# variable power supply for research project

Discussion in 'The Projects Forum' started by jobewon, Jul 19, 2015.

1. ### jobewon Thread Starter New Member

Jul 19, 2015
1
0
Gentlemen,

I could really use some assistance please.

I am working on a project as an amateur inventor.

I am not an electrical engineer nor do I pretend to be---that is why I am posting this call for help.

I need to know if there is a manufactured variable voltage, variable, amperage, and variable frequency DC power supply available for use in a test lab.

Before everyone tells me that I am a dummy and need to go back to school and all that stuff, I will explain the application.

I need to vary the output voltage from 0-18 volts DC.

I need to vary the output amperage from 0-30 amps.

I need to vary the output frequency from 0-40k hertz.

This is to set a voltage, amperage, and a frequency and take a measurement of the effect to manually build a graph to determine optimum voltage, amperage, and frequency for a electrolysis experiment I am conducting.

The output must be DC--polarity cannot change.

I need the power supply to plug into a normal wall outlet.

If one is not built commercially, is there any way to set this type of circuit up in a laboratory scenario?

Anyone's assistance would be greatly appreciated.

2. ### #12 Expert

Nov 30, 2010
17,899
9,318
Things to clear up: DC can not have a frequency up to 40KHz..or even one Hz.
Therefore, you must be talking about at least 2 different functions.
Adjustable DC power supplies are rather common, but 30 amps is not common for lab work, so that is a special case.
You can obtain very powerful audio amplifiers, but they tend to stop at 20KHz.

Rough calculations suggest 190 watts at 40KHz. Definitely a custom job.

Last edited: Jul 19, 2015
3. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,071
Another point you may be confused on: A laboratory power supply can have two knobs; one to adjust the voltage; a different knob to set the current limit.

An example: Suppose you buy the following power supply: Adjustable 0-18V. Capable of 30A max, but it has an adjustable current limiter from 0 to 30A.

You set up said power supply to deliver 10Vdc, at a maximum current of 20Adc. You connect it to a mysterious brew in your reactor that you don't much about. You observe that the supply is delivering only 3.5V at 20A. What is happening?

You set up said power supply to deliver 10Vdc, at a maximum current of 20Adc. You connect it to a different mysterious brew in your reactor (the only thing that changed is the mix). You observe that the supply is delivering 10V at only 1.5A. What is happening?

Hint: per Ohm's Law, I=E/R or E=IR, where R is an attribute of your mysterious brew...

4. ### GopherT AAC Fanatic!

Nov 23, 2012
7,287
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So, you really need three devices to build your project. You will need more to measure results or monitor various parameters.

1) DC power supply. Anything over a few amps is usually not variable. For example, you can find 0 - 15 VDC supply with 3 amp max current. And you will find 12 volt supplies with 20 amp supply. You should really work to decide what you need. Also, high amperage supplies can get dangerous because of heat during a short circuit. Fires are possible.

2) Signal generator or tone generator or waveform generator (name changes depending on the frequency range, wave shape, etc and even manufacturer - since features overlap.

3) most signal generating devices have a 50 ohm output impedence so you will need some type of amplifier to convert the signal to a driver of that signal (if you need to drive a load at multiple amps).

4) you will need volt meter, frequency counter (unless the dial / digital readout on the signal generator is accurate enough), oscilloscope (may have on-board volt meter and frequency counter on some models),

Good luck.

5. ### crutschow Expert

Mar 14, 2008
16,571
4,476
I have used a high power DC coupled AC amplifier from this company, and it worked very well, but they are also quite expensive.

Last edited: Jul 20, 2015
6. ### AnalogKid AAC Fanatic!

Aug 1, 2013
5,660
1,607
HP, who became Agilent, who became ??? used to make high power "lab" supplies. We have a couple of old ones at work that will fit the 0-18 V and 0-30 A envelope. Normally you adjust the output voltage to what you want, and the external circuit or devices draws the current it needs (up to the 30 A limit of the supply). As mentioned above, another control scenario is that you set a current limit at the supply from 0-30 A, and the supply output voltage varies depending on what the circuit or device needs. So far, catalog stuff. Sorenson makes 1U rackmount power supplies that will do this.

It's the 0-40 kHz part that is not a "normal" power supply output specification. If you need a device that will deliver a 40 kHz squarewave or sinewave output at 18 V (peak-to-peak or RMS or whatever) and 30 amps, that is not normal. Not impossible either. In a sense it is more like a weird audio power amplifier than a power supply. So a little more detail about the specs and the application will help us get a grip on your setup.

ak

Nov 23, 2012
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8. ### AnalogKid AAC Fanatic!

Aug 1, 2013
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Yet another HP name that refuses to stick in my brain.