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Need a BIG 10kv DC supply

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LAN_403

macona

Sat Jun 06 2015, 12:09AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

I am putting together an electron beam deposition system for my vacuum chamber. I need a big 10kv dc power supply for the filament bias, the gun I am using is rated up to 1.2 amps emission current, thats 12kw, I would be happy with even 4 to 6 kw (400 to 600ma)

I am trying to build a setup for doing dichroic mirrors and bandpass filters.

Any ideas?

Patrick

Sat Jun 06 2015, 12:25AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yikes !!!

Id suggest:
10 paralled automatically load sharing, each 1kw sections.
current mode (not voltage mode) feedback.
ferrite cored at 100khz or so.
power factor corrected, 240 AC rectified input would be a must.

Theres more but ill have to think on it. youll need to read everyone of the TI/Unitrode documents.

this is no trivial SMPS.

macona

Sat Jun 06 2015, 01:02AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

Yeah, it is a pain. Old commercial e-beam supplies are 3 phase transformers into a bridge for -10kv and then though a giant triode. Some use magnetic amplifiers to regulate the output current.

Then I need a filament transformer, 6v at 40amps and isolated for that 10kv. I am thinking of a MOT and then winding a secondary from some 8 AWG HV wire, if I can find any.

Some prints of the old tube based supplies here. These things are still incredibly expensive on the used market.

Sulaiman

Sat Jun 06 2015, 07:57AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

a few thoughts;

1 where do you expect the 12 kW to be dissipated?
... my expectation is that it will be in the target/glass ... can you cool it adequately?

2 how long would it take to deposit, for example, a 1/4-wavelength thick coating at 1.2A?
... not long I guess !

since deposition rate is proportional to current, you could use a lower current for longer,
this would allow a MUCH cheaper power supply
and finer control over total charge / deposition thickness.

if this is for hobby / very small scale use
then I suggest;
single phase ac - variac - NST/OBIT or similar - rectifier(s) .... NO capacitor(s)
. the NST/OBIT would provide short circuit / over current protection
. the low current output of an NST/OBIT and lack of capacitance / charge storage makes the power supply scarily painful but (generally) non-lethal

I'll add any afterthoughts later.

mikeselectricstuff

Sat Jun 06 2015, 10:28AM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

Does it matter is it's not smoothed? If not then something crude like a transformer, halfwave rectifier and ballast may do it.
But as mentioned, just because it's rated to 1.2A doesn't mean you need (or can) use it at that level.
Start off with something quick cheap & easy at a lower current, get it working then decide if you really need isane power.

Dr. H.

Sat Jun 06 2015, 11:10AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Fast thought- Single phase variac, two (three) MOTs in series (and in oil) plus a microwave oven style doubler ?

Bored Chemist

Sat Jun 06 2015, 11:23AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Fast response.
Don't try connecting 2 or 3 mots in series.
The insulation between the secondary and primary windings isn't built for it.
You might getaway with it for a while- or you might get a fire.

dexter

Sat Jun 06 2015, 12:22PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

Bored Chemist wrote ...

Fast response.
Don't try connecting 2 or 3 mots in series.
The insulation between the secondary and primary windings isn't built for it.
You might getaway with it for a while- or you might get a fire.

not even in oil?

Dr. H.

Sat Jun 06 2015, 03:34PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi Bored Chemist,

I have 2 coils using multiple MOTs in series and never had an issue (everything is submerged in oil). I don't claim it is a good idea or that the transformers are designed for this, but they seem to work. The longest I have ever run them non stop (two in series) is about 30mins though.

Disclaimer - everyone who tries to do this is on his own risÐº

Cheers

Patrick

Sat Jun 06 2015, 04:11PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Bored Chemist wrote ...

You might getaway with it for a while- or you might get a fire.

Like Vegas, the roll of the dice is where the fun is at !
(and if you burn your house down, you went to far.)

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