Precipitator HV Supply Hacking

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Rex Allers
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Precipitator HV Supply Hacking

Post by Rex Allers »

Looks like my thread about hacking/reverse-engineering of the Chinese Precipitator supplies is one that got lost in the forum move. I think I started it a little over a week ago ~8/21.

I see Mark Rowley's thread about success with Precip supplies survives, but I don't see his thread about these supplies then failing for him. I think the failure thread was more than a week ago.

When I post a long message to the forum I usually write it locally on my PC and then paste it into the forum message compose box, so I have a copy of some of my threads. From that I'm now reposting my thread using the same name:

Precipitator HV Supply Hacking

The message about finding out what the 16-pin chip actually is is new, as it was found out while the forum was moving.
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

I thought I would start a new thread about the circuits in the Chinese Precipitator Supplies. There has been at least one recent successful use of one of these in a small-chamber working fusor. There have also been reports of pretty fast failure in some of these.

There have also been speculations about these supplies for a few years with very little actual data.

A typical eBay listing title:
High Voltage Electrostatic Precipitator Power Supply 300W 400W 600W

To see what I could learn about these, I ordered two supplies:
one 30 KV 300 W
one 60 KV 600 W

I have spent some time reverse-engineering / hacking the circuits of these two supplies. I must admit that at this point I have not yet powered either one of these up. I just looked at what is on these boards and what they are doing.

After many hours, I think I have enough info and in barely good enough form to share. At this point only what I see, think I know, and know I don't know. I can't yet comment on suitibility, reliability or if they can actually come close to the rated voltage and wattage specs.

Hopefully my current level of information will help others to evaluate, speculate, fix problems, comment, or correct me.

At this point, I have created 4 zip files with the info I have created and some of my thoughts on what's going on in these circuits. I have placed these in my own web space for now. The files are several megabytes. If things are recieved well, and after any corrections or additions, I could put the info on the forum. Admins, let me know if that is desired.

--------------------
So here are links to download the 4 zips. You have to get the 4 full link paths correct or you will get not found, or no permission msgs...
In: www.xertech.net/precip-hv/ (just for info, you can't access the whole dir.)
total size: ~7.5M

1) ~940K
http://www.xertech.net/precip-hv/Precip-Gen-Info-01.zip

2) ~870K
http://www.xertech.net/precip-hv/precip-30-hack-01.zip

3) ~1.3M
http://www.xertech.net/precip-hv/precip-60-hack-01.zip

4) ~4.5M
http://www.xertech.net/precip-hv/precip-parts-01.zip

About the zip contents...

#1 Precip-Gen-Info-01.zip
Start with this. Contains a PDF doc that is an intro. It covers general information and also descriptions of circuit aspects that are mostly common to all the supplies. Also contains imgae files that are used in the pdf.

#2 precip-30-hack-01.zip
Details of the 30 KV supply circuits that I have found. '_notes' is a semi-random list of my comments about the circuits.

#3 precip-60-hack-01.zip
Details of the 60 KV supply circuits that I have found. '_60kV files_' is a brief description of the content of the files in the zip. '_notes' is a semi-random list of my comments about the circuits.

#4 precip-parts-01.zip
Is just a collection of data sheets for parts that are used in the supplies. If you want it, it should just save some time for finding them yourself.
------------------

Hope it helps. Let me know what you think. Especially let me know if you see anything I got wrong.
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

One open issue for the 60 KV supply is that it has a 16-pin chip with the markings ground off.

From looking at the circuit I'm pretty sure it must be a microcontroller of some kind but I haven't found a chip that seems to match the pin functions I have sussed out. On the elimination side, 16-pin micro chips seem to be prety rare, and 5V power on pin 6 may help ID too.

I'm hoping someone might have good microprocessor cred and recognise what this chip might be.

Here's an image I made. I think the analog pins are configured as inputs that way. The unmarked pins should be 5V-active digital in or out pins.

Let us know if anyone has a guess of what it is.
16-pin-chip.png
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

On the 60 KV supplies, I figured out what the 16-pin chip is. (The manufacturer grinds off the markings.)

Today I got my replacement for the 60 KV supply I had ordered that arrived with a broken HV output wire at the transformer. Looking at the top of the 16-pin chip, I saw some hints of numbers. With a tiny bit more sanding to take off the tops of swirls, a bit of water to blend and coat, and tipping for best light under a microscope -- I think I have it!

Saw something like this...

Code: Select all

-----------------
      15W408AS
 STC
      1824   ???
-----------------
I wasn't sure if this was just a partial or if I interpreted completely accurately, but after some web searching, it looks to be a complete part number and makes sense.

As I suspected, the chip is a microprocessor. It is made by the Chinese company STC. The part number (STC15W408AS) is a variation of the old, long lived 8051/8052 design and is in their 15 series.

