All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > The Projects Forum

Notices

The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

Reply   Post New Thread
 
Thread Tools Display Modes
  #11  
Old 08-08-2012, 08:27 AM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

I'm learning more and more (more than I intended to learn, but that's not a bad thing!)

I looked on Wikipedia about RCL circuits but mostly found a lot of incomprehensible formulae. My first attempt at this was this:
http://4hv.org/e107_plugins/forum/fo...pic.php?112240
I copied his homemade cap, which replaces the doorknob cap you mentioned. Lacking a capacitance function on my meter, I can't verify that it works correctly. I wonder how critical the capacitance value is. I saw many doorknob caps on Ebay, don't know which to choose. Do you think a variable plate cap like radios use to use would work?

The saturable reactor link you gave me is what I tried to copy, but only had a 12v battery trickle charger for the control circuit- maybe too little current; have to put together a transformer-rectifier.

I know inverter TIG's are the in thing now- relatively low cost and multi-function, but NOTHING is low cost here, and used equipment like that doesn't come up much because there's very little industry here- tourism and agriculture are about it. My TIG, a rectified Lincoln buzzbox, works, just have to start the arc on a piece of carbon then transfer to the work (bit of a nuisance) and don't have current control other than the preset taps on the main transformer. Besides, I get a lot of satisfaction from making something useful from junk. I'll play around a little more and then bug you again. Thanks again.

Rick A.
Reply With Quote
  #12  
Old 08-08-2012, 03:10 PM
shortbus's Avatar
shortbus shortbus is offline
Senior Member
 
Join Date: Sep 2009
Location: ohio,usa
Posts: 2,672
Default

Don't know how your finding the links, but great info. In the latest one the reply to you from Newton Brawn, "1- the capacitor CD could be 0.94 uF (two 0.47 in parallel ) or one 0.94 x 2000V from a microwave oven." That may work for you if you just use it as an arc starter(with a timer to drop it out) not a continuous HF as when welding aluminum.

The variable cap from a radio won't work as it would spark between the plates from the HV.

The trickle charger won't have a high enough current to work. A better way than just a 12V trans and rectifier with the potentiometer(for control) would be to include a PWM (Pulse Width Modulator) in to the circuit. With just a pot, you loose a lot of current to heat, and it drops voltage too. With PWM it keeps the voltage and regulates the current by pulsing it off-on to regulate.

With the reactor you also have to make sure the windings are kept in the right direction too. If done wrong the reactor won't work, the voltage cancels its self. So follow the links directions carefully.

What you said about the reactor not being used much any more is true, but not because its not a good idea. Its just cheaper to use a couple of chips in a circuit than iron and copper in a reactor. Plus its more compact. But your building some thing your self and basically doing it the old way. Nothing wrong with that!

I know about making stuff from junk! I have a ton of ideas of things to build and most of the junk to build it from! But I'll be dead before I get to do most of it
__________________
New members, Please put your location in your profile details.
Reply With Quote
  #13  
Old 08-09-2012, 07:43 AM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

Finding links is just a matter of spending time digging; I typically spend the evenings on the web- more entertaining and educational than TV!

The microwave cap idea sounds good- I've mounted a switch on the TIG torch so I can activate the HF circuit manually and, as you say, momentarily just to start the welding current on steel. There's a homemade plasma cutter design out there that also uses a HF start circuit. He wired in a reed switch which automatically starts the HF whenever the welding current is interrupted, like if you inadvertently get the torch too far from the work. Either way, the HF runs minimally.

You also mention a PWM DC current control for the saturable reactor. It so happens that I have a treadmill PWM motor controller which, I understand, I can operate with a pot activated by the foot pedal. It's 130v output, hope that wouldn't be too much.

I've been trying to build this HV circuit today per your advice, using a car coil (it's what I have available) and can get a .75" blue arc, but it doesn't come out of the TIG torch. It seems like the coupling coil (made from the 4hv.org link instructions) must be the culprit. It consists of a row of ferrite beads in a piece of pvc around which the coils are wrapped. The only other design I've found is a toroid core from a TV with the coils wrapped around it, but it's quite limited on space for the #4 secondary wire. Any thoughts?

Thanks
Rick A
Reply With Quote
  #14  
Old 08-09-2012, 10:32 PM
shortbus's Avatar
shortbus shortbus is offline
Senior Member
 
Join Date: Sep 2009
Location: ohio,usa
Posts: 2,672
Default

Yeah I do a lot of that too doing research for projects. But its all in the wording of the search.

I don't agree with some of the guy's saying to put a ferrite or iron core in the coupling coil. The HV is very low current and it would be trying to magnetize the core which take current. Beads on the wires leading up to the coupling coil would be OK (if needed) but not in the coil.

I've seen a lot of different winding schemes for the coupling but not sure how much difference the turn ratio makes. The plans from 4hv.org - http://4hv.org/e107_files/public/130...ng_coil_r2.pdf
would be a good start, you could add more on to the primary as needed. The primary being the HV in this instance. But think it better to put primary in the center of the secondary instead of at one end like he shows.

Like in the beginning of your thread, don't think the auto coil has enough current to do this. I know guys say they've done it, but no one shows a video of it working. One of the old style coils, the round ones, is that what your using? If using a car coil at least get one of the new style that looks like a transformer. The kind used in a GM HEI, they have about twice as much current.
__________________
New members, Please put your location in your profile details.
Reply With Quote
  #15  
Old 08-11-2012, 06:35 AM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

Talking about web searching, I always used Google until I got my present computer, which came with Bing installed. I've noticed that it lists search results in a quite different order. Now I sometimes use both when I'm looking for something.

