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GW Instek GPS 1850D Power Supply Clicking

char-123

I have a laboratory DC linear power supply model GPS-1850D. I have set this up in slave mode and connected my computer to control it. My computer has an output voltage range of 0 to 5 volts. I am currently trying to use a PID loop to take in a temperature reading (of peltier heater) through thermocouples, input that data into my computer, compare that temperature with my previous set point, and then output a voltage signal to control the power supply to get my Peltier heater to the desired temperature. 

I have the power supply in constant voltage mode, with the current limit around 4 volts. 

Whenever I try increase the PID setpoint by a few degrees Celsius, and the PID output voltage shoots up, the power supply will start clicking when it gets to around 4.3 volts. Why is it clicking and is it still okay to use?

Even when I increase the PID slightly, so that it the power supply would have to output 4.5 volts to keep the Peltier constant, the power supply starts clicking. It stops clicking when the voltage comes down, out of the 4.3 to 5 Volt range. 

Can anyone help me?

Also, I checked the current when the clicking is happening and it is at less than 1 amp, so I am not if the current limit is the problem or not. 

  • 0

    It might be normal; many power supplies have internal relays that will click when the requested output voltage is changed beyond a certain range. You can test that by manually adjusting the power supply (i.e. not using your computer) and you will probably still hear the click at that voltage level. If it clicks constantly only with software control, it may be a (lack of) hysteresis issue in your code.

  • 0

    As shabaz says, normal behavior for a multitap power supply. 

  • 0 in reply to shabaz

    When I manually adjust the power supply, not using my computer (power supply in master mode), the power supply clicks once as I go from below ~4.3 volts to above ~4.3 volts. However, when I do this in my computer controlled mode, it is a constant clicking anywhere in the 4.3 to 5 volt range, until the voltage comes back down from that range.

  • 0 in reply to char-123

    Probably because your control code is driving the power supply up and down by an amount all the time (oscillating). Add some logging to your code so you can see what it is sending to the power supply.

    Digital PID loops can easily do bad things due to quantisation errors and delays.

    With a power supply of this type in the loop you may need to drop the loop rate to below 1 iteration per second.

    You would do well to look at the output of the psu with a scope to see how fast it responds to commands.

    If you are using as serial port to control the PSU it will be easy to 'scope the TX from the PC to get the command timing - if you are using USB or LAN to control it then getting good command timing information is very difficult.

    MK

  • 0

    Sounds quite normal like Shabaz as mentioned. Linear power supplies will have multiple taps on the secondary of the transformer. This is to reduce the dropout voltage on the regulator stage. Say a 30Volt max DC powersupply to output 5 volts it has to drop a lot of voltage across the linear regulator ( as heat ) which is very ineficient. So Lab power supplies uses multiple outputs from transformer, rectify it and feed it to the regulator. This switching is controlled using relays. 

    You mentioned that you are using a PID controller. PID controller will adjust the output voltage based on the feedback loop. Thats probably why you are getting multiple clicks ( It's constantly adjusting the voltage up and down based on the feedback loop). What is the update rate for PID controller? If you drop the PID update rate you can observe less clicking, probably.