Hitachi SJ300 VFD problem

[Clive SteerParticipant @clivesteer55943]

I have a couple of Hitachi SJ300 low volts VFD’s that I’m testing on my Chipmaster lathe which has a 4 pole 2.2kw delta configured motor. Both the VFD’s show the same behaviour in that they will run the motor to the max programmed speed using the speed set potentiometer and ramp down to stop.

However if I set the pot to give a low speed, say 10% of max, it will run for a few seconds and then it stops suddenly as though DC braking had been activated.

All parameters are I think set to the basic defaults and the fact that the two VFD’s have the same behaviour on two different motors makes me believe there is a problem with the VFD but I can’t work out what as the DC braking is set to disabled.

If anyone has knowledge of the inverters I would appreciate any advice.

Clive S

[DiogenesParticipant @diogenes]

For want of ‘owner’ replies and on the principle that maybe a cr*p answer will draw forth a good one..

– could you clarify what ‘low speed’ / 10% of programmed speed is, please Clive?

..if you are trying to run them at say <10hz could be that they are just not making enough power..?

..is it a ‘preservative function’..

[Peter Cook 6Participant @petercook6]

Sorry no experience of VFD’s on standard three phase motors, but I have a BLDC 3 phase motor and driver on my little lathe that suffers from a similar problem at low speed. It will suddenly stop!

I think the cause in my case is that at low speed the back EMF from the windings is low and the drive current rises  high. The current level trips the over current protection in the driver and the motor stops.

I am guessing that the same inverse speed vs current behaviour may exist in your motor/VFD setup and the VFD is shutting down via over current protection.

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