need a circuit to generate a pulse for plasma erosion of electrodes
- Thread starter sirdavid
- Start date
someonesdad
- Joined Jul 7, 2009
- 1,583
I think it's a super idea -- cheap, will likely work, and he can be up and experimenting in short order. The OP just has to be careful, as he will be working with dangerous voltages.
He could get an extra one to use to drive a small audio speaker for mechanical positioning of the wires.
OK.beenthere said:
Do you both, and the others, agree that I should jump on this and buy 5 of these power supplies, while the sale lasts?
Would it be better to find variable transformers?
Then you could help me with whatever else I need to duplicate the study mentioned at the start of this thread?
Is there something else I should buy from these guys, like 2 of the 555s, or whatever else is needed, or can I buy them more cheaply from digikey or whoever?
I am on a very tight budget, but I want to do this right.
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I really have no experience with this plasma erosion thing you're doing.
But it seemed to me that four of these supplies, individually adjusted to 25v each to get your 100v requirement, wired in series, should also pass muster on your 4A requirement.
As far as current limiting - you'll need something like a large wirewound resistor about 25 Ohms; it'll have to be able to handle somewhere around 100W to 200W average power, depending on how you adjust the PWM ratios.
I have no clue what kind of current flow you would have if there were no limits on it, nor what kind of resistance exists in your rod material that you're eroding when it's doing it's plasma thing. Seems to me that you may need an adjustable power resistor in the range of 25 Ohms down to maybe 5 Ohms, but I really don't know. If the current draw exceeded 4.2A by much, I would expect the supplies to crowbar down until the load lifted.
MPJA sells a number of things, but they typically only have LEDs for semiconductors. They frequently have sales on items, and you can get some really good buys on items there if it's close to meeting your needs. They ship quickly, and I've never had a problem with any orders I've sent to them.
If you're just buying a few items, Digikey.com is probably the best bet for semiconductors. Their is no "minimum order", no handling fees added (it's built into the price of the parts) and they will ship SMALL orders via USPS 1st Class Mail, which usually winds up being cheaper than ordering elsewhere.
You're also going to need another power source to run the 555/556 timer and MOSFET gate charge/discharge circuit. I wouldn't want to try to "tap off" from the plasma supplies, as they'll be heavily loaded.
You could use a supply like this:
http://www.mpja.com/email/11-10-09a.asp?r=%%ref%%&s=7
12vdc @ 3.5A open frame switching supply, $6.95. That looks like about the best supply they have for your project. There are others that are less, but not much less - and you're going to have to wire everything up anyway.
But it seemed to me that four of these supplies, individually adjusted to 25v each to get your 100v requirement, wired in series, should also pass muster on your 4A requirement.
As far as current limiting - you'll need something like a large wirewound resistor about 25 Ohms; it'll have to be able to handle somewhere around 100W to 200W average power, depending on how you adjust the PWM ratios.
I have no clue what kind of current flow you would have if there were no limits on it, nor what kind of resistance exists in your rod material that you're eroding when it's doing it's plasma thing. Seems to me that you may need an adjustable power resistor in the range of 25 Ohms down to maybe 5 Ohms, but I really don't know. If the current draw exceeded 4.2A by much, I would expect the supplies to crowbar down until the load lifted.
MPJA sells a number of things, but they typically only have LEDs for semiconductors. They frequently have sales on items, and you can get some really good buys on items there if it's close to meeting your needs. They ship quickly, and I've never had a problem with any orders I've sent to them.
If you're just buying a few items, Digikey.com is probably the best bet for semiconductors. Their is no "minimum order", no handling fees added (it's built into the price of the parts) and they will ship SMALL orders via USPS 1st Class Mail, which usually winds up being cheaper than ordering elsewhere.
You're also going to need another power source to run the 555/556 timer and MOSFET gate charge/discharge circuit. I wouldn't want to try to "tap off" from the plasma supplies, as they'll be heavily loaded.
You could use a supply like this:
http://www.mpja.com/email/11-10-09a.asp?r=%%ref%%&s=7
12vdc @ 3.5A open frame switching supply, $6.95. That looks like about the best supply they have for your project. There are others that are less, but not much less - and you're going to have to wire everything up anyway.
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Thank you very much for the link on the DIY EDM!
Very interesting articles. I worked with 2 wire edms about 10 years ago that were used, meaning they were probably several years older. I guess that is old technology, but I'm or less familiar with EDM.
Keep in mind that my primary objective is the particle size on the electrode--the smaller the better.
I intend to start with silver, then gold, then perhaps aluminum, maybe even iron oxide.
I don't know how much of a factor electrode size is, but it will probably range from the 1mm size specified in the study, to significantly larger.
