Member postings for Colin Gibson

It mght be easier to re-instate the 4 Pole 0.37kW Motor and ABB ACS150 Inverter Drive you have, with a 4:1 belt ratio. This would give full power delivery to the Lathe from 342RPM to 685RPM for 50Hz to 100Hz and good torque performance from 100RPM to 342RPM.

Hello Paul, The two wires will be for a 'Klixon' type of over-temperature switch. These are usually required for speed control at full torque, as the cooling fan is only shaft mounted. The alternative would be to de-rate the motor (for torque) for low speed. Not a bother for you, as you will only run it at full speed.

Simon, It sounds as if you have lost the brake switch in the Inverter Drive. There should be a figure in the product manual for the minimum resistance for the external braking resistor. If a resistor is fitted lower than this value, the braking Current will be too high and the brake switch (brake chopper) will be damaged and left open circuit.

A Bosch drive at this rating from our web site calls for a braking resistor between 65 and 70 Ohms. This means 65 Ohms is the value where maximum Current passes through the switch for its rating and 70 Ohms is the point were maximum braking is still available.

The 6R8 resistor is only 6.8 Ohms and may well have taken your brake switch out.

The DC bus runs at around 300V, the brake chopper threshold will be around 350V to 380V and the overvolttage trip 400V or more? Not sure if the actual figures for an Altivar.

We keep large numbers of brake resistors and we are happy to supply one to you, but it will not provide you with any braking, if the brake switch is open circuit.

Simon, The 29Hz cheat works well and we (The Inverter Drive Supermarket) have supplied many Inverter Drives for home use machine tools and vehicle lifts. By not expensive, I mean a 2HP Inverter Drive will usually control a 3HP motor to 2/3 speed as at the 400V Amps, the motor is working to 2/3 Power output.

The RCD should trip, if there is a fault down stream of the electronics. Inside the small Inveters AC mains is fed through a rectifier to the DC link. DC is chopped up usually at 3kHz or 4kHz by the power transistors and pulse width modulated to reform AC at variable frequency and variable Voltage. If there is an earth fault, there is always a path to earth from the Main supply.

What was the value of the brake resistor vs the minimum resistance for the Inverter Drive. It must have been too high a resistance, if the braking was less than motoring torque.

DC Injection braking is ok for low intertia loads to be infrequently stopped, as the braking energy is dumped into the rotor of the motor. Better braking is with a DBR correctly sized, as it is under control of the deceleration ramp in the Inverter Drive. We have supplied fully regenerative Inverter Drives for Lathes, but they were large and must have been stopping very frequently to make the cost of a 'regen' Inverter Drive worth while.

Simon, there is no reason why a two speed 400V motor should not be used with an Inverter drive. Many of our Customers do this. This if you can accept the motor run to 2/3 of its normal speed at full torque, then reducing in torque progressively to its 50Hz speed and beyond. A 400V Inverter drive will follow the same VxF curve and therefore perform in exactly the same way as far as 29Hz x 230V on its way to 400V x 50Hz. You will only need to rate the 230V Inverter drive to match or exceed the 400V motor full load Current and not the kW.

I have seen the two speeds switched over while the Inverter Drive was running without a trip occurring, but it is impossible to say if this is ok for all applications. Switching while running is not recommended.

DC braking is untidy. Best to use an Inverter drive that has a brake switch built in and fit an external braking resistor. The is much more control, better braking and less stress on the motor.

The RCD problem is not clear. When an Inverter Drive trips an RCD, it is usually on power up and not in steady state conditions. This means the EMC caps are not charged and the instant of switch on could be at any point in the Supply Voltage waveform.

Single speed motors and Inverter Drives are not always expensive when purchased over the Internet.

John, thanks for the explanation. As The Inverterdrive Supermarket we supply large numbers of Inverter Drives, mostly to Industry, but a great many go to home users. When we get the chance, we advise Customers to use the types we know have low leakage or a means of removing the filter. One make I can think of has high leakage for its domestic level built in filters at 70mA (Manufacturers own figure). Many of the other makes are between 10mA and 20mA for their built in Industrial and one at leat for their domestic level. ABB, Bosch, Invertek, Schneider, Teco and Siemens all have links or screws to remove the filters.

Generally if the motor cable is screened 'SY' cable, is less than 10m or so, is correctly installed and permantantly connected to earth without loops and with a good cross section of cable, the leakage is minimised whatever level of filter is resident in the Inverter Drive. This is always necessary to comply with the Manufacturers installation instructions.

Screening with 'SY' cable is the right way to go, as described above. If this is a 230V inverter, take care if you fit an EMC filter and have an RCD protected supply. The Filters have capacitors connected to earth and the small amount of current passing through them may trip your RCD.

You can always use your 230V 1ph to 230V 3ph on either winding of the 415V 3ph motor, with the 'base frequency', set down to 29Hz. This as long as the Inverter Drive Current rating matches or exceeds the motor full load Current.

This works well in speed control as far as the 29Hz speed, then the motor torque is reduced towards its 50Hz speed. This is because a 400V Inverter Drive follows the same Volts x Hz curve as far as 29Hz, on its way to 50Hz - so has the same performance as far as 29Hz.

This is a low cost solution, if you only need the 0RPM to 29Hz speeds at full torque.