In this guide
When a drive fails, the temptation is to match the kilowatt rating and order. Most mistakes come from the other seven things below. Spending ten minutes on them avoids a second trip.
1. Start with the motor, not the old drive
Take the nameplate of the motor: power, voltage, full-load current, speed and frequency. The drive must supply at least the motor's full-load current. The old drive's rating is a useful hint but it may have been oversized or undersized.
2. Supply voltage and phases
Most industrial drives take a three-phase 400 V supply. Smaller drives are also made for single-phase input, which is common in light-duty and rural installations. Confirm what is actually at the panel.
3. Constant or variable torque
Many drives are given two ratings. The normal duty rating suits fans and pumps, whose load falls with speed. The heavy duty rating suits conveyors, crushers, mixers and hoists that need full torque at all speeds. A drive listed as 15 kW in normal duty may be an 11 kW drive in heavy duty. Choose by the load, not the headline kilowatts.
4. Control interface
List how the drive is started, stopped and given a speed reference today:
- Digital inputs for start, stop and direction
- An analogue reference, 0 to 10 V or 4 to 20 mA
- A fieldbus such as Modbus, PROFIBUS, PROFINET or EtherNet/IP
A like-for-like replacement keeps this wiring. A different brand may need an option card or a small change in the program.
5. Environment
Heat, dust and altitude all reduce what a drive can deliver. Many drives need derating above 1000 m, and many manufacturers specify roughly one per cent per 100 m, though the figure varies by product. Johannesburg sits at about 1750 m, so this applies to much of Gauteng and the Highveld. Check the datasheet curve for your drive and ambient temperature. Our IP rating decoder explains enclosure protection.
6. Braking
If the motor drives a high-inertia load such as a fan or flywheel and needs to stop quickly, the drive may trip on overvoltage. A braking resistor, a longer deceleration ramp or a regenerative drive deals with this. Say so when you ask for a quote.
7. Filters, reactors and cable length
Long motor cables can need an output reactor or filter. Sensitive neighbouring equipment may need an EMC filter. Note the motor cable length and any existing filters.
8. Parameters and commissioning
A new drive needs its parameters set. If the old drive still powers up, record or photograph its settings before removing it. If it does not, the motor nameplate and the machine's operating limits are the starting point. An engineer can help you commission the replacement.
What to send us
- Photos of the motor nameplate and the old drive's label
- The supply voltage, and the cable length to the motor if it is long
- The application and whether it is constant or variable torque
- How the drive is controlled, with a photo of the control terminals