i'm making a capacitive welder

[damorgue]

You won't die, blind maybe, but very much alive

Oh the irony, touch "live", and you won't be anymore...

[mkawa]

ahahahahaahah

[Melvang]

http://store.cyberweld.com/jahswehe1.html is the same hood I have at work and yes you can change out the poly carb lens.  I just recommend gold lens because you might want to see what you are doing and the gold tint gives much greater contrast around the weld than other color tints.  just make sure when/if you buy a different lens it is shade 11 and it is the same size as the hood you are putting it in.

[mkawa]

at least they're cheaper than racing helmets. my god those are pricey

[TheSoulhunter]

Perhaps also get some eye-drops (there are specific ones) in case you get a flash-burn anyway...
They are cheap, they help a lot, and it's a good idea to get em beforehand as you shouldn't drive or walk around with burned eyes, eh?

Also, from my experience:
Mild flash-burn: Eyes are stoned red, they might burn somewhat, they are over sensitive to light, it might feel like you have dirt/sand in your eyes -> Usually goes away after a 1/2 day
Strong flash-burn: Eyes are demon red, you can't even bear room lighting, eyes hurt, strong feeling of having dirt/sand in your eyes, degraded vision -> Go see a doctor, really!

[Melvang]

Perhaps also get some eye-drops (there are specific ones) in case you get a flash-burn anyway...
They are cheap, they help a lot, and it's a good idea to get em beforehand as you shouldn't drive or walk around with burned eyes, eh?

Also, from my experience:
Mild flash-burn: Eyes are stoned red, they might burn somewhat, they are over sensitive to light, it might feel like you have dirt/sand in your eyes -> Usually goes away after a 1/2 day
Strong flash-burn: Eyes are demon red, you can't even bear room lighting, eyes hurt, strong feeling of having dirt/sand in your eyes, degraded vision -> Go see a doctor, really!

This^^

My dad got flash burn at work last summer.  He wasn't the one welding.  But he was the fire watch inside of the stainless steel tank.  The temporary blindness is a very severe flash burn and hurts like nothing else you have ever experienced.  And just an FYI the UV rays can still be damaging at up to 50 feet.

[TheSoulhunter]

Also, when welding for extended time (not just some spots) it's a good idea to cover ALL your skin if possible!
Got my arms burnt (it's like a sunburn) more than once because I worked in a T-shirt next to a welder...
Kinda looked funny because my arms got red or tanned but the hands stayed pale (...gloves)

[Melvang]

Yup and the burn on your skin from welding in short sleeves is more like being in a tanning booth for to long than being in the sun to long.  I think the welding one hurts more.

[mkawa]

presented without comment

hey melvang, what do you think about the passive halo X jackson series helmets? i'm kind of starting to lean toward a 3M speedglass unit with a big lens and respirator. not for just this, but because i want to eventually move towards automotive work (stitch weld crash frame yaaaaaaaaaah), and going blind and/or dying are not on my list of things to do in the near future or really at any point thoughts?

[mkawa]

ok, one comment. the black square is a bridge rectifier that's rated for 500A peaks. and yes, that entire thing on the bottom is an alu extrusion heatsink.

[Melvang]

The 3m speedglass is one of the better brands from what I hear about the auto tint hoods.  I can't say really about that particular model line though, as I haven't decided to take the plunge into a speedglass yet.  But I don't think I have heard any complaints about that brand yet. 

What sort of thermal interface do you have between the heatsink and the components?

[mkawa]

the cap network is fiberglass composite insulated and then JB welded to the heatsink. the fiberglass a massively effective dieletric, but has reasonably thermal conductance. more importantly, the cap network has very large surface area. the rectifier has a non-conductive steel plate over the internals on the down-side which is JB welded to the heatsink. i have thermal epoxy, but JB weld has significantly higher thermal conductance than that crap and much much more shear and tensile strength once cured. the power mosfets and the buck drivers need to be insulated so they'll probably get thermal epoxied at low pressure to maintain the dieletric properties of the thermal epoxy. back-sides and pins will all be potted with various grades of RTV silicone rubber depending on thickness needed etc. i toyed around with the idea of using silicone rubber as the dieletric and then JB welding, but the silicone rubber is a pretty extreme thermal insulator, so i'm going to stick with the thermal epoxy and generous potting.

one thing to note is that everything is very low voltage, so the chance of arcing is minimal. the reason to pot is mostly accidental contact.