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someonesdad
- Joined Jul 7, 2009
- 1,583
David:
As I mentioned earlier, before you invest any money in parts or equipment, I think you should contact the paper authors and learn what you can from them before proceeding any further. The author that can be contacted by email will likely know a lot more and can probably put you in contact with the folks who did the electrical work. Remember that written papers rarely disclose the real experimental problems faced by the experimenters -- and they hinted at some things being crucial for the desired performance. They'll know a lot more than they published.
Don
As I mentioned earlier, before you invest any money in parts or equipment, I think you should contact the paper authors and learn what you can from them before proceeding any further. The author that can be contacted by email will likely know a lot more and can probably put you in contact with the folks who did the electrical work. Remember that written papers rarely disclose the real experimental problems faced by the experimenters -- and they hinted at some things being crucial for the desired performance. They'll know a lot more than they published.
Don
I sent the following email to the fellow named in the study.
I think it is at a polish university.
body {font-size: 12pt; font-family: "tahoma"; }
I think it is at a polish university.
body {font-size: 12pt; font-family: "tahoma"; }
Dear Sir,
I read your paper NOVEL TECHNIQUE FOR PREPARING A NANO-SILVER WATER SUSPENSION BY THE ARC-DISCHARGE METHOD.
I would like to try to reproduce your results.
Would you be able to assist me with more details of:
your equipment,
your procedures,
problems you encountered,
what you did to solve the problems.
My first inquiry regards the equipment you used to generate the arc.
What electrical equipment did you use?
Next, I would like to ask for clarification.
Your paper says: "the DC arc-discharge system provides a pulse voltage of 70-100 V for 2-3 ms and then maintains a pulse of 20-40 V for around 10 µs. At that moment the etching current can reach 4 A"
Was there a misprint in your paper? Is the initial 100 V pulse of about 2 μs, not 2 ms, followed by a 20-40 V pulse of 10 μs, or was the 20-40 V pulse 10 ms?
Also, how critical to obtaining the smallest possible particle size is the timing on the pulse step, and the timing between the pulses?
Next, I would ask, was the step in voltage programmed into your equipment, or was it the byproduct of the process?
If you would be so kind as to assist me in this endeavor, I would be most appreciative.
Sincerely,
David Treibs
David, is there another address to the site you listed in your first post?
I've tried to go there several times a day and keep getting a cannot find message.
Is this, nano silver particles, another form of colloidal silver? If it is you should really read what they are saying about it's safety! Google "nano silver"
If it's not what is it used for? Sorry but I'm just curious.
Cary
I've tried to go there several times a day and keep getting a cannot find message.
Is this, nano silver particles, another form of colloidal silver? If it is you should really read what they are saying about it's safety! Google "nano silver"
If it's not what is it used for? Sorry but I'm just curious.
Cary
I think I attached the article to this message.
I've read a fair amount about its safety, and I've used it some, and it seems to work well with some types of problems. And yes, that is one of the applications. But more than just that, I have some other ideas I'd like to play with involving nano sized particles of various metals.
If you have some specific sites that discuss problems with it, I'd be glad to read them. My wife is an RN, and she understands a lot about medical issues.
David, here are a few; http://nano.foe.org.au/filestore2/download/189/FoE Nanosilver report.pdf
http://www.coldtruth.com/2009/11/04...hing-favored-by-astronauts-hikers-and-babies/
http://www.sciencenews.org/view/gen...c__Nanosilver_disinfects_—_but_at_what_price?
Thank you for posting the whole article. For some reason the link you posted won't work for me.
Good luck with your project, Cary
http://www.coldtruth.com/2009/11/04...hing-favored-by-astronauts-hikers-and-babies/
http://www.sciencenews.org/view/gen...c__Nanosilver_disinfects_—_but_at_what_price?
Thank you for posting the whole article. For some reason the link you posted won't work for me.
Good luck with your project, Cary
Published stuff is often iffy. I got into designing after putting together a circuit out of an academic publication. I did not think it was quite right, and it did not work. The researchers did not have much to say.
I redesigned the circuit to work - the researchers did not have anything at all to say. My guy was happy, though.
I redesigned the circuit to work - the researchers did not have anything at all to say. My guy was happy, though.
I found another study by at least one of the same authors, and this one has email addresses. So, I'm going to try to contact them.
Meanwhile, I thought those reading this thread might like to see what they said about the setup the authors were using for voltage. It doesn't add much to the other study, but maybe a little.
"The Ag colloids used in this experiment were fabricated
with the five modules of arc discharge system, shown in Fig.
1. These modules include a 150 Volt DC power supply, two
silver electrodes (1 mm diameter), a glass container with
deionized water to collect the colloid, a stirring system and a
servo control system with a servo feedback loop to maintain a
constant gap distance (20-40 µm) in between silver
electrodes.
