AC to DC converter with selectable voltages?

[Audiophilenoob]

I guess it was stupid of me to post his in loudspeakers section so I moved it here

I need a AC to DC converter for testing transformers for my ribbons... but I can't seem to find one with selectable voltages...

I need a power supply that will let me run voltages from 0.01mv to 4v while caring a high amperage... say something like 30 amps at 4 volts minimum with the amperage increasing as you go down to 0.01mv

I guess this is a 120w PSU minimum... a 800w one would do my purposes better though

if there's some kind of circuit I can build to do this with a normal transformer let me know

thanks

 

[anatech]

Hi Audiophilenoob,
I'm lost. Transformers accept AC and don't like DC current. Same goes for transducers, something that goes down to DC would give you "wind".
Do you want a high current AC source. If so, a Krell amp might work. The big ones can melt the odd Looney (a coin).

-Chris

 

[Audiophilenoob]

I need it to be DC to test some DC xfrmers I'm using... not for ribbons though... it's for a motor/servo system design

that's why I need it... that and for another project I'm working on

needs to have 1mv-4v selectable with adjusting amperage

if there's some circuit that can do this that would be best... or some product I can buy?

 

[sss]

that kind of power supply will be very difficult to make by youself

a good pc power supply can supply more then 30A @ 5V
u can add high current regulators and "play" with the voltage...

 

[Audiophilenoob]

that kind of power supply will be very difficult to make by youself

a good pc power supply can supply more then 30A @ 5V
u can add high current regulators and "play" with the voltage...

can you show me an example of a regulator

 

[sss]

An externally hosted image should be here but it was not working when we last tested it.

this is very simple example of a regulator (dont use that schematic )
to the + u put the desired output voltage , thats the voltage thats gonna be on the load .
the transistor should be very high power in your case , for more then 30A current u must use something like 5 or more high current transistors in paralel , also ,use two or more driver transistors after the op amp ...

also , i dont know exactly what u are trying to do , do u wanna adjust the voltage on the load, or the current?

 

[darkfenriz]

DC Voltage as low as 1mV and of course 0.01mV is a bit unrealistic unless you want to use paralleled electrochemical cells or have efficiency of a fraction of 1%. The weak point is a rectifier.

 

[Audiophilenoob]

An externally hosted image should be here but it was not working when we last tested it.

this is very simple example of a regulator (dont use that schematic )
to the + u put the desired output voltage , thats the voltage thats gonna be on the load .
the transistor should be very high power in your case , for more then 30A current u must use something like 5 or more high current transistors in paralel , also ,use two or more driver transistors after the op amp ...

also , i dont know exacrl what u are trying to do , do u wanna adjust the voltage on the load, or the current?

preferably both voltage and current... where when you decrease vcltage current increases etc... it's like a regulated 500w PSU but you can change the voltages manually

lemme see what I can come up with.... if you have any suggestions on a unit I could modify etc that can already do thist that woudl be way better

 

[sss]

DC Voltage as low as 1mV and of course 0.01mV is a bit unrealistic unless you want to use paralleled electrochemical cells or have efficiency of a fraction of 1%. The weak point is a rectifier.

true , with currents that high u will have more then 1V on the wires connecting the load , thats why i think he needs a current regulator , not voltage

 

[Audiophilenoob]

DC Voltage as low as 1mV and of course 0.01mV is a bit unrealistic unless you want to use paralleled electrochemical cells or have efficiency of a fraction of 1%. The weak point is a rectifier.

for the design I would say it's necessary to have that low mv ability

what about 0.001v? I think this is acceptable as the low point

I need it to be selectable... because I need to find the exact voltages this works within

 

[darkfenriz]

Hmmm...
another possibility of pseudo-DC voltage this low and adjustable and high current and so on is to build a microprocessor controlled PWM supply (switching between GND and 5V) with high speed, good low pass filter and low Rdson of mosfets. Not to mention good regulation of 5V and high slew, low dead times ...
But this option seems only realistic to me.

 

[Audiophilenoob]

I somewhat see what you're getting at with this design... but can you go into more detail about the multiprocessor

Also realistically I think I can cut this down to less than 5A... of needed current after talking with someone about it

this solution will require me to build two psu's eventually once I locate the optimal voltage... I need the selectability to find it though

worst case scenario 3A as the minimum amperage

thanks for the help

 

[sss]

so now its 3A? thats not a big problem , check out LM350 from national , there are aplication notes how to make adjustible reg with it in the datasheets ...with 2 of those u can make 6A reg ,check the datasheets.

 

[Audiophilenoob]

so now its 3A? thats not a big problem , check out LM350 from national , there are aplication notes how to make adjustible reg with it in the datasheets ...with 2 of those u can make 6A reg ,check the datasheets.

great! I will look into it... thanks

 

[peranders]

I think you may get better advices if you explain your test setup better. What is DC transformer? 30 A? 0.01 mV? 800 W? I don't understand a thing what you are up to. The post you hint that a normal 3 A lab power supply will do?

 

[Audiophilenoob]

I think you may get better advices if you explain your test setup better. What is DC transformer? 30 A? 0.01 mV? 800 W? I don't understand a thing what you are up to. The post you hint that a normal 3 A lab power supply will do?

sry

what I'm trying to do is create a PSU that will allow me to turn a knob... or something can control the output voltages

between 1mv and 4V

the amperage should also increase as you decrease in voltage (same total wattage I guess)...


I originally was looking for a 800 w PSU... but since this is just for testing... I think that I can do low amperage... say around 5A or so at 1mv... and I guess w/e I can get at 4v...

I need to test a theory... but don't know the voltage I need to supply (it's voltage that matters not current) the current was just to make it easier to tell...

selectable PSU from 1mv-4v with as high an amperage as I can get... but at least 3A ... 5A would be better....... if possible if i could make it turn in 1mv incriments that would be best.. but I'm unsure of the practicality

 

[peranders]

1 mV and 5 A, what do you have to manage that? 200 microohms, what is this?

 

[anatech]

I'm trying to figure out what you are trying to accomplish. I can't even begin to suggest anything to help you with this much information.

What I have so far is you need a DC supply at high current with mV precision. Tall order because the noise may be more than 1mV at higher currents. Tempco and connection resistance in the mV region become important, as does thermocouple potentials.

You may possibly be beyond a primary laboratory's ability to quantify the measurement.

-Chris

 

[Eva]

I feel quite dumb because I haven't still got the point of that thread nor the actual purpose of that power supply.

 

[peranders]

Audiophilenoob, what is a DC transformer?