TIG HF circuit earthing opinions

[Mark Harriss]

Hi people, I've just built an arc stabiliser circuit for TIG welding
based on the first schematic at:

http://www.geocities.com/CapeCanaveral/Hangar/6160/welder/arcstarter/hf.html

My circuit is actually this:

http://members.dodo.net.au/~ningauble/

I have used a 10A mains filter unit (centre right of lower pic) with an
earthing point and one half of a 10KV neon sign transformer which has the
centre tap internally connected to earth. My query is this: is the earthing
of this circuit acceptable or have I got some problems on my hands? even
though the output is transformer isolated.

I've tested the circuit and it runs fine when welding aluminium with a small
AC stick welder and produces a small amount of screen noise on the TV set 3M
away.

tia
Mark Harriss

 

[John Crighton]

On Fri, 23 Jul 2004 05:48:38 GMT, Mark Harriss <anotheremail@this.com>
wrote:

Hi people, I've just built an arc stabiliser circuit for TIG welding
based on the first schematic at:

http://www.geocities.com/CapeCanaveral/Hangar/6160/welder/arcstarter/hf.html

My circuit is actually this:

http://members.dodo.net.au/~ningauble/

I have used a 10A mains filter unit (centre right of lower pic) with an
earthing point and one half of a 10KV neon sign transformer which has the
centre tap internally connected to earth. My query is this: is the earthing
of this circuit acceptable or have I got some problems on my hands? even
though the output is transformer isolated.

I've tested the circuit and it runs fine when welding aluminium with a small
AC stick welder and produces a small amount of screen noise on the TV set 3M
away.

tia
Mark Harriss

Hello Mark,
congratulations on a fine looking arc starter.
I like it! Good for you!

I could see the picture OK but the circuit diagram did not
appear for me, could you send me the circuit via e-mail please.

I started collecting bits to make an arcstarter myself and
then an old Lincoln unit fell at my feet for next to nothing.

The high voltage capacitor associated with the spark gap
is hard to find. I am assuming your capacitor is made up
of many caps in the white tube. What types are they, where
did you get them and how much did they cost?
Tell me about your spark gap. What is the base made
out of? I am assuming tungsten tig rods for the gaps,
what diameter?
You found a nice little neon sign transformer too. The one
I was going to use is enormous. I didn't come across any
small ones when I was looking for them. What are the
dimensions of your cabinet so that I can estimate the size
of the bits and pieces?

Back to your question. I can't see any problem having
one side of the secondary earthed. It would be nicer
for us if one side the secondary wasn't earthed but we
have to use what we can find.

Funny how we have different takes on what is important,
I haven't worried about noise filters but plastered my rectifier
unit with heaps of capacitors to protect the diodes. I use
O.1mfd caps across the welder terminals and to ground also.
I can't see a High Freq by pass capacitor in your picture on
the welder side terminal inside your arc starter. Maybe it is
there but I cant see it. I just want to make you aware of adding
protection for your welder or rectifier or nice inverter tig welder
should you connect one up to your arc starter. I am probably
over cautious here, but couldn't give a monkeys about the
electrical noise.
The heavy current black coil to front panel studs, how
is that done? Is it a copper tube?

Excellent job Mark!
Regards,
John Crighton
Sydney

PS
Here are some pictures of my old Lincoln arcster
http://users.tpg.com.au/john_c/

 

[Mark Harriss]

        Thanks for the feedback John, I've fixed a mistake in the page so the
schematic should now load ok and added some extra text and photos to provide
more detail about the unit, if you'd care to take another look at it, I can
answer any more questions.

Thanks
Mark

 

[Mark Harriss]

Thanks for the picture of your Lincoln John.
It's the first look inside a commercial unit I've seen so far.

Mark Harriss

 

[John Crighton]

On Sat, 24 Jul 2004 04:58:40 GMT, Mark Harriss <anotheremail@this.com>
wrote:

        Thanks for the feedback John, I've fixed a mistake in the page so the
schematic should now load ok and added some extra text and photos to provide
more detail about the unit, if you'd care to take another look at it, I can
answer any more questions.

Thanks
Mark

Hello Mark,
that is brilliant mate!
You even made your own capacitor. WOW!
I was thinking it was probably a bunch of regular
1000 volt polywhatevers in series parallel to acheive
around 2000pF 10KV rating stuffed in the tube and here
you have made one single capacitor. That is great!

