Christmas Comes Early!
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
The spellman power supplies do parallel nicely and will not sustain damage. I have paralleled 2 of the 40kV version on my fusor, see:
viewtopic.php?f=6&t=10294&start=100
One thing to remember is that these supplies are not stiff voltage sources, they are cockroft-walton multipliers; current only flows in one direction. If you parallel two of them and set them to different voltages, the output voltage will be the one of the supply set to greater voltage with that one supplying all the current. In practice, running them in constant current mode will definitely work in all conditions, but I have also found that by connecting the current program line of the "slave" supply to the current monitor line of the "master" supply and running both voltage program lines at the same voltage set point will cause both supplies to current share equally. You may need to adjust the slave supply to a slightly higher voltage to make this work, but in my case I did not need to do so.
The control loops of these supplies could be modified easily, but there is no need to do so.
viewtopic.php?f=6&t=10294&start=100
One thing to remember is that these supplies are not stiff voltage sources, they are cockroft-walton multipliers; current only flows in one direction. If you parallel two of them and set them to different voltages, the output voltage will be the one of the supply set to greater voltage with that one supplying all the current. In practice, running them in constant current mode will definitely work in all conditions, but I have also found that by connecting the current program line of the "slave" supply to the current monitor line of the "master" supply and running both voltage program lines at the same voltage set point will cause both supplies to current share equally. You may need to adjust the slave supply to a slightly higher voltage to make this work, but in my case I did not need to do so.
The control loops of these supplies could be modified easily, but there is no need to do so.
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
Re: Christmas Comes Early!
Interesting. Though still not something I would try with my own supplies.
There's another result of them not being "stiff": they take time to change between voltage and current mode, and can output a much higher pulse current then the control is set to. This means they can electrocute you even if the current is set to a "safe" level, and it also means that, unlike, say, an NST, they aren't good for arcing because the pulses of very high current heat stuff up.
There's another result of them not being "stiff": they take time to change between voltage and current mode, and can output a much higher pulse current then the control is set to. This means they can electrocute you even if the current is set to a "safe" level, and it also means that, unlike, say, an NST, they aren't good for arcing because the pulses of very high current heat stuff up.
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
They do have filter capacitors on the output and thus can output a higher current pulse during an arc, but the energy storage is small. That being said since they can output 5mA or more continuously they can electrocute you, pulse or not. It's never good to intentionally arc switching power supplies continuously at a high rate, but this is not the normal operation in a fusor unless you are doing it intentionally. The PTV series of supply are an ideal candidate for a fusor, and I would recommend this model, you could probably get near 1e6n/s once it is modified for 350W.
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
Re: Christmas Comes Early!
Do you still need a ballast resistance?
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
I've never used one with my switching power supplies.
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
-
- Posts: 1850
- Joined: Wed Apr 21, 2004 10:29 pm
- Real name: John Futter
- Contact:
Re: Christmas Comes Early!
Ian
Unless you can guarentee that you will not have plasma breakdowns then I would use a ballast to limit dI/dt excursions in the psu
I will put up a photo of what happens to a multiplier stack if you let the supply continuously collapse the output voltage.
the first components to complain are the multiplier capacitors usually somewhere near the centre of the multiplier
Unless you can guarentee that you will not have plasma breakdowns then I would use a ballast to limit dI/dt excursions in the psu
I will put up a photo of what happens to a multiplier stack if you let the supply continuously collapse the output voltage.
the first components to complain are the multiplier capacitors usually somewhere near the centre of the multiplier
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
Ian,
As John said, the word is "continuous"; an occasional spark won't harm the supply, but if you are continuously arcing(like surface tracking on your ceramic grid insulator) the supply may be damaged. More advanced supplies designed for x-ray tubes, like the DXM series, have an arc fault counter that will shut down the supply after a given number of arcs in a time window. The PTV does not have this feature (it does have current limiting), so don't leave it arcing.
I tend to favor not using a ballast resistor since it complicates the HV component train by adding another series component between the supply and grid which then needs to be insulated as well resulting in a larger more complex system. Also consider cooling issues, lets say you want a 100k ballast resistor and have a 10mA system at 40-50kV. At 50kv, an arc/short will draw a peak current of 500mA from the capacitor. During normal operation, the resistor will drop 1kV at 10mA dissipating 10W. It's not a lot of power, but if in an enclosed/insulated system it may overheat. Also consider an RL snubber (parallel resistor and inductor), that way the resistor will snub the di/dt spike, but the inductor will provide very low DC resistance for normal operation.
