Batteries and a PWM for Stick Welding?

Batteries put out constant voltage. Stick welding likes constant current.

I have a 48VDC 400Amp Curtis Golf Cart PWM controller.

Would the output of the PWM be candy or poison for stick welding?

Has anyone done this?

BoyntonStu

Reply to
stu
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Stu

Pulse Width Modulation is candy (good) to use for adjusting the welding current. The Constant Voltage from 48 VDC could be made Constant Current with an inductor.

I think 48 volts open circuit might be a little low for stick welding.

Jerry

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Reply to
Jerry Martes

Starting the arc would be tough at only 48 volts. Most arc welders have

80-90 OCV to get the arc started. Once the arc is going, the voltage is 25-40 volts. The older TIG machines used a spark-gap oscillator to superimpose a high-voltage, high-frequency, low-current spark across the gap. I have seen these as external units, sold separately. Lincoln makes one.
Reply to
IBM5081

42 Volts is the maximum allowed for welding in closed containers (at least here in Germany). And this is enough for at least 250 Amps. Maybe it works even without inductor, but the PWM might suffer.

This PWM-thingy is good for converting a DC-TIG to AC for aluminium welding :-)) (No, it won't work)

Nick

Reply to
Nick Müller

Nick

Stick welding commonly has alot of impedance in series with the stick itself. I suspect that nearly all stick welders have open circuit voltages greater than 65 VDC. I thought Miller used pulse width modulation to control the current from their DC welders. It seems to me that, if there was a device that controlled the DC out from a control unit, that device would work OK as a welding current controller.

Since I dont actually know what the "PWM thingy" is, I cant comment on how it could be used for welding.

Miller doesnt use the pulse width modulated SCRs to produce their AC. They use the SCRs to control the *amount* of current, AC or DC.

Jerry

Reply to
Jerry Martes

But this requires a chocke coil. You wont get DC with PWM.

As said, PWM (pulse width modulation; kinda AC), requires a coil (or capacitor) to get DC.

Well, a PWM thingy is a PWM-device. :-)

As I said, PWM-current can't be used as AC-current. It (PWM) doesn't alternate, it just pulses.

Nick

Reply to
Nick Müller

Nick

You probably understand how all this circuitry works for making SCRs recticy welding current and voltage. I suspect you distinguish pulsating DC from pure DC. There is little to be gained from getting involved with semantics.

I thought you wrote "This PWM-thingy is good for converting a DC-TIG to AC for aluminium welding :-)) (No, it won't work)" to indicate that the PWM device makes AC. But, in the attached post, you indicate that you realize that the SCR doesnt make AC.

I do want to make it clear that Pulsed SCRs are a good way of controlling welding current for both AC and DC welders.

Jerry

Reply to
Jerry Martes

OK

No, it doesn't make AC. And I said this. Looking at the voltage, it might _look_ like AC. But if the voltage is low (zero), there is no current. That's why it isn't AC (Alternating Current; reverse in current flow).

I didn't comment SCR. I said that a PWM'ed current is not an AC current. So hooking that PWM-controller behind your DC-TIG doesn't make an AC-TIG out of it. Yust a pulsed. And you need (well not need, but prefer) AC for aluminium.

Well, pulsed SCRs _controll_ current. But it's not the _pulse_ that makes AC, it just controlls current flow.

To make it clear for lurkers: Yes, a PWM ist OK for controlling DC-current. But you need a choke coil. Don't ask me for the inductance.

Nick

Reply to
Nick Müller

Nick

There is no need for inductance in a DC welder thats PWM controlled. Why do you state that a choke is needed??

Jerry

Reply to
Jerry Martes

PWM can be either AC or DC. AC PWM would be pulses of alternate polarity and varable duraton (in a constant frequency system). For example, it is found in switching regulators powered by the

3524-3425-3426 series of chips, the TL494, and others intended for push-pull operation. This requires a transformer designed for the application.

Stick welding is a constant-current process. Most PWM controllers, e.g., your golfcart controller, are voltage controllers. They'd make great MIG welders, lousy stick or TIG welders.

If the control loop is rearranged to maintain a constant (adjustable) average voltage *across a series impedance*, it would then become a current controller that might work OK for stick welding if the control loop were fast enough. Use of some series inductance would make it weld a lot more smoothly because the inductor will respond instantaneously with voltage drop or boost if something (like arc length) tries to change the current.

Reply to
Don Foreman

Thanks for all the thoughtful replies.

Let me state the question another way:

Starting with a four 12V battery supply (56 VDC), what would you suggest to place between the batteries and the welding stick cables?

Some people have used a long length of #10 AWG wire wrapped around nails in a piece of plywood as an inductance and a variable series resistor to the welding cables.

I thought of using a PWM Golf Car Controller as an easy to contol current limiter.

I am looking for the simplist, easiest to control, homemade welder, given the parts that I already have or would need to buy.

BoyntonStu

Reply to
stu

Stu

Building a welder from the parts you have access to can be a fun experience. But, any welder you build will probably be very impractical to

*weld with*. The golf cart current controller could provide a capability that would probably never be appreciated in a home made stick welder. The comment you wrote about having 56 volts available from 4 batteries suggests that maybe you havent considered that four12 volt batteries supply only 48 volts to a welding stick.

Perhaps a web search will give you some ideas about how you can build a stick welder that includes the parts you have access to. I have alot of information on designing and building welders and would share that information with you.

Jerry.

Reply to
Jerry Martes

PWM does not control current unless per se. If 56 volts (or 48 volts) from batteries is PWM'd, the average voltage will be battery voltage times duty cycle.

It is possible to set up a PWM device with current sensing so it does control current. Some PWM supplies do have varying degrees of current limiting. The current limit is not typically adjustable, except in some lab supplies -- and, of course, in commercial inverter-type welders and plasmacutters.

However: if you have impedance in series, the impedance can limit current to some extent. For example, if you had 0.1 ohm in series, terminal voltage would drop 0.1 volt for each amp of current. Arc voltage is typically in the neighborhood of 24 volts. 100 amps would be 10 volts (and 1000 watts!) across your 0.1 ohm resistor. So, if you set your PWM to an average voltage of 34 volts, it would be delivering 100 amps to the arc. This would not be like using a real welder, but it would work. I would suggest water-cooling of your resistor. You'd be done welding (or your batteries would be flat) before you'd boil a 5-gallon bucket of water. 10 feet of #10 copper wire would be about 0.1 ohm. Iron wire (as baling wire) has higher resistance, so less of it would be needed.

Inductance does not limit DC current, whether PWM'd or not. It might smooth it, but it won't limit it. Peak voltage will still be battery voltage, so getting an arc started should not be a problem.

Reply to
Don Foreman

Postscript:

I couldn't find data on arc voltage vs current for stick, but some plasma data indicates that arc voltage changes little with current but significantly with arc length. This is consistent with how arcs generally behave. Arcs have low dynamic resistance. Some lower-current gas discharges even display negative dynamic resistance.

With a constant current source, this means that arc current won't vary much with arc length. However, with a voltage source and low series resistance, arc current would vary significantly with arc length.

This isn't necessarily bad, but stick welding with such a device would be quite different than it would be with an arcwelder. If one could learn to maintain very good control of arclength (no trivial trick in stick welding), it might be a very capable welding power source. It would have the interesting property of being able to control heat input (both arc current and arc voltage) just by changing the arc length. This property could present either additional control or lack of control, depending on how well you can control your arc length.

Reply to
Don Foreman

The float charger to my 48V battery string is set to 14.2 V per battery or 56.8 volts. If the battery is taken off the charger it will come down to about 12.8 V in some hours.. I have never mesaured a fully charged battery at 12.0 Volts. My reason for stating the higher voltage is that I wanted to be accurate in case there was a voltage threshhold for arc starting. In addition, I plan to weld with the charger connected.

I believe that #10 AWG wire has a resistance of almost exactly 1 ohm in

1,000 feet (not in 100 feet).

10 feet of #10 should have a resistance of 10 miili ohms.

I appreciate your offer to share your welding experience .

BoyntonStu

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Wire Gauge Resistance per foot

4 .000292 6 .000465 8 .000739 10 .00118 12 .00187 14 .00297 16 .00473 18 .00751 20 .0119 22 .0190 24 .0302 26 .0480 28 .0764
Reply to
stu

Stu

If there is anything I can say to discourage you from using lead acid batteries for stick welding, without insulting you, let me know.

For instance, you might want to review the problems involved with sparks in the vicinity of charging batteries. And, if the charge is relied upon to add significant power (voltage above 40 volts), it will have to be as big as the welder this set of batteries is expected to replace.

Constant Voltage DC power sources arent easy to use for stick welding. Batteries near the welder can be dangerous, due to combustible gasses from the batteries.

Jerry (who actually likes to build welders)

Reply to
Jerry Martes

I seem to remember an article about a homemade battery welder for off roading. Karl

Reply to
Karl Vorwerk

Why not? OK: You said it's a DC-welder. But the PWM doesn't make DC. Every switched voltage regulater needs a coil to produce DC.

Nick

Reply to
Nick Müller

ACK. But the AC has two rails. Not doable with _one_ golf cart controller and nothing more.

That's right. I thought about the subject yesterday and came to the same conclution (but didn't have time to post it).

ACK. But that will be behind a simple plug & play job.

That's what I said (so you get another ACK :-))

So what were we diskussing about?

Nick

Reply to
Nick Müller

Just do be more specific: Strick welders output voltage drops about 20V for every 100A (or 0,2V/A). With this value you get a good working stick welder, no matter how constant the "constant current" is. MIG/MAG sources drop 0,02V/A maximum.

Nick

Reply to
Nick Müller

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