Author Topic: Welding on clean DC  (Read 13064 times)

BruceM

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Re: Welding on clean DC
« Reply #60 on: July 07, 2019, 02:35:29 PM »
The old school AC welders were just big linear, adjustable step down transformers.  No EMI from  power switching electronics but horrendous ELF magnetic fields both at transformer and at the welder where the welding leads are separated. Plus some healthy EMI due to AC arc- starting and stopping of the arc generates broad sprectrum EMI.  Likewise, those old DC units with linear transformers plus rectification for lumpy "DC" generate a great deal of EMI from the diodes- at start and stop of conduction, diodes make a little burst of high frequency EMI proportional in strength to the current.  So old tech doesn't solve the problem, but direct linear use of batteries does get rid of all EMI sources except the actual DC arc start/stop and current variation.

After it stopped drizzling yesterday I did hook up 12 foot of 3/16" diameter mild steel rod along with the extra 6V battery for a total of 30V nominal plus rod resistor.  It worked well in terms of welding with 3/32 7018 with the luxury of stable arc and the ability to "whip it". I checked via meters and camera in video mode, the rod was dropping 3.5 V at a current around 110 amps.  The rod did heat up quite rapidly, which concerns me, but I hope it will work out OK.  Steel electrical resistance increases with temperature.  I also tried the same resistance rod from 24V, to see if 1/16" 6013 would then be OK for thin stock. (It's way too hot on 24V.) That results in about 55 amps and while miserable to start and maintain arc, it does work. I tried it on some very thin stock to small square tube and it did the job. 

I also tried brazing the 3/16 rod to make a bronze coating for electrical connection. That works fine.  My plan is to bronze a spot every couple feet or so, and to use my spring type electrode holder with bronze jaws to clamp to the rod; that will by my simple current adjuster.  I'll paint the rest of the rod with high temp spray enamel to avoid corrosion. The fixed end of the rod will connect via 2 gauge wire and welding connector to either 24 or 30V battery connection (and arc stabilizing choke).  I bought the screw clamping, type electrode holder to try for the electrode as Mikenash had suggested.

So now I'm ready to build a new case for the three batteries and rod resistor. If I'm not happy with the rod resistor regulation, I'll hack one of my PV regulator boards.

I did some cutting on oxy-acetylene and have no problems with that outside with a light wind.  Brazing flux stinks but is doable outside.  I haven't tried gas welding with steel rods yet.  Much practice is needed on all fronts.


mikenash

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Re: Welding on clean DC
« Reply #61 on: July 07, 2019, 03:50:20 PM »
Hey Bruce, I hadn't realised you were dabbling in oxy/acetylene as well . . .

Check out this product "steel brazing rod"

https://www.globalweldingsupplies.co.nz/range-page.php?sku=R_TWNS

See specs?  Especially temp chart?

The general engineer up the road used to use it for things like repairs to truck parts.  Said it was really strong & caused less distortion than arc welding in some of his applications

Possibly a mild steel solution up to maybe 5mm or more

Not necessarily that particular product of course - that's just one vendor's take on things.  Maybe google "steel brazing rods" or something like that?

Cheers

BruceM

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Re: Welding on clean DC
« Reply #62 on: July 07, 2019, 04:45:51 PM »
I've got some copper coated mild steel filler rods for gas welding, just haven't put in the time yet.  That would have the advantage of no flux but more skill is needed since blow out of the base material is possible. 

High strength brazing rods like nickel silver are interesting- keeping temperature below steel deformation is a plus.

Back to woodworking today, I must bang up a new case for 3 batteries.  I have wire and terminals on order for new interconnects and connection to the steel rod resistor/regulator.
There will be 3 welding connector sockets, one negative, plus 24V, plus 30V. The resistor rod will have a whip to connect to any of these, the electrode cable will have an electrode holder on each end, it always connects to the rod on bronzed spots. That gives me reverse polarity, adjustable low current <=24V, and adjustable higher current <=30V. 

Being able to adjust current is a huge help. I hope electronic (linear) regulation isn't needed,
but will see how it works out.


BruceM

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Re: Welding on clean DC
« Reply #63 on: July 07, 2019, 05:27:28 PM »
By my calculations, 26 gauge steel sheet (0.476 mm) in 37.375 mm wide strips will have the have the same cross section as 3/16 steel rod, but has 5 times the surface area for better air cooling.  Hmmm, I should get out the tin snips. 

