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Author Topic: Welding on clean DC  (Read 3983 times)

mikenash

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Re: Welding on clean DC
« Reply #60 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

glort

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Re: Welding on clean DC
« Reply #61 on: June 30, 2019, 08:01:38 AM »

Spose it depends on what you want to weld.
I find most of what I want to do is at the lighter end of the scale and that's what gives me the most difficulty.
I can count the number of times I had turned the old welder up beyond 3/4  but the more power you are cranking out the easier I find it is to get good, nice looking welds.

I'm hoping the new machine will eliminate many of the problems I had on the lighter stuff.  The lighter the material is the narrower the margin for error.

Bruce probably a Dumb suggestion but as a matter of interest at least, would it be possible at all to control the output with some plates in a water bath with caustic or salt as an electrolyte?  Maybe it would be possible to have a drum with large flat plates separated by nylon Bolts and washers as I imagine you would want the plates quite close for the amps you need.  You might be able to control the amperage by the plate distance or how much of the plates was submerged in the electrolyte. The electrolyte strength would make a difference as well but I imagine you would want more ajustability and I think raising and lowering the depth of the plates would be an easy way to get that.

Another hair brained possibility that comes to mind would be instead of limiting the current in such a way, what about a Dummy load that you switched in?  This could be done by a man of your electronic genius by PWM'ing some mosfets ( or some better method) with a foot pedal like a TIG.  Maybe run a setup where you have a voltage divider that turns on a bank of Mosfets in say 5A or whatever steps if it's difficult to get a linear loading.
This may not be the most efficient setup but that's not really the important thing.

I have used this electrolyte  method for Dummy loads for testing generators and you can sink a lot of amps that way.  You might want a 200L drum of water as you would be effectively making a kettle ( as me how I know) but I would imagine the setup would work just as well in current limiting as it does current sinking.  I know I have made a strong soloution of Caustic in a 4" PVC pipe with plated welded onto some thin rod and spaced them in an end cap and could sink 80A or more into something that small pretty easily.  Got hot quick but it was a very simple, compact, cheap and easy way to create a Big load.

BruceM

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Re: Welding on clean DC
« Reply #62 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.





glort

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Re: Welding on clean DC
« Reply #63 on: June 30, 2019, 04:20:29 PM »

 This would be a short lived thing, as the steel wire will oxidize,

Submerge it in oil.

BruceM

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Re: Welding on clean DC
« Reply #64 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 #65 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 #66 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.

 







glort

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Re: Welding on clean DC
« Reply #67 on: July 02, 2019, 05:18:09 AM »

I would not have forseen so much resistance in steel rod of any sort.

If you wanted to make this adjustable and to nullify any corrosion issues, perhaps you could make 3 Permanent taps and just connect whichever one you wanted.

I welding gas expensive in the states?  Price has got a bit out of hand here. I think TIG has gained in popularity because of gas prices as have Plasma Cutters. Gas would certainly be ideal for your needs though Bruce.
I was wondering if TIG can be used for brazing or even Stick rods so shielding gas could be avoided.

Years ago I made myself a gas torch for using LPG with compressed air.  Through brute force it could braze yellowtip rods.  Not near as good as Oxy/Lpg which I have a torch for but was certainly better than the normally aspirated torches.  Clear to see the effect the other gases in the mix have on the flame temp though.

I have been watching vids where a guy built himself a very elaborate HHO machine.  Tiny torch like a jeweller type but seems to have no trouble getting 1" copper fittings to heat.
So far he seems to have survived using it often.


BruceM

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Re: Welding on clean DC
« Reply #68 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.



glort

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Re: Welding on clean DC
« Reply #69 on: July 02, 2019, 12:25:33 PM »

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

Yeah, it's cheap allright.
I don't know what a B tank is size wise.Different to what we have here but does not mater.  Our smallest is a  D tank and that costs $187 for Oxy and Acetylene. You wouldn't do much cutting with that, mainly used by tradies whom have to cart them around for doing brazing.  Many of them now use MAAP gas and disposable cylinders are becoming popular too although I think the amount of gas you get for the price would make the regular Bottles look like bargains.

MIG/Tig gas starts at $108 and $199 for a medium Bottle.  I'll be sticking with gasless at those prices.


Quote
H/O generation via electrolysis cell is an appealing way to turn surplus PV into useful fuels.

Surplus PV?
I have distant memory of that. Wish I had some now. Made 38 Kwh today, 36 yesterday. Used 67 Kwh today and 64 Yesterday. I didn't even kick the water heater in which could take another 20 Kwh to bring up to speed.

 
Quote
Compressing them is the scary part, I think.   If there's cross contamination due to a leaky separator membrane... BOOM.

Yeah, I'm not exactly pedantic when it comes to safety but that's a matter of self preservation in my book.
The setup this guy is using is " On the fly " so no compressed or stored gas other than what is in the lines and generator.  By the size of the cell though, there would be a fair amount of gas in it during operation and if it did backfire, I wouldn't want to be in the same garage that's for sure.

I do think the thing is probably well built however there are always circumstances and events you can't predict as well as failures.

I have never seen one of these HHO gas machines where they at least run the gas to the torch separately which to me would add a lot more confidence in a system. Shouldn't be hard to make separate cells and run a connection between the 2 T'ing them together at the bottom below the cells so all gasses were above that level and couldn't mix.

BruceM

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Re: Welding on clean DC
« Reply #70 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 #71 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.



 


glort

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Re: Welding on clean DC
« Reply #72 on: July 02, 2019, 11:20:08 PM »

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.

What sort of battery is It?
A C20 discharge rate isn't over the top but may be more than the battery is rated for as I would Guess in it's native application the amps are lower and the endurance is high.

You may also need to look at 2 of these not only to get the C rate down but also the DoD.  Never a good Idea to  discharge any battery too deeply and the less you hit it the longer it will last. For 100ah you would ideally want somewhere around 200Ah capacity even on a deep cycle battery and that would still be on the limit for what i'd go into one.

I noticed on fleabay there are plenty of golf cart batteries  that would do both the C rate and have over 200Ah capacity for around $130.
I couldn't find the one you mention, wallfart have the most retarded online search engine that simply does not work by the filters given but if it is a similar Type battery to a trojan etc you might be Ok depending on its specs.

Would small tube give increased resistance in light wall thickness?

Does everything not change in your calculations and desired output  as the batteries Discharge and the amps and Voltage vary the longer you weld?
At the Current you are using, does not take long to knock 2V off even a large battery when Fully charged and then thee is also the standing/ recovery voltages that would occur between welds.

I'm thinking your calculations are more precise than the battery's characteristics in the first place and your specific desired outputs may be thwarted by the source of the power, the battery's, right from the start. 

BruceM

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Re: Welding on clean DC
« Reply #73 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 #74 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.