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

[Kin]

I guess i underestimate how poorly graphite conducts, I thought it might be decent.. I am thinking a graphite rod, with a copper cylinder fitting very tightly over the graphite rod until 1cm from the end, where there is a 1cm tall, 8mm diameter pointed cone. Would that 1cm cone be introducing too much resistance and thereby limiting the current? I apologize, I suppose this could could be calculated but I don't quite know the values and figure you might have an intuitive response.

[rkosiorek]

I didn't see anyone using graphite as a electrode.

I've used graphite electrodes for doing thermocouples. They don't contaminate the weld with foreign metals and don't need all that much current... graphite does not conduct all that well.

what was your source for the graphite? any pictures or suggestions for electrode construction?

do you prefer the graphite or elkonite?

rick

[texaspyro]

what was your source for the graphite? any pictures or suggestions for electrode construction?

The bottom electrode is a graphite block from:
http://catalog.dcccorporation.com/viewi ... c=100|1019

A friend of mine machined the rod electrode/holder for me out of some funky reactor grade graphite. You might be able to use an electrode from a dry cell battery or an arc light electrode.

Be aware that graphite can conduct heat/electrons differenly along and across the grain.

[dask13]

ok...just bought the pyramid power supply. im hoping i can get some assistance in the build of this puppy. read 6 pages of this thread and will finish all the pages before i attempt the build. im going to make very detail pics, instructions and youtube videos in order to make sure im assembling this properly and make it easy for others to follow and to build their own. i have between 10-15 power packs for tools that have gone bad and want to bring some of them back to life and to also help out some friends with their battery packs.

Alex

[dask13]

found this scr thyristor on ebay...will it work in this application or is it overkill? the price is right...around $50 bucks with delivery or since its used am i risking getting a bad product?

http://www.ebay.com/itm/EUPEC-thyristor-SCR-425A-1200V-forDIY-battery-TAB-spot-WELDING-Induction-Heating?item=110878467012&cmd=ViewItem&_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D5%26po%3DLVI%26ps%3D63%26clkid%3D8405388627237851564

[texaspyro]

It looks like it should be OK... 14,500 amps peak. I could blow it, though.

[Kin]

Hi Texaspyro, hoping that you monitor this thread and that it's better to ask the question in public:,

I just started working on some arduino projects, which are very simple to use, cheap, microprocessor boards with a C based, but somewhat simplified, environment. I was thinking it would be relatively easy for me to build a program that turned on a number of transistors with a certain length of pulse.

I don't have much experience with fets, and I don't know if it'll be enough to simply apply the voltage to their gates for X milliseconds, then turn off. But if that is enough, and if it's reasonable to turn on a bunch of mosfets with a few different pins simultaneously, then I could think about making something slightly more useful than just a thyristor switch.

And, if you think this might be something that could work, how would I go about learning about what sort of pulses might help me? I now that you want a micro pulse to burn off the oils before a more serious pulse, but I don't know much else. I'm also looking at contenders for the fet, and found a bunch of creatures that are rated for 100-300A and not too expensive, but I'd look more thoroughly to compare the resistances etc of everything.

So, because I realize I am just getting into this, I'm mostly looking into whether this would even be possible to do. I'm also wondering if there's much sense in it, obviously your setup is much more sophisticated and the code is more complicated, but I'm curious as to how much I might be able to benefit by using a $20 microprocessor board and $20 of FETs. Probably, I'm just going to gain some resistance in the whole situation >.<.

[Alan B]

Arduino (AVR) pins don't have enough drive for these short pulses, a driver is needed between the micro and the FET gates.

[Kin]

Arduino (AVR) pins don't have enough drive for these short pulses, a driver is needed between the micro and the FET gates.

I was thinking of using a smaller transistor to activate the mosfets either in pairs or otherwise (sets of some sort, or I guess I could activate them all at once), though I'm not sure how effective the timescales are, because I don't know much. Maybe it's just not worth it, given that I don't know enough about hardware in such precise time measurements. When you say Arduino pins don't have enough drive for these short pules- what do you mean? I know the pins are capable of turning on and off certain mosfets in other situations, so I assume it has something to do with the scale and speed.

[hillzofvalp]

viewtopic.php?f=2&t=2633&start=840

Arduino is fine using DelayMicroseconds instead of just delay. I have some code somewhere if ou want to see my example. I had it working for 5 welds but I think I damaged my arduino or fet driver... Something wrong with my circuit...

[texaspyro]

I'd start by reading: http://www.turtlesarehere.com/html/cd_welder.html

Then I'd take some drugs and go back to bed...

[Alan B]

To turn these MOSFETs on and off quickly takes more current than Arduino pins can safely handle. The MOSFET gates have a lot of capacitance. Use a gate driver. But be warned that most folks burn up a lot of parts figuring out how to do this, commercial welders cost a few thousand bucks for a reason.

[Kin]

Thanks everyone. I only got through page 50 or so, so I missed some of those great links on page 57.

Texaspyro, the link you gave me was dead, but it just started working again. So, ehm, it's not dead.

Again, thanks for the information, this all is great.

[mortain]

hello guys
Is anybody knows what do you think about ultra capacitors ( maxwell and others) for cd welder application or for high pulse discharge machining? How compare these caps to the audio caps???
and why???
Thanks to the fantastics men....

[texaspyro]

Ultracaps have much higher ESR than good audio caps. I max some Maxwell 58F, 15V caps. They have a 12 milliohm ESR and can only deliver 1000 amps. If you want to make long, relatively low current pulses they could work.

[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.