Hi People
Ok so the transformer idea may have been a little premature, I don't know how much power it was drawing but I know it burned out the IRF510. I'm still having major issues with Mosfets and wanted to know from an expert about the schematics, because they're not always clear --

Which side is the front? Let's say the heat sink is the back.
Also, one of these is designed to gate using a positive voltage input signal right? And one is set up differently? This I don't understand.

As always your time and effort is appreciated.

 

See Intersil's datasheet for the IRF510, attached. Note that the drain is connected to both the center terminal and the heatsink tab.

The IRF510 is an N-channel MOSFET.

You should keep the ON-time low enough so that the current through the MOSFET doesn't exceed more than a couple of amps, or it won't last very long.

If you're getting 170V spikes on the 20-turn secondary when you have 10 turns on the primary, then you're getting roughly 1/2 that on the primary side. Your MOSFET probably got "zapped" when the primary side exceeded 100v, which is the maximum voltage rating for the MOSFET.

You might try using a couple of capacitors designed for automotive ignition points. They called these things "condensers". Use one on the high side of the coil to ground, and another from the source terminal of the MOSFET to ground.

You should be able to get them from any automotive supply store. When the nosy parts person asks what car and engine, tell them it's a 1967 Ford Mustang with a 289 V8, 2 barrel carb, no air conditioning, power steering, manual transmission (they WILL ask you all that stuff before you can actually get the part).

Don't try getting one for a GM engine past around 1968, because they went to a one-piece points/condenser design that won't be easily usable for your purpose.

 

Pay special attention to Figure 4 in the datasheet Sgt.Wookie has linked. If you know your pulse duration and your voltage, you can find the maximum safe current.

It may also be that the enamel coating failed... does anybody know it's voltage max?

Check with the manufacturer's documentation. It is likely 450 to 600 VAC.

 

Since I got over 10x the voltage increase with a 2x step up transformer, I want to try experimenting using my stereo as the power source. Originally I thought its voltage output was too low, but now I think if I apply speaker signal to the transformer I might get high volts. HOWEVER I don't want to blow my stereo, so the question is, how do I protect it from back emf spikes, high voltage, whatever the heck it is that made my last fet blow up. Would a diode on the primary side help?

I have a tone generator program that I'll be using to drive the receiver via my laptop.
Thanks

 

Since I got over 10x the voltage increase with a 2x step up transformer, I want to try experimenting using my stereo as the power source.

Bad idea. You are likely to wind up with the power output transistors of your stereo reduced to a small, smoking pile of rubble.

Stereo systems are generally designed to drive loudspeakers that have an impedance of 4 Ohms or 8 Ohms at 1kHz. If there is a significant impedance mismatch, particularly at higher power levels, the result will be smoked transistors.

Besides, your stereo was designed to amplify signals in the audio spectrum, not square waves. An "ideal" square wave is the sum of all of the odd harmonics of a fundamental frequency; therefore in order to approach that ideal square wave, one needs a tremendous amount of bandwidth. Your stereo's bandwidth rolls off rapidly after 20kHz or so.

The reason you were getting such a voltage spike on the secondary was due to the rapid turn-off of the MOSFET.

 

Thanks A LOT for the info. Highly educational.

Stereo systems are generally designed to drive loudspeakers that have an impedance of 4 Ohms or 8 Ohms at 1kHz

I thought about back in my car stereo mod days when an amp was matched with either 2 ohm or 4 ohm speakers. I would assume this is matched to 4 ohms, since that's the resistance across contact points of my speakers, and it drives them fine up to about 3/4 full volume, then they start to distort. We're talking big floor speakers, 12" subs that move some air. The receiver is rated for 100W, so I figure at 1V levels, it should handle near 100 amps, way more than we would need to drive a transformer. And as long as I keep the volume in check, and maybe use a fuse, run mono output and tap into both channels, wouldn't we be ok?

How feasible is it to wind a transformer (maybe with the right resistor(s) in series?) that is close to 4 ohms across primary?

Does the wire diameter, number of turns, or load of the secondary have any impact on how much current the primary will draw?

Thanks!

 

Don't try it, unless you want a fried stereo.

I'm not going to try how to tell you how to wind a 4 Ohm/8 Ohm coil @ 1kHz across the Internet.

You're looking at DC resistance. The impedance @ 1kHz is how they are rated.

 

Since I got over 10x the voltage increase with a 2x step up transformer,

That's with an open secondary, yes? Try again with a load. You will learn an important concept about electricity.

 

I'm going to take a leave of absence. This project has had it's fair share of effort for a while. For now, I need to focus on something that I Know can make money.

I thank you all for your support and advice. To those of you who doubted, well, congratulations, you win. May we all not burn in hell.

