VFD questions

Those are also in my manual.

I think misunderstandings spring from the unfamiliar terms.

I'd sum it up as:

The graphs for constant/variable torque are for different types of load, while 'torque boost' is actually used with 'constant torque' and intended for things that require extra grunt to keep rotating at low speed - i.e. the torque/speed graph is pushed up a bit at zero and drops to normal at rated speed. While this is mainly intended for starting heavy loads, it's also useful for lathes etc. at the expense of more rapid heating.

I think a lot of it is aimed at real inverter rated motors Neil. Not what we use and what one well know supplier pushes out as inverter rated. I vaguely remember reading that the same supplier up rates inverters some where recently as well.

When ever this subject crops up some one always says that they have used low speed for ages without problems. They are doing so because the loads are not fully loading the motor or they only use them for very short periods.

Many people who fit them fit a larger motor which will also helps. Some do this following experiences with set ups that they have had on their lathes before. Some also report that flux vector control is better than the set ups they had before. That as far as I am aware is a constant speed mode. Fitting a larger motor also helps with the power drop off when they are driven above base speed.

One thing for sure if all of the problems that can crop up due to the use of inverters are worried about too much the whole area is a bit of a night mare. These even include high frequency switching wrecking bearings due to circulating currents. When I bought my set up I did find a supplier that could provide a motor with our level of power output that wouldn't have any problems at a cost. It was also spec'd to be driven at 100Hz or more. No signs of them now. There were a number of detailed differences in it.

John

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Edited By Ajohnw on 29/07/2016 10:08:12