The zinc plating will increase conductivity...how much is a subject for testing.
« Last Edit: July 07, 2019, 06:04:12 PM by BruceM »

BruceM

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Re: Welding on clean DC
« Reply #64 on: July 07, 2019, 08:55:06 PM »
I made a test welding resistor cut into alternating 1.5" strips as shown in my test setup below.   13 strips total, so roughly 26 feet of 1.5 inch wide 26 gauge galvanized steel sheet.  Full length it is providing about 5 volts drop at 85 amps.   So the zinc plating is nearly halving the resistance, but that's good for radiating surface area.  It doesn't get very hot for a full stick of of welding in one go, so it's a winner.  I'll mount it on the new welder case side via some sort of standoffs to get airflow on both sides. I'm still thinking about standoff materials and moveable cable connection.


mike90045

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Re: Welding on clean DC
« Reply #65 on: July 08, 2019, 12:42:01 AM »
.... 26 gauge galvanized steel sheet..... It doesn't get very hot for a full stick of of welding in one go, ....

Mmmmmm   zinc fumes if it ever heats up too hot.  Be careful.

BruceM

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Re: Welding on clean DC
« Reply #66 on: July 08, 2019, 02:07:18 AM »
Good warning, Mike.  This should stay under 250F. It was under 165F, where you can't hold you finger on it for more than 3 seconds. 393F is the max safe temperature for exposed zinc.  I'll check it out carefully but thanks very much for the reminder. 


« Last Edit: July 08, 2019, 02:16:27 AM by BruceM »

BruceM

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Re: Welding on clean DC
« Reply #67 on: July 09, 2019, 03:53:07 AM »
Foil won't hack it, all connected wires radiate, which includes LCD panel and PV panel(s). Can't shield those. 

Any sustained electrical arc will generate plenty of UV, so I'm sure plasma cutters do too.

Maybe this winter I'll work on the linear circuitry for the digital one I took apart. I'm doing pretty good with the shade 8 lens, so I'm not in a hurry.

I have the new 3 battery case put together on wheels. Much work left to do, pondering the best way to hook up the "resistor" panel, so I can have either less than 30V, or less than 24V.  I had to hook up the whole thing on the shop floor again to weld the 5/8 axle stubs to some steel angle.  Sure is easier welding with the right power.  I did it with 1/8 6013, almost 3 sticks in fairly rapid order.  The galvanized stayed below 210F and rapidly cools while I'm picking slag and wire brushing. 

I'm not impressed with the performance below 24V, on 1/16 6013.  I tested that yesterday via the resistor on 24V.  The arc is tough to start and stops often. I suspect that a much larger choke (which can have smaller wire due to current down to around 50A) might be needed just for low current operating (below 24V).  I'm not sure it's worth the effort.

Figuring how to best mount the sheet resistor is next.  I want it 2-3 inches out so that there is good upward airflow behind it when it heats up.  Wood isn't going to hold up well in direct contact with the metal so I may use some silicone tubing as an insulator.



« Last Edit: July 09, 2019, 04:00:26 AM by BruceM »

BruceM

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Re: Welding on clean DC
« Reply #68 on: July 12, 2019, 04:18:53 AM »
Almost done with the new battery welder.  The zig zag strip galvanized steel power resistor was enlarged to the whole side of the new larger, 3 battery case, with strips going horizontal so I could use 2.25"x0.75" vertical maple stand offs to attach it. Maple has long history of good heat tolerance.  In testing today, I found that thanks to the much longer strip, at the very top of the strip, it does 1/16 - 6013 rods for very thin stock nicely.

What's left is moving the big wheels axle forward a bit and making some sort of push bar for moving it around.  I'm very happy with the performance; today I tested several different types and sizes of rods, and marked the best power setting for each right on the strips. In all cases, the sheet steel stays well below 210F.

So, no electronics required, beyond the custom gapped toroidal choke used as an arc stabilizer.

I'll post some pictures soon.

BruceM

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Re: Welding on clean DC
« Reply #69 on: July 14, 2019, 01:52:32 AM »
Here's some pictures of the new 3 battery welder; two 12V marine group 29 and a 6V cart battery, with my custom gapped toroidal choke as arc stabilizer.  The case needed a complete redo to house the third battery.  It's a bit wider, longer, taller and heavier.

I used it this afternoon for some welding; the push bar for the case was made of some scrap 1" square tubing with 1/16" wall thickness. Since the oxy-acetylene rig is down waiting for a replacement valve body, I tried my hand at stick welding that 1/16 wall tube with 1/16" 6013.  Tricky business but I got it done and a decent job of it.  I switched to 3/32 rod for welding to the 3/16 thick mounting plates, which was much easier since it's really welding 3/16 with brief excursions to the 1/16.

In the first photo you can see the 26 gauge galvanized strip resistor which is used to limit current from the 30V battery series string. In the top (lowest current, most resistance) setting it is lower current than on straight 24V, which is only useful for 1/16" 6013. This strip has worked out very well, and was dirt cheap to build. The lowest positions marked are for 1/8" 7018 or 7014.  The sheet strips have good airflow on the back and front, and stay below 210F so could be directly screwed to the maple stand offs.  I'd planned for silicone washers under screw head and strip, but they aren't needed.

