h a l f b a k e r yI never imagined it would be edible.
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Cheap welder
Use inexpensive power supplies in parallel for welding. | |
A welder is a high current low voltage power supply. MIG welding uses constant voltage just like the power supply for my computer. I bought a 250 watt power supply for $12 that is rated for 9 amperes at 12 volts. Five of these power supplies in parallel would produce 45 amperes at 12 volts. That should
be enought to weld some thin sheet metal projects.
A diode on the output of each power supply rated conservatively for the 9 ampere output would protect the power supplies. Even these cheap switching power supplies have their outputs isolated from the input using transformers and optoisolators.
Because these are switching power supplies, they don't weigh much, are high efficiency (compared to linear power supplies), and do not produce much heat individually. If they were purchased in bulk straight from China, the price could even be less. If they were optimized to run at 20 volts instead of wasting resources on 5 volt and 3.3 volt outputs, they could be made smaller and more energy efficient.
MIG welding data
http://www.esab.com...files/PulsMigEn.pdf
[Ling, Jan 25 2005]
Use this MIG setup
http://store.weldin...DP.html?id=wdM2pIFD
Designed to be run from 12v or 24v batteries. Alas, it isn't really very cheap. [bristolz, Jan 25 2005]
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What are the advantages over an inexpensive OTS arc welder? |
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Utterly unsurprised at the double e component in the username. ;-) |
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The cluster-welder is cheap and relatively efficient. As the crappy reclaimed Sparkle PC power supplies die, the weld voltage/current sags till you have a cluster-brazer. When enough of them die off, you have a cluster-bedwarmer. Nice. + |
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bristolz: The local hardware store has an economy flux core welder for $198. Thats a pretty good price. My setup involving 5 computer power supplies costs $60. Even 5 of my power supplies together weigh less than the store unit because mine uses much smaller transformers due to the switching technology. |
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My welder costs less, weighs less, and like phlogiston says, it's somewhat useful if one power supply dies. The best reason to do it is for the personal satisfaction of creating something useful. |
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Ultimately, a Chinese-made switching welder should cost $40 or less. |
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I can see [nathan] carrying around a beat-up tackle box and telling people it's a welder. |
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I happen to like the idea - It's mind-numbingly simple. |
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The effectiveness of this idea would depend in some measure upon how the power supplies behave when loaded. If the power supplies sag when loaded, then there will be a reasonable degree of load sharing among them. If they don't, whichever supply happens to output the most voltage will supply all the current, up to its limit. |
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That seems like a reasonable assumption. |
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That they would sag, I mean. |
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<i>That they would sag, I mean.</i><p> |
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It's not implausible that such a thing would happen, but it's hardly a given. Some power-supply designs will increase voltage with temperature, while others will decrease it. Some will 'sag' gracefully when loaded to capacity; others will drop out altogether. |
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If the power supply costs more than $15, there's a good chance someone's tested it and posted a review. Also, it seems to me like a vast majority of power supplies do behave this way. You're absolutely right; I'm not trying to contradict you, I just don't think it's likely to be a big problem. |
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One important characterstic of arc welders is that the arc voltage is high at first. This is to help strike the arc. The "on load" voltage is less.
A drooping, or constant current power supply is perhaps more suitable.
A conventional switched mode power supply would be difficult to use, I think. But maybe it could be modified so that the voltage droops. But how to get multiple sets to droop in a similar fashion?
There are plenty of IGBT welder sets about, but they are always expensive. Maybe there isn't enough demand.
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I don't have any welding experience but I know that stick arc welders are constant current. They start out at high voltage and droop. MIG welders are constant voltage. They stay at the same voltage. No droop. |
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Even my cheap switching power supplies have feedback that maintains the voltage output. When the load increases, the duty cycle of the switching increases to keep the voltage steady. They should all respond similarly. |
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Semi-topical aside to the EE:
I have a VERY cheap stick welder (spelled: FREE) that is absolutely nothing but a large transformer with a variable core (stack of laminations that move to increase/decrease coupling between the primary and secondary) to set the output current. |
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What causes the initial high voltage and subsequent droop that you mention exists in a stick welder? |
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[nathanEE], yes, it seems that short arc MIG welding uses constant voltage since arc length is controlled by automatic increase/decrease of current and subsequent wire melt rate. Pulsed MIG welding can use voltage droop as well. See the link.
