Need help, maybe need a circuit design?

Hello all, I'm here on a suggestion from a friend to hopefully get this problem sorted out.

I currently have a function generator that just isn't cutting it anymore. What I need is to pulse DC current, probably 12+ volts through a solution at about 20 amps. I need to be able to control the frequency from 100 hz to like 500 khz, I currently do that by running 2 12 VDC power sources in series with a solid state relay on the negative side before the solution. The SSR is controlled by the function generator, but it occured to me recently that the SSR can't function that fast so I need a new method. Maybe a circuit? Some specialized relay?

As you can tell I'm pretty newbish at this, but am a fast learned since this is a very necessary piece of equipment at the moment

I look forward to any advice that you all can offer, Thank you

-Nathan

michaelkellett over 13 years ago

Do you really mean 500kHz ?
It can be done but it's way outside Solid State Relay territory.
It's a serious design project - do you have a budget to buy something or are you hoping for a DIY solution >

Michael Kellett
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
Former Member over 13 years ago in reply to michaelkellett

Its possible I'll only need up to about 300khz but i guess 500khz was too much wiggle room lol

A DIY solution would be nice, but I've got to get it all set relatively soon
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
billpenner over 13 years ago in reply to Former Member

By a solution do you mean a liquid? If not, is the load inductive? You might consider one or multiple power MOSFET(s).

Bill
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
Former Member over 13 years ago in reply to billpenner

Yeah its about 75% water. Pretty darn conductive. I was suggested MOSFETS and was told to buy a certain 6, 3 of each kind, but no one has been able to instruct me on how to wire everything up after that. I can do basic circuits if I have a design, but mostly I'm quite helpless
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
billpenner over 13 years ago in reply to Former Member

Do you need to reverse the polarity? that is in effect, use an alterneting current or just pulse it off and on. Is the duty cycle 50% or does the pulse width change? Sounds like you are electroplating and/or polishing.
Bill
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
michaelkellett over 13 years ago in reply to billpenner

The last time I wanted to do something a bit like this I bought a big audio power amplifier (1450W per channel 2900W bridged into 8 R) for about £200. Currently CPC (a Farnell company) have a Behringer EP4000 listed which will do 4000W into 4R bridged.
Now thats about 32A RMS or 44A peak so it should be OK with your 20A. Put a big resistor in series to limit the current (4R rated at 1000W min) and you are there - except that the amp may not like putting out pulses of the same polarity all the time. You could probably get round this by putting a big diode in series with your load and providing a path for current in the other direction with another big diode and a second power resistor.

If you could provide a bit more detail about the waveforms you would like to achieve it would be easier to help. If it is for electroplating I assume that you know that you could just buy a suitable supply designed for the job.

Michael Kellett
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
Former Member over 13 years ago

the easiest way to explain it is the hydrolysis of water. Currently i just am using the square wave setting on my function generator and thats what i want to continue using. I will just need to pulse it on and off at the speed i choose.
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel