 Charging capacitor for air gap flash
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neondion
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Mon Oct 21 2013, 09:49PM
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Registered Member #38645
Joined: Thu Oct 17 2013, 01:36PM
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Posts: 1
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I am working on a project to build an air gap flash for high speed photography and need to better understand how to charge a high voltage capacitor.
I am following this schematic: 
Which is from this build:
I like this build because it uses a compact 25kV power supply that is relatively inexpensive to buy.
I have purchased all of the parts for the project except for the high voltage power supply.
For my capacitor I was able to obtain a Maxwell capacitor rated at 50kV, .04uF, and .017uH internal inductance.
My question is regarding how the current needs to be limited while the capacitor charges. In the schematic it looks like the cap is hooked up to the power supply without a current limiting resistor. I'm guessing this works because the power supply he is using can be using in either current control or voltage control mode. Here is a link to the power supply website it is part number HV250(+):
The power supply vendor indicates that if the power supply is run in current control mode that you won't need a current limiting resistor, but that the final voltage of the capacitor might be higher than the power supply's rated output because the power supply voltage will tend to 'soar' over the rated voltage. How can I determine how much overhead my capacitor will need in its voltage rating to accommodate the 'soaring voltage'?
Any insights would be appreciated. I have worked on many low voltage, digital electronics projects in the past, but never anything with this high of voltage and figured I should get familiar with what I am doing before attempting anything.
Thanks!
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Pinky's Brain
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Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
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Couldn't you put a massive stack of TVS diodes on the output to limit voltage? (About 10 Euro worth of P6KE440A_Q at mouster, if you buy them before they run out.) Put a LED in the string to know when the desired output voltage is reached.
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