But I don't think that your cheap welder will be a MIG type - I assumed it would be a stick type.
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I was wondering that same thing. Mention is made of MIG using constant voltage just like the power supply. There's a whole lot more to a MIG rig than the power supply. I might, if I had way too much time on my hands, attempt to build a MIG welder, but I certainly wouldn't expect it to be cheap. |
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By the way, the transformer you have relies on a variable reactance principle to reduce the output voltage when under load. There are two types, as far as I know.
The first uses a "choke" where an iron core is in series with the main winding. The reactance of the choke can be varied.
The second uses high flux leakage, where the magnetic linkage to the secondary can be modified. This sounds like your transformer.
I don't think that the open circuit voltage is changed much, when adjustments are made. It will affect the current as you mention. |
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[Ling] My switching power supplies don't vary the reactance. They vary the duty cycle of the switching frequency. A switching power supply rectifies the input AC, then switches that rectified signal at around 200 kHz. The duty cycle is controlled by feedback from the output. |
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[half] Your free constant current welder should start out with a high open circuit voltage because it is constant current. Ohm's law says if your load is small (nothing or right when the arc starts) and current is fixed, the voltage will change according to the load. So when you load it with a something like a very conductive piece of metal (big load), the voltage should droop and the current should stay the same. |
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[half and Ling] For it to be MIG, it just needs some Argon and a wire feed, right? Or can it just use some flux core wire? |
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It's the TIG welders that tend to be the most exotic in terms of controls and such and certainly cost. I've seen MIGs at Home Depot for $400. My husband always disparages them and I don't know if it's the cheap welder or MIG in general. |
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Some MIGs can use flux core. "Maybe all of them." (I asked my husband.) |
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He says that you control a TIGs current (amperage) precisely as you weld with a foot or trigger control. |
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I think, technically, if it uses a flux core, it is known simply as "wire feed". MIG=Metal Inert Gas. Without the IG, I think it's _technically_ not MIG, though the terms MIG and wire feed are often used interchangeably and can both be accomplished with MIG welder. |
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MIG makes cleaner welds (less spatter and no slag) than flux-core wire feed, at least in my incapable hands. Though they can be a pain; variable wire feed rate, variable current and variable gas flow rate (not to mention different blends of gas) and all of those moving parts, MIG welders can do nice work, very quickly. |
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While I don't currently own one, I'd like to have a MIG because it's cheaper than a TIG and I can still weld fairly light sheet metal with it. |
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Aluminum is a different ball game. It takes a TIG welder (and a better operator than me) to do it right. Not only the aforementioned precise amperage control, but high frequency current aids in proper welding of aluminum. |
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So long as none of you ever see my welds, I can pretend that I know what I'm talking about. |
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Now I just need a helmet, some leathers, flux wire, and bake this idea! (while frying some power supplies) |
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Why [half]? Are yours of the melted licorice variety? |
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//[Ling] My switching power supplies don't vary the reactance.//
I was referring to [half]'s transformer. |
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Just because nobody else mentioned it here, I thought I'd
add that I've done emergency trailside repair using two 12v
car batteries linked in series, jumper cables for my leads,
and some 6011 stick that was rolling around in my toolbox.
It's not pretty, it's not permanent, but it's cheap and it
works. |
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I'd heard of such things but never met anybody who would admit to it. My hat is off to you, sir. |
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Well, I _am_ an exceptionally talented welder. |
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I don't get the premise of this idea - if a MIG welder
costs $198, and includes the wire feed, snake,
gas-cup and gas controller, where's the benefit
in being able to make the power supply alone for
$60? Or did I miss something? |
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(But, while I'm here, a salute to the inventor of
switched-mode power supplies - they are wonderful
things.) |
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I didn't get the benefit either, but then again I am
privileged to use professional-grade equipment (and
equally 'privileged' to pay big $$$ for it). Frankly, I only
popped in
to see if anyone mentioned car-battery welding, which
they didn't, so I did. It's not, as many believe, a myth, but
it's not very effective, either. If you use it, the weld _will_
break, but hopefully not until you get home. |
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