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Author Topic: Welding on clean DC  (Read 17778 times)

mikenash

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Re: Welding on clean DC
« Reply #45 on: June 30, 2019, 04:24:38 AM »
I had to replace the Optima yellow top in my car; 6 yrs old and seems to have an open cell.

I thought it was prime for some welding experiments.  I opened some of the top with a carbide burr, and soldered a copper tab to the center lead connector to make a center tap at 6V.  Then cut a slit in the lid I removed for the copper tab and duct taped the lid back on.  One 6V side had the bad cell (open under the slightest load but looks fine on volt meter) , as expected, but the other side is in great shape still.

Welding on 30V was an entirely different experience; long arcing is easy, but it's TOO HOT, easy to over penetrate, more spatter/spray. I need to see how it goes on 1/8" rods on 1/4 steel, and practice more with 7018 now that I can long arc and move the electrode around. I did try some 6011 and at 30V it's too hot for 3/32 6011; it eats up the rod fast and I can hardly keep up lest I burn through.  On 24V 6011 just won't stay lit. I can see now why arc welders have adjustable current regulation...dialing it in for any rod and material sure would make things easier.

I may open up the Optima again and solder copper tabs at 2V and 4V (26V and 28V total) to give them a whirl.


Here's a thought for you, Bruce

This is something often done when you are welding and find that you have set the welder 5 amps too high but you're in the middle of something a bit critical, or just don't want to stop

It also used to be common when setting the amps wasn't as easy as just turning a dial

And it's a common technique in positional welding . . .

You can really only get away with it with Low Hydrogen rods as they won't leave you with slag inclusions

Now, as you're working, there's a point at which you have gotten 100% of the penetration you can with your weld, and the whole puddle is just about to turn too liquid and fall through - leaving a big hole.  Just before this point, you normally keep moving forward with your weld/puddle, and that's how you know you have gotten a good penetration etc (I'm over-simplifying here, but you get it . . . )

If the welder is turned a bit low, you can sort of sit there moving the puddle from side to side and making slow forward progress and a so-so weld - within reason

But if it's too hot, your options are limited.  What sort of happens is that, to avoid making a too-hot, too-liquid puddle and having it all just fall away, you tend to move forward faster than you might like - so that the new, cold metal is taking the heat away from the puddle constantly.  You tend to end up with a thin, scrappy weld

But what you can do - if you have Low Hydrogen rods - is move ahead a bit to where new, cold metal pulls some of the heat out of your puddle - and then move back . . .

It only takes a small fraction of a second for your weld puddle to cool from liquid to plastic (sort of) . . .

So if you start your weld and work along, watching as it gets "too" hot - then quickly move the electrode forward, sliding along the metal so you don't lose that arc, about maybe a half an inch - then come back to your puddle which has cooled in the fraction  of a second your arc was away from it, and is now just a perfect temperature to carry on welding for another second or so - then move forward quickly another half inch - then back to your weld . . . and so on . . .

What's happening is that you're depositing little bits of weld on the metal "ahead" of your weld and then coming along a second or so later and welding over them.  If the whole thing is nice and hot and you keep your arc short and you're using Low Hydrogen rods - it's a controllable process and weld quality can still be very good

It's a technique often used on "vertical up" welding, where, because the "work" is vertical not horizontal, the tendency for the weld puddle to "fall down" is much exaggerated.  When the puddle gets too hot - you just move away from it for a quarter or a third of a second or some such and then come back to it as it cools . . .

If you have a google, somewhere there will be temperature charts for the process of arc welding and, because your hot weld is surrounded by cold metal, that cooling from "too hot" to "just right" happens very very fast once the heat source (the arc) is removed

Once you get your head around the physics of what's happening (and you'll understand that better than I do) you can see that moving ahead a little or a lot is an easy way to do a good weld with an arc that's "too hot" and is quite a controllable process

If you watch a video of a pipeline welder "keyholing" a root run - basically blowing right through and then filling back in in one action , so as to be assured of 100% penetration, that's sort of the same process

Have a "play", you'll see

Cheers
As your weld puddle forms a

BruceM

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Re: Welding on clean DC
« Reply #46 on: June 30, 2019, 05:15:21 AM »
30V is way more than a 5 amp problem, it's a 50 amp problem, but your note on how to cope with a bit of overage is a good one. 

