Regarding switching Power supplies

[flinx]

I has a question (obviously).

Looking for answers from people who have real world done this.

These ubiquitous power supplies that are everywhere.


I have several and they are somewhat adjustable. I have recently learned that they can be modified to be adjustable from a pretty low voltage up to a voltage higher than they may be sold as putting out.

In my case I have one that says it can do 15vdc at 40 amps or 600 watts.
In fine print it says not to exceed 80% rated output continuously.

It could be adjusted from 14.96 to 21.38vdc.

To make it easier to adjust I installed a physically larger POT and a small digital volt meter. Since I did not have an exact match for the original pot (1k) I used a 1.4k. Now it is adjustable from 13.2 to 21.1vdc.

I would think that if I ran the thing at 21 volts then I would have to limit the current to about 28 amps max? But could I also run it at 13.2 volts and 45 amps? barring some kind of current limiting the complete lack of a datasheet does not inform me of.

I don't actually intend to run this thing full tilt at any high amperage for any great length of time, but am curious if anyone has and how well did that go?

[eccerr0r]

Re: Regarding switching Power supplies

depends on the psu design.

primary design(mostly) determines max power output.

secondary design determines maximum amperage. a lot of the time there are limits to current passing, resulting in lower total wattage.

the coupling of the two will determine output voltage range.

also note that if you're out of range, weird stuff like oscillation may happen. oscillation is probably a better result than magic smoke leakage which is a much more common result of going out of range.

[sam_sam_sam]

Re: Regarding switching Power supplies

I would recommend the following to you I have tried what you are talking it really depends on the switching power supply because some of them will fluctuate the voltage up and down when turned to the lower voltage so low that it can be reliable

Case in point I have a 5 volt 5 amp switching power supply when you go below 4.5 volts it is not stable but it pot control will go some what lower than the 4.5

[flinx]

Re: Regarding switching Power supplies

I would be curious to see if they make these power supplies and sell the same power supply under several voltages and just change the sticker on the side. Some of mine are adjustable up to 5 volts up or down from the factory.

The 15v one (that's what it was sold as) I have could only be adjusted down to 14.96 as I got it, but up to 21.38

I could see them selling it as a 15, 16, 18 or 20 volt supply.

[eccerr0r]

Re: Regarding switching Power supplies

The wider the range, the higher it costs to build. One could say the same for a plain tapped transformer - the taps themselves cost a little money, but more importantly the secondary wiring has to compensate for the wattage where it's not necessary if it's one fixed voltage.

[sam_sam_sam]

Re: Regarding switching Power supplies

Some of the 15 volts clam that you can adjust down to 13.5 or something like that
I have not tried this yet so I could not tell you one way or the other if works or not

[eccerr0r]

Re: Regarding switching Power supplies

Usually a few percent isn't too much of an issue for designs that were made for a single voltage, the range is meant to cover manufacturing tolerances, not to tailor the output to the user's whims...

[PeteS in CA]

Re: Regarding switching Power supplies

I would be curious to see if they make these power supplies and sell the same power supply under several voltages and just change the sticker on the side. Some of mine are adjustable up to 5 volts up or down from the factory.
...

Several factors are in play, but the basic answer is that for any specific design there is a practical limit to the adjustment range. On the other hand, with some significant component changes multiple models can be of the same basic design.

Three interrelated factors are the transformer, the frequency, and the usable pulse width. For a given transformer turns ratio there is a maximum pulse width that the regulator can provide, and thus a maximum voltage. Similarly, there is a finite minimum pulse width due to the turn-on and turn-off times of the switch devices. The switch frequency also changes the available usable pulse width, though as switch frequency decreases, the size of the magnetics increase and it becomes audible below ~20KHz.

Another factor is that the compensation for the control amplifier has to change when the transformer is changed to get a different voltage range. Then there are things like the PIV of the output rectifiers, the voltage rating of output capacitors.

So, yes, one can have a family of models, but not a one-size-can-do-all-voltages model. Test equipment power supplies are very different from the switching supplies you're asking about - more complex and more expensive.

[flinx]

Re: Regarding switching Power supplies

what is everyone's opinion of what this guy did?
https://youtu.be/JL4FS4QOd0M

his webpage pointed out something I had to immediately check. That the output filter caps were of a voltage over the maximum output you set with the pot.

in my case they are 25v.

[sam_sam_sam]

Re: Regarding switching Power supplies

I will have to try the modification that he talks about because I have needed a special voltage that there is no switching power supply for