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[Reply #45 on:]

Now I wonder if the discharge isn't too fast so that I will blast one end of the needle off rather than heating it up...

Instead of guessing, give it a try and see how it works.  

[Reply #46 on:]

Now I wonder if the discharge isn't too fast so that I will blast one end of the needle off rather than heating it up...

This is what I'm not sure about. How to effectively transfer the energy from the capacitor(s) into the needle. Some kind of special switch is going to be necessary. I'd like to see how you make out with this experiment.

[Reply #47 on:]

If you need to slow down the discharge, just add a suitable inductor in series.

Udo

[Reply #48 on:]

@Udo Klein: Thanks! That was what I was looking for.

[Reply #49 on:]

And I forgot to mention: if the caps are electrolytic, a freewheeling diode would do no harm. However compute the resulting currents and be sure that it will be big enough.

Just out of curiosity: what are you going to do with this thing?

Udo

[Reply #50 on:]

what are you going to do with this thing?

Wreak vengeance on bad tailors?

[Reply #51 on:]

Why not just shine an orange LED on the needle.

[Reply #52 on:]

This is what I'm not sure about. How to effectively transfer the energy from the capacitor(s) into the needle. Some kind of special switch is going to be necessary. I'd like to see how you make out with this experiment.

Perhaps some kind of high-power/high-voltage SCR...? Probably wouldn't be cheap (nor small)...

[Reply #53 on:]

Use it to start fireworks . Have several and have a timer set to automatically ignite them

[Reply #54 on:]

Remember to not lick it when it's heated to a orange color.

[Reply #55 on:]

have a timer set to automatically ignite them

The timer of choice used to be a Casio watch

[Reply #56 on:]

Parts are ordered now, and the final built will include an arduino board!

But there are still some things I'm not sure about. When I charge the bank, I can use a low voltage switch(to connect), but after charging can I safely disconnect the charging-circuit from the cap bank?(with the same switch) I'd guess yes since the potential on cap-bank and charging circuit is equal... but not sure and don't want to risk it.

[Reply #57 on:]

I'd guess yes since the potential on cap-bank and charging circuit is equal..

I think your right. It's the voltage that determines if something will arc or zap bare skin. If its charged with a 9V battery, it will be just as dangerous as a 9V battery.. In terms of risk of electric shock and arc distance, anyway. I'm no expert though. So I'd recommend exercising caution anyway.  

Can't wait to see the result. Is the arduino going to be protected from this explosion??

[Reply #58 on:]

I work at an auto parts store. My old manager built an ignition coil tester from a gm hei distributor (no cap just disbtrutor and module). It attaches to a 12v battery, then attach negative and positive to a 12v coil. Where the coil would attach to the coil boot we use a paper clip and wrap it around it and leave about an inch between that and the distributor. Whenever you spin the distibutor (there's a handle on top of the rotor to spin) there should be a nice blue spark. If no spark, replace the coil, if a yellowish spark replace the coil. What's fun is when a new guy would be hired we'd grab a condesor (from a points system) charge it up and leave it on the counter. When the new guy picks it up he gets a nice ZAP and most of them have fell on the floor.  8-)

[Reply #59 on:]

Test with 150V at 220uF on a 400V capacitor, energy 2.475J piece of stranded copper wire.