How to use DC Power Supply and remote sensing correctly and safely

Matsusada Precision is a manufacturer of general power supply equipment.
Here we will describe the correct operation in order to use your DC power supply safely for many years.

Installation

Proper installation is important in order to use your DC power supply for a long time.

Installation conditions

  • 1. Use the power supply on a horizontal surface.
  • 2. Avoid using the power supply in locations that are subject to dust and corrosive gas.
  • 3. Do not install the power supply in a sealed cabinet or similar enclosure, or provide ventilation to ensure that exhaust heat from the air intake/exhaust openings does not return. (Refer to the instructions in the catalog or the instruction manual for your power supply.)
  • 4. Do not install the power supply in locations that are subject to condensation.

Installation method

When installing a rackmount power supply in a rack, avoid securing the unit only on the front.
Be sure to also support it from the bottom with an L-angled support or similar item.

  • Bad:Securing the unit only on the front
    This image shows how to support the power supply only on the front.
  • Good:Support it from the bottom
    rear view: an L-angled support or similar item

Service life

The service life of a power supply drops by half each time the ambient temperature increases by 10 °C.
(The standard service life of a power supply is based roughly on a temperature of 20 °C.)

STOP! Uses that shorten the service life

In narrow or sealed locations, heat will become trapped, leading to high temperatures that will shorten the service life of the power supply.
Blocking the air intake and exhaust areas will cause the internal temperature of the power supply to rise and shorten the service life.

Ensure a space of at least 10 cm from the exhaust opening and at least 30 cm from the air intake opening to allow heat to be released.

In narrow or sealed locations, heat will become trapped, leading to high temperatures that will shorten the service life of the power supply.

If a power supply is installed in a location that is subject to a large amount of dust or near the floor, dust will be drawn into and collect inside the unit, causing a drop in performance and a shortening of the service life.This image shows a power supply is installed in a location near the floor.

Dust collected inside a power supply
This image shows dust collected inside a power supply.

Connecting a Load

In order to draw out the full performance of a DC power supply, it is important to make correct connections and ground the unit.

Use short wires of sufficient gauge.

Use PVC cable (105 °C) that can sufficiently withstand the working voltage.

When wiring a connection to a load, it is necessary to consider the current capacity of the wire and the limitation of the length of the output wire due to sensing (0.5 V/lead). Refer to the following table to determine the gauge of the wire.

AWG mm3 Max. current (A)
18 1.1 2
16 1.3 7
14 2.1 11
12 3.3 18
10 5.3 23
8 8.4 39
6 13 67
4 21 106
2 33 170
1 42 209
1/0 53 270
2/0 67 330
3/0 85 350

When connecting multiple loads in parallel, wire them individually such like following image.

  • wire1.png
  • wire2.png
    Supplied voltage to load 2 and load 3 is smaller than load 1.

For inductive loads, to protect the power supply from load kickback, insert a diode that is rated higher than the output voltage and the output current of the power supply.

This is a circuit diagram with a diode to protect the power supply.

How to Use Remote Sensing

Remote sensing is used to compensate if a voltage drop that cannot be ignored occurs in a connector or wiring.

Principles of remote sensing

This image explains contact resistance and wiring resistance.

Remote sensing is used to compensate if a voltage drop that cannot be ignored occurs in a connector or wiring.

V0' = V0 - (Contact resistance + Wiring resistance) x I

This image explains contact resistance and wiring resistance.

If remote sensing is provided at both ends of the load to compensate for a voltage drop, the power supply outputs will be the set values at both ends of the load like this image.

Please pay attention to the following points when using remote sensing.

  • The sensing wire has high impedance. Use a twisted pair or shielded wire so that it is not affected by other circuits and wiring.
  • In some cases, stable operation can be achieved by placing an electrolytic capacitor at the sense point. Regarding capacity, use an electrolytic capacitor with a withstand voltage not less than the rated output voltage at about 0.1 to several hundred μF.

Connecting Multiple Power Supplies

Series operation

  • When connecting multiple power supplies in series, be sure to check the instruction manual for the maximum output voltage.
  • When using master-slave control, refer to the instruction manual for detailed procedures.

good series peration

Connect the power supplies as shown in the figure on the left.
For D1 and D2, choose diodes with sufficient reverse voltage withstand and forward current withstand for the rated output of the power supply.

good series peration

This kind of connection is also possible.
When using remote control for the power supplies, note that the control potential will change.

bad series peration

If connections are made as shown in the figure on the left, the current of one power supply will flow into the other due to the difference in rising speed.
This could cause a constant current operation, preventing the power supplies from starting up.

Parallel operation

When connecting multiple power supplies in parallel, there is always a difference in the output voltage of the power supplies, so it is necessary to balance the current.
* When using master-slave control, refer to the instruction manual for detailed procedures.

good parallel peration

Connect the power supplies as shown in the figure on the left.
The forward voltage and current characteristics of the diodes are used to achieve balance. Consider the withstand voltage, current, loss power, and heat dissipation when choosing diodes.

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