Build your own CD battery tab welder for about $100.00+-

[mortain]

yes, ok...but what' s the trouble when you increase the capacitance of the circuit?, because I see few ultra capacitors which have very very low ESR ( bcap1200p270T05=0,56 mohm!!!) much better than audio car caps . I remember the threaads p 32 of this forum ( thanks to cesare250495 and Jeremy Harris) and the texaspyro comments... If amperage is pregnant, is it possible welding with a very low voltage (i.e 2.7V/0.001=2700A)????...just a question of simple man...
Thanks for answer...

[zakipu]

I've followed this thread (and a few others), so I think I'm ready to make a cheap-as* welder. Looks like about $200 and not $100, but whatever. I've been following this thread for many rereads. As an aside, I've been an embedded systems engineer for well over a decade. Not quite as cool as texaspyro's intro, but I think it works. I do know how to handle mosfets and the like, but that might happen later. I've tried to keep everything as simple as possible. Seems to work, but I know I couldn't do a any sort of tig style welding with my power input.

I have only one question for texaspyro: what are you using for vent sensing?

Anyway the whole she-bang is cheap: about 40 usd if anyone is interested. That is just for a charge controller, but I did find a cheap power supply at 19 usd for 100 watts. Not the quickest, but it's cheap. Also, I will have a few SCRs that are well suited to this torture. Those can be had for 75 usd. All prices do not include shipping, but they do include testing. And testing as a set if one buys it that way.

I've found that the following ebay searches work very well for the caps you'll need: (don't bother with anything else)

monster cable cap
rockford rfc1
rockford punch cap
scosche ecap1

I've gotten an older rockford punch cap that does not have the bar code on the bottom. It only measures about 0.7 farads. Seems solid enough otherwise. It has a very simple white label.

~Z

[zakipu]

yes, ok...but what' s the trouble when you increase the capacitance of the circuit?, because I see few ultra capacitors which have very very low ESR ( bcap1200p270T05=0,56 mohm!!!) much better than audio car caps . I remember the threaads p 32 of this forum ( thanks to cesare250495 and Jeremy Harris) and the texaspyro comments... If amperage is pregnant, is it possible welding with a very low voltage

The main tricky bit with low voltage is the severely decreased welding current. It might not be enough to generate a large enough current to melt your metals.

As for an 'ultra' cap having a low ESR, can you give us a link? We can use that.

~Z

[mortain]

Hi, Sokapu, Texaspyro and every body.
"52F is very, very big, probably massively too big for a CD welder for this application. I can blow holes in the end of cells with just under 2F at 20V, which equates to about 400 Joules of energy. Even at the lowest practical voltage for a welder of this type, around 10V, a 52F capacitor would deliver 2600 Joules; charged to 20V a 52F capacitor would deliver a massive 10,400 Joules, around 26 times more than the maximum you need." p 32 of the forum Jeremy Harris said.
and he continued:
"The big risk with using the big capacitor/lower voltage approach will be heating. The weld current pulse length is determined by the total circuit resistance and the capacitance, rather than the voltage. If we assume that the total circuit resistance is around 30mohms (capacitor ESR plus wiring and weld resistance loss), then the weld current time constant will be 1.56 seconds, which is massively too long. The weld needs to take only around 50mS to 200mS, which would be achieved with a capacitor of between 1.6F and 6.7F.
So:
1) Where do these "400 joules" come from as good energy to the job? Experimental or scientific argues?
2) what is the formula to obtain the result above ( 1.56 s for heating steel and+- 400J pass through ( diffuse? ).
3) If Jeremy is right,( it's only an hypothese ) he is not wrong, and so (I repeat again my question) Why i can not weld with high capacitance, low esr, low voltage, ? please explain me, i don't understand...thanks

4)for caps follow this link :

http://www2.mouser.com/Passive-Componen ... dfZ1z0ixu8

untill 0.28 m ohm esr!!!
...

[mortain]

ok the link is failed...sorry.
so go to mouser>supercapacitors > apply the filter by choosing low esr...You find 22 results...

[amberwolf]

LInk works fine for me.

Only 2.5 or 2.7V, though, so you have to series them for more voltage (presumably you would want higher voltage for more power to weld with). That means adding the ESRs together.... So to get that 10V minimum, you'd need at least four of those caps in series, so four times that ESR, or about the same as the car audio caps, or worse, IIRC.

