Ballasting Resistors?

[River Marlowe]

Hey Everyone,
I am currently in the process of selecting parts for my HV circuitry for my demo fusor and, with the help of the FRQ's, came to understand a lot more about electronics. However, one component I can't find much information on is the ballasting resistor. From what I could find on the internet, this component seems to limit the current of a line, but why is that important in fusor applications? Why exactly is it needed? Lastly, is this an acceptable ballast resistor for my demo fusor?

https://www.zaversone.com/index.php?mai ... _id=242263

Thank you!
River M.

[Richard Hull]

Did you read my FAQ on Ballasting resistors?

viewtopic.php?f=29&t=13497&p=87915#p87915

These are usually 5-inches to 12-inches long in the value and wattage we would typically need. They are rather rare now as they were much more common to the vacuum tube era.
The thing is that they are rather large and ugly and are green or brown in color. I attach an image of the type thing you will need if your supply demands a ballast resistor. pay no attention to the value in the image as it is too low, but the wattage dictates the size.

Richard Hull

[John Futter]

River
the ballast resistor helps the power supply to not collapse totally in output quickly ie it limits dV/dt
I use those same resistors that you have found but I use 5x 10k ohm ones in series a single resistor will flash over to the aluminium case at a few kv. and as you can guess 30-100k ohms is about the right size for a fusor

[Richard Hull]

The aluminum case is the killer. Never use those resistors. During a ballast action, all of the load voltage might appear across the resistor. The resistor I show is pure ceramic and cannot arc over. the only metal allowed is the internal, fine, high resistance wire and the large two end lugs. No metal body allowed.

Richard Hull

[River Marlowe]

I read the ballasting FRQ but was under the false impression that ballasting the NST and a ballasting resistor were two separate components. I am using a 60hz Franceformer so ballasting won't be an issue for me.

Thank you all!
River M.

[Richard Hull]

Yes, that is what FAQs are all about......Explaining, in some detail, specific issues.

All classic, heavy, old school, neon sign transformers are magnetically shunted and cannot be overloaded with even a dead short!! They are a beautiful example of 1920's magnetic design.
The feather weight new class of switched electronic designs are rather useless for demo fusor purposes. "If it weighs a ton, you have won." "If it is feather light, you have lost the fight"

Richard Hull