No US companies seem to make modest sized 2V lead batteries.  I looked at lithium batteries, but they seem to be nuts, price wise, to get to 100 AH. 

mikenash

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Re: Welding on clean DC
« Reply #47 on: June 30, 2019, 06:01:51 AM »
If you have a 50A problem you can probably go from 2.5mm to 3.2mm rods (or imperial equivalent?)  You'll be surprised what you can get away with if you think in terms of moving the heat around a lot.  Much more than you would normally think to do.  Cheers

BruceM

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Re: Welding on clean DC
« Reply #48 on: June 30, 2019, 03:35:13 PM »
My normal range of thicknesses for stick welding would be 1/8 to 1/4, so rods above 1/8 are impractical.  Thinner is tricky, but I did get some 1/16 -7018 rods that work on 24V, which I can try on thinner stock. I was thinking more towards brazing for thinner. 

I saw on the web that one bloke used 36V in batteries and then a big adjustable resistor made of heavy steel wire, wound around a large cement paver.  He clamped on the wire with a jumper cable clamp at differing locations to change his welding voltage/current.  This would be a short lived thing, as the steel wire will oxidize, but the concept could be improved by using nichrome wire to avoid the rust to death of the resistance wire.  A zig zag of heavy nichrome on ceramic posts on the side of the welder comes to mind, starting at 30 or less volts.  Something to be avoided if possible, but doable.

High frequency PWM to a small filter choke is how current regulation is done in the "inverter" type units, starting with 80V or so.  This is about the only way to do it electronically, as the currents are so large; linear transistor control from say 30 or 36V uses them as resistors and the heat dissipation and number of transistors is quite large and impractical.  The switching approach using switching power transistors (IGBT or MOSFET) can cope with full on or off  with minimal heatsinking by comparison. Only a few switching transistors in parallel needed, too. Alas, the switching approach takes very fast rise/fall time high current gate drivers to overcome the gate capacitance and avoid "letting the smoke out" of the switching transistors. The high current spikes of the gate drivers plus the starting and stopping of diodes and ringing from the fast swinging output generate massive EMI.  I can't be near these welders at all.  Designing such a high current buck converter from 36V would be the obvious solution for a battery rig, but it does me no good.  The direct battery solution with minimal linear (non switching) or no regulation avoids the massive EMI problem entirely.  So old school it must be.

I did find one company in China with a listing selling a suitable 2V cell at single quantities. I'll contact them and see...

Having just two selections via welding cable connectors at 24 and 26V would be marvelous.





BruceM

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Re: Welding on clean DC
« Reply #49 on: June 30, 2019, 04:38:52 PM »
Yep, an oil filled container would hold heavy steel resistance wire nicely to prevent oxidization, and the oil mass would keep temperatures down for low duty cycle welding.  An interesting idea, Glort, thanks.
 

BruceM

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Re: Welding on clean DC
« Reply #50 on: July 01, 2019, 03:15:59 PM »
Found some perfect 2V batteries on Alibaba (China), despite the listing stating minimum of 1, they won't sell sell under 500 units.  Pity, with 24, 26 and 28V I'd have lots of flexibility.

Adding a 6V battery (30V) and resistance for current limiting may be the more practical approach.

BruceM

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Re: Welding on clean DC
« Reply #51 on: July 02, 2019, 01:53:56 AM »
I took apart a dud 18AH 12V AGM battery to see if a new one might be hacked to have all cells in parallel, thus 108AH at 2V and a good match for my Marine wet batteries.  Alas, the cases are glued together internally and not just at the outer edge, and designed in such a way that makes reworking it impossible.  For hacking a battery for lower voltage, wet lead-acid is a better bet.

