Christmas Comes Early!

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Andrew Seltzman
Posts: 815
Joined: Sun Feb 01, 2004 8:02 pm
Real name: Andrew Seltzman
Contact:

Re: Christmas Comes Early!

Post by Andrew Seltzman »

In that design, it was in an insulating tube in air. For your fusor you could go either way
Andrew Seltzman
www.rtftechnologies.org
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Andrew,

The RL snubber is a good suggestion. I'm calculating something on the order of 100mH in parallel with a 100kohm (5us short, 50kV, and 10nF output capacitance) to limit the current pulse to 3A. Does this make sense to you?
Last edited by Garrett Young on Sat Jun 10, 2017 8:10 pm, edited 1 time in total.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

That's a very large value resistor, for a big ceramic one.
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

And also a pretty big inductor. Seems like this might need to be made with smaller components under oil or paraffin.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Christmas Comes Early!

Post by Richard Hull »

VCU (Virginia Commonwealth University) had a major issue with there grossly under powered, yet very expensive, Spellman supply on their fusor. They had to carefully select a ballast resistor due to the current limit tripping out the system when the plasma struck. Ultimately, they hit the correct value.

They have a 0-30kv 10ma model $$$$. They are limited to running at about 25 kv due to the gobbling up of voltage in the ballast. Thus, their fusion is minmal to marginal. Their good detection system was appropriated for some unknown reason and they were givien a virtually useless battery powered neutron detector of a type useful only in a real neutron field near a reactor. A complex scenario to be sure. They never seem to ask for assistance until they are up against it and it is late in the senior year. The effort is a continuing senior only project.
Thus, each new team must start cold. Not good. U of W has it right....Bring in all classes as pure volunteers letting the freshman be step-and-fetchits, machinists and low level techs. Each ascending class is allowed to become more involved at higher levels of operation and finally research.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

My power supply arrived and it appears to be brand new. This particular X-version of the supply was private labeled for Hurletron. The only modifications required for 350W were as follows:

C39 0.022u/100V (i.e. KEMET R82EC2220DQ50J)
R50 4.7k 5% 1/4W

I didn't add a fan because of the short operational duration and low duty cycle for my application.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

Man, thanks for doing the homework. What type of capacitor is that, a film one? Would ceramic be expected to work?
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

A ceramic capacitor has the drawback that the capacitance changes with applied voltage so I would use a film capacitor (as used in the original design)
- Garrett
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Christmas Comes Early!

Post by Dennis P Brown »

Where did you get the info on how to up the rated current on your unit?
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Schematics included in this thread. viewtopic.php?f=11&t=4852
- Garrett
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Actually, the V/mA feedback from the multiplier must be different between the 200W and 350W version.

Either R23 or R24 needs to be changed as well to adjust the gain of the opamp (currently a gain of 2, this would need to be reduced in order to increase output current).
- Garrett
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Please ignore all my previous posts regarding modification.

Here is my tested to 504W (42kV @ 12mA, 1M++ n/sec) configuration:

1. JP2 Moved to Jumper Pins 2 and 3 on the enable header (this will enable the supply by default - Note: besides the additional danger this modification requires the input EMI filter to be spaced away from the housing several millimeters to accommodate the jumper in the 2-3 position)

2. R23 changed to 294kohm 1/4W 1% which decreases the current feedback op amp gain from 2 to 2/3 and increases the regulated current from 4mA to 12mA.

3. Removed CR11 (added for the X2947 version) which I believe provided OL (over load) protection.

4. Changed C39 to 0.022u/100V (i.e. KEMET R82EC2220DQ50J) and R50 to 4.7k 5% 1/4W (these are part of the current error integrator circuit and are the slower response values for the 350W version. Generally, additional tuning of the feedback and compensation loop is probably required since the supply is operating at a power greater than 350W. Some audible noise/instability can be heard and it passes through the transition from constant voltage to current. Ultimately, once in constant current mode it seemed stable.)

5. Changed the input fuse to 6A (was 4A).

6. Refer to Spellman's PTV model documentation for the 9-Pin control/monitor header. I used the reference voltage from pin 1 to set the current to the max (pin 2) and bias a 50kohm potentiometer to control the voltage (pin 4).

--Warning---
These changes are my own and not recommended. Power supply failure is very possible. A fan will only cool the un-potted components and this will place stress on the multiplier diodes. Proceed at your own risk.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

Huh. Nice job.