You mentioned Aluminium solder. I want to know all
about that. Where did you get it?

You have plenty of room in the box to build a gas flow timer
to keep the gas flowing after you stop welding for several
seconds and upwards. Protects your cooling tungsten and
your cooling weld from contamination.

For DC welding steel, once the arc has started you don't
need the HF to run continuously as you do with Aluminium,
so you might look into fitting a sensor circuit to switch
the neon sign transformer supply off after the arc has started.
This will save wear and tear on the spark gap points and
your capacitor.
I press a button on my tig torch handpiece, well, it is just
a taped on microswitch which causes a relay to switch
power to the high voltage transformer. Another relay
drops out or clicks in, I cant remember, when the welding
transfomer or DC supply open circuit voltage drops from
about 50/80V to around 25V. Meaning heavy current is
now flowing so there is no more need for the HF high voltage.
For Aluminium welding I can switch to continuous HF high
voltage.

Have you told "Bill the Arcstarter" about your project?
I am sure he will be delighted that you used his notes
and achieved success.
There is a DIY Welder mailing list that has been out of
order for a while but is just starting up again now.
http://www.diywelder.com
http://forums.diywelder.com/forum/index.php
I am sure the people there will be delighted to see
your arc starter also. They are all struggling with this
stuff. You would give them inspiration Mark.

I can't quite see from the pictures how you joined the
heavy black cable to the studs.It looks very neat How
did you do that?
You have inspired me Mark, I will have to join the list
again.

So many hobbies and so many things to do.
Lifes Good.

Regards,
John Crighton
Hornsby

 

[Mark Harriss]

Hi John,
I did try multiple 630VDC capacitors up to 40 KV in
series/parallel arrangements but they all died in under 5
seconds no matter what. The aluminium solder was bought ages
ago from Dick Smith and is made by Multicore. It needs a hot
tip which will suffer corrosion from the flux (it stripped
2mm of scale from a 150W Birko iron in minutes.

The gas timer will be next cab off the rank for my unit.
I still need to get my own handle yet though buying one from
the states looks to be about 30% of the local price.

Does TIG welding aluminium require actual high current HF
power or is 50Hz good enough?.


Thanks
Mark Harriss

 

[Phil Allison]

"Mark Harriss"

Does TIG welding aluminium require actual high current HF
power or is 50Hz good enough?.

** Ask 2GB if you can borrow their 873 kHz transmitter for a small welding
job - should work a treat.


What macaroon !





.......... Phil

 

[Mark Harriss]

Funny you should mention that,but a friend of mine
qualified as a broadcast engineer while working at 2GB in the
sixties. I have personally seen a tech strike a small welding
arc across the bottom egg insulator of a guy wire at the Bald
Hills shortwave transmitter in Brisbane.

Regards
Mark Harriss



Phil Allison wrote:

"Mark Harriss"

Does TIG welding aluminium require actual high current HF
power or is 50Hz good enough?.



** Ask 2GB if you can borrow their 873 kHz transmitter for a small
welding
job - should work a treat.


What macaroon !





......... Phil

 

[John Crighton]

On 24 Jul 2004 03:12:54 -0700, marcus36@dodo.com.au (Mark Harriss)
wrote:

Hi John,
I did try multiple 630VDC capacitors up to 40 KV in
series/parallel arrangements but they all died in under 5
seconds no matter what. The aluminium solder was bought ages
ago from Dick Smith and is made by Multicore. It needs a hot
tip which will suffer corrosion from the flux (it stripped
2mm of scale from a 150W Birko iron in minutes.

The gas timer will be next cab off the rank for my unit.
I still need to get my own handle yet though buying one from
the states looks to be about 30% of the local price.

Does TIG welding aluminium require actual high current HF
power or is 50Hz good enough?.


Thanks
Mark Harriss

Hello Mark,
thanks for the info on the solder. Pity about the multiple capacitor
bank. I think the Tesla coil boys use a particular polycarbonate
type that are more rugged than normal polycarbonates for pulsed
use and have some slight self healing ability. I remember checking
them out price wise and they were about four or five dollars each from
a mob called Crusader or a name something like that down at Padstow.
The Tesla group have all the details on this capacitor. Anyway, they
were too expensive for me. Did you use resistors (in the megohm
range) across each cap in your original multiple mini capacitor bank.

