VFD drive Faults on series I cnc Bridgeport

[colin1544]

Hello out there I have been running my series I cnc Bridgeport Mill on a single to three phase inverter with the standard 2 HP motor for about 2 Years I origonally had a panasonic DV 700 inverter running it but this went down with a fault I then recently changed it to a Teco Speedcon 7200 MA 220 volt 3 HP rated with maximum 6.5 Amps output it is a vector self tuning drive which got me back on track again but today I have had the inverter trip twice with motor overload I then contacted the supplier who is extremely helpful and when we check the current draw of the motor it is running at 6.2 amps running free with no belt connected this is I think which caused the failure of the Panasonic inverter Question Is has any one else had problems like this or is it normal for these spindle motors to run at maximum current ratings of the motor (220 - 230 volt at 6.3 Amps) it is not getting hot even at low speed, just for information I measured the resistance across the windings they returned 2.0 ohms equally so its not as if there appears to be an inbalnce of the windings, any help would be appreciated
Cheers Colin 1544

[Al_The_Man]

Normally the plate current of a motor is FLA (full load amps) so at no load it should be considerably less, make sure you test the currrent at 50hz and test each phase for balance.
The winding resistance will not really tell you anything, as you would not detect a shorted turn.
Often motors that are not inverter rated fail because some older motors do not have the resistance to switching spikes, due to insulation quality etc.
Does it trip on over-voltage or overcurrent?
Because if it does not have good internal braking quality, then if you have too short a decel, it causes over voltage (regenerative).
Al.

[colin1544]

Hello Al the inverter trips on overcurrent after about 20 minutes running this is when it has been running at approx 25% frequency it does not get warm even at this speed Cheers Colin

[Al_The_Man]

I would get the motor checked on true three phase and do a phase current test for balance, other than that it could be shoot through on spikes between phases.
A three phase motor does not normally run at plate current off load.
Al.