Quieting An Inexpensive Bench Power Supply

[Mike] just purchased this Atten APS3005S bench power supply for around $80. It does the job, but boy is it noisy! We were pretty surprised to hear it fire up in the video after the break. To make matters worse, the noise is persistent since the fan never shuts off. Having worked with other bench supplies he knew that a common feature included in many models is temperature controlled case fans. He set out to quiet the fan and implement a temperature switch.

For this project [Mike] had the benefit of looking at a nearly identical model that does have temperature switching. He discovered that the board on this one has a through-hole zero ohm resistor populated in place of a thermostat switch. That switch closes the connection at or above 45 degree Celsius, thereby turning on the cooling fan. Bridging the traces with a zero ohm resistor to save on production costs is what caused the fan to run continuously. After replacing the resistor with a KSD-01F and swapping out the stock fan for a high-quality version [Mike] has takes a noise maker and turned it into a device that’s kind to the ears.


27 thoughts on “Quieting An Inexpensive Bench Power Supply

  1. Great hack!

    I’ve been looking at older linear power supplies lately… And this kind of thing tips my preference in their favor vs. newer designs that tend to over-economize. And noise. Noise is bad.

  2. I’ve never seen/heard of a through-hole zero Ohm resistor before…

    I’ve used SMT zero Ohms for configuration (I2C address, for example) on boards as it allows you to use a reel of zero ohms and a pick/place machine in production.

    are pick/place machines used for thru hole also? i have never seen this before. perhaps i am too young.

    might as well just use a jumper wire if hand soldering…

    1. Yes, machines are also used for thru-hole components. This includes placing components, soldering and then “cut / clinching” the excess leads.

      A link (0-ohm resistor) is very common. Also the colour code is very easy to remember!

  3. This was a good video…one problem, as an unspoken rule; when disassembling anything, for hacking, on video, record the first screw being removed, then skip to the last screw, also being removed. To show all screws being removed, in fast forward, to boot, is no different then not speeding up the whole screw removal process. It’s akin to “take your time, hurry up. Testing each mod went faster.

  4. Thanks for sharing. I like your power supply.

    Three points:

    1. The marks on the back side of the heat sink were made by the CNC punch press that made the panel. See how they’re all parallel at 90 and 45 degrees? That’s the positioning frame rapiding from place to place and dragging the panel over something scratchy.

    2. Put your iron in the holder dirty. Clean it when you pick it up to use it. Your tip will last longer AND you’ll get cleaner solder joints faster.

    3. I didn’t see you put thermal joint compound on the back of your new thermostat and bolt it to the heat sink, although there is a hole right there for it. Then you would be measuring the heat sink instead of the air next to the heat sink.

    3a. Check the data sheet to make sure that the mounting tab is not connected to either of the two pins. If it is, use a TO-220 transistor insulating mounting kit, which costs maybe a dollar.

    1. I glad everyone liked the modification. Since this was my first how-to video, I did not capture everything on video (my camera battery died and I didn’t notice it until too late). If you notice in the video when I’m placing the part, I take a moment to look and verify the bolt hole is lined up on the heat sink. I left it slightly off of the heat sink initially so I could verify the tab was isolated (right before I mounted the new fan in the supply… you’ll see the power cord magically appear connected). I used thermal compound and bolted it using an M3 bolt. I have other plans for this supply so stay tuned for future enhancements!

      1. Hi Mike,

        We have send the video to the factory. ( they can not view you-tube). They liked the video ;-) But like I told before we send the complaints of the noise to them last year and the have confirmed that the new production will have the temp sensor installed standard from this year on.


        1. This message from Atten.Eu was posted in 2012, but the new Atten PPS3005S I received yesterday 08/2014 has a noisy fan that runs all the time.
          My only question is about the NC (normally closed) KSD01FD45. Does the normally closed part act just like the wire jumper it replaced, and keep the fan running until the temperature reaches 45c? What am I not getting about this mod?

          We all have at least one bad habit, so others should lighten up on this video. We are all free to work as we wish, it was not watching his work habits I hoped to get something from, it was the analysis of the supply, and suggested fix that interested me most.

          My supply came with a DB9 serial port, and I converted it to USB
          I noticed that my Fluke 87 said that when the supply was set to 5.0, it was really 5.2. It was poor quality control to let the supply leave the factory without a burn-in, to make any fine adjustments it needed.

    2. 2. Put your iron in the holder dirty. Clean it when you pick it up to use it. Your tip will last longer AND you’ll get cleaner solder joints faster.

      This makes a lot of damn sense. Thank you for teaching me something I hadn’t realized before.

  5. What I didn’t see was the new fan being tested! He replaced the zero ohm with the thermistor first, and therfor the fan didn’t kick in at the end when he powered it on because it wasn’t hot enough.

  6. Hi.
    It is always best to screw the device (in this case the thermostat) down, using insulated mounting if required, BEFORE soldering to limit mechanical strain on the leads and joints.
    Good basic demo ‘tho. :)

  7. Hi Mike,

    We from ATTEN.EU did get a lot of feed back about the APS3005S / 3D series! They all liked it but if there was a complain it was always the noise. Some called it a vacuum cleaner. We have send these complaints to the factory. I do not think that this temp sensor and quiet fan is standard now it is optional. We are ordering only low noise unit now.

    The PPS3005 series did come standard with a quiet fan the 3D version has fan control.


  8. There’s a very easy solution for this, at least if you use bench power supplies like most people do (that is, mostly for low-power electronics and only occasionally for more power-hungry applications): put a switch on the fan. If it’s only having to generate low voltage and current, the power supply doesn’t actually need much cooling. Of course do remember to power the fan back on if you need those five amps.

    Or you can always replace the fan. I have two bench power supplies with the same specs (0-30V 5A); one is whisper-quiet and needed no modifications, the other one is annoyingly noisy and I usually keep its fan off.

  9. I have a nearly identical power supply at 30V 5A, but I got lucky and it came with a lower RPM fan, so it seems like the easiest fix would be to replace the fan with a lower decibel unit. I wonder if a variable temperature resistor might be able to be used to vary the current through the fan, maybe without even a transistor current amplifier or an op-amp, if I put the temp resistor on the main heatsink to dissipate the heat generated from the current draw of the fan.

    Also, I have modded my power supply with different colored LED displays, and I ordered extras if anyone is interested. I have blue, green, and purple in the standard 3 digit 12/11 pin package…

    I should also add the fact that I have used switching programmable regulated power supplies before, and, while they are much more flexible in their operation, they will still show switching noise on the output greater than the level you would see from a linear supply. I understand that filter caps can take care of most of the noise, but I thought I should mention the difference in the power supplies, straight from the output terminals…

    1. Really??? You do know that 120 Volts through the resistance of the body is not lethal, right? Unless you have a specific heart condition, any normal person can literally HOLD a 120 Volt AC source in their hand and never suffer any effects other than the small spasms in their arms. I’m sure most of the people here that have hacked anything have gotten shocked by 120 VAC and never had a problem. Of course, injuries can be caused by the reflex action of the muscle when energized, but most people that would try to work on a live circuit would know not to place your limbs in a place that reflex will harm you if you get shocked.

      As for the others that don’t know this, well, don’t mess with anything more than 48 Volts until you know what you are doing, IMHO….

      1. Without an isolation transformer you just don’t stick your fingers inside a device while it is still mains powered. End of story. If you start being sloppy at ‘just’ 110V, you will end up doing the same in different situations. And touching 110V is not the right way to find out that you do actually have an otherwise harmless heart condition. Darwin Award.

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