building my own welder

Or buy a welder and use it ;-)

My el chepo "buzz box" (230a AC welder) really isn't much more than a big transformer with a sliding slug of iron that changes the flux to select current. I suppose if I added some big rectifiers I would have a DC welder but I never tried it. I assume the transformer itself is the current limiter. Mine does have a thermal switch that shuts down the power if the transformer starts heating up too much. It certainly is not a "production" unit and it will shut itself down if you push it more than about a 15-30% duty cycle depending on ambient air temp.

|>I'm sure I'll get a suggestion to go buy a welder and tear it apart and |>see what is inside. | | Or buy a welder and use it ;-) | | My el chepo "buzz box" (230a AC welder) really isn't much more than a big | transformer with a sliding slug of iron that changes the flux to select | current. | I suppose if I added some big rectifiers I would have a DC welder but I never | tried it. | I assume the transformer itself is the current limiter. Mine does have a | thermal switch that shuts down the power if the transformer starts heating up | too much. It certainly is not a "production" unit and it will shut itself down | if you push it more than about a 15-30% duty cycle depending on ambient air | temp.

The uses for a "high current source" I have in mind are experimental and not really welding. But it might be close enough to it that adapting a welding power source could be sufficient. But I'd rather understand it and leave open the option of building it from scratch as that may be more optimal (this depends things I find out).

I have seen transformers in some online product pages that have secondaries in the 6 to 12 volt range with currents in the 1000 to 2000 amp range. But I'd like to get up above the 10000 amp range. Like some people enjoy the high voltage pleasures with tesla coils and other things, I want to do some stuff with high currents (AC or DC).

An AC buzz boz has a pretty high open circuit voltage (around 100v) but I have not really seen what it does under a load. If it is any indication, this is rated at 230a on the secondary and I have never tripped a 30a 240v breaker I have feeding it. I would say that if you really want 12v at some very high current you might be better off with a transformer built for the purpose. These welder transformers have a pretty short duty cycle. OTOH you might be able to buy a buzz box pretty cheap on the used market and play with it.

Speaking as one who has used buzz boxes, I don't think their duty cycle is all that short. They can heat up, but a good welder working on a long bead can keep going a long time without burning them up.

uray

Just go out and get a old FPE panel!

Obviously, I need a lot of amps. But how many do I really need? What voltage would I need as a minimum?

Obviously, I need some form of current limiting so the system does not self-destruct or self-damage with that level of current (e.g. the work being a solid short). Inductive, rather than resistive, might be the way to go. But can this impedance be made a part of the transformer itself (as opposed to a separate winding) by designing the transformer to handle its own fault current availability without damage (e.g. wires thick enough to not overheat at the design current maximum while that maximum is achieved via the secondary impedance).

Will I need to have the ability to select the current?

What safety features must it have, both electrically, and mechanically? I'm not trying to make something to be UL listed, just to make it be actually as safe as something like this can be expected to be.

I'm sure I'll get a suggestion to go buy a welder and tear it apart and see what is inside. But that's really not what I want. I want to know the numbers (like amps and volts and impedance) and other theoretical stuff, but based on today's real world needs, too.

--

----------------------------------------------------------------------------- | Phil Howard KA9WGN |

| | (first name) at ipal.net | |

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Ah there's my problem ;-)

secondaries

P = VI may constrain what you can do. If you have 5 volts at 10^4 amps, that's 50KVA, outside the range of any domestic service that I've encountered.

It would probably have to be reduced to 1 volt, or wait until I have the cash to buy one of those big generators on EBay.

Do you want a sustained high current or just a high current for a short time. An array of regular lead acid batteries in parallel will give you huge currents for a little while.

Finally! Positron emission tomography?the home version.

--s falke

| Do you want a sustained high current or just a high current for a short time. | An array of regular lead acid batteries in parallel will give you huge currents | for a little while.

Sustained for at least a few minutes.

10,000 amps? What on earth for? My only question would be, in the casket do want to be laid out with your arms at your sides or across your chest ? :)

?????

|>I'd like to get up above the 10000 amp range. | | 10,000 amps? What on earth for? | My only question would be, in the casket do want | to be laid out with your arms at your sides or across | your chest ? :)

Cremation ... in an electric crematorium, of course.

Greg's idea of batteries seems reasonable.

20 Golf cart batteries (6V 220amp hour) would provide 10,000amps at about 5.9V dropping to about 4.8V after 12 minutes.

They would then need a proper recharge cycle.

They can be purchased for around $50 each.

You will need serious bus bars and cables to deliver your 10ka and switching it on and offf will not be easy.

PS If you are foolish enough to try this, please include me in your will. Remove SPAMX from email address

On Mon, 21 Jun 2004 03:11:00 -0500 Jim Michaels wrote: | On 16 Jun 2004 18:33:40 GMT, snipped-for-privacy@ipal.net wrote: | |>On 16 Jun 2004 15:53:55 GMT Greg wrote: |>

|>| Do you want a sustained high current or just a high current for a short time. |>| An array of regular lead acid batteries in parallel will give you huge currents |>| for a little while. |>

|>Sustained for at least a few minutes. | | Greg's idea of batteries seems reasonable. | | 20 Golf cart batteries (6V 220amp hour) would provide 10,000amps at | about 5.9V dropping to about 4.8V after 12 minutes. | | They would then need a proper recharge cycle. | | They can be purchased for around $50 each. | | You will need serious bus bars and cables to deliver your 10ka and | switching it on and offf will not be easy. | | PS If you are foolish enough to try this, please include me in your | will.

What about those people who run various high voltage experiments? Isn't that also dangerous? So why no suggestions on how to make this safer?

BTW, I still want to do this with AC. And AC would give me an easier way to shut it off (switch at a lower current or shut down the generator).

I suppose I could have separate isolated contactors for each battery with a fuse on each as well.

You are talking way above normal welding currents, of course, so any normal welder will not supply what you want. A welding trnsformer has enough leakage inductance in its windings/core to limit the current to some reasonable value. The voltage characteristic is very drooping so that the open circuit voltage of 75 volts or so drops to near zero when the rod sticks on or you pull a welding current that it is designed for. The transformer necessarily has a very poor power factor - that is what keeps the arc going. For this reason, many welders have a power factor correction capacitor on the primary side.

If you want 10,000 amps you will need a transformer with a low output voltage and a very low secondary impedance - like one or two turns of 1/2" diameter copper wire.

Good luck. Come back and tell us how you are doing from time to time. Just take care.