When in series, the F of the caps is decreased, so you would end up with 1/4 of the capacitance.

Also, you could run into this problem:
viewtopic.php?p=510049#p510049


Regarding joules--it's just an energy measurement. You would convert the energy supplied from the capacitors into that to see what you get, or vice-versa to see what capacitors you need (whcih is what he already did to get that F figure).

[texaspyro]

I have only one question for texaspyro: what are you using for vent sensing?

I took some pieces of two conductor high density ribbon cable (IDE drive cable) and stripped the insulation back at the end (I left it hanging on the wires to keep the conductors apart). The stripped part of the cable goes over/around/near the vent (depending upon the vent type). It is tacked down with superglue.

A 10 megohm pullup resistor hooks to a processor pin. The other end of the ribbon cables are connected in parallel and go between the pullup and ground. Idea is if the vent spews conductive electrolyte, the closely spaced ribbon cable wires get shorted out and pull the processor pin low.

[texaspyro]

The problem with ultracaps is that they are low voltage (typically 2.5V). You need 8 in series to get a 20V cap so your cap ESR is multiplied by 8. With good 1F car audio caps you might parallel three of them. My best three Monster Cable caps in parallel have an ESR of under 250 micro-ohms. The welder can generate over 20,000 amps wit those caps. With the ultracaps I can do around 1000 amp pulses (but for much longer)

My welder is FET based so it can generate any pulse width that I want. An SCR welder has to fully drain the cap each pulse. That makes ultracaps rather unusable/uncontrollable.

I took two 58F Maxwell modules (internally they are six 320F caps in series, each about the size of a D cell) in series to make a 29F,30V cap and did some welds with them. The main problem is that my discharge resistor would fry trying to drain that cap when the welder shuts down.

[mortain]

Ok, thanks everybody. one moment, i have hoped that we could weld under the 15 volts and why not with only one or two parallel caps@2.5V ; so in this set the esr should be correct...But, not possible...well understood, so i retain the rockford fosgate and others indications from Texaspyro.
I'm going to set a machine with fet from Texaspyro, Fritz, ultrakeet works and every.... I dont know (i think you do) if you know the very interesting job of Benjamin Fleming regarding edm. Process seems to be close I think. I'm going to read or re-read the 62 pages of the threads...thanks.

[texaspyro]

Ok, thanks everybody. one moment, i have hoped that we could weld under the 15 volts

You can do many types of welds below 15V, but not the heavier tabs. I do a lot of work on small batteries around 12V.

When I was playing around, I series connected two of the Maxwell ultracaps to get a 30V rating since my welder power supply can generate 20V and those modules were rated at 15V. My welder electronics can handle 30V. I haven't found a use for using the ultracaps in the welder.

[FastDemise]

I'm starting up my own little welder now. Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR. As far as weld leads go was just curious how people connected their thick cables from the caps to the weld leads. Just gonna try and use some thick copper bar and wondering how I am going to attach my 8 or 4ga wire to it.

[texaspyro]

Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR.

Why pay $400+ for those caps when a Rockford/Monster Cable/Scosche cap can be had for $50 or so and will probably work better?

To do serious welds you will need around 3F. And that SCR will be vaporized.

[texaspyro]

A very good read about the development and issues of doing a welder:

http://www.turtlesarehere.com/html/cd_welder.html

[FastDemise]

Just curious how much capacitance do I really need? I am getting (.8F) 8x of these http://www.digikey.com/product-search/e ... 104U016X5C getting a 1000v 200a SCR.

Why pay $400+ for those caps when a Rockford/Monster Cable/Scosche cap can be had for $50 or so and will probably work better?

To do serious welds you will need around 3F. And that SCR will be vaporized.

I was able to get them for $12 a piece. Though I do see how quality audio caps might be cheaper. When you say quality welds I only need to weld the aluminum A123 batteries to nickel strip. Won't need to be more robust than needed. If I need 3F just for that I'll rethink my setup. So one of those 'hockey puck' scr might be needed.

*Added*
With each caps being 7 mOhm having 8 in parallel drops my cap resistance to something like .875mOhm (12kA @ 12v) if my math is right. Wouldn't that be low enough that I can use less capacity warranted I get a SCR that's beast enough.

