Trying to ignite a gas turbine, I decided to control it with an arduino, OK I could have gone with a NE555 to generate pulses but it's going to control some other things too in the end :-)
So here is my thought : I'd like to control a circuit as the one below. It's basically a DC-DC converter charging a high voltage capacitor which is then grounded by a Thyristor and discharges through a coil (not represented).
Now, here's the deal :
My application needs a lot of energy, quite a lot more than a bike / car for that matter. Basically, a normal piston engine CDI will give anywhere between 50-200mJ and I need around 2 Joules. But also I don't need the high frequency of recharge! 1-5Hz is fine.
Doing the math, a 44µF capacitor charged at 300V would store 2 joules (doesn't mean it will give all of them back...).
A couple of questions for you CDI specialists out there ;-) :
- Is the circuit pictured correct to charge a cap that's almost 50times bigger than originaly intended? I'm also trying to find out the recharge time to check the max frequency but my knowledge stops there...
- The 22nF and 27R on the high voltage side are there to discharge the cap when powered down, right?
On all the CDI schematics that I've seen, I've sometimes seen the 1N4007 in // with the power cap. Sometimes not and sometimes the other way around... What it's purpose to begin with?
Last but not least : I was of course thinking of controlling the thyristor directly from the arduino... Is that safe in any way? I was, of course, thinking of using an optocoupler but I've heard some bad things about it's rise/fall speed and that in HV ignition switching, this speed was of a prime importance...
But then again, I'm trying to make an indecrutible / as reliable as possible circuit (within my limited skills : -) so I'm open to any suggestions that could make it so!
Thanks for the feedback!
P.S : http://www.sportdevices.com/ignition/inverter.htm to give back to Caesar!