Here's the web page for this part's info...
http://stcmicro.com/stc/stc15w408as.html

In the middle of that page are links to...
General Overview: STC15W408AS_Features.pdf
Data Sheet: STC15F2K32S2.pdf

As I suspected the 4-pin header near the chip could be used to load firmware onto the chip. There are tools for development if you follow links on the stcmicro pages. I haven't tried to install them and read the code from the chip. It may be locked or encrypted and even if clean, it would be a big task to disassemble / decompile.

So not sure if this new info helps much to more fully understand the supply operation, but at least we know what the chip is.

Here is an image of the chip pin-out from the datasheets that I have modified by adding my deduced functions (about the 60 KV supply) for each pin, outside the vertical lines that I also added.

Micro pins usage.png

Looking at this new blending of info, the pin-14 signal which I have called 'Switcher Osc Mon', could possibly be configured as an interrupt, occuring at the switcher Osc rate. (More guessing.)
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Hi Rex
I noticed the same as well. I have a rough copy of that post which I’ll put here:

———————————————————————————————-
18Aug19

Well, it happened...
The 60 just took a nose dive. I’m reluctant to say it was a flyback failure as I barely taxed the supply. I’m thinking it was a cheap overseas MOSFET or similar. I’ll dig into it over the next few days. Maybe beefing up the driver won’t be too difficult.

This how it went down. I just got set up for a run and slowly inched it up to 15kV with about 25mTorr of deuterium. There couldn’t have been more than a 1.5mA draw and suddenly no output. No spark, pop, pressure disturbance, notable current increase, etc. Both ready lights remain on and no overload relay “clicking” present.

The supply has never been pushed close to its limit (which was the plan for later today). The only mentionable run it had was last night (10 minutes at 3.5mA /25kV / 40mTorr / 346cpm neutrons with the small SNM14 tube.

—————————————————————————————-

29Aug19
So here’s the update since that last post:

Well that was an easy fix. At least for the 60kV unit. As expected, the MOSFET driver chip (IR2153) was toast.

Interestingly, I replaced the chip a couple days ago and it still didn’t work. In fact it began to blow the 5a fuse which it didn’t do before. So I once again checked everything and found all to be ok. Ended up being a bad replacement chip.

I’m going to try another “push to the limits test”, but this time with the original voltage control pot. As indicated by others, the added capacitance of the 8’ extension lead could’ve been the culprit. For safety, it’ll be a simple task to add an acrylic extension to the control.

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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Mark, interesting info that replacing the IR2153 chip fixed your 60 KV supply. Maybe your long extension wires for the V pot are involved. I'm thinking maybe not so much extra capacitance but acting as an antenna. Spikes or surges on the HV output into the fusor load might cause an EM wave that couples back into that extension wire.

Spikes on the input side of the chip probably could blow it if outside the normal 5 V signal range.

Just a speculation.
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Bob Reite's supply failure sounds somewhat similar and also employed the V extension (i think). If the chip fixes his then we at least know where a trouble spot is.

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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Today I fired up the 60kV unit after replacing the faulty driver IC and re-installing the original voltage control potentiometer. Rather than using the wired extension, I added a 7” lucite control rod (pictured). It’s still not conclusive the extension is what killed the IC, but best to try another run without it. After filling up the deuterium syringe reservoir, I initiated a non-stop run at approx 30kV, 3mA, 35mTorr deuterium pressure. This maintained for about 35 minutes without any issue. In the next day or two I’ll bump up the secondary voltage control to achieve a 10kV starting point and give it a go at 35kV with some higher current.

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Re: Precipitator HV Supply Hacking

Post by Cristiano_Machado »

Hello Mark and Rex,

I received my 30kV unit today and I was wondering what is the use of these white connectors? Can I use them to measure the voltage output? I saw your schematic and I understood it can not be used to control the voltage.


30kv hacked.jpg
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Cristiano,

If you downloaded the zip files of my hacking efforts, you should be able to see from the layout circuits that those connectors are just in parallel with the red and green LEDs that are close to them, so not of much use unless you wanted to remote the LED signals. Not much information contained in them.

As I have mentioned earlier, none of the circuits in the 30 KV or 60 KV supplies actually monitor the output voltages. The secondaries of the transformers and their internal full wave rectifier diodes are floating with respect to the circuit boards.
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Rex,
I just sent you a PM.

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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Rex and I were chatting earlier about how to disable the automatic current limiter on the 60kV supply. The method ended up being quite simple. The red wire going through the current sensing transformer just needs to be rerouted around it instead of through it. This stops signal voltage that’s proportional to the current from being sensed in the unmarked 16 pin processor chip.

Other than shutting down the limiter function, I have yet to see any adverse effects. Just make sure the supply doesn’t go over 10ma.

