What are the options for tying multiple product outputs together in parallel or series?

• Knowledge Base ID: 1008
• Category: Configuration

Multiple Magna-Power products may be tied together in parallel or series, providing flexible expansion. There are two different methods for parallel or series operating: direct mode, where the DC outputs are connected together, but the system does not provide active load sharing between units, and master-slave mode, where an interconnecting communication cable enables active load sharing and master control over the start-stop functionality.

Parallel or Series Direct Mode

The power supply outputs can be directly connected together in parallel or series. No external blocking diodes are necessary in this direct arrangement. The primary disadvantage of parallel series direct mode is each unit need to be programmed independently and the units will not share the load equally.

The simplest parallel connection involves attaching the positive terminals of all supplies to be paralleled to the positive point of the load and attaching the negative terminals to the negative point of the load. The output current controls of each power supply can be separately set. The output voltage control of one power supply (master) should be set to the desired output voltage; the other power supply (slave) should be set for a slightly higher output voltage. The master will act as a constant voltage source; the slave will act as a constant current source, dropping its output voltage to equal that of the master.

The simplest series connection involves attaching the positive terminal of the first supply to the negative terminal of the second supply. The load is connected between the negative terminal of the first supply and the positive terminal of the second supply. The output current controls of each power supply are operative and the current limit is equal to the lowest control setting. If any one output current control is set too low with respect to the total output current, the series power supplies will automatically crossover to constant current operation and the output voltage will drop.

Parallel or Series Master-Slave Mode

In parallel master-slave mode, the interconnected units will share the load current nearly equally while providing the same output voltage, with the master unit commanding slave unit's voltage-current settings along with start, stop and fault commands. In parallel master-slave, the output terminals must be connected at a common point, either at the load or the output terminals, but before any type of protection circuitry such as contactor or blocking diodes. In series master-slave mode, the interconnected units will share the voltage nearly equally while providing the same output current. The master unit will command the slave unit's voltage-current settings along with start, stop and fault commands. Figure 1 illustrates the terminal connection for master-slave parallel operation, while Figure 2 illustrates the terminal connection for master-slave series operation. The control cable can be fabricated by the user or purchased as an option, UID47, from the factory. The slave power supply must be configured for EXT PGM input. The master unit can configured for ROTARY, EXT PGM, KEYPAD, or REMOTE input.

Magna-Power highly recommend paralleling identical units, as the power supplies will share current as a percentage of their full scale rating. If multiple identical units are paralleled, the total output current from the system is easily calculated as n*text(current output) where n is the number of units in the master-slave string and current output is the master unit's output current. In a system where units have mixed rating, this calculation of the total system current becomes more complicated. A simple example, consider a 20 kW TSA1000-20 (master) in master-slave parallel with a 10 kW TSA1000-10 (slave). If you are programming the master from the computer interface and you set it to 10 Adc, the master will go to 10 Adc (50% of full scale) and the slave will go to 5 Adc (50% of full scale), giving you a total of 15 Adc on the DC bus. If two 20 kW TSA1000-20 units are tied together in master-slave parallel, both units will provide nearly equal output current, providing more convenient feedback.

Figure 1. Interconnection of 37-pin JS1 connectors for master-slave parallel operation

Figure 2. Interconnection of 37-pin JS1 connectors for master-slave series operation