Consequences of adjusting output voltage of PSU?



  • So, I have a 12V 20A = 240W (no-name) PSU. It does have a potentiometer as most of these PSUs have where I can adjust the output voltage. It came with voltage being set to 12.6V and I increased it in the mean time to 13.6V. It would even go up to 15V it I turn the potentiometer to the max but I am afraid of frying my fans as at least two of them specify a max voltage <14V.
    Increasing the voltage should lead to faster heat-up times as well as a slightly higher possible motor speed before getting into the range of loosing steps.

    Anyway, here are my questions:

    1. If I increase the output voltage from e.g. 12V to 15V (i.e. by 25%) does this also mean that I at the same time increase output current from 20A to 25A and thereby make it a 300W PSU? I ask because of the following question:
    2. As far as I understand Ohm's law (and we are no friends 🤦 ) as well as U = R * I and my heated bed has a fixed resistance of (for the sake of simplified calculation) 1 Ohm that means when powered at 12V it will draw 12A and when powered at 15V it will draw 15A. But if the output current of my PSU does not scale along this reduces the current "reserve" for all other components, doesn't it?
    3. Will the PSU wear out faster with this increased output voltage? And if so then why? I actively cool my PSU with a large (92mm) fan so I guess heat should not be an issue.
    4. Is there any advantage or disadvantage I missed?


  • I can answer some of this as I have upped the voltage on my CR10 to 13.8v.

    I'm not sure I can answer your questions exactly as you've put them so,

    Your heated bed has a fixed resistance, so a voltage increase will increase its wattage (output), and the gains are fairly impressive.

    If you take a 12v 1ohm bed - 144w output
    13.8v and 1 ohm bed - 190watts output

    and I can confirm on my cr10 before doing this I could not get past 90 deg C on the bed, now I can hit 110.

    Peak power demand - when heating up the machine before printing will be 2-3 times greater than the demand maintaining temperature. So you need to cover bed at max, hotend at max and all motors running at maximum speed, when determining what wattage PSU to buy, fans and LEDs can be factored in but unless they are massive don't use much power.

    Adequate cooling (extra never harms the electronics - might offend your ears though), is a good idea.

    The other issue is that the voltage regulators on your electronics will have to work a bit harder if your PSU is outputting more than 12v. On duet with many machines running on 24v and no issues there - it will make no difference if you go from 12v to 15v. On lesser controllers like arduino/ramps the 5v reg was notorious for failing.

    EDIT- what I don't know is whether the total wattage of your PSU will increase or remain the same.



  • Your PSU is designed to handle e.g., 250W. This will not change. The thermal design, trace width, etc. are all manufactured to sustain 250W.
    You might get lucky and can run it at "125%" but in the long run it could case damages (overheating, thermal protection kicking in, etc.)

    Imagine an internal combustion engine in your car: it is designed to put out 100hp, you might be able to use chip-tuning to get 120hp, but you will loose your warranty because the engine+gearbox+transmission is not designed for it. It might work for 2 months - and then it dies...

    Bumping the voltage "a bit" is fine. But don't draw more than the rated power.



  • As said above, the power supply's maximum output current (Amps) will not increase, simply because you increased the voltage (depending on the model, it will slightly decrease when outputting higher Voltages, to remain at around the correct rated Watts), and everything will draw more power (Watts) at the higher voltage. Remember that current on the low side of the regulators = the current on the high side, which means the regulator needs to get rid of the rest of the volts at that current (so when drawing 1A at 5V from 12V, means that it will need to get rid of 7V @ 1A = 7W -> this is why they can get extremely hot, when one is not careful).

    Since for a heater (resistive load), the Ohms remains the same, at higher voltages it will increase its Watts, thus allowing faster heatup times as well as higher potential temperatures (usually the reason why people increase the voltage).

    It should be noted that, since the adjustment is possible, it should not hurt the unit too badly. Just keep in mind that most power supplies work most efficient at around 80% load - factor that in, when buying or adjusting your unit. If you are already at 90%, don't adjust it higher since that will increase the stress on the unit, which may lead to a premature failure of the unit.

    Since you have a Duet mainboard, which is rated to max 25V, that slight increase will not cause issues on the board itself. However, you need to evaluate your hardware for the maximum allowed voltages: you mention having fans that are rated for max <14V. This will be your limiting factor, as running fans at higher than rated voltage will damage them, or some may even blow immediately when exposed to higher than rated voltage (I once serviced a printer that ran on 19V and the owner bought 12V rated fans, since the stock fan was 12V rated - his replacement fans simply blew immediately).



  • Hello

    I'm using 15v on CR-10 with DuetWifi without Problems
    and ca. 14v on original Anet A8

    Heating is much better
    maybe you have to korrekt your pid tuning

    most fans are pwm controlled or with extra resistance (fan regulator)
    or you can use an cheap voltage step down board for fans or LED lights


  • administrators

    @knaudler said in Consequences of adjusting output voltage of PSU?:

    Hello

    I'm using 15v on CR-10 with DuetWifi without Problems
    and ca. 14v on original Anet A8

    Heating is much better
    maybe you have to korrekt your pid tuning

    most fans are pwm controlled or with extra resistance (fan regulator)
    or you can use an cheap voltage step down board for fans or LED lights

    If you turn the voltage above 13.6V then I suggest you connect 2 silicon diodes in series with the fans, to reduce the fan voltage by about 2V.



  • @dc42 said in Consequences of adjusting output voltage of PSU?:

    If you turn the voltage above 13.6V then I suggest you connect 2 silicon diodes in series with the fans, to reduce the fan voltage by about 2V.

    I have nearly no knowledge of diodes except they exist and what they basically do, so my question here after a (very) short research on that topic: would something like a 1N4001 diode be appropriate for this use case or did I just find something totally wrong for this purpose? None of my fans come even near the 1A these diodes are rated at. Otherwise to match the 1.5A limit of the fan mosfets I also found 1N5391.


  • administrators

    Yes, 1N4001 diodes would be suitable.



  • Thanks for all your responses. To sum up what I have taken from this:

    A 240W PSU will only ever be a 240W PSU independent of output voltage. That means at 12V it will be able to provide 20A and at 15V it can only provide 16A. I mean this are the designed limits what it is built for. It might handle higher outputs but it is rather likely to break in any way if done often or over a prolonged period of time. So to stay safe never exceed the rated power.

    At the same time increasing the voltage will increase current drawn by any heater (or anything with a fixed resistance) with the same factor as the voltage increases. This will be problematic if this increase will excess the capacity of the PSU as described above.

    In my specific case it could be critical to turn the PSU up to 15V as my heated bed would also draw around 15A while heating up (reducing the draw when going to only sustain the heat though) what would be very close to the limit the PSU is able to handle.

    Regarding cooling: I use a ultra-silent 92mm fan that I can barely here at full speed - and I only run it at 75% or so, so nothing that will offend my ears but definitely something to keep my PSU alive a little longer.

    Once more thanks for all the input, very appreciated. 🙂


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