Switching Power Supply Service Manual
Even the most efficient switching power supply will not function properly if the installation, wiring or connection is not correct. Follow the installation, wiring, and connection instructions specified by the manufacturer before using switching power supplies.
3.1 Installation
3.1.1 Heat Dissipation
a. Make sure the unit is properly ventilated.
b. Install the power supply in the correct position.
c. Make sure the unit has proper heat conduction.
d. When you install two or more power supplies, leave enough space for cooling.
e. Forcing air over the unit will improve heat dissipation.
3.1.2 Output Derating
Output power depends on operating temperature. Derate the output of the switching power supply according to the derating table shown on specification.
3.1.3 Securing Screws
3.2 Wiring and Connections
3.2.1 Input and output wiring
a. Separate the input and output wires from each other, so the external surge voltage of the input line does not cross over to the output side. This will insure that the noise terminal voltage will not increase.
b. Use short, thick wires for the output line. Wire thickness will also depend on the current capacity.
c. When connecting wires to the switching power supply, use the appropriate terminal screws, solderless terminals and tools.
3.2.2 Grounding
Connect the grounding terminal of tile switching power supply to the frame of the equipment with a short, thick wire ensure safety and prevent noise.
3.2.3 Remote Control and Remote Sensor
a. Remote Control of the Output The output of some power supplies can be controlled by supplying an appropriate TTL signal to the +RC & -RC terminals. A low TTL signal (0 volts) will turn the power supply output on. A high signal (³1volt) will turn the output off.
Remote control of the output can also be accomplished without the TTL signal. There is a 1 volt difference across the +RC & -RC terminals. If these terminals are shorted, the power supply output will be turned on. If the terminals are left open, the output will remain off. Power supplies are shipped with a jumper across the +RC & -RC terminals.
b. Remote Sensor Power Supplies equipped with a Remote Sensor capability can detect voltage drop at the load. This feature is especially useful when the power supply and the load are separated by a long line. Power supplies with the Remote Sensor have +S & -S terminals (as shown in Fig. 10). When the +S & -S terminals are connected to the load side of the output, the power supply will be able to detect voltage drop at the load. The power supply will raise the output until the proper voltage is provided to the load.
3.2.4 Inrush Current Control
WENZHOU MINGWEI Power Supplies have a large capacitor in the input circuit. Consequently, there is a high inrush current when input power is applied (20 amps @ 110 volts; 40 amps @ 220 volts). When using several power supplies in a single system, do NOT apply power to all of them simultaneously. Note: ten power supplies would draw an inrush current of 200 amps @ 110 volts. A preferred power application would be a "delay power circuit." Another method of controlling the inrush current is to individually apply power to each unit.
3.2.5 Parallel Use
Power supplies are commonly used in parallel to increase output current. WENZHOU MINGWEI's PS Series is designed for parallel use. The PS Series has a "P" terminal circuit that is designed to sense other power supplies that are connected in parallel. This circuit controls output and allows a more efficient operation of each parallel supply. Each power supply that is hooked up in parallel should have their "P" terminals connected together as described in Fig.12.
Power supplies should not be used at full output when they are connected in parallel. Small output voltage differences and power dissipation from added protection circuits can overload individual power supplies. The following information is a recommended percentage factor for the reduced output of each power supply when they are used in parallel.
#Power Supplies Parallel Maximum % of Total Output
4 90%
6 85%
8 80%
Example: Four 12 volt, 10 amp power supplies are connected in parallel. The total output current is 40 amps.
The maximum current that should be used in this set up is (40 amps)x(0.9) = 36 amps.
Fig. 13 describes a method for connecting power supplies in parallel that do not have the "P" terminal circuit. The series diode used in Fig. 13 must have a higher voltage and current rating than the combined parallel power supplies. Design considerations are extremely important when using the sample circuit shown in Fig. 13. Adequate cooling is recommended for large capacity diodes.
