Variable frequency AC supply

[asimpson]

Doing some expirements on low inductive load and I need a variable frequency AC supply. 0-200 kHz, 30 W. Reasonably clean sine wave.

What would be a cheap way to do this?

Have function generator.


Thanks in advance

 

[benta]

DC-coupled audio power amplifier. Thcould be an option.e National LM3876

Benta.

 

[OperaHouse]

I use a board cut out ( I love thin cut off wheels on a grinder) of cheap 6 channel theater system for inductor testing with a Clarke Hess 256. The audio board has three TA8258 20W stereo amplifiers that I connect in parallel through 4.7 ohm resistors from each amplifier. The input is transformer coupled to the audio oscillator to prevent ground loops. And yea, it takes a couple of fans to keep it cool. The applications the TA8258 and other chips are designed for don't see 200KHZ as a feature at all. Still It seems to still work well a little over 100KHZ. I just think a number of amps in parallel works better than driving a single amp hard into a highly inductive or capacitive load.

 

[Warpspeed]

OperaHouse is on the right track.

This type of testing can generate some very low and reactive load impedances which can easily let the smoke out of many typical audio amplifiers.

Either a single monster amplifier, or several amplifiers, but make sure there is some additional series resistance placed between amplifier and load.

A resistive tee attenuator network would be even better as it also offers some protection from high reflected voltages.

However you do it, there is likely be a great deal more heat and power involved than you might expect, to reliably generate a measly thirty watts into a "difficult" load.

 

[asimpson]

thanks for your replies.

i am afraid you may be crediting mo with more knowledge of electrical engineering than i have.

any ready-made products out there?

 

[Warpspeed]

Any ready-made products out there?

Not that I am aware of.

The problem is this type of testing is fairly obscure, and so the test equipment needs to be custom made to suit the specific application.

A lot of this type of analysis is done these days by computer simulation, often using "Spice".
But that can only take you so far.
Magnetics can often exhibit strange non linear characteristics that are best measured directly under real operating conditions.

 

[VEBill]

There should be some 'test equipment' type LF power amplifiers of the sort used for E3 compliance testing. But you did ask for "cheap", and that disqualifies E3 test equipment... ;-)

One company name is Amplifier Research. I'm not sure if they offer LF amps. They do offer very wide frequency range RF amplifiers. We have a 75 watt one where I work.

The "0" Hz in your frequency requirement is something to consider carefully. Make sure you require exactly what you're asking for at the low end of the stated bandwidth.

 

[OperaHouse]

Mine only cost a buck at a flea market! I only need a couple of volts for my testing. What voltage are you looking for. Curious what a mechanical guy would be doing with this? There are supplies by Pacific, California and Belhem for the 50 to 2K range that can be had for $150 used. Going over 30K is a specialized market.

 

[Skogsgurra]

Kepco Bipolar Opamps deliver +/- 30 to 100 volts, or more, at 5 to 10 amps, or more. They include 0 Hz (DC) but are limited to somewhere between 10 and 20 kHz (the ones I have seen). Can be found on eBay at low to moderate cost. My box does +/-72 V and +/- 6 A four quadrant. Love it.

I use transformer if I need to do high voltage (grid simulation with 'funny' waveforms) or high current at different frequencies for impedance testing and primary injection tests.

The 400+ watts are awesome and I can't live without it.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...