Martin Wyatt, business development manager, of Carlo Gavazzi
A faulty starting capacitor is often one of the most common causes of malfunction in single phase capacitor start/capacitor run (CSCR) motors. This type of motor is often used to drive equipment with a high starting torque such as scroll compressors used in refrigeration equipment and heat pumps. If a start-capacitor deteriorates, the value of the electrical charge stored can change, which can lead to problems with starting torque that could prevent the motor from starting, tripping the motor’s overloads. Similarly, if the start capacitor short-circuits this could result in motor winding to burn out.
Now, Carlo Gavazzi has launched a soft starter for single phase capacitor start/capacitor run (CSCR) motors which eliminates the need for a starting capacitor altogether. The (patent pending) High Dynamic Motor Starter (HDMS) features an innovative algorithm that ensures sufficient torque is generated to start a CSCR single phase motor. By eliminating the start capacitor, Carlo Gavazzi expects the HDMS to help manufacturers extend the lifetime and reliability of equipment reliant on a single phase CSCR motors.
Traditionally, CSCR motors have incorporated two capacitors:
• The start capacitor is used to increase the phase angle between the start and run windings of the motor. This helps create greater torque at start up and enables the motor to be cycled on and off rapidly. The start capacitor stays in the circuit long enough to rapidly bring the motor up to a predetermined speed, which is usually about 75% of the full speed, and is then taken out of the circuit.
• After this, the motor will work more efficiently with a run capacitor. The run capacitor will bring the motor’s start winding back in phase with its run winding to provide the running torque once the motor is up and running. Run capacitors are designed for continuous duty while the motor is powered.
Now the algorithm used in Carlo Gavazzi’s HDMS electronic soft starter eliminates the need for a CSCR motor to have a start capacitor. The HDMS has a maximum ramp-up time of one second, making it particularly suitable for starting scroll compressor motors which, generally, must start within 800 milliseconds to avoid excessive wear and tear on the orbiting scroll. In addition, the HDMS’s algorithm will enable the motor to be started with less than 1.5 times the compressor’s rated current.
A major advantage of the HDMS, when compared to direct on line (DOL) starters, is that the soft-starter can reduce start-up current by up to 75%, which can also help improve reliability by reducing alarms in applications with a weak power supply. And, in some instances, a lower start-up current might even help reduce utility tariff costs.
The HDMS has been designed to ensure optimum motor performance. It features Carlo Gavazzi’s third generation self-learning algorithms, which means the unit is able to continually improve motor starts without the need for user input. The unit is shipped from Carlo Gavazzi with default current limit settings, equivalent to 1.5 to 1.8 times the rated HDMS current. For every motor start, the HDMS takes a number of measurements so that over time it will adjust the internal parameters to reduce the starting current during the subsequent motor start. And because the self-learning routine is active at every start the unit will ensure an optimal start even when load conditions change and when the motor ages.
A unique function of the HDMS is the high pressure function, which is designed to detect a locked rotor condition during start. Should this occur, the HDMS will increase the current limit to a maximum of 1.5 to 1.8 times the nominal current of the HDMS to try to start the motor within one second. If this is unsuccessful, the HDMS will activate the ‘end ramp-up’ alarm to protect the bypass relay from switching in a high running load current. To reduce machine downtime and the need for user intervention in case of recoverable alarms, when the alarms condition is cleared the HDMS will follow an automatic recovery routine to re-start the motor.
In use, the HDMS’s Modbus RTU RS485 interface offers the option for remote monitoring and quicker fault-finding while also allowing connection to a PC for realtime monitoring of energy and operating variables.
Furthermore, the unit’s NFC feature enables stored data to be downloaded to any Android smartphone and tablet when the HDMS is in off-state to allow data to be downloaded and shared. The history file contains data on the first eight starts, last 24 starts and up to 143 alarm events to facilitate troubleshooting. All data can be downloaded in .csv format to make it easy to share using a mobile phone.
Machine downtime is further reduced through the use of conformal coatings – a thin polymeric film - applied to the printed circuit board (PCB). This helps protect the PCB’s components from the environment and corrosion.
Other features of the HDMS that will be of benefit to equipment manufacturers include: an operating voltage range of 110V to 230V AC, and a frequency range of 50/60Hz; while its tool-free design makes fitting the starter quick and easy.