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

[steveo]

I will probably end up buying copper electrodes & molybdenum ; i will probably be tab welding copper to nickle tab & nickle tab to actual cells!

Ok...

ok so i got my 250amp src peak of 2500amp lets say... ( i have to check specs sheet)
i got my electrodes selection down ... i'll buy both molybdenum & copper electrods depending on what i'm tab welding
I have a ton of 6 - 4 gauge wire

****************

Ok ...

-i need a nice switch to activate the src
-a capasitor setup
-power supply voltage/amps


keep the recommendations comming... I'd rather ask everyone here and get things right the first time

-steveo

 

[The Mighty Volt]

I have a variable voltage controller with a display. It's good to get one with a display as they allow you to take notes about what parameters work best with different materials and different thickness of materials.

 

[oatnet]

You only need to make the trade-off of sacrificing electrical conductivity for heat tolerance if you're looking to have a very high repeat rate on your welds. Copper, or copper/tungsten would be a way better choice for doing hand welded cells one at a time.

Wasn't RLT blowing the tips off copper and elkonite electrodes, having to regrind them frequently?

-JD

 

[liveforphysics]

You only need to make the trade-off of sacrificing electrical conductivity for heat tolerance if you're looking to have a very high repeat rate on your welds. Copper, or copper/tungsten would be a way better choice for doing hand welded cells one at a time.

Wasn't RLT blowing the tips off copper and elkonite electrodes, having to regrind them frequently?

-JD

As far as I'm aware, if you don't have proper contact pressure, or impurities on the surface between the contacts, then it's going to vaporize the tips. If you do have those things correct, then the connection between the aluminum and the nickel tab should always be the point that ends up eating the energy (and making the weld).


Have any of you guys seen the 240v el-cheapo spot welders they sell at harbor freight by chance? The have a nice set of ~3/4" solid copper bars in them with nice tips that unscrew to grind or replace. If I remember correctly, the label on them says something like, 240vac 40amps peak input, output 3v at ~2500amps (or something in that neighborhood).

 

[liveforphysics]

Not suitable for tab welding as they sit, but just in case somebody wants to give using parts from them a shot:

http://www.harborfreight.com/dent-repair-stud-welder-kit-8878.html

This one claims it does 2,500amps:

http://www.harborfreight.com/230-volt-spot-welder-45690.html

 

[steveo]

what do you think guys

6 - 1/2 farad rockford capacitors to a total of 3 farad... rated at 1.5mohms each?

240$usd shipped ....

sounds really expensive?....


yes or no?

-steveo

 

[oatnet]

As far as I'm aware, if you don't have proper contact pressure, or impurities on the surface between the contacts, then it's going to vaporize the tips. If you do have those things correct, then the connection between the aluminum and the nickel tab should always be the point that ends up eating the energy

... and if you are welding copper, then the trode and the work material have the same melt point. With aluminum, you will always have the impurities of aluminum oxide. I liked the Molybednum idea, I picked up 12" of 1/4" rod on eBay, and hope the teacher in my Saturday 'machine tools technology' will let me cut it in half and cut a point on it with a lathe, if so I get to use my first carbide turning tool.

 

[texaspyro]

6 - 1/2 farad rockford capacitors to a total of 3 farad... rated at 1.5mohms each?

PM me... I can hook you up with some 1F Rockfords for around $50 ea. Tested for capacitance and ESR on my ESI VideoBridge and in my FET welder. Real 1 farads, around 1 miliohm ESR.

 

[steveo]

hey everyone,

just messed up my "230amp" rated scr on my new a123 tab welder .. only got like 4 welds out of it @ 14v

can u use a kv200 contactor instead? .... rated at 500amp & much higher peak ...

i guess if i use a contactor .,.. i need a very big diode also?

-steveo

 

[steveo]

hey everyone,

just messed up my "230amp" rated scr on my new a123 tab welder .. only got like 4 welds out of it @ 14v

can u use a kv200 contactor instead? .... rated at 500amp & much higher peak ...

i guess if i use a contactor .,.. i need a very big diode also?

-steveo

bump!!


anyone?

 

[Jeremy Harris]

A contactor won't survive more than one weld, as it's contacts will probably weld shut on the first pulse.

