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Re: Christmas Comes Early!

Posted: Wed Jun 14, 2017 5:40 pm
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).

Re: Christmas Comes Early!

Posted: Wed Jun 14, 2017 11:12 pm
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.

Re: Christmas Comes Early!

Posted: Thu Jun 15, 2017 12:56 am
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?

Re: Christmas Comes Early!

Posted: Thu Jun 15, 2017 11:20 pm
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.

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 4:59 am
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?

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 9:33 am
by Garrett Young
This version requires a jumper change to be enabled by default (see note 1 from my previous post)

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 3:20 pm
by ian_krase
And without that it won't turn on at all?

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 3:47 pm
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

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 9:44 pm
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.

Re: Christmas Comes Early!

Posted: Fri Jun 16, 2017 11:47 pm
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.)

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 12:00 am
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.

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 12:24 am
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.

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 12:41 am
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.

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 1:04 am
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.

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 1:16 am
by Garrett Young
Turn off the lights and you may be able to see where the corona is happening.

Re: Christmas Comes Early!

Posted: Sat Jun 17, 2017 12:32 pm
by Garrett Young
Correction: Standard banana does work.

I'm now offering a high voltage cable (2.5 ft.) and all of the high power mods for $300 +shipping (including the price of the supply)

PTV50N200X2947 power supplies

Posted: Mon Jun 19, 2017 2:46 am
by ian_krase
How are you making the cable that's for sale? Does it have a shield?

The corona (I assume) was more hissing than cracking.


Anyway I got mine completely working, with my front-end and my op-amp boosters all set up.

And then I tested it out, and something rather scary happened.


I had the PSU sitting on a table, with the (roughly 3-4 foot long) HV cable going out to the right where it was held pointing up using a clamp. I had the grounded case of the supply attached via wire to a pin at the end of a nice long nonconducting rod, to which I attached one end of a neon flashlamp tube with the other pin sticking out. My body was always at least 500mm away from any high voltage conductor (other than that inside the ground-shielded cable) and my body was not grounded by any method (wearing rubber-soled shoes, standing on a non-conductive floor, not touching anything else.


I turned the PSU up to the point where corona hissing was audible, then brought the flashlamp on the end of the chicken stick nearer the HV terminal, at which point it illuminated. I moved it away, and of course it went out.

Then I touched the PSU case (to turn it off!) and got a shock. Not a really painful one, more like a really bad getting-out-of-the-car or touching-the-doornob one.


Did my body get electrostatically charged up by the corona? Or is something else bad happening that isn't solved by the grounding of the case?

Re: Christmas Comes Early!

Posted: Mon Jun 19, 2017 5:43 am
by John Futter
yup
charged up!!
it hurts
but doesn't kill

Re: Christmas Comes Early!

Posted: Mon Jun 19, 2017 11:33 am
by Richard Hull
Naked high voltage, in air, with or without major corona will always charge nearby insulated items. (induction).... To what level? It depends on the surface area and leakage rate of the isotrpic capacity. In general, a human, no matter how well insulated, is a really leaky isotropic capacity due to the fine tips of hair, mainly on the arms. If the hair on the head starts to stand up, you are really leaky but have acquired a rather huge charge. If you are on a concrete floor such a charge will blow through your shoes and should you survive, it will hurt.

I have felt myself charging near a Spellman 120kv ladder stack in "lifter" experiments. If this happens, you are too close to the source. Back off and let yourself leak, naturally....No one enjoys an electrical shock, even a mild one. Even a tesla coil at high frequency can charge nearby items via corona or an almost touching arc. (ionic rectification through air)

Richard Hull

Re: Christmas Comes Early!

Posted: Mon Jun 19, 2017 3:49 pm
by ian_krase
Yikes. Can we have an FAQ about this type of hazard?

Also, how can one detect the lower levels of this? Can one discharge safely through a large resistor? Is it mitigated by faraday-caging everything?

Re: Christmas Comes Early!

Posted: Tue Jun 20, 2017 2:10 am
by ian_krase
Oh, by the way, what's a good way to mount your ballasts (so that arcing won't be an issue)?

Re: Christmas Comes Early!

Posted: Tue Jun 20, 2017 2:01 pm
by Richard Hull
A FAQ about a person getting charged from an HV supply is probably not needed. Humans are leaky enough so that only a mild "winter door knob shock" would be possible and our voltages are no where near the needed 70kv++ level of large accumulated isotropic charge. Just know that if the hair on your arm starts to rise you are charging. Move away and leak down naturally. At our super low voltages of 40kv or less it would demand a huge corona and horrid construction to charge a person. Nearby grounded objects will usually stop such leaking corona from charging nearby humans.

You can easily take a two foot, 200,000 volt arc to a wrench in your hand from a "well built" Tesla coil....Provided...... you pluge the wrench into the arc. Approaching the discharge terminal in a timid manner prior to the arc will produce nasty leakage streamers directed at the metallic item and you will feel a nasty, lower current DC rectified voltage that will not be pretty. Van de graff generators can be nasty. The larger the terminal (capacity), the more horrid the shock. Smaller "toy" electrostatic generators are not very dangerous due to a much smaller terminal capacity.

Richard Hull

Re: Christmas Comes Early!

Posted: Tue Jun 20, 2017 3:33 pm
by ian_krase
Ok, that's reassuring. (and all I got were doorknob shocks).

Re: Christmas Comes Early!

Posted: Sun Jun 25, 2017 12:01 pm
by Dan Knapp
Earlier in this thread there was some discussion of paralleling two PTV supplies. Andrew stated that he had done so successfully by connecting the current monitor output of one to the current program of the other. I suggest that an FAQ on connecting power supplies in parallel would be a useful addition. Might Andrew be willing to write one?

Re: Christmas Comes Early!

Posted: Wed Dec 06, 2017 8:28 am
by Jackson Oswalt
What is the complete list of modifications required for 350 watt operation?

I've added a fan and replaced both R50 and C39. What do I need to change R23/R24 to?

Thanks!