18650 DC arc welder

[goatman]

anyone using 18650 batteries for a DC arc welder. ive used 2 truck batteries in series for 24v welding. I think ive seen J Mantzel weld with solar panels but haven't seen anyone using 18650s

[john61ct]

volts is volts, amps is amps

Measure your Ah per session usage first so you know how big a pack to build.

Select your cells so your peak amps usage is well below what the testers here say they can handle.

Ignore vendor claims about their C-rate.

[goatman]

volts is volts, amps is amps

Measure your Ah per session usage first so you know how big a pack to build.

Select your cells so your peak amps usage is well below what the testers here say they can handle.

Ignore vendor claims about their C-rate.

I have 25r batteries 14s4p, so basically can I just use a 40 amp or whatever amp shunt so I can burn the rod steady.
truck batteries and jumper cables are ok for doing spot welds or you have to start and stop in rhythm or else you smoke the rod, its a technique but its dangerous.
I like simple and a shunt sounds simple. different shunts for different rods/metal

[john61ct]

The only shunts I am familiar with are used to measure current not regulate it so I dunno.

My comments were just based on electricity in general, know nothing about welding.

I assume you know the volt/amp specs for the machine you plan to use?

[goatman]

The only shunts I am familiar with are used to measure current not regulate it so I dunno.

My comments were just based on electricity in general, know nothing about welding.

I assume you know the volt/amp specs for the machine you plan to use?

not a clue about specs, I usually just wing it but I have a blown 40 amp controller so ill take those shunts solder it to some copper and see what happens I guess

[goatman]

now I get it, a shunt measures the current and the controller controls the current? but why do you butter shunts to get more amps, that's what made me think a shunt regulated current to 40 or whatever amp its rated at

[john61ct]

why do you butter shunts to get more amps?

I don't even know what side my own toast is buttered, much less how or why to butter a shunt!

[HK12K]

now I get it, a shunt measures the current and the controller controls the current? but why do you butter shunts to get more amps, that's what made me think a shunt regulated current to 40 or whatever amp its rated at

afaik, which is admittedly very little, the shunt in the controller is essentially just a resistor with a known resistance inserted in parallel with the circuit. As current flows through it the resistance changes predictably and the controller then uses those changes in resistance to do it's calculations. Adding material to the shunt lowers it's resistance and skews the numbers. (Someone please correct me if I'm wrong.)

However there are apparently a number of different types of electrical shunts each with varying applications, according to wikipedia.

https://en.wikipedia.org/wiki/Shunt_(electrical)

[spinningmagnets]

Add a temp-sensor to the center of the 18650 pack, and keep the temps below 140F, and 120F is better.

If you can only weld for a short time, keep enlarging the pack until it can weld continuously while only getting warm.

[goatman]

there has to be something simple like a potentiometer to knock the voltage down to roughly the LVC of the pack so the voltage is steady and another potentiometer downstream to control amps.

spinning magnets, I was curious about the effects of essentially short circuiting the non protected 18650s and getting thermal runaway but my thinking is if you have 8p of 25r batteries that's 200 amps so 50amps steady shouldn't bother them and when I say steady I mean being able to burn a full rod at once if youre in a jam somewhere

[spinningmagnets]

Theoretical discussion is very useful in the prototype stage, but...nothing beats testing an actual prototype under real-world loads...

Nothin' to it, but to do it...

[goatman]

I think ive found a solution. a mppt solar charge controller, 48v 100amp.
instead of the solar panel its the 18650 pack supplying the power and the leads that would've went to a battery bank are now the welding cables and I believe you can connect a CA 3 to a mppt.
ill see if I can find any cheap used mppt to see if it will actually work before buying something good

[goatman]

an mppt probably isn't what I want, I want simple. I don't know electronics lingo so potentiometer may be the wrong word. am I looking for a resistor?
lets say I need 48vdc@50 amps continuous all I need is a 2400 watt resistor, is that right? or 48vdc@100amp 4800 watt resistor

also dc reverse polarity welding, you take the positive wire and clip it to the metal your welding and the negative wire connects to the welding rod clamp, do you put the resistor on the negative or positive lead

[amberwolf]

A regular resistor that size could be about as big as a car engine (much smaller if fan-cooled).

(A 50w resistor is about as big as a pinky or thumb, depending on construction).

A set of heating elements from a stove, placed in parallel to lower resistance for use at lower voltages than original, might handle that kind of power, but they'd be very very hot (probably glowing at least a little).

There *are* wirewound potentiometers for high voltage medium wattage (AC mains voltage, around 1000w or so) used in stage lighting control, that might work, but they're bigger than hubmotors, and again, they get very hot.

Whatever resistance you used would also be dissipating (wasting) all of that energy as heat. Extremely inefficient, very very wasteful.


