Is your meter measuring primary voltage to transformer or high voltage across cap? I am having some problems with dye laser flashlamp measuring voltage on cap. My meter works great under stable voltage conditions, but fries op amp when lamp discharges.
I am using a 10 Gig Ohm voltage divider so 20KV reads as 20V. It is buffered through op amp as unity gain follower to meter. Right now I am researching amperage. I think, maybe, the rapid change in voltage creates too much current for op amp. i=c x dv/dt. cap= 1uF, time=<100ns, voltage change is 20v.
I love those cheap little digital voltmeters, but they have way too low impedance for Gig ohm divider... hence the op amp.
I can try a diode on the 20v input if you think this would help.
I also added diodes just to balance things out a bit when adding the diode the voltage will drop by -/+ 1% deepens on the diode what i did i added step up power supply module so i can adjust the output power max 30V /2A since the capacitor's max working V is 8V but the arc is 5 inch so i use 5V to 5.5V 2A just to be safe
Your project reminds me of a gradeschool science fair project I did on lightning rods. I connected a neon sign transformer to a doll house to show that lightning hit the house without a rod, and hit the rod when it was added.
I have always found it interesting that high voltage seems to have a mind of its own. No matter how many rules you follow or what your insulation is rated at, it will do what it wants.
I concur with Cyparagon here, 150Kv will jump between 15-16cm, which is beyond what you are outputting here.
Damaging insulation will eventually lead to carbon tracking inside the ignition coil windings and eventual failure of the components by way of short to ground across the secondary windings.
Keep your wiring simple. If you do want to run a "lightning" simulator I'd highly suggest a 10-20 stage marx impulse generator with 40Kv rated ceramic 2nF disk caps and resistors.... This will give you FAR more than 150Kv to "play" with
DO NOT shock yourself with a marx generator. A small one will hurt like hell. A larger one can pack enough current to blast your fingers off or worse.
Walton cockcroft voltage multiplier
Marx generator (~350-360Kv)
Very lethal. 3J per pulse