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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Do you not need some form of current limiting in order to prevent voltage sag?
Can you limit beam current by regulating filament current?
Do you need a 'load impedance' (ie resistor) to limit current?
(I'm not certain about this, but I think it's relevant, from my understanding of these things.)
EDIT: I think this is what the triode does. I designed something similar for 'pulsing' a magnetron for a similar type of application. I've not built it yet, though.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
for 10kv all you really need is a large ferrite core and a forward converter or generic halfbridge/fullbridge. Sadly, you will need something a bit larger than a flyback core for 10kw average (unless you decide to go down the route of paralleling a bunch of supplies), but something like should work well as long as you are careful to pack the wingdings close and run at 50+khz to keep the power density high.
A good starting point might be a solid state x-ray supply, like , unfortunately they are usually configured for a bit too much output voltage so you may need to open it up and remove some of the doubler stages.
Registered Member #3272
Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101
Sulaiman wrote ...
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.
This is the gun, made by Sloan and is still made by another company, YTI. According to the manual, 99.9% of the energy goes into the material and will handle up to 12kw. Depending on the material there are different methods that are used to evaporate it like scanning over the surface or using a single spot. With a gun like this you are going to need about 3kw minimum to get anywhere using a graphite crucible.
Registered Member #3272
Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101
mikeselectricstuff wrote ...
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.
It does need to be smoothed somewhat. How much, I dont know. I have not found any specs on what kind of ripple it can take. The ripple will cause the electron beam to move in the direction that it is bent. Lower voltage makes a tighter bend. Thats probably why most of these supplies are three phase, less ripple.
Registered Member #3272
Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101
Ash Small wrote ...
Do you not need some form of current limiting in order to prevent voltage sag?
Can you limit beam current by regulating filament current?
Do you need a 'load impedance' (ie resistor) to limit current?
(I'm not certain about this, but I think it's relevant, from my understanding of these things.)
EDIT: I think this is what the triode does. I designed something similar for 'pulsing' a magnetron for a similar type of application. I've not built it yet, though.
Yes, some sort of limiting is needed because you dont want the gun to run at full power all the time. Different processes require different currents.
You ought to be able to limit emission current with the filament. I was considering this for a basic design, I figure if it works in my SEM, it ought to work here.
The triode is used as a voltage regulator. Current is limited by the "transductor" which is just a mag amp. Old, simple tech used in some welders too. It might be possible to use a movable core inductor to do the same thing.
Registered Member #3272
Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101
... wrote ...
for 10kv all you really need is a large ferrite core and a forward converter or generic halfbridge/fullbridge. Sadly, you will need something a bit larger than a flyback core for 10kw average (unless you decide to go down the route of paralleling a bunch of supplies), but something like should work well as long as you are careful to pack the wingdings close and run at 50+khz to keep the power density high.
A good starting point might be a solid state x-ray supply, like , unfortunately they are usually configured for a bit too much output voltage so you may need to open it up and remove some of the doubler stages.
I have been considering building some sort of switching supply. I have quite a few large half bridge IGBT modules. I used to be a miller service tech and have worked on quite a few inverter welders and have lots of parts lying around. I have a bunch of 300 and 400 amp modules.
For the transformer I am wondering if I could use this x-ray transformer I have as a donor, it was supposed to be something like 100-120kv. I am never going to do anything with it. It has a laminated steel U core with a 1.5x3" cross section. I am not sure what the alloy is, I could put some filings under the SEM and use the EDX to find it's composition if it really matters.
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
I wouldn't scrap such a lovely transformer! At least try selling it if you arn't gonna use it. Could probably get enough money to get a custom transformer guy to wind you a new one.
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Need a BIG 10kv DC supply