Yes, 50 Hz is fine for welding aluminium using an ordinary common
transformer machine. Some welders have a "balance control"
that can bias the AC current waveform to be slightly more positive
or negative as required.
Electrode negative heats the job more than the tungsten electrode.
Electrode positive heats the tungsten electrode more than the job
but has a nice cleaning action on the aluminium. So playing with
the balance control allows the operator to have more, or less
cleaning action, according to what the job requires.
People have being using plain ordinary transformer welders
with no balance control for decades. You'll be fine.

With the expensive inverter machines full of bells and whistles
the AC welding current can be varied from 20 Hz to a few
hundred Hz. The higher the welding current frequency the
narrower the heat cone becomes. One of the students
at the Meadowbank Tafe welding night class brought
in his new $6000 suitcase size inverter tig machine and
let us all have a play with it. At 20 Hz the heat cone was
fluttery and wide. At the higher frequencies, I noticed a definite
narrowing of the heat zone. Good for penetration on thick material.
I only had a five minute play but it was great.
We all wanted to play with it. Variable pulse settings, variable
background current settings, adjustable sequences, for heating
up and gradual cool down to avoid craters and memories for
recalling the settings for particular jobs. What a machine!

I bought a cheap auto darkening helmet which helped me
enormously but later I found out that the view through it was not
as clear as other students autodarkening helmets. I paid $200
for mine, I have seen the same model go for $100 new on
ebay. Try a few on the job before you buy one. The one I
liked owned by a fellow student was a $300 Preditor brand.
To me, the clarity of this student's Preditor helmit was
as good as our teachers expensive Speedglas helmet.
Avoid this one. AG3 (AG111)
That is the model I have It is not good.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&category=633&item=3829460081&rd=1
Give that brand/model a miss.

Hey Mark, you still haven't told me how you joined the
heavy black cable to the front panel studs.

You mentioned buying a tig torch from the USA.
Silverwater welding down here in Sydney have a
small tig torch, 100 amps max for short periods for $110.

Have you bought stuff from the USA? Any problems with duty
or customs? I have been looking at used electronic test equipment
from the USA on ebay and it looks so good, price wise.

Regards,
John Crighton
Hornsby

 

[Mark Harriss]

        Hi John, sorry about the delays but the news server I'm using hardly
updates these days. The cable is joined to the 1/2" threaded brass rod with
1mm tinned copper sheet that is formed on a round mandrel and soldered to
the brass rod, then the narrower copper cable is inserted and crimped closed
with pliers. The copper does not closed at the top and solder can be fed
through to completely fill the voids. The outside is wrapped in the scotch
23 tape (butyl?) which eventually fuses into a single mass.

        My cap banks did have multiple series parallel units of four parallel
and about 40 series units but no equalising resistors as I thought they
would average out over multiple parallel units. They were no-name mains
suppression caps and I think they just weren't of a suitable quality for the
job.

        So the switchmode TIGs only go up to a few hundred Hz?. It should be
possible to make a controller for a conventional welder but switchmode
welders are getting cheaper every day. The TIG handles here:

http://www.welding-direct.com/

sell for US$57 for a 200A unit with a 4m cable but need all of the
accessories bought to go with it such as collets and nozzles.The same unit
from BOC Australia is A$480 so as you can see it's a fair bit cheaper.
As far as getting the stuff into the country I just get it posted and have
had no problems so far.


Mark Harriss

 

[Richard Freeman]

"Mark Harriss" <marcus36@dodo.com.au> wrote in message
news:33be72df.0407240212.6c216662@posting.google.com...

Hi John,
I did try multiple 630VDC capacitors up to 40 KV in
series/parallel arrangements but they all died in under 5
seconds no matter what.

Yes that would be right !! DC Capacitors can fail due to ionisation between
the plates known as the corona effect destroying the Dielectric at Voltages
Higher than around 100V AC ...
Try again only using Capacitors specified for High voltage AC and you should
have a much lower Failure rate

Some references :
http://www.sbelectronics.com/cterminology.htm
http://www.azom.com/details.asp?ArticleID=1266
http://www.avxcorp.com/docs/Catalogs/cdesc.pdf

The aluminium solder was bought ages
ago from Dick Smith and is made by Multicore. It needs a hot
tip which will suffer corrosion from the flux (it stripped
2mm of scale from a 150W Birko iron in minutes.

I purchased some for a job a few Months ago so afaik DSE still stocks it
.....

Regards
Richard Freeman