[texaspyro]

It all depends upon the thickness of the tabs that you are welding. I think Mighty Volt needed 3F/18V to get decent welds onto A123 cells with his (10 mil?) tabs. If you are welding 3 mil foil, 1F/12V might do.

[FastDemise]

I have 5mil thick so it maybe possible.....


*Added*
So my SCR is rated at 1600v 200a = 320kW
Using the 320kW but at 16v that's 20,000A it should be able to handle?? With the math showing the low resistance of the caps able to push 12,000A. Am I wrong in thinking the SCR I have will work on paper or am I just using ohms law all wrong?

[amberwolf]

So my SCR is rated at 1600v 200a = 320kW
Using the 320kW but at 16v that's 20,000A it should be able to handle?? With the math showing the low resistance of the caps able to push 12,000A. Am I wrong in thinking the SCR I have will work on paper or am I just using ohms law all wrong?

You already answered your own question: The SCR is rated 200A. You need 100 times that current.

POOF.

(realistically it depends on lenght of pulse, various SCR specs, etc., but just remember that once you start the pulse going, you aren't going to be able to stop it, so if your caps are larger the pulse will be longer, and the SCR has to handle the high current longer. Probably still POOF).

[zakipu]

Unfortunately SCRs are rated for current and voltage not power. The 200A rating is what it can handle continuously at any voltage. The peak current rating should be around 6-7000A, so the SCR should survive depending on the total resistance of the setup and the voltage. Also, hockey puck SCRs are notoriously hard to connect to.

My SCR is rated 14,500A peak, 425A continuous. Datasheet. I have 8 more on the way. PM me if you're interested.

I have about 2.9F from three car caps. Monster: 1.1F, Scosche: 1.0F, and Rockford Punch: 0.8F. Those are just preliminary numbers using a 10 ohm resistor and voltmeter. I'll have better numbers when I get my charge controller up and going. I'm going to use copper bar to connect the caps and SCR then about 2 feet of 1/0 welding cable to the electrodes to keep the total system resistance as low as possible so the most amount of energy goes into the weld. I'll post a schematic and pictures when I get a chance.

[FastDemise]

CD welder.jpg (22.28 KiB) Viewed 858 times

I just replaced using a resistor with a small 15w DC-DC convertor I got from Lyen to adjust the trigger voltage just right. Just waiting on the SCR so I can start making sparks. I'll start off small with just .4F of capacitance and see what I get and test my wiring setup. Then just keep stepping it up until my welds are good.

[malcav]

I'll start with I am sorry i did not read the whole thread so my Q may have been answered. But what is the best type of cap to use? Like aluminum or ceramic?

[Kin]

I'll start with I am sorry i did not read the whole thread so my Q may have been answered. But what is the best type of cap to use? Like aluminum or ceramic?

I've never seen a 1 farad ceramic cap... I think you'll need alu electrolytic caps. In the last 4 pages (i.e, from this page, somewhere in the four previous pages), texaspyro links to where in the thread he describes the good brands of car audio caps. They will be good caps to use.

[pwbset]

Had a weak 1s10p string in my battery pack so de-duct taped the whole pack and found quite a few tab welds had popped apart. Meh. Current setup is identical to the first post in this thread, which is borderline I guess. So last night I ordered a Scosche ECAP1 to go parallel with my old Volfenhag at 16.2v. Hopefully that will get me some deeper welds. Going to re-grind my copper contacts for finer points also so that should help a bit too. Love this tab welding stuff, but need more power!

[texaspyro]

Finer/sharper points are not necessarily better points. They can give tiny weld spots and current densities that are too high and blow out the weld point. And flat points are a no-no... you will never get the electrodes square to the material, yielding the same problem as sharp points. Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

[pwbset]

Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

Good advice. Much appreciated, thank you.

[The Mighty Volt]

Finer/sharper points are not necessarily better points. They can give tiny weld spots and current densities that are too high and blow out the weld point. And flat points are a no-no... you will never get the electrodes square to the material, yielding the same problem as sharp points. Nice rounded tips work best. The diameter of the point is best determined by trial and error and sparky smoke.

What I do is I push my blunt but rounded tips, {sort of like a pencil whose tip has worn down}, into the tab, making an indentation.

Then I lift the electrodes off and then gently nestle them back into the same indentations.

I apply a small amount of pressure, and fire.

Works great everytime. The indentations cup the electrodes and catch more of the discharge, making for a better weld.