There has always been a need for variable speed motors; dc motors were the first cheap, simple variable speed motors. They superseded NS motors, Schrage motors and eddy current drives with variator gearboxes trying to inefficiently compete mechanically.
The dc motor offered a compact, relatively efficient reliable motor with good speed control and excellent starting torque. The trouble is they are expensive to buy, they are non-standard and expensive to maintain. They have commutators that need skimming, brushes that need buying and changing, the carbon from the brushes can get into the windings which then need cleaning out. They also have no idea at what speed they are running so need a flimsy tacho speed measurer and the feedback to control the speed closed loop circuit. I’ve tried many times to get dc manufacturer’s motor efficiency data but the best I’ve ever had was verbally “I’d like to think about 85% efficient”. There wasn’t the regulation and testing in those days….
AC to DC Motor and Drive Conversions – Present Day
We now have super high efficiency squirrel cage motors (IE3 up to around 96%) with all standard frame sizes are readily available. Additionally an ABB inverter makes these motors variable speed with all of the dc motor performance but without the drawbacks. ABB’s unique ‘DTC’ inverters give perfect open loop speed control for all but ‘safety’ type applications (+/- 6rpm for a 1500rpm motor). Given the inverter’s efficiency of 98%, there is a 15% – 20% increase in energy efficiency moving from an old dc motor and drive to new ac technology.
ABB ac Drives Versus dc Drives
In summary, these are the advantages of ABB ac motors and drives versus old dc drives and motors:
- Improved energy efficiency typically 15% – 20%
- Off the shelf inverter and motor
- Lower capital cost
- Reduced maintenance – no more brush replacements, commutator skims
- Improved reliability – no tacho to fail, no carbon in the windings
- Greater motor speed range
What IDS Can Do For You
IDS are both inverter and motor partners for ABB. We are happy to carry out a survey of your old dc motors and specify new ac equivalents. We will ensure that the torque / speed curve of any new ac system is suitable for your application and recommend any special cooling requirements needed.
We can then supply the new motor and inverter, carry out all the electrical and mechanical installation work and commission at a time that suits your production schedule.
ABB have just released their IE4 SynRM motor