Hi,

I am starting a new project and it has to do with pulsing large electromagnets. To do this I need a PMW - 50 AMP pulse @ 144volts - 17hz 60% cycle. It would be great if I could adjust the frequency and duty cycle. I know I need a 555 timer and a large amount of parallel MOSFETS, but I am at a loss of have to do this all without killing myself in the process

Thanks

 

You might consider IGBTs instead of MOSFETS. Regardless of which you choose, don't forget to use a driver!!

For generating the PWM signal, have a look at this thread: http://forum.allaboutcircuits.com/showthread.php?t=12711

 

http://www.jim-gibson-co.com/ighipofu1m60.html

Thanks for you answer for the above. It led me to that link.

 

What you are talking about is something with pretty high peak power. With circuits like this, your entire circuit can be destroyed in a flash (literally, accompanied by smoke). And that can get expensive, particularly if you are using $30 transistors on the output.

If you really need to build this yourself, try to get a circuit of something very similar and modify it.

 

Thanks for all the help so far. I did find a IGBT that can handle 400 amps and 600 VDC for $45 used. So I won't get to mad if I burn it up, but I of course would like not to. It's from here:
http://www.jim-gibson-co.com/ighipofu1m60.html

The seller told me I would need to protect the switch from large transient voltage spikes that will be generated from my inductive load, the large electromagnets I am pulsing. How might I go about doing that? and what might the over all circuit look like, i.e. were would I put the spike suppressor exactly and what might I use? I did find this:
http://www.vsholding.com/news release/protection of solid-state switch.pdf

Any suggestions? Attached is picture of my circuit idea.

 

One way to provide protection is to use a "snubber." Here is some good reading: http://focus.ti.com/lit/an/slup100/slup100.pdf and also: http://ken-gilbert.com/images/pdf/snubber.pdf

 

Shouldn´t the diode be in parallel with the electromagnets, instead of series?

 

I read up and found a circuit just for my cause from the site. I did design mine wrong. I think to much like a plumber as I am new to working with power.

http://www.vsholding.com/

So, I adapted the circuit design with some surplus power diodes I found online. Please have a look at my circuit diagram. Does it make sense to you? I found 125 Amp 1200 PIV, Diodes, I thought 6 would do hooked in parallel. I think that way they would absorb up to 7200 negative volt spikes, or do I need a reverse polarity power diodes?

There is also a question on my diagram about where I put my 50amp resistor to control my battery bank from dumping to much power into the circuit. I am only trying to use this for a few minutes at a time.

Attached is my diagram

Thanks everyone!

 

Resistors do not come rated in Amps. And 12 Volt batteries generally don't provide 160Volts. You only need one diode.

Let's back up a few steps...

Your requirements as I understand them:

17 Hz at 50% or 60% duty cycle
144 V across the electromagnets (is that average, or peak?)
50 Amps through the electromagnets (presumably peak value, for an average of 25 to 30 Amps.)

and... a 12V battery for your supply?!?

Can we talk you out of that last one?

 

Hi Thanks for all the input. I'm learning lots! and all the feed back is getting this project straighten out and safe.

Well, I was thinking of wiring the 12v deep cycle batteries in series to add up to the desired voltage.

Yes, my peak Amps would be about 50 for the pulse peak to the magnets at 160DVC peak - using the battery bank. So the average would be around 25Amps to 30Amps as you said.

My major hurdle here is I have to protect my IGBT switch from the high transient voltage the magnets will produce from this pulsing of the circuit. I have learned I need to add a snubber circuit to my plan and that can be a diode, but I think there is more involved. I read in Wikipedia about a Zener Diode and that is what type of diode I think need, but I am not clear on what the value needs to be. If you look at my diagram attached there is also resistors and capacitors involved. Not sure what their values are to be.

Attached is a revised circuit diagram

I will be sure to post a picture of everything when it is built.

 

Did you read the material from the links given in post#6?

I will be sure to post a picture of everything when it is built.

Excellent! I look forward to this!

 

These were great, but I think the math is over my head as to how to determine the values of the components. I need to take a eletronics class for sure as I am a web designer righ tnow just learning about the world of electronics.

If you look at my newest circut diagram it shows where I am at and how much I have learned so far.

Thanks so much.

 

So it's been about one week and I am still stuck here. I really need help with the values in the circuit design. I think the design is going to work, but I am newer to this hobby and the readings are a bit over my head when it comes to doing the math. I am more of a mechanic so electronics is a whole new world. Please see my last post for the circuit design. Any more tips would be great, like tutorials sites for newbies.

Thanks

 

You'll fry that Zener... and then the IGBT will go up in smoke.

Try putting a Zener across the IGBT and or a rectifier diode across the coil.

If you want a great tutorial site for newbies, try the blue tabs at the top of the page. I suggest the one on the left as a starting point.