Checkpoint in case of switching power supply failure



Switching power supply does not output! People who don’t know what to do.

「It worked fine until now, but suddenly the power went down. The power supply stopped after about half a year.
I changed the power supply, but there is no output.
Please tell me where to check the power supply. 」


I will answer these questions.

Is the “new power supply” not output, or is the power supply that was working until now “suddenly broken down”?

There is a possibility that the power will be turned off or it will get wet in the rain during transportation, but …
It is highly unlikely that a new power supply will not output.
Most of the time it is used incorrectly.

On the other hand, if the power supply you have been using does not output, it is important how many years you have been using that power supply.
This also rarely stops “suddenly” while the power is running, and often does not output even if the power is turned on in the morning or even if you try to move it after a lunch break.

Although it depends on the ambient temperature, the life of the electrolytic capacitor is high if it has passed 4 to 5 years or more.
If it is still less than 2 years after use, the life of the electric controller is short, so the ambient temperature of the power supply may be extremely high or other factors may be considered.

Below is a summary of what to check for each symptom.


When not outputting

If it does not output, try replacing it with a power supply with the same output voltage (capacity is higher).
If it outputs, there is a problem with the power supply, and if it does not output, there is a problem with the input side.

Wrong input voltage

You may accidentally input 200V AC to a power supply dedicated to 100V AC input. In this case, the input circuit parts are destroyed, so even if AC100V is input, it will not be output. Even if it is output, the parts are damaged, so be sure to send it for repair. Many AC100V dedicated machines are board type, so it may be better to buy a new one rather than repairing it.

On the contrary, even if AC100V is input to the AC200V dedicated machine, there is no problem as it does not output. In addition, although the number has decreased recently, there is a type of power supply that manually switches the input between AC100V and AC200V, such as a connector.

Recently, most wide inputs are continuous inputs (AC85 to 265V), but in the past, wide inputs were generally discontinuous inputs such as AC85 to 132V and AC185 to 265V. The non-continuous input does not output even if the voltage between them is input.

It is OK if you input in the correct input voltage range.

After that, check if the load line is correctly connected to the output terminals (+ V, -V) of the power supply. It may be loose or accidentally connected to a different terminal.

Overvoltage protection function is working

The symptom is that the output display LED turns on for a moment and then turns off immediately.

It is common to turn the output voltage variable volume when the power supply stops, causing the output voltage to exceed the operating voltage of overvoltage protection. For example, when the operating point of the overvoltage protection of the 24V output power supply is 27V, the output voltage is set to 28V. As soon as the power is output, the overvoltage protection is activated and the output is stopped.

To restore the power, turn the input off (reset) and then turn it on again …
If you input as it is, overvoltage protection will be applied again, so turn the variable output voltage volume counterclockwise to lower the output voltage before inputting.
On the other hand, if the output voltage volume is returned too much, the output voltage will drop and the LED will not light.

Maybe you’re touching the volume of overvoltage protection?
Depending on the power supply, the voltage at which the overvoltage protection operates can be changed, and the voltage may be lowered to the voltage at which the overvoltage protection function operates.
In that case, turn the overvoltage protection volume clockwise all the way to free it.
Then adjust the output voltage with the variable output voltage volume.
After that, the voltage is lowered to the voltage at which the overvoltage protection works.

If that doesn’t work …
Return it to the manufacturer for adjustment. It doesn’t take many days.

Remote sensing is open



The symptom is that the output display LED turns on for a moment and then turns off immediately.

If the short piece of the remote sensing terminal is removed or loosened (open state), the output voltage rises and overvoltage protection operates and the output stops.

I will explain remote sensing.

The remote sensing function is a function that corrects the voltage drop from the power output terminal to the load.
At the time of shipment, the + S terminal and + terminal, and the -S terminal and-terminal are connected with a short piece (pictured above).
To use this function, remove the short piece and connect the + S terminal to the + terminal on the load side and the -S terminal to the-terminal on the load side. By doing so, the voltage on the load terminal side will be fed back.
When this sensing terminal is removed, the OV signal of the load terminal is fed back to the power supply, the voltage continues to rise from the power supply, overvoltage protection operates, and the output stops.

If you are using the short piece check and sensing function, make sure that + S and −S are firmly connected to the + and − of the load device.

* Some power supplies do not have a remote sensing function, and there are no + S and -S terminals.

Over current protection function is working

The symptom is that the voltage display LED turns on and off (output voltage fluctuates).

The cause is that the load is too large for the power supply capacity (W) or the load is short-circuited.
The power supply has overcurrent protection, and the output voltage drops when a current exceeding the rated current flows.
When the overcurrent condition is resolved, the voltage automatically returns to the rated voltage. However, the power supply of 300W or more will shut down when the overcurrent protection works for about 30 seconds, so turn off the input and then turn it on again after a while.

Check if the power supply capacity is sufficient (current value) to operate the load device.
What you have to be careful about is the case of motor load. Since a peak current that is several times the rated current flows when the motor is started, the output voltage drops due to overcurrent protection of the power supply. Since the voltage applied to the motor drops, torque is not generated and the motor does not operate.
In terms of a car, it’s like starting in 5th gear. Select the power supply based on the peak current value at startup, not the current value when the motor is stable.


Remote control is shorted

If you short-circuit between the power supply + R and -R that have a remote control function or keep applying a voltage of 0.5V or less, the output will remain OFF.

The remote control is a function that turns the output ON / OFF by the control signal while inputting. External voltage is applied to the connector (+ R, -R or RC, RCG, etc.) on the board to control it. Another power supply is required separately.
The voltage to be applied differs depending on the model, but for example, when 4.5V or more is applied, the output turns ON, and when 0.5V or less is applied, the output turns OFF.

* A power supply without a remote control function is irrelevant.

Life of electrolytic capacitors

The output of the power supply does not stop just by the life of the electrolytic capacitor.
The life of the electrolytic capacitor is defined as the time when the capacitance at the time of shipment decreases by 20%, but the output of the power supply does not stop even if the ripple voltage increases slightly.
If you continue to use the power supply after that, peripheral parts will fail (secondary failure) and the output will eventually stop.
It is necessary to measure the capacitance and tan δ of the electrolytic capacitor to determine whether it is the life of the electrolytic capacitor.

However, it is possible to give an indication of whether or not the life of the electrolytic capacitor has expired.
If the power supply manufacturer’s HP has “Expected life data of electrolytic capacitors”, please apply the ambient temperature and load factor of the actual power supply. If the period of power outage is clearly shorter than the applicable lifespan, the actual ambient temperature may be higher than expected.
The ambient temperature of the power supply is not the room temperature or the ambient temperature of the control panel or equipment, but the ambient temperature of the power supply.

Generally, if the power supply is used within 2 years, the usage conditions are strict and the ambient temperature is often high.
Failure within one year will have a short life if the power supply is used in a sealed state or the board is turned up.


Fan life

The life of the fan is when the fan’s ventilation capacity (rotation speed) falls below a certain level to 70%.
Just because the fan has reached the end of its life does not mean that the power supply will stop immediately, but the temperature inside the power supply will rise slightly.
However, if you continue to use it as it is, the rotation speed of the fan will drop and heat will be trapped inside the source, and the electrolyte of the electrolytic capacitor will come out and reach the end of its life. Depending on the model, an alarm will be issued when the fan speed decreases, or the output will stop due to thermostat protection inside the power supply.

Unlike electrolytic capacitors, fans do not have a calculation formula, but because they have mechanical elements, the time when the residual rate reaches 90% is shown in the table as the life of the fan. Generally, the actual life of a fan is 4 to 5 years, but if there is a lot of dust around it, the grease will deteriorate faster and the life will be shorter.

* A power supply without a fan does not matter.