Just a couple reminders....
These supplies do not respond well to flashover arcing. I’m a strong proponent of potting the whole thing in oil. Take every precaution and engineering effort to make the fusor arc/flashover proof.

Extending the voltage control pot with twin lead may have been the culprit regarding the earlier IR2153 failure. Speculation at this point but there’s been no issue since I removed the extension. I’d advise against attempting it until a better arrangement can be determined.

The following picture shows the location of the current sensing transformer (circled in yellow). There’s another one near the 220v input that’s not relevant to this modification.

Thanks Rex for all the work you’ve put into this!

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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Mark,

I never heard back from you. Did you try just turning that current level pot max clockwise?

Moving that wire out of the sense transformer definitely does disable current sensing in the primary switching of the supply, but I didn't actually suggest this.

Well, what works, works -- at least for now. Just wondering if there was a change that would minimize tripping but still let some extreme current kill the output.

Since I have yet to put one of these into any real test environment, only looking at the circuits, I can't know a better way.

Good to know that my work has helped, even if I wouldn't highly recommend this way.
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Exactly, we had no definitive conclusion as to a method and you made no recommendation to reroute the line. I really didn't want to move the discussion to personal emails but I respected your wish to not go further with the fusor website messenger emails. All is good and very appreciative of the communication. I'm still thinking that upping the value of the resistor from 1k to 2k may allow for higher current capabilities but still offer a shutoff in the case of a dead short. I may try that at a later date.

Full clockwise on the current limiter puts it into shutdown mode. 50% clockwise allows for very little current flow...still almost instant shutdown. In fact, just barely tweaking it clockwise wont allow for much more than a few seconds of operation without tripping. I confirmed this is normal with these supplies as my spare 60 does the same and a friend who has one reported the same as well.

I'm not observing much evidence of the supply being taxed from the modification. Probably the only risk on my end would be if the tungsten grid melted and shorted to ground.

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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Interesting, Mark.

That current pot behavior is exactly the opposite of what I expected.

You mentioned possibility of changing a resistor value for current sense. In this pic is where I think the current from the sense transformer (bypassed in your change) is converted to a voltage that is passed to the micro.
Bigger current = higher voltage, because E = I * R. So E which is passed to the micro goes up with current.
So if we want the micro to be less sensitive to the current we want E to be less for a given current. So we actually want R to be lower, not higher.

Changing the the current sensing R to a lower value might work. Here's where it lives from my circuit hacking. The 1K R just above the C circled in this image.

curr sense res.jpg

After thought: You could tack-solder another resistor across this sensing one. Another 1K tacked in parallel would lower its sensitivity by 50%.
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

I think I have a few 510 ohm 1/4 watt resistors in the shop. Or, I most certainly have a few 1k pots which may work better at determining the effectiveness of a value change.

I'll give it a shot and report back.

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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Rex,
Last week I picked up a second 60kV supply for an upcoming ion gun project. Low and behold, the numbers on 16 pin mystery chip weren’t fully scraped off. :)

It’s a cheap and relatively abundant 15W408AS 16 pin microcontroller.

Here’s an eBay auction for one;

https://rover.ebay.com/rover/0/0/0?mpre ... 2256556105

Hopefully this helps solve the final questions about how the 60kV unit operates.

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Re: Precipitator HV Supply Hacking

Post by Bob Reite »

Now to figure out the programming of the microcontroller.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Mark,
Yes, correct on the chip, but I already figured that out. See my post in this thread of Aug 29. It is yet another version of the 8051 chip design.

Edit: Going back, I now see there were lots of posts on Aug 29
Let's see if this link goes more directly to the post I meant...
viewtopic.php?f=11&t=12919#p83946

Bob. I never felt inclined to try to read the chip's code. One would have to unsolder and put it in a reader. If the code is not protected then maybe one could begin to disassemble and start to figure it out. A lot of work if possible at all.

Here is another approach for these boards. I wanted to try this but never got it to the top of my list.

A while back I made a prototyping test board for playing with switcher supply circuits. It is a 3525 switcher controller chip that is very popular in many switch mode supplies. The one I used is SG3525A but there are many clones from different vendors out there.

Here's what I made:
Proto board
Proto board
Proto board Front Panel
Proto board Front Panel
The two pot adjustments on my device set:
The frequency -- between about 28 and 90 kHz
The duty cycle -- between zero and 47%

The 47% is one half the cycle for each of the two phases, so essentially full maximum drive.

The output of this board is two signals with pulses for the A and B or High and Low switch drive into the two power switch devices of the supply.

On the design of both the 30 KV and 60 KV versions of the precip supplies, the main switching control chip is an IR2153. This has H and L outputs that drive the gates of the two switch MOSFETs. The 2153 also has an oscillator like a 555 chip that makes the frequency of these gate drive pulses. These supplies seem to control the output by adjusting the frequency of this oscillator within the 2153.