Do you have a suggestion as to what to do for just the 330W mod? Go by the schematic?
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Another note:

7. Remove several turns (3-4) from the inductor (L1) in series with the primary of the high voltage ferrite transformer (T2). This will allow higher peak current through the primary. (Careful removing too many turns will cause problems).

Previous warning still applies.

For 350W operation - my suggestion is to follow the schematic but either R23 or R24 needs to be changed as well in order to adjust the gain of the opamp (currently a gain of 2, this would need to be reduced in order to increase output current). The fact that the table at the end of the schematic doesn't indicate this is slightly concerning and either the current feedback (V/mA) is different between 200 and 350W models or I'm missing something.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

I got mine today but wasn't able to get it operating. (Also, I don't yet have ballast parts or a working vacuum chamber to test it with, just a high voltage probe...)

The interior looks fairly different from that thread about the 40kv unit.

Am I correct that just leaving pin 7 of the connector floating should turn the unit on?
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

This version requires a jumper change to be enabled by default (see note 1 from my previous post)
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

And without that it won't turn on at all?
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

I assume by driving JB3-7 high or low will enable it as well (but moving the jumper is easy) ... take a look at the schematic
- Garrett
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

I've now optimized the control loop components and the supply operates smoothly at 600W. I'm still operating at a low duty cycle, but it's very usable for fusion.

If anyone is interested I could purchase supplies and modify and test them to 350 - 600W (depending on what you want) for $250 including the cost of the supply. I'll make all the necessary component changes (including an upgrade of a couple of key parts in the half bridge), tune the supply's control and power stages, add a fan, and test to the desired wattage. Message me if you are interested.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

i managed to get it working.

Unfortunately I think something is wrong with either the voltage feedback or my cable. At about 2/3rds of the voltage dial I start getting corona type noise.

Also I think it is interlocked to the cablebeing plugged in.

Does your voltage output work? What are you using for the cable? I have rg-213u.


(please excuse my typing, I am out of desk space.)
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Did you pull pin 7 low?

I've powered my fusor with this supply at 50kV/12mA. The HV cable is a non-standard length between the threaded connection and the internal high voltage terminal. In addition, the pin diameter needs to be smaller than the standard Spellman cable. I just mocked something up with some high voltage wire 2mm bullet terminal and a liberal amount of silicone grease.
Last edited by Garrett Young on Sat Jun 17, 2017 12:46 am, edited 1 time in total.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

Wait, a 2mm bullet? I just used a banana and it seemed to work. And yes, I used the PL259+hugelongcablebanana type arrangement.

I was able to use corona (I think it's corona?) to light a small flashlamp from several inches away. No vacuum chamber to test on, of course, and not quite sure what to do about the corona since I don't have any metal balls.

The real question is what is up with my voltage monitor. My 10 volt meter (galvanometer style, tested) barely deflected at all. As far as I can tell, TP3 (which is before the voltage monitor buffer) outputs 10V just fine but somehow R31 (and nothing else) drops this down more than 10x.
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

I think a standard banana plug is too large to actually engage (at least it seemed to me). That may be why you are hearing some cracking. Silicone grease may help.

What is the full scale current of your meter? If the meter is 10V FS and 1mA FS then it should work because the output impedance is 10kohm. If the FS current is higher than 1mA then it will not deflect appropriately.

I'm not sure what you mean about interlock to a plugged in cable, because that doesn't seem to be present in the schematic and mine doesn't operate that way.
- Garrett
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

Re: Christmas Comes Early!

Post by ian_krase »

That is exactly the problem. And I paid 8 bucks for the thing! My meter has an impedance of less than a kilohm!

I think that the corona noise is at the end of my cable. Not sure. Any suggestions on how to locate it?

I guess I need to add an op amp buffer to drive the meter. I considered shorting out the 10K resistors but it looks like the LF444 degrades significantly as it reaches the needed currents.
User avatar
Garrett Young
Posts: 123
Joined: Fri May 26, 2006 9:51 pm
Real name: Garrett Young

Re: Christmas Comes Early!

Post by Garrett Young »

Turn off the lights and you may be able to see where the corona is happening.
- Garrett
Post Reply

Return to “High Voltage - Fusor Input Power (& FAQs)”