I did some research on the resistance method.  Nichrome is out-  it's too resistive for the largest (9) gauge available, and large rods around available. It's just not suitable for 120-150 amp welding currents.

Next I looked at steel wire/rod. About 4 meters of 3/16 iron rod would give the needed max of 4V drop from a 6V battery at 120 amps. That could be wound on the side of the welder and held on some sort of hold offs. Resistance does vary greatly with alloy so testing would be needed.

Stainless steel rods of 3/16 diameter are more electrically resistive than mild steel so only about 10 feet or 3 meters is needed. With special welding rods, SS can be arc welded, so the rods could be connected together in that manner.  Stainless might hold up OK with direct air exposure, a big plus.

My new oxy-acetylene rig is all put together and leak tested on all fittings.  It's ready to go but it was getting late so I decided first flame and first cut would be tomorrow AM when I'm fresh and after I've reviewed my proper cutting pressures and start/shut down procedures.

 







BruceM

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Re: Welding on clean DC
« Reply #52 on: July 02, 2019, 07:00:37 AM »
Fixed taps would be easier, but I have to build something adjustable first to find were to put them. The electrode holder I'm using is bronze jawed with a broad face, brutal spring force.  That would be a one way to make a moveable connection.

It cost me $40 last week to have my B tank acetylene plus larger oxy tank filled.

H/O generation via electrolysis cell is an appealing way to turn surplus PV into useful fuels. Compressing them is the scary part, I think.   If there's cross contamination due to a leaky separator membrane... BOOM.



BruceM

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Re: Welding on clean DC
« Reply #53 on: July 02, 2019, 03:17:17 PM »
Glad I'm not buying welding gasses in Australia.  US- B size acetylene tanks are small, roughly 40 cubic feet of gas, about 1.1 cubic meter. My oxy tank is 80 CF, twice that size. 

Separation of the gasses, plus a flash back arrestor for both at the torch plus regulator seems wise for HH/O - electrolysis.  I don't know about cutting with Brown's gas; normally a disproportional amount of oxygen is needed so you'd have to have a safe way to vent excess hydrogen pressure assuming the electrolysis cell is being run at some directly useful pressure under 50 psi. 

For heating the Brown's gas would be an ideal; for welding I'm not sure. I would think hydrogen alone to mimic the hydrogen rich, oxygen poor inner flame tip region of oxy/acetylene would help prevent oxidization of the weld pool. 






BruceM

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Re: Welding on clean DC
« Reply #54 on: July 02, 2019, 06:10:55 PM »
Round two of resistive material calculations, using some better data.  Steel varies in resistivity greatly depending on alloy so some variance is to be expected. 

Using a desired 4V drop from 6V at 120 amps welding current gives me a desired 0.0333 ohm desired power resistor, with the ability to dissipate the resulting intermittent 480 watts of heat to the air.

For steel rod 3/16" , 4.76mm diameter- 3.29 meters or 10.8 ft (5x 2 foot tall connected rods)
For steel rod 1/4" , 6.35mm diameter- 5.8 m or 19 ft (10 x 2 foot tall connected rods)

For stainless steel rod 1/4", 6.35mm diameter- 1.37m or  4.5 ft (2-3 x 2 foot tall connected rods).

These all seem viable.  the 19ft of 1/4" steel rod would  stay cooler.

Walmart has a floor polisher 6V battery on sale for $90.  Much more than the 100AH needed but the price is right.  A complete redo of the wood case will be needed.



 


BruceM

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Re: Welding on clean DC
« Reply #55 on: July 03, 2019, 01:03:11 AM »
Good point on the max amps draw rate for the floor polisher battery in the store.  I can't find the damn thing on line; Walmart's search engine is pathetic.  I'm going to have to call and get the make and model so I can check the max current draw specs.  Thanks, Glort.