[Melvang]

the cap network is fiberglass composite insulated and then JB welded to the heatsink. the fiberglass a massively effective dieletric, but has reasonably thermal conductance. more importantly, the cap network has very large surface area. the rectifier has a non-conductive steel plate over the internals on the down-side which is JB welded to the heatsink. i have thermal epoxy, but JB weld has significantly higher thermal conductance than that crap and much much more shear and tensile strength once cured. the power mosfets and the buck drivers need to be insulated so they'll probably get thermal epoxied at low pressure to maintain the dieletric properties of the thermal epoxy. back-sides and pins will all be potted with various grades of RTV silicone rubber depending on thickness needed etc. i toyed around with the idea of using silicone rubber as the dieletric and then JB welding, but the silicone rubber is a pretty extreme thermal insulator, so i'm going to stick with the thermal epoxy and generous potting.

one thing to note is that everything is very low voltage, so the chance of arcing is minimal. the reason to pot is mostly accidental contact.

Gotcha.  I just wanted to make sure you had something in there to help move that heat around.  I know you being mkawawiki that you probably knew this but just making sure.  Sometimes even the best of us overlook something big like that.

[mkawa]

semiconductor ratings are always functions of temperature at the semi. the datasheet generally gives an approximation of the derating vs temperature. let's just say that if the entire thing hits 100C, things are not good in this circuit.

[mkawa]

cap network, 500A peak rectifierr, 33mfd smoothing cap, 750A of high speed power mosfet capacity. waiting for welding helmet before i make the first spark (have two copper chromium spot welder electrodes waiting for first spark as well). if i'm not seeing enough current at 18v, i will buck boost to 5v with a 200A (input, h_{fe} is about 1000) peak of darlingtons.

[MKULTRA]

(Attachment Link)

cap network, 500A peak rectifierr, 33mfd smoothing cap, 750A of high speed power mosfet capacity. waiting for welding helmet before i make the first spark (have two copper chromium spot welder electrodes waiting for first spark as well). if i'm not seeing enough current at 18v, i will buck boost to 5v with a 200A (input, h_{fe} is about 1000) peak of darlingtons.

So uh is there any chance this will blow up in your face?

[mkawa]

no

[JPG]

Any chance you will record/stream this event?

[Melvang]

record please I doubt I will be able to catch a stream

[mkawa]

IT WILL NOT BLOW UP LA LA LA LA AL LALA LA LAL A LALAL LALA

but i did order a jackson halo x and some pigskin gloves.

but not in case it blows up, because it won't

[JPG]

I am confident that it won't blow. But it could melt, spark, do nothing at all, etc. 

I want to see you first attempt!

[mkawa]

for my own ego^H^H^H^H safety, i will not be recording first spark.

i will be focusing on not dying, however. i've heard that this is quite important.

[Melvang]

if all you are doing is basically spot welding then I wouldn't worry about the leather gloves.

[mkawa]

i got pretty cheap ones just in case. the problem is that i don't have a hands free spot welding setup yet, so i'll be holding the electrodes in some form

[damorgue]

I would get a nice grounded rod with insulation to be able to discharge everything from a distance in case something is wrong. You do not want to have nothing happen and don't know why or what is charged or not.

I wonder how long it would take that charge to diminish naturally. Might as well build a concrete wall around it, add a pond on top and call it a day.

Edit: That sounded overly negative (pun), but I am just messing around. Looking forward to the results.

[engicoder]

When you are looking at building mark II, I am pretty sure I could get you a number of these for next to nothing.

http://www.avx.com/docs/Catalogs/bestcap.pdf

I think they would probably work better for your purpose.

[mkawa]

When you are looking at building mark II, I am pretty sure I could get you a number of these for next to nothing.

http://www.avx.com/docs/Catalogs/bestcap.pdf

I think they would probably work better for your purpose.

MY GOD, YES. PM INCOMING

I would get a nice grounded rod with insulation to be able to discharge everything from a distance in case something is wrong. You do not want to have nothing happen and don't know why or what is charged or not.

I wonder how long it would take that charge to diminish naturally. Might as well build a concrete wall around it, add a pond on top and call it a day.

Edit: That sounded overly negative (pun), but I am just messing around. Looking forward to the results.

did i not take a picture of my collection of huge ceramic resistors? i can discharge the entire network in about a minute.

also the black stuff you see in the other pictures is carbon fiber textile weave. my desk is lined with it. i regularly plop stuff at 500C+ onto it with a completely disregard for flammability (because it's not).

[mkawa]

it works.



muahahahahaah

[Game Theory]

Welding late at night?!

[JPG]

it works.



muahahahahaah

Picture or it didn't happen!

[mkawa]

 

[Photekq]

Just saw this thread. That's real neat-o kawa. Nice work!

[mkawa]

two fun things:

quick spark tests on a case hardened steel rod



a 300w (rated, have put way more through it) 8ohm resistor

[rowdy]

Every time I see this thread I have an image of mkawa doing something like this:

[mkawa]

that's cool and all, but it's huge, impractical because you can't move the electrodes or rectify it, and you have to pull all that amperage from the grid all that once. there's negligible energy storage in a transformer. basically he stole the transformer from a telephone pole.

[mkawa]

this is more related, as it involves energy storage and then a huge quick discharge: http://205.243.100.155/frames/shrinker.html