I don't think you want a resistor--you want a current limiter, which is basically the same as a brushed motor controller. I don't know if you could just use one of those or not, but it would limit current to prevent battery damage from overcurrent, and would also have an LVC to prevent battery damage from overdischarge. The catch is that these are not designed to handle the extreme RF from the arc, so there is a risk that could destroy FETs, etc. (brushed motors do arc by their nature, but until you get into the *really* big ones, hundreds or thousands of amps, the arc is nothing like that in stick welding).

I recommend looking at the various homebuilt arc welder circuits you can find on the web, to see if any of them will do what you want. SOme of them are in this search:
https://www.google.com/search?&q=DIY+DC ... r+circuits

[DogDipstick]

Might as well build a homemade plasma cutter.. lol. Home made DC welder sounds a little dangerous. Lol.

Either or, I do not think 18650 is the correct choice for this.

[cooking monkey]

What a great topic. I love welding. I am what you call a self taught welder. I wish I had the proper education and training but I don't. (though I have been to both Lincoln Electrics factory in Cleveland and Millers in Appleton). I have not let that stop me though. I am also familiar with welding off solar panels and batteries, both with stick and flux core mig. I will throw in my 2 cents, 4.5 cents with inflation later Friday or Saturday. Cant right now as I have been testing my home made mead wine and am lucky to still be able to type...

[goatman]

Might as well build a homemade plasma cutter.. lol. Home made DC welder sounds a little dangerous. Lol.

Either or, I do not think 18650 is the correct choice for this.

I think 18650 25r will work but im trying to go the wrong way about it by not understanding what im looking for. I found rheostats for a diesel powered welder, a miller bobcat 225. and theyre dealing in 10 and 14 ohms and watts were maybe 100? so im going to look for a small gas powered 48vdc welder and see if I can get schematics then simplify it to burning a 1/8 rod at 100 amps or find one with a blown motor or generator and replace with a 18650 pack. yes welding with batteries is dangerous when its just 2 sets of jumper cables and 2 batteries in series but once you get the hang of it its easy and does a really nice job. you basically have to start and stop the arc repeatedly in a rythym without getting the rod stuck or smoked
safe and stupid simple cant be that hard

[john61ct]

can structural aluminum be welded this way?

[goatman]

can structural aluminum be welded this way?

I was just looking for aluminum arc welding rods and they do sell them, blue demon e4043 1/8 inch for welding dissimilar grades of aluminum and theyre low heat so I think that means less energy required. ive tried those bernzomatic brazing rods but wasn't impressed

[john61ct]

Yes apparently hotter than minimum causes weakening

[Ianhill]

A welding machine needs adjustable current before the weld to set up arc and then on the fly so a long weld on a thin piece will need less energy towards the end of the weld to the beginning as the part becomes heat soaked.

Sounds crazy but if you want simple I would try a tub full of salt water two sacrificial electrodes and use it as a variable resistor for the pack run a crude shunt and volt display so you have an idea on your welding current coming out and adjust the strength with the electrode distance in the tank simple as possible and the batterys can be kept in check not to exceed the c rating but it probably be cheaper in parts with blown holes in or weak welds to just pick up a igbt welder.

Myself I'd get a second hand mig welder and never look back can't be a gas shield weld nice clean surface and self tinting mask, had arc eye and it ain't no joke.

[amberwolf]

ive tried those bernzomatic brazing rods but wasn't impressed

if you were using hem for welding, well, they're not meant for htat.

if you were brazing wiht them, remember they're meant to braze specific metals together, and those have to fit pretty closely, becuase essentially you are soldering them together with brass rather than lead/tin. they'll fill a certain amount of gap, but not much unless you have the skill / equipment to do that right.

and brazing, like welding, has it's own skillset and techniques, that if not used right, don't make very good joints.

[goatman]

ive tried those bernzomatic brazing rods but wasn't impressed

if you were using hem for welding, well, they're not meant for htat.

if you were brazing wiht them, remember they're meant to braze specific metals together, and those have to fit pretty closely, becuase essentially you are soldering them together with brass rather than lead/tin. they'll fill a certain amount of gap, but not much unless you have the skill / equipment to do that right.

and brazing, like welding, has it's own skillset and techniques, that if not used right, don't make very good joints.

those rods are meant to be used for new material with propane or map gas and youll need a turbo nozzle, I had a crack in an aluminum hot water tank in my travel trailer , so yes its older contaminated aluminum, I could seal with the rods but at 45 psi it was porous and would slowly get wet, waste of money and cut it out and used an epoxy or jb weld instead . I spent years as a plumber soldering and am well aware of how to solder and braze.sometimes its a pain in the butt to get a generator and welder 40 miles into the bush to fix a 10 yph washplant that I built, my shaker runs at 745vbm/rpm and the vibrations can cause cracks. 2 truck batteries are heavy so I was thinking an ebike battery and some jumper cables could work but it needs to be safe