This seems a strange way to control the output vs the many typical switching supply configurations. PWM is the most common method to vary output.

My idea for trying a new hack of these supplies is to replace the IR2153 chip with an IRS2106. The 2106 is a simple driver chip with no oscillator. The power pins and the output drive pins are the same between the two chips. The inputs (pins 2 and 3) on the 2153 control the oscillator frequency and on the 2106 are just input drive pulses.

My though is to unsolder the IR2153 (Mark has done this for repair) and to put in an 8-pin socket. Then I would put a 2106 into that socket. The traces on the board would need to be cut around pins 2 and 3 to isolate them so they can be driven just by the two H and L signals from my 3525 board.

Next would be experimenting to find the best operating frequency and learning about setting duty cycle vs output V and I. After a good frequency for operation is found, this could be set with fixed components on the 3525 circuit.

The control abilities of the 3525 could then be used to take feedback of the HV output to regulate the supply.

Something like that. Should be fun to try and hopefully could make these precip supplies have a lot more finesse.
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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Rex,
That post was somehow integrated into the missing posts/site migration discussion that was specific to this thread. For whatever reasons it never showed up on my feed, hence the subject matter of my followup reply on the link you provided.

I have a nearby friend who's hobby is microprocessor programming. I'll see what he says about decoding....way beyond any of my interests and water under the bridge concerning any fusor application. The 60 has been operating great as-is and can provide very decent numbers for the cost.

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Re: Precipitator HV Supply Hacking

Post by Mark Rowley »

Rex,
I like the 2106 idea. Sounds like a cool project and may give it a try after the first of the year. By then I'll have two 60's operating on different machines.

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Re: Precipitator HV Supply Hacking

Post by Alan Sailer »

First I'd like to thank Rex for his terrific write-up on the presipitator supply. It allowed me to repair a blown up 30kV unit.

I would like to say that the "mystery" half bridge driver chip can be replaced with an IRS2153 with no obvious problems. I have not
yet re-attached the unit to the fusor but the voltage does go through it's paces.

Cheers.
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Alan,

Thanks for the good words on my shared results from hacking these supplies.

The two mystery chips (markings sanded off) were only mysteries for a while after the hacking began.

In one of my zips for the 60 KV unit there is a file with this:

------
Two chips used on the 60 kV supply

1) 8-pin driver for the switching transistors is an
IR 2153
it is a combined half-bridge driver and is switched by its own
internal oscillator, similar to a 555 timer.

2) 16-pin chip is a microprocessor, seems to be an
STC15W408S (STC = chinese chip mfgr)
a member of the 8051 family
----

So, yep, IR 2153 is a good replacement.

I found there were newer versions of this chip. I'd have to dig into my notes to get the numbers. My thought was that at least one other PN should work but I never tried to prove that.
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Re: Precipitator HV Supply Hacking

Post by Rex Allers »

Oops, I see you used IRS... vs original IR...

Good to know that worked. As I said, I found a few chips that seemed they might work. I'd have to go look at the datasheets again to remember what the differences were.

I'm no power supply design engineer but the function of these supplies seems unusual to me. If I got the circuit right, the voltage adjust pot is controlling the frequency of the 50/50 switching pulses. There is no PWM. If I remember right, lower frequency gives higher voltage output.

That's a key reason why I wanted to try replacing the sw driver chip with one that has direct inputs rather than the internal oscillator. That replaced chip could be driven by an external (off board), more typical, switcher chip with adjustable PWM and separately frequency. -- Another thing on my list of -- not done it yet.
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Re: Precipitator HV Supply Hacking

Post by Alan Sailer »

Rex,

I don't have a complete explanation but I did work a bit with flybacks for an earlier project.
All the flybacks I messed with* had a resonance somewhere in the 10's of kilohertz. The
resonance was due to the parasitic capacitance resonating with the secondary inductance.
At that point the impedance of the transformer is at a minimum and large currents and
voltages are created.

The voltage at this resonace is at a maximum but it is not a good place to operate the transformer.
I killed two by doing this.

The area you want to operate is below the resonance in the area where the transformer is
acting as an inductor ( above resonance it acts capacitive). You can vary the output voltage by
changing frequency which moves you along the slope, changing the output voltage as you do.

I did one circuit that used PWM at a fixed frequency to change the voltage but the range was
not as high as the frequency shifting technique. Maybe 9-12kV.

As a final note none of this operation is true flyback operation (which I don't understand). It apparently
uses a sawtooth drive to ramp up the magnetic energy in the transformer core and then
abruptly release it, causing an output current spike. Which results in a large voltage spike V=L(di/dt).

When I was a kid my Dad showed me how to make a self-oscillating circuit using a relay. When the relay
contacts opened, causing a collapse of the current in the relay coil, you would get a painful shock if you touched
the coil.

Cheers.

* Vintage off Ebay and new from China.
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