors by applying power stepwise to the drive, but what kind of life do you think i could still get out of the drive?

Thanks for any input.

jrwb4gbm · Jul 26, 2015

I don't think it will hurt to test the drive with a smaller motor for a short unloaded run. It is just a guess how well it will last after being in storage that long without power.

Bering C Sparky · Jul 26, 2015

You will have no problem running 1hp motor on a 3hp drive.
Drive parameters will adjust down to your 1hp motor no problem.

I cant quote it but I think the manual says to leave the drive powered on for 24 hours before running the drive if it has been stored for long periods.

We have lots of Siemens Drives onboard, Some are 15 years old and still kicking.

BCS

jdbrandt · Jul 26, 2015

Jieve said:
Hello,

I have an older 3-phase (400V), 3hp Siemens Micromaster VFD that I want to test to make sure it still works. I have access to 400V 3-phase, but only access to 1 hp squirrel cage 3-phase motors. The drive manual says not to run any motor smaller than half the rated vfd power (1.5hp). They don't specify their reasoning, but i'm assuming the motor parameter settings wont go low enough to be set for the smaller 1hp motors. I was thinking i could either test it by running 2 motors in parallel in V/Hz mode, or run a single motor off of single phase 230V (or could even do single phase-phase 400V for that matter) since the vfd input current would be significantly increased. But still not sure if i can set the parameters that low in the single motor case (havent tested it yet). What would you guys recommend in this case? I have phase-neutral 230V, 3-phase 400V (phase to phase) available.

Also, this VFD was hardly used at all, i think it might have been used for educational purposes for a very short period but nothing more. Its probably been sitting around for 10 yrs but looks to be in outstanding shape. I know I need to condition the capacitors by applying power stepwise to the drive, but what kind of life do you think i could still get out of the drive?

Thanks for any input.

I seem to remember seeing a specification in the MicroMaster series where it said that they did not recommend running any motor with a FLA rating less than 13% of the drive's nameplate maximum current. I do not recall a reason, but the 13% did stand out.

Bering C Sparky · Jul 26, 2015

Its not 24 hours I guess,
a quick look shows 6-8 hours for 3 years or more in storage.

Jieve · Jul 26, 2015

Guys, thanks so much for the responses.

Exactly, the manual says to up the voltage 25% every 2 hrs for 8 total if it's not been powered up for over 3 years, will have to figure out how to do this with three phase since I dont think we have anything adjustable. Anyone see any issues doing this with a variac on single phase? Not sure if we have anything adjustable up to 400V phase-phase though.

Jbrandt, i know the 13% is the case with the siemens G120 drives. I didnt find that in the micromaster manual, it only says no motors sized less than 50% of the drive's rated power.

Once I get it up and running I'll see what parameters i can set. Any idea why they would say to not run any motor smaller than that? Could it be somehow connected to the auto-motor parameter measurement in SVC mode? The manual doesnt specify mode, just says don't use the smaller motor, period.

DickDV · Jul 26, 2015

I would expect the smaller motor to run fine but the drive probably cannot be dialed down low enough to properly thermally protect it. If the test is just an unloaded motor, that shouldn't be any problem. You can monitor the motor temperature manually for the duration of the test.

Bering C Sparky · Jul 26, 2015

We are in the middle of the ocean and cant run out and pick up Exactly what is needed most of the time and don't have the room (or given the budget) to stock every size drive for every size motor.

Although we try to match as close as possible, there are lots of times I have to run smaller motors on larger drives just because that's all that is available at that moment.
Maybe not good practice but it will work.

I would not want to get crazy and put say a 5hp motor on a 50hp drive or anything but for your example you will be just fine.

Biggest concern is if you are installing this in an application where the CODE actually matters (which is probably every application except fishing boats it seems

) then you will need to make sure your conductors are sized to the drive and not the motor.

You are only doing this just as a test on the bench, so no worries.

EDIT: not sure how you will up the voltage to the drive 25% every 2 hours, we usually just leave the drive powered at 440 volts on the bench overnight and then install it the next day.
Heck sometimes you have no choice and have to pull it out of storage and install it right away.
Have not had any trouble doing this yet.

BCS

Testing VFD with low HP motor

Jieve

Member

jrwb4gbm

Lifetime Supporting Member

Bering C Sparky

Lifetime Supporting Member

jdbrandt

Lifetime Supporting Member

Bering C Sparky

Lifetime Supporting Member

Jieve

Member

DickDV

Member

Bering C Sparky

Lifetime Supporting Member

Similar Topics