I have some spare SCRs that will survive heaps of abuse on one of these welders, but as we found when I offered them on here a while ago, the postage cost to the US is crazy, more than the things are worth. FWIW, here is the post I made offering them last year: http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=165#p69959

They weigh about 0.275kg (about 0.6lbs) in the box, so would cost far more to ship to the US than they cost. I still have two or three here spare if anyone in the UK wants one.

Jeremy

 

[dannym]

I just now got my tab welder together.
2.1F of 15v big-ass Malloy capacitors bolted straight into linear aluminum busbar rails and 2ga stereo wire for cables, and solid copper split bolts (hardware store item) to strap that directly onto the electrodes.
C154E 220A SCR (13500 I^2*t fusing current). It's huge, was like $20 on eBay.

I turned handles out of 1" nylon rod stock with 0.198" hole drilled into it, which is slightly less than the copper core. I threw the nylon in the oven at like 300F for about half an hour. It expanded enough that the copper slides right in, when it cools, it locked them in very tight. If I ever lose so much of the tip due to filing that I need more, I can always disconnect the cable and reheat them and push out more rod for the tip.

These welds look better than anything the original site had. They're not "dots". They're not blasted apart either. They're smooth melted craters about 1mm wide, I looked under a microscope. In fact they're not really craters with a built-up rim- the center just melted and "fell out" downward and stuck clean to the AA batt back.

IMHO the original plans are flawed, you need much thicker cable and better interconnects than depicted. And my initial feeling is that the lower voltage (<15v) is just a better weld all the way around.

I don't believe much in stereo caps. There's just no way to tell what you'll get. The markings are meaningless. And frankly, looking at the total volume of capacitors on my 2F 15v setup, it just seems somewhat implausible that one of these ~1 liter of volume capacitors could be 5F or even 1F. I guess I could believe some "special" construction inside with magically high power density, but I buy new small electrolytic capacitors as PCB components and never noticed a remarkable change in the technology on the market, not without aerogels or other specialty items.

Also, 1.2v or 1.5v of a single cell is not enough to trigger my gate properly. My SCR is specified for 150mA max gate current, and could drop as much as 3.0v. My gate draws like 70mA with the cell across it. I think there are two problems here- one, it probably needs like 4 batts and a current-limiting resistor (~12ohms) to provide a predictable high current to the gate. Two, any regular button switch "bounces"- it contacts, then not, then contacts, then not, then contacts for real. It's only a few nanoseconds of on-off uncertainty but this may be significantly slowing the SCR's turn-on leaving it absorbing a lot of power like a resistor rather than being a solid open-then-closed switch. I may need to build a circuit with a schmitt-trigger that won't bounce on-off at all.

I will try some A123's on it soon.

Where's this 0.010" tab material I'm reading about? Admiral Steel? I found the site... there's only the 6x12 pieces of 0.010" though. Is that it?? Is it worth getting and cutting up?

 

[dannym]

hey everyone,

just messed up my "230amp" rated scr on my new a123 tab welder .. only got like 4 welds out of it @ 14v

can u use a kv200 contactor instead? .... rated at 500amp & much higher peak ...

i guess if i use a contactor .,.. i need a very big diode also?

-steveo

How did you mess it up? Details? This doesn't seem right to blow it through excessive anode current. If the turn-on gate pulse wasn't aggressive, it could fry it via slow turn-on. Or if you somehow delivered excessive current into the gate and blew the gate.

I agree with Jeremy- a contactor isn't going to perform here at all. SCRs were employed for a reason.

 

[liveforphysics]

hey everyone,

just messed up my "230amp" rated scr on my new a123 tab welder .. only got like 4 welds out of it @ 14v

can u use a kv200 contactor instead? .... rated at 500amp & much higher peak ...

i guess if i use a contactor .,.. i need a very big diode also?

-steveo

Ebay my friend. Get the right SCR for the job. For the difficult task of welding A123 cells, I would considder nothing rated for less than 1ka.

 

[Jeremy Harris]

Also, 1.2v or 1.5v of a single cell is not enough to trigger my gate properly. My SCR is specified for 150mA max gate current, and could drop as much as 3.0v. My gate draws like 70mA with the cell across it. I think there are two problems here- one, it probably needs like 4 batts and a current-limiting resistor (~12ohms) to provide a predictable high current to the gate. Two, any regular button switch "bounces"- it contacts, then not, then contacts, then not, then contacts for real. It's only a few nanoseconds of on-off uncertainty but this may be significantly slowing the SCR's turn-on leaving it absorbing a lot of power like a resistor rather than being a solid open-then-closed switch. I may need to build a circuit with a schmitt-trigger that won't bounce on-off at all.

