Author Topic: Will welding shorten lifespan of batteries? (Read 10537 times)

gizmoguy · « **on:** November 06, 2009, 03:44:26 PM »

I saw this video on youtube describing how to hook up 3 12 volt car batteries in series to make a DC Arc welder.

http://www.youtube.com/watch?v=8tHJ0NSjZnM

My question is...Can you damage a 48 volt 440AH battery bank if you use it for stick welding? I understand that if you discharge the batteries too far that it will damage them...but it seems like, barring deep discharge, that this should be safe to do. Am I wrong?

Thanks!

Gizmoguy

willib · « **Reply #1 on:** November 06, 2009, 04:09:02 PM »

I'll admit that i did not watch the whole video . but i think that you dont need 36V to weld.

Isnt most welding done with much lower voltage?

and isnt the current what is needed for a good weld?

so i'm thinking that three batteries in parallel would be better.?

gizmoguy · « **Reply #2 on:** November 06, 2009, 04:24:38 PM »

He sets up the batteries in parallel at the end of the video to see if it works but he can't get an arc to start at 12 volts. I haven't tried myself.

Gizmoguy

joestue · « **Reply #3 on:** November 06, 2009, 06:01:57 PM »

I never had much luck with dc on 6011 rod, welds were full of holes and looked about as good as the ones he was getting in that video.

Car batteries are what, 50AH on a good day?

440 ah cells should have no problem delivering .5C for short periods of time, and at that current and voltage (200A) you will go through an 1/8th inch rod in 20 seconds or less.

I'd be more concerned about your battery interconnects than the batteries in the event of an accidental short.

gizmoguy · « **Reply #4 on:** November 06, 2009, 08:15:31 PM »

Ah yes...most people would worry about their battery interconnects but I worry about my batteries more than my interconnects. My interconnects are 6 1/2" long 1/4"x1" solid copper bar. If I melt that...I'm in trouble!

Gizmoguy

Flux · « **Reply #5 on:** November 07, 2009, 12:32:20 AM »

I haven't watched the video but you meed a minimum of 36v to strike an arc reliably. When running the arc drops to something over 20v. Low hydrogen and other tricky rods need a fair bit more.

With only 36v to start with you have little room for a ballast resistor to stabilise things. If this is direct connected without any ballast then it is a last hope get you home process, not something to be done regularly.

The whole thing works infinitely better with a big choke in series but that defeats the idea if it is an emergency job. I don't think I would want to try without some form of ballast resistance but if the cables are under rated this may give enough protection.

If you can limit the current to something sensible then batteries will cope with this for a short time. I am not sure that it is a satisfactory long term method of welding without a choke , suitable ballast, perhaps a bit more than 36v and a massive battery bank. Batteries only give a limited number of charge discharge cycles and this would be pretty drastic if done regularly.

At one time ( here in the UK at least) there was a contraption on the market that had an electromagnet in the rod holder and when the rod touched the job it vibrated like an electric bell. With the inductance of the coil and the constant starting of the arc it was claimed to work at 12v. A friend had one and claimed it was marvellous, it certainly stuck things together but I wouldn't have classed it as welding.

Flux

tanner0441 · « **Reply #6 on:** November 07, 2009, 08:43:16 AM »

Hi

Most welders I have come across have been 50V and 90v. 90v gives much better penetration and starts easyer. I have welded using a collection of 2V cells from a telephone exchange (40ish V)and it welded beautifully with a hiss from the arc.. If you are using low hydrogen rods on DC or AC we used to heat them up in an oven until they were too hot to pick up without a gloved hand. As Flux says some form of ballast in the welding cable does stop the initial extreme current surge until the voltage stabilizes.

If you are welding cast iron you have to heat the workpiece as well as the rods and do it in short runs and ping the weld with a small hammer between runs.

If they are your main batteries then I would think twice, if you have a collection of old car batteries and need more current than a little portable welder will give then go for it. I did not damage the phone exchange batteries but I had a mental picture of what the plates were trying to do every time I struck the arc.

Brian

PeterAVT · « **Reply #7 on:** November 07, 2009, 10:16:59 AM »

Speaking as a former welder, now retired...

Yes, it can be done but I wouldn't recommend it. It is maybe one of those things that is best for emergencies and etc. It also requires a fair amount of skill and knowledge, in my experience.

Your batteries will definitely suffer and hate you for it, with reduced lifespan and etc.

The best welding machines that I ever used (in north USA) ran on 480 volts 3-phase AC, or else they had a diesel engine driven generator. That should tell you something.

You can easily strike an arc with DC between 20 and 30 volts with practice, but how much are your batteries worth?

dnix71 · « **Reply #8 on:** November 07, 2009, 11:46:40 AM »

I've tried stick welding with 12v and it didn't work. The Voc on my cheap box welder is high 20's to low 30's. Three in series sounds right.

I don't see how it would shorten the life of a car battery as long as you recharge immediately. It just like a starting load. That assumes of course that all three batteries have about the same capacity.

scottsAI · « **Reply #9 on:** November 07, 2009, 12:28:27 PM »

No!!! (if done right, you must understand the issues involved)

Your vehicles battery is <60ah

Starting requires 300a to 500amps to start it!

Why is using 200amps a concern?

Once arc is struck the current drops way down, most welders are rated well below 200amps.

Welding can be done at 24v, arc starting is very difficult enough so most will say it does not work, 36v much better arc starting.

Additional searching, people recommend a 12 inch length of coat hanger used as ballast resistor works well.

Have fun,

Scott.

gizmoguy · « **Reply #10 on:** November 07, 2009, 07:43:59 PM »

I was considering using my RE batteries....not my car batteries. I have a 48 volt 440 AH battery bank. I don't have that many car batteries.