3.2.6 Series Use
Power supplies are often connected in series to produce higher voltages. Two types of series connections are described below.
Some WENZHOU MINGWEI Power Supplies are designed for series use and have a built in reverse protection diode. Refer to individual data sheets..
a. Fig. 14 describes a sample set up for separate distinctive loads.
b. Fig. 15 illustrates a sample set up for power supplies not designed for series use and or power supplies that do not have a reverse protection diode.
3.2.7 Output Ripple and Noise Control
Fig. 16 is a diagram of a sample circuit that will control the output of ripple, noise, and Electromagnetic Interference (EMI) or Common Mode Noise. Below is the suggested order for the component set up of the circuit.
a. Connect C3 & C4 on the load side of the circuit.
b. Connect C1 & C2 to the output side of the power supply.
c. The final (and optional) piece of the circuit is for EMI. Connect L1, C5, & C6.
As stated above, Fig. 16 is a sample circuit. Design considerations are essential for specific applications.
Note: C1 & C3 control the output ripple. Their capacities should be between 47µf - 100µf. C2, C4 & C5, C6 control the output noise. Their capacities range from 0.01µf - 0.1µf. L1 inductance 0.5µH - 5µH.
3.2.8 Minimum Load Requirement
Multiple output power supplies are calibrated and fully regulated on Channel 1 (known as the master channel) of the unit. Channel 2 and higher are quasi regulated from Channel 1. If Channel 1 is not used, the output voltages of the other channels might be out of tolerance. Therefore, a minimum load on Channel 1 is recommended as a calibration factor.
Example: A WENZHOU MINGWEI D-120B (dual output) power supply was connected in a circuit. The specifications for this unit are as follows.
Channel Output Voltage Tolerance Output Rated Current Output Current Range
1 5V ±2% 6A 2A ~ 10A
2 24V ±7% 4A 0.4A ~ 4A
A 4 amp load was connected to Ch. 2. No load was connected to Ch. 1. The Ch. 2 output voltage was ~23 volts. A 2 amp load was then applied to the 5 volt output. The Ch. 2 voltage rose to -24 volts.
Another test was conducted with a 6 amp load on Ch. 1 and no load on Ch. 2. The Ch. 2 output voltage was ~26 volts. A 0.4 amp load was then connected to Ch. 2. The Ch.2 output voltage dropped back down to -24 volts.
3.2.9 Surge Voltage Control
Fig.17 outlines a sample circuit used to control voltage surges that may be caused by power fluctuations or stray fields due to lightning. Fig.17 shows varistors connected between AC/L - AC/N, AC/L - FG, and AC/N - FG. This type of circuit is recommended in areas where there is frequent power fluctuation.
3.2.10 Low Temperature Environments
WENZHOU MINGWEI Power Supplies use a thermistor that limits inrush current under cold start conditions. In a low temperature environment the thermistor resistance is high. The input current may become too low for the power supply to function. (This usually occurs under -10ºC). Use the procedure below when first applying the input power during cold climate conditions.
a. Apply the input power for 2 seconds Then turn the power off for 2 seconds. Repeat this procedure several times until the inside of the unit reaches a temperature that allows the power supply to operate.
b. Decrease the load on the output until the power supply is fully operational.
c. If the power supply is in an environment that is frequently cold, install a heat producing device in the power supply case (such as a large resistor, a lamp or a heating unit).
3.2.11 Charger Use
When the switching power supply is used as a battery charger, a series diode and a fuse (or circuit breaker) should be installed in the output line. These components will protect the unit if the battery voltage is higher than the output voltage of the power supply. These components will also protect the unit if a reversed polarity situation should occur.
All information is based on the WENZHOU MINGWEI Switching Power Supply User Manual - Version 1 and is provided in good faith, but without any warranty or guarantee as to fitness to purpose. It is solely left to the discretion of the user as to the suitability of the information for their application.