It's not that hard to include either one, but then again my fusor runs very stably, arcing isn't a major concern for me, and I haven't had any problems.
As John said, the word is "continuous"; an occasional spark won't harm the supply, but if you are continuously arcing(like surface tracking on your ceramic grid insulator) the supply may be damaged. More advanced supplies designed for x-ray tubes, like the DXM series, have an arc fault counter that will shut down the supply after a given number of arcs in a time window. The PTV does not have this feature (it does have current limiting), so don't leave it arcing.
I tend to favor not using a ballast resistor since it complicates the HV component train by adding another series component between the supply and grid which then needs to be insulated as well resulting in a larger more complex system. Also consider cooling issues, lets say you want a 100k ballast resistor and have a 10mA system at 40-50kV. At 50kv, an arc/short will draw a peak current of 500mA from the capacitor. During normal operation, the resistor will drop 1kV at 10mA dissipating 10W. It's not a lot of power, but if in an enclosed/insulated system it may overheat. Also consider an RL snubber (parallel resistor and inductor), that way the resistor will snub the di/dt spike, but the inductor will provide very low DC resistance for normal operation.
It's not that hard to include either one, but then again my fusor runs very stably, arcing isn't a major concern for me, and I haven't had any problems.
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
Re: Christmas Comes Early!
How would you make the inductor? Coil of HV wire?
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
I've had good success wrapping copper magnet wire directly around the resistor from terminal to terminal. This was a snubber for a 100kV, 50A system though and the resistor was about 2ft long 1.5" dia, for a smaller resistor for a fusor you might need better insulation to prevent flashover between the windings.
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
Re: Christmas Comes Early!
Cool. Makes sense, I guess. Does the assembly get potted or oil-onsulated, or just stay in air?
(And also what values would you use for a current controlled switched supply, contrasting with the faq which is for transformers mostly)?
(And also what values would you use for a current controlled switched supply, contrasting with the faq which is for transformers mostly)?
Last edited by ian_krase on Sat Jun 10, 2017 5:20 pm, edited 1 time in total.
-
- Posts: 810
- Joined: Sun Feb 01, 2004 8:02 pm
- Real name: Andrew Seltzman
- Contact:
Re: Christmas Comes Early!
In that design, it was in an insulating tube in air. For your fusor you could go either way
Andrew Seltzman
www.rtftechnologies.org
www.rtftechnologies.org
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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?
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
Re: Christmas Comes Early!
That's a very large value resistor, for a big ceramic one.
Re: Christmas Comes Early!
And also a pretty big inductor. Seems like this might need to be made with smaller components under oil or paraffin.
- Richard Hull
- Moderator
- Posts: 15024
- Joined: Fri Jun 15, 2001 9:44 am
- Real name: Richard Hull
Re: Christmas Comes Early!
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 $$$$. They are limited to running at about 25 kv due to the gobbling up of voltage in the ballast. Thus, their fusion is minmal to marginal. Their good detection system was appropriated for some unknown reason and they were givien a virtually useless battery powered neutron detector of a type useful only in a real neutron field near a reactor. A complex scenario to be sure. They never seem to ask for assistance until they are up against it and it is late in the senior year. The effort is a continuing senior only project.
Thus, each new team must start cold. Not good. U of W has it right....Bring in all classes as pure volunteers letting the freshman be step-and-fetchits, machinists and low level techs. Each ascending class is allowed to become more involved at higher levels of operation and finally research.
Richard Hull
They have a 0-30kv 10ma model $$$$. 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
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
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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.
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
Re: Christmas Comes Early!
Man, thanks for doing the homework. What type of capacitor is that, a film one? Would ceramic be expected to work?
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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
- Dennis P Brown
- Posts: 3187
- Joined: Sun May 20, 2012 10:46 am
- Real name: Dennis Brown
Re: Christmas Comes Early!
Where did you get the info on how to up the rated current on your unit?
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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).
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
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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.
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
Re: Christmas Comes Early!
Huh. Nice job.
Do you have a suggestion as to what to do for just the 330W mod? Go by the schematic?
Do you have a suggestion as to what to do for just the 330W mod? Go by the schematic?
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Christmas Comes Early!
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.
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
Re: Christmas Comes Early!
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?
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?