WiFi controlled pulse generator and spark coil driver

Well, it appears there's no really good way to do this here. This will contain various bits of code used to support the fusor, which presently includes everything from embedded 8 bit uP code to stuff to run under Linux in some HLL (often perl) to interface-specific stuff for commercial hardware, sysadmin tips and setups, and running on whatever machines I have in the tree here. So any one piece might fit some other category too, but...there's no pigeon-holing even computer science without losing the app-specific stuff and inter-relations of it all in a specific usage.
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Code sharing for fusor data aq and control software

WiFi controlled pulse generator and spark coil driver

Postby Doug Coulter » Fri Jun 16, 2017 4:51 pm

(this is under construction - I've lost the schematics to such a simple thing and I'm now tracing them all out again for ya.)
Here's a fairly badly done demo (I'm under the weather a little today, sorry)



Basically, for various possible fusor support tasks, I wanted a fairly simple pulse generator with a decent amount of control - remote of course - so I built one.
This uses an ESP-8266 as the computer and WiFi as well as a pretty simple variable duty pulse generator.
It has a pulse amplifier using 2 each 2n3904 and 2n3906, the necessary power supplies, and well, that's about it. A couple of leds show power and if it's pulsing.
I should have the schiz-s in a few.

The reason this took two tries is that the kickback voltage of a really good (in this case Bosch but usually GM or Ford are also good - from the old days, can of oil, iron and wire) is insane if the turnoff time is fast, and here, we want insane! We were easily hitting >600v kickback at the primary when we had a decent amount of stored energy in the coil and no load.
Thus my first try - with an IRF-450, even with fancy spark gaps across the drain-source - nope..the fet got bent and while it still worked some, it wasn't the good ol days of the spark just jumping out of the coil tower to the nearest anything (the primary wiring).

Some research showed me that in the few cases where I could get a schematic for the conventional solid state ignition (this isn't CD)...they actually used some dividers and high voltage zeners to turn the main switching device back on during kickback when the voltage exceeded a couple hundred on the primary. Wimpy! Obviously, they do work but I wanted more.

So, enter IGBT with enough rating to not need protection. In fact at this point you could fry an unloaded coil with it arcing internally...
This matters till you find a good one or two.
Why? Because if I want to jump-start an ion generator, it can take quite a few microseconds to start drawing current, during which time, other stuff fries. With the biggest slowdown capacitor that worked well...starting the ion source still took too long (once going it loads things down to a measly 5-10kv).

The IGBT I used, since I found it first, was a now obsolete Fairchild G40N150D (it works fine).
Since I like to have a backup, and found out these are obsolete and more expensive on Amazon than a DigiKey with shipping...I got some H30R1602. Either has way more ampacity than required for this. These will also withstand much higher gate-source voltage than the fets, so the 12v or so zener lashup across the input is not really needed anymore, even with lots of noise around. The fact that the pulse generator is low impedance probably doesn't hurt a bit.

So, once the right parts are there, this part is pretty simple.
CoilDriver.JPG
The basic things you'd expect

CoilSide.JPG
Other side of the same stuff


(schiz here soon if you're blind. Oh, wait!)
CoilDriver.png
Schiz. You're still blind.
CoilDriver.png (11.16 KiB) Viewed 340 times

I wanted negative going pulses, same as in an auto, so I used the coil polarity as stamped on the coil; + to the battery, - to the IGBT.


Turns out the ESP-8266 code is pretty simple too. We're just using one output pin...generating a web page CGI in C++ is a pain, but it works...
It's mostly the stock type stuff. I let you choose a high time (in milliseconds) a low time (same) which between them set the repetition rate, and have an enable checkbox and a "do it" button.
This also uses my "LANDNS" code, to broadcast it's name and IP pairing to listeners on my lan. It hasn't disturbed anyone else's thus far, it's pretty benign.

PulserWebUI.png
The control panel

FrontPanelSide.JPG
Front panel side - it just fit better this way, move along

Pulser.JPG
The parts used


(schiz will go here..)
PulseGen.png
Not rocket surgery



Nothing else really special. A 2 transistor inverter/level shift/inverter drives a complimentary emitter follower pair with 47 ohms to the output.
It seems really hard to break.

What wasn't as simple as I wanted turned out to be the doggone power supply. I wanted 12v for the pulse amp, and of course 5v for the ESP. Well, using two linear regulators overwhelmed my supposedly 100mA wall wart, so I unhooked one and substituted one of those simple switcher modules available all over. So if you look at the pics and see two linear regulators in there, know that one of them isn't used now. It was less work to leave it in there.




ESPPulse.ino.zip
ESP code for arduino ide
(4.09 KiB) Downloaded 12 times
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Re: WiFi controlled pulse generator and spark coil driver

Postby Doug Coulter » Fri Jun 16, 2017 7:52 pm

Here's a current (blue) and voltage waveform from another run of this. Hantek current probe, GWInstek scope.
Accounting for parasitics, the current buildup is near=theoretic here.
Spark gap was short, so not really super high voltage.
pulse.png
A little of how it looks when it's right.
pulse.png (3.33 KiB) Viewed 335 times
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 2944
Joined: Wed Jul 14, 2010 8:05 pm
Location: Floyd county, VA, USA


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