In the third photo you can see the custom clamping attachment I made from some scrap 1/4" steel that allows me to easily move to any power setting.  I marked the positions with the specific rod size and type determined experimentally.  The increments are usefully moderate.  It has a soldered on brass welding connector, and solder tinned faces for the clamping electrical surfaces. It needs some spray paint.  Polarity reversal only requires switching the cable connectors.

As before, the front, rear and side panels come off for battery removal or service.

I do bulk charging with three "smart" 15A max chargers, Schumacher SC1280 6/12V Rapid Battery Charger and 15A Maintainer ($44 ea), one for each battery.  The case is wired with a 6 pin sermos type connector, and now so are the chargers.

Next I'll redo my low power, low EMF maintenance charger, to make it 3 separate chargers as well.  The 6V battery requires 2.2 amps at full charge, so I need to order a 3A linear regulator for that.  It would be really nice to do it with three secondaries on one core but I've got some old small toroidal transformers that I'll use up instead.

I'm very happy with the new version, my welds have improved greatly with the extra power for "whipping" the electrode and the ability to tune the power for rod and material thickness.

Boring for you who can just use a $100 welder, but a big boon for me.





« Last Edit: July 14, 2019, 02:00:44 AM by BruceM »

BruceM

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Re: Welding on clean DC
« Reply #70 on: July 14, 2019, 02:48:39 PM »
Yes, portability has suffered now that it's over 200 lbs.  I can still haul it in my trailer, but I'd have to use a come along or block and tackle to winch it up the ramp. Powered wheels would do it but then I'd be out of power before I could start welding.   ;)


BruceM

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Re: Welding on clean DC
« Reply #71 on: October 12, 2019, 12:20:47 AM »
Mikenash or other welders- I need to draw on your experience as I'm still novice level.  I'm planning a mobile welding table with roughly 2'x4' top.

I've struck out at the 2 area scrapyards looking for suitable material for a welding table top.  The two area suppliers won't sell anything less than 4x8 foot sheet stock.  What I can get is 20 foot lengths of either 4 inch wide 3/8 flat, or 6 inch wide 1/2" flat.  Is 3/8 inch thick enough for a slat type welding table top, or should suck it up and go 1/2 (twice the price)?
« Last Edit: October 13, 2019, 04:06:49 PM by BruceM »

mikenash

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Re: Welding on clean DC
« Reply #72 on: October 14, 2019, 09:46:42 AM »
Hey Bruce.  FWIW I would say 3/8 is heaps heavy enough if it is well-supported by pieces of steel underneath

If you made the top out of inch plate it could probably be completely un-supported.  If you made it from quarter plate it might need support every few inches

If you make it out of 3/8, just by smacking the top around a bit you'll get a feel for what support it needs underneath.  And underneath stuff you can knock up out of any old material lying around as no-one will see it . . .

Be imaginative  :)

EdDee

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Re: Welding on clean DC
« Reply #73 on: October 14, 2019, 10:48:03 AM »
Hey Bruce!

I have (Knocked down to component level) a 20mm thick solid welding surface 6ftx4ft - The reason its knocked down: TOO DAMN HEAVY TO MOVE!!

What I eventually settled on for minor mobility and stiffness (Price too) was a 6x4ft piece of checker plate - 1/4" thick...

4x Pipe legs at the corner, a 6" vice strategically welded into place, and, as a stiffener, 1x125mm wide galvanized lip channel welded underneath down the center of its length - the required braces are on the legs, the stiffener makes it more than adequate... As a bonus, the lip channel makes a handy clamp point for the earth leads....

Obviously, the rough side of the checker/tread plate is not the top of the bench!

With a decent run up and a sore shoulder later, I can move the thing a few inches at a time!!

Regds
Ed
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BruceM

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Re: Welding on clean DC
« Reply #74 on: October 14, 2019, 03:38:14 PM »
Thanks for the good ideas and help, Ed, Mike, Glort.

Yep, mobility does lean one towards a less hefty and cheaper design.  I've got some 4 inch all-locking castors which should do the mobility bit. I just have to come up with something to allow the occasional pounding on the vice anvil...perhaps just a wood or steel lift under the vice end to protect the castors.  I saw some scrap 1 inch threaded rod at the junkyard which gave me ideas but I expect the price of those nuts would make me wince.

I've done my best looking for some sort of scrap piece for a top and have come up dry. No engineering in these parts, and the fence/fab shop doesn't carry much in heavy sheet.

A slat type welding table top I can make from a single 20 foot 3/8 x 4 inch flat stock for $75, so I'll do that and beef it up with supports as needed as MikeN suggests. Some guy's seem to like slat tops- not my first choice but  I can put a piece of Hardyboard over it for non-welding table use.  A table with vise to use outside on the 20'x20' shop apron will be very useful for me.

Thanks for the good thoughts, guys!