"The power supply system provides a stable pulse voltage
to etch the Ag electrodes by ionizing the aqueous medium.
Ionization in the gap (10-40 µm) is reached after 1-3 µs,.
"Here, the pulse is maintained at a high open voltage of
80-120 V. Once the medium is ionized, a large discharge
current passes through, bringing the applied voltage down to
a range of 25-40 V. The on/off discharge pattern is
maintained all the way through the entire etching process."
Meanwhile, I thought those reading this thread might like to see what they said about the setup the authors were using for voltage. It doesn't add much to the other study, but maybe a little.
"The Ag colloids used in this experiment were fabricated
with the five modules of arc discharge system, shown in Fig.
1. These modules include a 150 Volt DC power supply, two
silver electrodes (1 mm diameter), a glass container with
deionized water to collect the colloid, a stirring system and a
servo control system with a servo feedback loop to maintain a
constant gap distance (20-40 µm) in between silver
electrodes.
"The power supply system provides a stable pulse voltage
to etch the Ag electrodes by ionizing the aqueous medium.
Ionization in the gap (10-40 µm) is reached after 1-3 µs,.
"Here, the pulse is maintained at a high open voltage of
80-120 V. Once the medium is ionized, a large discharge
current passes through, bringing the applied voltage down to
a range of 25-40 V. The on/off discharge pattern is
maintained all the way through the entire etching process."
I found this on the MPJA website, it has a little more amperage and is a little cheaper (what do you think?):
24.5VDC @ 5 AMP POWER SUPPLY
MFG: NORTH AMERICAN
P/N: 9T89Y1038G02
Input: 115V 60Hz
Output: 24.5V @ 5A
Specifications/Features:
USED, Enclosed switching supply. Overvoltage/ Current. Header terminals input, 2 X 3 pin connector output. UL/CSA listed.
L: 8" W: 4-3/4" H: 2-1/2" WT: 1.78
Stock No.:
12912 PS Price:
$ 7.45
24.5VDC @ 5 AMP POWER SUPPLY
P/N: 9T89Y1038G02
Input: 115V 60Hz
Output: 24.5V @ 5A
Specifications/Features:
USED, Enclosed switching supply. Overvoltage/ Current. Header terminals input, 2 X 3 pin connector output. UL/CSA listed.
L: 8" W: 4-3/4" H: 2-1/2" WT: 1.78
12912 PS Price:
$ 7.45
David, I know the more experienced people told you to use a switcher/regulated supply but if it was me, I wouldn't.
Reread your description of what the circuit does/how it operates. Starts with a high open circuit voltage and voltage drops as the current rises. Again, just the exact same as Electrical DischargeMachining. In that type of circuit you just use a transformer/bridge diode/filter capacitor. No regulation.
It needs to "droop" like a arc welder transformer. Thats how you get the voltage drop as current rises.
Switcher supplies also don't like short circuits. And you will get short circuits doing this.
I don't know where your from but you really should invest in this book;
https://secure.villagepress.com/store/items/detail/item/797
before spending a lot of money on a machine to make your nano-silver. This machine has been built and tested.
Just my $.02 Because I've been where your at and spent a lot of money on building a EDM, before I had any real knowledge of what was needed.
Cary
Reread your description of what the circuit does/how it operates. Starts with a high open circuit voltage and voltage drops as the current rises. Again, just the exact same as Electrical DischargeMachining. In that type of circuit you just use a transformer/bridge diode/filter capacitor. No regulation.
It needs to "droop" like a arc welder transformer. Thats how you get the voltage drop as current rises.
Switcher supplies also don't like short circuits. And you will get short circuits doing this.
I don't know where your from but you really should invest in this book;
https://secure.villagepress.com/store/items/detail/item/797
before spending a lot of money on a machine to make your nano-silver. This machine has been built and tested.
Just my $.02 Because I've been where your at and spent a lot of money on building a EDM, before I had any real knowledge of what was needed.
Cary
At some point, I'm just going to have to show my hand, so to speak, and I'm holding pretty much nothing. I hate to admit it, but I know very little about electronics or electrical circuits. What I do know is the end result I'm seeking. I'm also reasonably intelligent, able to follow instructions, worked in two machine shops for about 12 years, and several of those years I operated several wire EDM machines. And I did make and test an LED flashlight circuit successfully, if that counts for anything. I hope everyone doesn't run off and not help because they think I'm a hopeless case.
But anyway, not the cat's out of the bag. On to what you said.
From reading the description, the power supply I pointed out is a switching supply, which you are suggesting is not a good thing for several reasons: it will not allow the power to follow it's natural curve of high voltage when the resistance is high, then when the arc is formed, the voltage drops until it is shut off by whatever is controlling the circuit; also it will not handle shorts very well, which will inevitably happen with the setup--2 electrodes very close together eroding each other into oblivion, trying to maintain a constant and very close distance.
