Fusion Success with Precipitator Power Supply

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Bob Reite
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Re: Fusion Success with Precipitator Power Supply

Post by Bob Reite » Sun Aug 11, 2019 3:38 am

Yes, it annoys me that they ground off the part number of the ICs.

I was using the fusor operating with air as my load. I can pretty well control the flow rate with the mass flow controller and the pressure with the exhaust valve controller.

I'm not sure what arced to what.

Next thing I want to do is install an insulated extension shaft and change the mounting such that I can safely operate the output control while it is running. That way I can get a stable plasma going then adjust that control. I have been turning the shaft a few degrees at a time with the power off, then checking my results by switching it on with a switch at a distance.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Mark Rowley
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Re: Fusion Success with Precipitator Power Supply

Post by Mark Rowley » Sun Aug 11, 2019 5:24 am

Installing an extension for the voltage control was the first order of business. It’s a 10k potentiometer which I replaced with a standard panel mount on an 8’ lead. I then mounted it in a plastic experimenters box and affixed an acrylic rod for control.

Aside from the mystery chip any thoughts on the two unmarked dip switches along the left side?

Mark Rowley

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Richard Hull
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Re: Fusion Success with Precipitator Power Supply

Post by Richard Hull » Sun Aug 11, 2019 5:36 pm

14 and 16 pin ICs were typical of the early PWM chips. Just a thought.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Chris Giles
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Re: Fusion Success with Precipitator Power Supply

Post by Chris Giles » Sun Aug 11, 2019 9:31 pm

An example:
http://www.ti.com/lit/ds/symlink/tl494.pdf
If you want to identify the chip, I suggest finding out which are the VCC and GND pins and matching that to various 16-pin controller ICs - look for the most common / cheapest ones.

Once you have identified the chip then you would stand a better chance of working out what the DIP switches are for.

Regards
Chris

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Re: Fusion Success with Precipitator Power Supply

Post by Rex Allers » Mon Aug 12, 2019 2:55 pm

I've joined the fray too. I ordered one each of the 30kV (two transformer) and 60kV (4 transformer) supplies.

Unfortunately, the bigger one arrived with the HV output wire broken off where it comes out of the transformer. After a few emails with the seller, he is sending me another one of those supplies. But it's coming from China and will be a while before I get it.

Meanwhile, I started hacking the circuit board of the bigger supply. One good thing is that the circuit board is single sided -- only one layer on the bottom. I have begun my usual method.
1) I scan the board in a flatbed scanner to get an image of the traces.
2) In a photo editing program I draw in red circles on top of all the vias and then lines over each trace.
3) I select all the red as an object, cut it and paste it into a blank image.
4) I use a tool to flip it horizontally, so now I have an image of the traces as seen from the component side.
5) I print it out and start penciling on symbols for each of the components, so I can begin to see how things are connected.

I haven't got all the components on yet and I may have to redo some as enlarged sections because it is messy crowded. Anyone else care to join me on trying to figure it out?

So far:
The 8-pin chip. Pins 5 and 7 each have a 10 ohm resistor in series to the gate of the two big MOSFET transistors. So I'm pretty sure its a standard dual gate-driver chip. The first one I guessed didn't work with the power pins for the chip. A little searching and an IR2101 or 2102 seems to match pins.

Looks like there are two opto isolaters feeding the inputs to the gate driver chip. It doesn't look (to me, so far) like simple outputs from the 16-pin chip are doing the switching. I'm only getting the lay of the land at this point.

I hacked a CCFL supply a few years back. They used a gate driver chip and sampled voltages on the FET drives to make sort of a big flip-flop transitioning at zero crossings and resonate with the transformer. Maybe something like that is happening here.

The 16-pin chip. So far it doesn't look like a switching controller that I recognise. There is a 4-pin header near one end of the chip. Maybe the chip is a microcontroller and the header is to allow programming firmware.

There are two current sensing transformers on the board. One is sensing the AC input and the other is in the HV transformer primary drive.

There is a blue transformer. It takes the AC input and drops it down. That lower voltage feeds a 7812 regulator to make a +12V rail. It feeds the 8-pin chip. That rail then feeds a 7805 to make 5V. I think that the 5V is the supply for the 16-pin chip.