My other two 12V marine deep cycle batteries are 100AH, I was just looking to match that, and use 50ah before charging.  Yes, battery voltage sag is a potential issue but I haven't noticed it so far.  I took my measurements just AFTER welding (camera recording meters video- I can hear the arcing stop). This is the good case for a linear electronic regulator- it would attempt to hold the specified amperage as battery voltage drops.
Or, for lots of steps or continuous adjustment; welding is not a continuous business and while stopping, manually adjusting for a bit more juice is OK.


BruceM

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Re: Welding on clean DC
« Reply #56 on: July 03, 2019, 01:23:45 AM »
The wet floor polisher batteries seem to be similar to T105's.  They have data charts showing 250 amps current draw, so it should be fine for the welder.  I suspect that some rural locals may be using them in their small off grid systems.   Thanks again for mentioning that important bit which I'd forgotten.  3/16 steel rod is very cheap at Home Depot so I'll start with around 10 feet of that as my 0.033 ohm power resistor. 

I can't tolerate sustained welding myself, so there's no problem with stopping to charge while I take a break.

BruceM

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Re: Welding on clean DC
« Reply #57 on: July 04, 2019, 06:08:49 AM »
Lucky break for me, back on Bromelain, which I'd run out of, and once again feeling much less head pain in stores and driving/riding.  Did a big shopping run with my neighbor Jeff and got the new 6V battery and the 3/16 rods. Got a nice collection of scrap steel for $10 from the fence co. for my further welding/cutting education, and was offered more to pick over next week.  When you've been mostly homebound for a few decades, shopping in stores is a treat.

I've been stewing over using my newer linear PV charge regulator PCB as a welding regulator. It is a low side regulator, 7 TO247 or TO3 style large Mosfets in parallel, linear mode, an op amp and current sense resistor for each for current matching.  Very little mods needed though I'm concerned about arc EMI and what I should do to address that.  Found a couple Fairchild Mosfets, 75 and 100V that have good linear capability, while still having low on resistance, around $5 ea. One 75V one can handle 50A at 6V drop, with just one, so 7 would be loafing.  All together about $100 in parts to build one, not counting what I need for arc EMI supression.  Chokes rated 200 amps are NOT standard products.  Surge supressor devices might be helpful with some modest line to line metal film capacitors, and perhaps I can get some large ferrite and powdered iron cores.



 

BruceM

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Re: Welding on clean DC
« Reply #58 on: July 04, 2019, 04:51:18 PM »
Sorry you're down, Glort. The statistics on current SSRI/Tricyclics for depression are quite poor. I've read the books of Datis Kharrazian, quite impressive guy. Teaching at Loma Linda now.  https://drknews.com/  I think the future of medicine is in the group now known as functional medicine.

I looked more at the PV board for welding regulator-  it was designed for much lower currents and higher voltages so traces and wires for power are going to be a challenge.  It would need a spider's web of additional large wires added.  I will try the simple resistive method first.  Operating MOSFETs in linear mode, you must stay well away from the safe operating area specification, and a massive heatsink will be needed.  If dropping 4V at 150 amps, you must heatsink 600W (!), sharing that among 7 mosfets still leaves a very hefty 85W of heat dissipation per mosfet.
Because of short welding duty cycle, either a big slab of aluminum or a water filled heatsink might be effective, sort of a hopper cooled welder.   PWM is normally used for this reason.  I hope the 3/16 steel rod method will work and will save me a lot of educational lumps in working with such extreme currents and EMI as welding has. 






mikenash

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Re: Welding on clean DC
« Reply #59 on: July 07, 2019, 03:36:47 AM »
Hey Bruce - stupid question perhaps. but are these old-fashioned type of welder somethinh you can tolerate?

No electronics, obviously.  And I wondered if the pull-in-and-out (voltage?) adjustment might serve you in some way to modify your DC

I would guess there are still a few rattling around Old Farts' workshops

Cheers