The coupling coil in your link is the one I've been copying; I started with his design, then added primary turns until I had as many as in the secondary, then went back to just a few. It may be that, like you suggest, there's not enough juice in the car coil. I tried a more modern coil as you suggested, but no help.

I ran across this thread and the last entry suggests that the correct tank cap size may be critical. The discussion in the earlier posts is over my head- you would understand it. I've found instructions for building variable caps and wonder if I maybe should make one and then be able to play with it until I found the optimum value for it. Sound logical?

Thanks
Rick A
Reply With Quote
  #16  
Old 08-11-2012, 04:26 PM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

Forgot to include the link to which I referred:
http://4hv.org/e107_plugins/forum/fo...6.0#post_54786
Reply With Quote
  #17  
Old 08-13-2012, 03:03 PM
shortbus's Avatar
shortbus shortbus is offline
Senior Member
 
Join Date: Sep 2009
Location: ohio,usa
Posts: 2,672
Default

I don't think that the cap value is all that important to this. The spark gaps, the distance between them is more critical, I think. Same with a variable cap,how would you control "flash over", sparking between the plates of the cap?

What are you using to test the arc starter? Do you have a Tig torch and argon? In the last link the one guy said his didn't work until he used argon. The spark is ionizing the gas in that area to cause the low voltage to 'ride' the HF-HV. The ionized gas is what allows this to happen.

There was a picture in one of the links that showed the coupling coil with the HV windings wrapped side by side with the LV. I'll see if I can find and link to it. Its really hard to convey ideas over a long distance and not in real time, for me. But lets keep at it.
__________________
New members, Please put your location in your profile details.
Reply With Quote
  #18  
Old 08-14-2012, 06:19 AM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

I appreciate your patience, Shortbus. I agree, it's hard to visualize what's being described without being there.

I've seen some references to the arc starting much better in argon than air. I built this TIG from an old buzzbox and have been welding with it, starting the arc on a piece of carbon and transferring it to the workpiece. I put a tee in the argon line to my mig and am using a solenoid valve with a trigger switch on the torch handle to control the flow. When I try out my latest iteration of the hf circuit it's always in argon.

What I was thinking of for a variable cap was a suggestion in an article about making caps. He said an old radio/TV tuner immersed in oil would hold considerable more charge than in air. Alternatively, in a table of resistance for various materials, mylar is listed as much higher than anything else. Maybe could use layers of that.

As far as spark gap, I've tried varying that, but all the references I can find suggest about .008", so I've been using that.

The best I've been able to get so far is a weak arc at the torch tip in argon, but it wasn't enough for the welding current to follow. I'm setting the welding current at 40 or 60 amps, near the bottom of the scale on the welder.
Reply With Quote
  #19  
Old 08-14-2012, 03:42 PM
shortbus's Avatar
shortbus shortbus is offline
Senior Member
 
Join Date: Sep 2009
Location: ohio,usa
Posts: 2,672
Default

Are you sure your mig gas is 100% argon? Most mig gas is 80/20 argon/CO2. 100% argon for steel doesn't work near as well, not as much penetration and more spatter.

If you go back to the link for the tig I gave, near the bottom of the page - http://www3.telus.net/public/a5a26316/TIG_Welder.html Read what he said about how he got the HF to finally work.

If your getting any HF at all, maybe its time to step-up to a neon sign trans. A car coil is just not enough amperage. Plus in a car it has a capacitor and a sharper square wave powering it, which gives more spark energy than the circuit in this application.

Also make sure the windings in your coupling trans are "in phase". Both wound the same direction. Out of phase cancels.
__________________
New members, Please put your location in your profile details.
Reply With Quote
  #20  
Old 08-15-2012, 07:00 AM
Rick A Rick A is offline
Junior Member
 
Join Date: Jul 2010
Location: Hilo, Hawaii
Posts: 25
Default

Good points; I'm using 100% argon- a friend inspected cylinders for a living and got me a lifetime supply of argon and oxy/acy.

I had looked at that link long ago, but his design is so heavy into electronics that I knew it would be over my head to try so I never read all the way to the end. A most enlightening paragraph on the hv circuit. I think my next step, per your advice and his experience is to get in touch with a friend on the mainland who may be able to get me an OBIT.

I wound the coupling coils the same way, just maybe not enough current going through them, as you've suggested.

It'll be awhile, but I'll let you know how things progress after I've found the right transformer. Until then, thank you very much for your advice and patience.

Rick A
Reply With Quote
Reply   Post New Thread

Tags
, , ,


Related Site Pages
Section Title
Worksheet Arc flash and arc blast


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to start a LED using a TTL circuit ADHD Homework Help 12 01-25-2011 09:32 PM
Trying to understand a circuit Artfldgr General Electronics Chat 4 09-20-2010 04:50 PM
Generator start circuit blhoward The Projects Forum 8 01-23-2010 11:32 PM
Simple but big circuit Challenge to all Chris15 The Projects Forum 13 07-08-2009 09:32 PM
Sensor circuit, Flasher circuit 123456 Homework Help 11 08-03-2006 10:58 AM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 11:52 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.