Anyway, that's some observations after a few hours of digging. I haven't gotten most of the components drawn around the 16-pin chip yet.

I'll post more if I get more details.

I do have a lot of apprehension about the daisy chaining of the 4 HV secondaries of the output transformers. I expect the low (minus) end of a secondary is near the core and probably wasn't expecting to be sitting on top of the high end voltage from previous transformers. That could be where Bob's arcing came from.
Rex Allers

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Bob Reite
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Re: Fusion Success with Precipitator Power Supply

Post by Bob Reite » Mon Aug 12, 2019 10:03 pm

I asked my seller about the purpose of the 2 dip switches and the four pin header. He did not respond to my question about the header. As far as the switches all he said was "You can just ignore them for normal operation", so I left them as shown in the photo.

I did get a .docx instruction sheet from the seller. Grab a copy at: http://telcen.com/gbopix/CNC7353-600.docx

I came to pretty much the same conclusions as Rex Allers. I do find it interesting that the instructions specify "Positive and negative discharge distance should be less than 8cm" to protect from over voltage. Apparently arcing the output won't damage the supply, but letting the HV get too high will.

The voltage control is wired as a two terminal device, that will make it easer to remote it. I'll report back when I get it set up so I can safely adjust it hot and see if can get more current out of it at a higher voltage.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Mark Rowley
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Re: Fusion Success with Precipitator Power Supply

Post by Mark Rowley » Mon Aug 12, 2019 10:44 pm

Hi Rex,
That’s some top-notch sleuthing! I’m looking forward to your results.

I have yet to test the 60 to any reportable degree due to some flashover issues with my 30kV feedthru. I’ll post more about that in a different thread.

Finn was fairly clear about his concern regarding a flashover between the core and output wire. Main reason I’m running my supplies under mineral oil. Not worth chancing the potential damage by running it in open air.

Bob, thanks for reaching out to the seller. It was on my list but hadn’t done it yet. Even though the instructions are anemic, the info about “locked state” is a good thing to know. Had no idea.

Mark Rowley

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Bob Reite
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Re: Fusion Success with Precipitator Power Supply

Post by Bob Reite » Tue Aug 13, 2019 1:38 am

Somehow I killed the driver circuit after extending the voltage control. It might have been because I had an open circuit.

In any case, I was planning to trash the factory drivers and build my own, but I decided to research the issue of driving these flybacks in parallel and connecting the outputs in series. I used my trusty bullet proof audio amps with the function generator to drive the primaries. Even though I was putting in only 70 V RMS, I was able to get 35 KV at 7 mA out of the things. I increased the load impedance (by lowering the chamber pressure) and got the arcing again at around 48 KV. I was able to determine that it was the highest potential transformer arcing to the core. Even though the core is on an insulated board, I suspect that it was also arcing from the core to the primary.

Bottom line, I don't think these will be usable for full fledged fusors, unless derated perhaps to 40 KV tops. In the intended application, the electrostatic precipitator, plus and minus are left floating so there is no stress from the HV winding to the core, certainly not as much as when one end of the output is grounded.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Mark Rowley
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Re: Fusion Success with Precipitator Power Supply

Post by Mark Rowley » Tue Aug 13, 2019 2:28 am

I disagree, at least at this point. Proof will be in the doing and I’ll be moving forward with the tests.

If I end up being wrong then so be it. But that being said, Ive yet to blow out either of my supplies.

And what is the definition of “full fledged”? A spherical large cavity fusor? I’ve logged close to a full hour of neutron production at 30kV with the smaller supply with no hiccups. I contend that after the feedthru mod is complete a similar result will follow with the 60.

You’re too quick on the naysayer button. Give it a chance.

Mark Rowley.

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Bob Reite
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Re: Fusion Success with Precipitator Power Supply

Post by Bob Reite » Tue Aug 13, 2019 8:08 pm

As I said, if you derate the supply to 40 KV it should work fine as it stands. The small cross fusors seem to do quite well at 30 KV. I am going for higher Q in an 8 inch cylinder, and I want to get to 50 KV at 10 mA. The grid design I'm using now can handle 500 watts input. I dismantled my supply transformers and there is no evidence of damage from the arcing, which is good news. I plan to make some changes that should solve the arcing problem at higher voltages.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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