Blessed be

 

Best wishes towards obtaining that gainful employment, Farlander. Not easy at the present time - but there are always opportunities. A roof over your head and food on the table are certainly high priorities.

Treat this as a hobby, not a means to an end. I suggested in my very first reply to this thread that gainful employment must be your primary goal.

Be employed in an endeavor that you know about, or can learn quickly in.

When you can afford it, whether through time, money or both, educate yourself in topics that pique your interest.

I'm not talking about "Stanley Meyers" type education. I mean the real thing.

If you ever want to go through a good course at no personal investment, I'd suggest the Navy NEETS course. It's available online here:
http://www.tpub.com/content/neets/index.htm
It will probably take you a year to go through it, if you spend 40 hours a week reading it and working through the problems. But it will be well worth your time, and you will be far more knowledgeable about electricity and electronics than you are now by the time you complete all of the modules.

I took the predecessor course in 1974.

 

Blessed be

M.M.&M.P.&M.M.A.

 

Thanks for the advice Sarge...

Ok so I must have lied, I'm a WFC junkie, I just got back from raidoshack with a few new FETs but I still have no clue what the difference between P type and N type is. Will they both work with the 555 circuit? Please help! I know this sounds selfish but I swear I spend about every free minute reading about this stuff I just can't get to it all fast enough!

I have now in possession an IRF510 N-channel, 60V 4A max.
Also a Darlington TIP120; a TIP42, P-channel? they're the ones that say collector-emitter-base.

I intend to reconnect my homemade transformer to the pulsing circuit, hopefully without blowing the FET this time. If there are basically 0 ohms across the primary winding, would adding a series-resistor keep my current down so I don't burn up my FET again? I want to keep it to a 3-4 amp max. Also, will adding a load to the secondary increase the current/resistance across the primary?
Muchisimas gracias

VOLTROLYSIS

 

Also, will adding a load to the secondary increase the current/resistance across the primary?

No/yes. Do you even know what you asked?

 

That was hilarious!
Farlander, have you put a diode in parallel with your primary yet??
And what temperature is your mosfet running at? Heatsinks/fans are often extremely helpful with keeping them alive..
And not quite related, what are you using for an electrolyte in the cells? NaOH? (lye)..

 

My schematic shows putting a diode in parallel with the primary, why would I do that?

Yes, I know what I was asking, will putting a load on the secondary increase current flow to the primary? I would assume yes, it's drawing off the magnetic field, which means more room for current to flow on the primary side.

 

Yes, I know what I was asking, will putting a load on the secondary increase current flow to the primary?

Thank you for the clarification. Reflected impedance into the primary will be equal to load impedance times the square of the turns ratio.

A load will in no way "draw off the magnetic field." To "draw off the magnetic field" you need that "Q" guy from Star Trek - the one who can do impossible things.

 

Hi guys,
well it's been a while. I gots me a job now but it kicked my ass so hard now I'm home sick.

Ok, I've settled on using the IRF510, which has a MAX rating of 4 AMPS. My ATX supply outputs a max 12 amps... could anyone tell me what value resistor(s) or matrix(s) of resistors I would need to keep current within tolerance? I plan to place the resistors between the ground and FET source.

One other question from before, why is there always a blocking diode between hot and ground?

 

Place the resistors on the drain side of the FET. Otherwise, the voltage on the source caused by the current through those resistors will cause the FET to cut off when the source voltage increases towards the voltage on the gate. The difference between the gate and the source is what controls conduction.

For a limit of 4 amps and a 12 volts source, you need 12/4 = 3 ohms. Four amps and 3 ohms is 12 watts of dissipation, so that is the minimum size of the resistor. Digi-Key has a 3 ohm 12 watt resistor part #B12J3R0 @ $3.38. It's going to be hot, so make sure it has space for air circulation.

The diode is supposed to keed current going in one direction only.

 

I have a 10W 10ohm... so lemme practice here:
12 / 10 = 1.2 Amps Check, that's what my ammeter reads.
1.2 Amps x 12 V = 14.4W... too much for the resistor to handle right? It gets hot very quickly and I haven't run it more than about 5 seconds... thought I detected a little crackling but the ohmmeter puts it right at 10 still.

Ok so there's a radioshack down the street, I'd love to be able to use what I already have (1/4W and 1/2W resistor assortments) to make this work. Digikey is outside the affordability right now when one factors in shipping and waiting... I am still working with some people to develop the WFC resonant frequency generator circuit, and here is the latest spice model, showing 30kv ressonance with 12V 50% duty cycle input at the water capacitor measuring 10nF.
MMM....

 

Oops, I blew it. That should be I^2 * R. That is 16 * 3, or 48 watts. You'll need a 50 watt resistor. That's a L50J3R0 @ $7.64.