Next question: what source of power do you suggest? (Let me guess: it's in the book. I'm already looking for it.
)Speaking of welders, I have some sort of welder under the mobile home. I think it uses sticks. I've never used it, but the guy who gave it to me said it works. Maybe that would be helpful as a power supply?
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David, for what you doing I would stay away from the welder, way too much current for what your doing(usually 100A or over for a stick welder)
Your right the book I linked to shows it all for a little money! It even contain a way to build the servo mechanism that you need to control your gap! If you are serious about this it will be the best money you will spend on the whole project.
The book was a series of articles from Home Shop Machinist magazine.
Again don't know where your located, but check with your library, they may have back issues of the magazine. The series walks you through the whole build, gives some theroy and tells how to chose alternate components.
As far as the power supply some people that build these machines go with a rewound Microwave Oven transformer. Read this thread; http://www.practicalmachinist.com/vb/showthread.php/home-made-edm-152388.html
The guy Awake is a member of another forum I'm on and has built one, using the MOT. I don't know if his video is still up on youtube, if so you can see his working.
Cary
Your right the book I linked to shows it all for a little money! It even contain a way to build the servo mechanism that you need to control your gap! If you are serious about this it will be the best money you will spend on the whole project.
The book was a series of articles from Home Shop Machinist magazine.
Again don't know where your located, but check with your library, they may have back issues of the magazine. The series walks you through the whole build, gives some theroy and tells how to chose alternate components.
As far as the power supply some people that build these machines go with a rewound Microwave Oven transformer. Read this thread; http://www.practicalmachinist.com/vb/showthread.php/home-made-edm-152388.html
The guy Awake is a member of another forum I'm on and has built one, using the MOT. I don't know if his video is still up on youtube, if so you can see his working.
Cary
While looking for the book, I found an interesting website, and another book.
I wonder if you've had a chance to see the following?
1. the interesting site: http://cscott.net/Projects/FabClass/final/edesign1.html
2. interesting book:
(248) 391-2974I wonder if you've had a chance to see the following?
1. the interesting site: http://cscott.net/Projects/FabClass/final/edesign1.html
2. interesting book:
5 1/2 x 8 1/2 Paperback 161 pages
Price $24.95 Buy Me
Click to compare with our other EDM book
NEW- Revised edition with more photo's drawings and sources
Electrical Discharge Machining (EDM), sounds very expensive and high tech, but you can build this affordable tabletop machine from surprisingly common components, most of which are available from Radio Shack. No exotic parts or special tuning required, and no circuit boards to etch.
The basic idea is to move an electrode very close to the work piece, and repeatedly produce a spark between the two while flushing out debris with a dielectric fluid. You first create an electrode in the shape you want out of copper, brass or graphite. It is then fed slowly down into the metal workpiece while maintaining a precise spark gap. The electrical discharges blast little bits of metal away while a fluid cools and flushes away particles. This is called “Sink” or “Ram” EDM and it can produce impossible shapes in metals too hard to machine any other way, and it doesn't create heat and ruin the temper of your workpiece.
Most people mount the Ram assembly on a mill or drill press for convenience, but there are no forces or deflections to deal with and the ram itself handles the
This is a truly useful piece of equipment that can pay for itself quickly, you might even create a small business around it. Let your imagination run wild with this amazing process!!
David, the c.scott site is commonly known as the Garden of EDM plans. It was a proposal for a graduate school thesis. It was never built and was using concepts that are not used in any EDM design that I've been able to find in the 12 years I've been at this. The design as drawn is VERY DANGEROUS!!! There is no isolation of the mains!! It is wired directly to the main house wiring. The open circuit voltage is way higher than any commercial machine uses.
The other book is another of the ones that I have. It uses a lot of concepts that none of the other home built machines/plans use. While a lot of these have been built, there are a lot of faults in the design.
Between this book and the first one I linked to, the first one in my opinion is the best. The HSM/Langlois book goes much more in detail on the build. It gives a lot more on the theory and how things work. It's also the one that anyone goes out on their own design sites as their starting point.
Over the years there has been 7 or 8 different plan sets or magazine articles on building a EDM, I have all but one of them and the HSM is the most complete. Just my opinion.
Cary
The other book is another of the ones that I have. It uses a lot of concepts that none of the other home built machines/plans use. While a lot of these have been built, there are a lot of faults in the design.
Between this book and the first one I linked to, the first one in my opinion is the best. The HSM/Langlois book goes much more in detail on the build. It gives a lot more on the theory and how things work. It's also the one that anyone goes out on their own design sites as their starting point.
Over the years there has been 7 or 8 different plan sets or magazine articles on building a EDM, I have all but one of them and the HSM is the most complete. Just my opinion.
Cary
