Can I use a 1.5kW or 2kW VFD for a 0.6kW load?

I want to operate a small spindle motor (0.55 kW, 200 Hz, 230V) from my 230V 50Hz mains. So I need an inverter. Here in Germany there are good used ones available at low cost, but for 1.5kW (2HP). Is it OK for me to use one of these for a smaller load? I assume that after I program it with the nameplate data (voltage, max current, max frequency) then the inverter won't overload the motor. Or is there more to it?

I own three inverters but all were purchased for the motors that they are connected to and match the nameplate ratings on the motors.

Apologies in advance if this is a FAQ.

Yes you can.

The only issue you'll run into with an oversized inverter, is the amount of load current range, and motor impedance it's EXPECTING.

If you were trying to drive a 500w motor with a 10kw drive, you'd certainly have problems. A 2.5kw drive on the 500w motor might still... but a 1/2hp drive with a 1.5hp motor will likely work within reason. You MAY have to spend extra time getting all the adjustments set... but you may also find that the inverter manufacturer's software has parameters for motor power ratings that will get it dialed-in without much effort.

If it doesn't like it, you'll get lots of error codes... but you won't damage anything.

JCByrd24 -- thanks for the clear reply.

Dave -- you wrote:

DaveKamp said:

If you were trying to drive a 500w motor with a 10kw drive, you'd certainly have problems.

A 2.5kw drive on the 500w motor might still...

but a 1/2hp drive with a 1.5hp motor will likely work within reason.

Click to expand...

You listed 3 cases above, but not my case (2/3 HP motor with 2 HP drive). Do you agree with JCByrd24 that this is OK?

You need to look at the VFD specifications/parameters and ratings. Most VFDs have motor parameters that need to be set for each application. There is typically a range of kW (amps) that can be set along with base speed, poles, etc. More modern VFDs have autotune functions which help fine tune the motor parameters to the VFD. In addition you can set the overload parameters. In some cases the motor rating will be in increments of kW, so I would size up to the closest kW (0.7kW) and be conservative on the overload parameters.

As a gross general rule, MOST drive brands (and in particular older ones) will recommend not using a motor that is less than 50% of the current rating of the drive, which is the case in your situation. This is for two reasons:

1) The motor Over Load protection in the VFD may not be capable of adjusting below that or be accurate below that. This can be overcome by using an external OL relay if that is the problem.

2) if you want to take advantage of Sensorless Vector Control capabilities in the drive (better torque at low speeds, more accurate speed control etc.), the drive must be "tuned" to the motor, and the tuning capability may not allow low enough values for a motor less than 50% of the drive rating. If you are only going to use V/Hz control, this would not matter.

The latest generation of VFDs coming out now are typically capable of a 10:1 size utilization factor, but those are not going to be the ones you see available cheap on the used market yet.

The above is about the size of it....

The usual issue is that the measurement system in the VFD has "units" of a certain size. If there are 256 "units" in the full range (8 bit conversion), then for a motor of half the maximum, you may be using only around 100 of the "units" as "full scale".

If the motor is smaller, or the conversion is to fewer bits, the increments get "coarser" (fewer for "full scale", and resolution is worse, so you may not be able to hit the exact numbers you need. Problems of early or late current limiting, etc, may result.

As VFDs get more powerful in processing, the conversions may get to finer increments, and the problem is less.

Jraef said:

1) The motor Over Load protection in the VFD may not be capable of adjusting below that or be accurate below that. This can be overcome by using an external OL relay if that is the problem.

Click to expand...

That was the case with the last Teco unit I bought. I forget the model number, but it was a 4-hp unit and I wanted to use it on a 0.75-hp motor, and I could not dial the full load amps down low enough to protect the motor.

Yes, the scale may not go to zero (why would it need to?). And the example above is only 0.187 x the nominal full power capability.

The scale usually goes up to at least 150% of the nominal current output, because that is the most common short term limit on current overload. Based on that, the motor limit in the example is around 1/8 the max current scale.

That is extreme enough that there is no reason to expect the VFD to be accurate at, or perhaps even capable of measuring that level of current. Even if the sensor and converter can measure that, it is quite possible that the software ignores the very low end of the range, because it contributes very little to motor heating.