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Re: Electron gun- what's wrong here?

Posted: Mon Aug 22, 2016 8:56 pm
by Steven Sesselmann
David,

That's correct, whatever power supply you use to heat the filament needs to float, so you need an isolation transformer.

In a fusor situation it is unlikely that you will need 10's of kV isolation because (as you discovered) you only need a few hundred volts to 1000V on the filament to make it emit electrons, those electrons will ionise some gas and keep your fusor lit at low pressures.

Steven

Re: Electron gun- what's wrong here?

Posted: Wed Aug 24, 2016 7:59 pm
by David Kunkle
Is there any problem with using a battery for the filament PS? I had a 12V lead/acid motorcycle battery in mind. The whole battery would be floated to whatever HV potential is used on the filament.

Re: Electron gun- what's wrong here?

Posted: Wed Aug 24, 2016 8:15 pm
by Steven Sesselmann
David,

No problem at all, I do the same on my rig, floating two 18V cordless drill batteries to power an MFC a USB hud and a DAQ.

Check the current draw and work out how long the battery will power it.

Steven

Re: Electron gun- what's wrong here?

Posted: Thu Aug 25, 2016 12:35 pm
by David Kunkle
Thanks. Just wanted to make sure. It sounded OK in my head, but on the other hand, I could do without a battery exploding. I'll just make sure it's electrically insulated well enough from everything else.

My filament will use 6W @ 12V. So it should last many, many times longer than I need before I'd have to recharge if I go with the motorcycle battery.

Re: Electron gun- what's wrong here?

Posted: Sat Aug 27, 2016 3:09 am
by Rich Feldman
>> I do the same on my rig, floating two 18V cordless drill batteries to power an MFC a USB hud and a DAQ.

You can also electrically float a cordless drill with _no_ batteries, and use its motor as a generator.
DSCN0973.JPG
As shown on fusor.net in 2010: viewtopic.php?f=11&t=4771&p=27609
The old image thumbnails have not been treated nicely.