Viewing 8 posts - 1 through 8 (of 13 total)
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  • #9725
    piero55
    Participant

    I'm making the classic 0-30V 0-3A power supply that I bought online from China, in KIT. I used a CPU cooler that was a recovery of an old PC to dissipate the power transistor. E’ a highly finned block of aluminum with a copper block in the center, where I drilled a hole for a screw that fixes the D1047 transistor. I have noticed that while it is running it dissipates a lot of heat, the fan starts regularly and cools the fins but touching the transistor, it turns out very hot. As soon as I unload the load, in about ten seconds, the transistor cools down. What do you think, these heatsinks can be used for these purposes?

    #9727
    Amilcare
    Keymaster

    If the transistor is much hotter than the fin it is a symptom of poor thermal conduction, start by putting a good thermal paste between the fin and the transistor to see if things improve. Attention 45 degrees of temperature to the touch may seem many but for the final it is still an acceptable operating temperature. get a thermometer to detect the actual temperatures then with real data you decide what to do

    #9729
    piero55
    Participant

    Naturally, there is thermal paste, silpad foil ( those gray color recovered from former ATX power supply), thermal paste and transistors. For the thermometer, I am waiting for the delivery of a thermoscanner then we see the real temperature. As you may have noticed, I really like the recycling of electronic components and accessories…. For the fan, I am using the circuit with the 12F683 object of another 3D and it works perfectly.

    #9731
    Amilcare
    Keymaster

    Great but I would have controlled the fan with a thermal switch, they are available for all temperatures and it is certainly less bulky than a mcu plus a temperature sensor supplied. If, on the other hand, you want to monitor the temperature in real time, then the mcu with relative display is welcome

    #9733
    Picmicro675
    Moderator

    I would recommend fitting a 75 ° thermal fuse, at least you are sheltered from any unexpected cases.

    #9748
    piero55
    Participant

    Amilcare, I have another big 20A power supply always self-built for the HF radio more than 20 years ago he has a thermostat to turn them on 2 fans (ON/OFF) on big heat sinks: I had tried with NO thermal switches but then I preferred a thermostat with hysteresis. A linear variation in speed would have been very interesting to minimize noise. For this project instead, i opted for a PIC that manages the relay i switch 12 o 24Vac based on Vout and manages the fan by starting it at 30 ° with minimum speed up to maximum speed at 50 ° beyond which a flashing red LED lights up. This also reduces the fan noise. The temperature, I detect it with an LM335 fixed next to the transistor also with thermal paste. It works in PWM at 50Hz and is very good, already experienced on another project. I have indeed been able to experience that with higher frequencies, it is very difficult to obtain the speed variation. A 50 Hz instead I have a lot of margin: if you are interested you can talk about it. Originally the pic, a 16F876, it should also have managed an LCD with indication of the Vout and Iout but then I put a voltmeter / ammeter that I had bought online. I don't like it very much because it is very slow in responding but now it is. The construction is very compact, inside an EX ATX PC container.

    Hi Picmicro… unfortunately I don't have the thermal at 75 °. I own some from 50 ° NC that I got for the treadmill motor. I wait for the laser thermometer to arrive which reaches 300 °, more than enough for the purpose…

    #9750
    Amilcare
    Keymaster

    I like the use of PWM for linear speed management as a function of temperature. I had in mind to make a power supply completely managed by PIC or Arduino with determination of the output voltage through an R 2R network and the adc to monitor output voltage and current that can be set via encoder and LCD display at 4 lines that allow me to view both the operating temperatures and the powers supplied. Sooner or later I will find the time to turn this idea into reality!! The problem is time to do everything.

    #9754
    Picmicro675
    Moderator

    unfortunately I don't have the thermal at 75 °. I own some from 50 ° NC that I got for the treadmill motor

    At least you can try those, always to ward off the worst. I have no idea what temperature is bad for the transistor you put on the radiator. Maybe we play a little on the more or less distant positioning.

    @Amilcare
    , I once had in mind a power supply that was a bit like an amplifier. In fact, the principle approaches. it would be enough to send certain data to the power manager and the power supply would work as an audio amplifier.
    However, there should be an Arduino power supply project.

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