Thanks!

Gizmoguy

scottsAI · « **Reply #11 on:** November 07, 2009, 08:55:22 PM »

Gizmoguy,

Suspected RE. Welding using them will be fine, if your careful.

Mentioned the vehicle battery, its weaker than a deep cycle for large currents!

Total power used will be low as shown in the video, he can start the car afterward.

48v battery will work just fine. Beware of the shock hazard this voltage presents.

Home welders keep their voltage below 48v for this reason. I've only checked couple small cheap units.

Why build your own welder?

http://www.dansworkshop.com/electricity-and-electronics/homebuilt-arc-welder.htm

Have fun,

Scott.

Flux · « **Reply #12 on:** November 08, 2009, 12:47:36 AM »

If you weld from a 48v battery you really should have a suitable ballast resistor in series to control the current.

At 36v it is probably fairly self regulating as the arc drop can be made high enough to limit the current.

With 48v the initial striking current will be dangerously high and with a normal stable arc the volts are in the 25v region so you will have a high excess voltage and you won't be able to control the current.

Finding a suitable variable resistance might be a challenge but some taps on a steel wire or a strip of stainless sheet might be all you need.

Make absolutely certain that you can't accidentally short the electrode holder to the work without some limit resistor being present. For that reason alone I wouldn't think of doing it without a ballast resistor A 300A fork lift fuse in series may be a good idea.

If you stick to modest size rods ( below 200A) and you don't do it for long periods I don't think it will hurt the battery but regard it as an occasional trick and don't do it in place of finding a welder if you have lots of heavy fabrication to do.

Flux

kurt · « **Reply #13 on:** November 09, 2009, 07:20:51 AM »

they actualy make mig welders that are designed to work this way off battery.

http://www.readywelder.com/

Ungrounded Lightning Rod · « **Reply #14 on:** November 09, 2009, 05:27:12 PM »

This sounds like a "tap disintegrator" - a low-tech (high voltage, high current, no dilectric) version of electrodynamic machining. (I think the rod is usually carbon.)

A tap disintegrator is used in building things like engine blocks. When you have a tap break off in the block while tapping a hole, you'd like to pull the remains out and finish machining the workpiece rather than scrapping it. But taps are REALLY hard and twisting them out once they've broken off is difficult-to-impossible.

A tap disintegrator is applied to the center of the tap and bores its way in until the center is gone - or at least cut away from all but one of the cutting thread segments. Then you can remove the thread segments, clean up all the spark residue, and you're ready to drive another tap down the hole and then return the block to the normal production line.

I understand it's a very flashy process. Lots of noise and sparks. (Unlike the usual EDM machines which have a little sparkle where the tool is working the workpiece under the water, oil, or whatever.)

Ungrounded Lightning Rod · « **Reply #15 on:** November 09, 2009, 05:34:26 PM »

Starting requires 300a to 500amps to start it!

Only while the starter motor is stalled and getting inrush current. Current drops considerably once the engine is cranking.

scottsAI · « **Reply #16 on:** November 09, 2009, 10:22:14 PM »

Ungrounded Lightning Rod,

What you say it true, if you mean about half.

Engineering Instrumentation project documented AH required to start a vehicle.

We plotted current, voltage, start time. Interesting facts:

Some vehicles can be started in 0.1 sec! To count it as a start required generator charging battery after the start. Many vehicles can be started in 0.5 sec. These vehicles are predecessors of start/stop showing up in vehicles lately.

My vehicle requires 3-5 sec to start.

Documented enough vehicles to know any generalization I make an exception can be found.

With that said, initial starting current can be well over 400a (some may not even hit 200a), dropping down to 300a, with high and lows with each compression/exhaust stroke on the engine, current varies about 30 to 50% (saw tooth shaped). Currents dependents on gearing, starting motor, wiring etc. Same model vehicle can easily have 20% different currents readings.

Point here is a 60ah battery can be expected to deliver 200a without harm if done right. Batteries are systematical, can be charged just as heavily as discharged. Always assuming you know what your doing. Very dangerous if you don't!

Have fun,

Scott.

Ungrounded Lightning Rod · « **Reply #17 on:** November 10, 2009, 01:37:17 PM »

Thanks, Scott.

It's always good to have real-world data and any errors or misleading statements corrected. B-)

youmanskids · « **Reply #18 on:** November 13, 2009, 09:04:20 AM »

along the same lines as the original basic question.. what is the maximum safe discharge rate for standard RE batteries- what is their "C" rating? Ive not seen the C rating given in the manufacture info. (someone above mentioned 5C as a guide) My experienc is with Lithium ploymer batteries and they have a max discharge rate based on their total capacity- if the rate of discharge is too high, the battery will melt and catch fire! Do lead acid batteries have a maximum, non-damaging discharge rate? and if so what is it? thank for helping a newbie wind farmer.

joestue · « **Reply #19 on:** November 13, 2009, 06:09:00 PM »

Most lead acid cells should be able to handle 1/4th of short circuit current for 10 sec or so without damage, but this is a physical property, not a chemical property.

A cell could be optimized for .05C discharge and 20 year life, it will still have a 30-40C short circuit current, but this will kill it faster than it would a battery designed for a 15 minute discharge, with the same 40C short circuit current.

3C is as high as would go for OTS sealed cells. I've seen too many fail in UPS backup supplies under 10-15 minute discharges, which is about a 3C discharge.

youmanskids · « **Reply #20 on:** December 16, 2009, 05:12:16 AM »

that is exactly what I needed, thanks for the info- my 3kw invrter arrives today and my 24v test bank of UPS batteries is ready to go! thanks again.

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Author Topic: Will welding shorten lifespan of batteries? (Read 10537 times)