I found the same thing about gate drive. The harder you drive the gate, the faster the SCR switches, at least initially, and that tends to make it work more effectively as a discharge welder. To drive my SCR gate I used a simple trigger relay circuit, that uses the voltage on the capacitor bank to drive the gate. This has the added advantage of disconnecting the capacitors from the power supply during discharge, which mean that you can use a bigger power supply without fear of latching the SCR on. Here's the circuit I used:



Jeremy

 

[dannym]

The relay's subject to the bounce problems too, though. Only a solid-state switch like a schmitt-trigger (properly designed) would get rid of it completely.

How much peak gate current did you go for? Did you respect the datasheet's limitation, or go-for-broke since it's a momentary thing? I wasn't sure.

Actually, a circuit to provide one ~20mS gate pulse per press of the button would be a good idea.

Didn't you say you blew an SCR by having it triggered, no gate drive, and then touched the electrodes to the material? Would that kill the SCR if the gate were being driven by an accidental button press when the electrodes are being applied to the material? A single-pulse switch would avoid that.

 

[Jeremy Harris]

The relay's subject to the bounce problems too, though. Only a solid-state switch like a schmitt-trigger (properly designed) would get rid of it completely.

How much peak gate current did you go for? Did you respect the datasheet's limitation, or go-for-broke since it's a momentary thing? I wasn't sure.

Bounce is a total non-issue in practice, I've done hundreds of welds with this, as has The Mighty Volt with his (which uses the same circuit) with no problems. The SCR turns on very fast, much faster than any relay bounce, so is already latched hard-on before the contacts on the relay have even started thinking about bouncing open again.

The main advantage of the relay is in preventing latch up. The latching current for my SCR is around 1A, so without the relay the SCR would stay latched on, shorting the power supply, unless the charging current was limited to well below 1A. You really need at least 3 or 4 amps from the supply to give the lowest acceptable recharge time, IMO.

I stuck to the data sheet figures for gate drive current, hence the 8.2 ohm current limiting resistor. You may need to change the value if your SCR has a different max gate drive figure. Igm for the SCR I used was 3A, but the resistor limits this to around 2.2A at the maximum charge voltage of around 18V, so it's always in its safe area. My SCR has a nominal gate current to meet the switching specs of 1A, so I'm still overdriving it even with relatively low capacitor bank voltages.

Jeremy

I just realised you've added a bit to this post whilst I was replying. My original problem, where I blew an SCR, was because I stupidly fitted another big power resistor across the electrodes, as a supposedly "safety" discharge feature. This would pass enough current to allow the SCR to latch, which is what happened - I accidentally triggered the welder with a momentary press of the push button before I put the electrodes to the workpiece. There was then a spectacular shower of sparks when I did, with the result that I blew the SCR. I removed the "safety" discharge resistor and all has been well ever since, as the SCR now cannot latch on unless the electrodes are in contact.

 

[7circle]

... This has the added advantage of disconnecting the capacitors from the power supply during discharge, which mean that you can use a bigger power supply without fear of latching the SCR on. Here's the circuit I used:



Jeremy

It might be worth noting that a Current limited supply would be worth using to charge the cap up to desired voltage.

I built a Capacitor Durabiltity Rig 15 years ago with a triggered SCR that had nuisance issues of missfiring/latching that blue 20 50W parallel 8 ohm resistors what a mess.
It even had a BIG IGPT Blocking DC.

Gota get tab spotty running.
▼☺☺
(+) (-)
| |
| ┌┐ |
| | | |
V V V V
========

Do you suggest series linked electrodes for getting 4 spot welds.
Sorry, you probably already have covered this.

 

[Jeremy Harris]

It might be worth noting that a Current limited supply would be worth using to charge the cap up to desired voltage.

I built a Capacitor Durabiltity Rig 15 years ago with a triggered SCR that had nuisance issues of missfiring/latching that blue 20 50W parallel 8 ohm resistors what a mess.
It even had a BIG IGPT Blocking DC.

Gota get tab spotty running.
▼☺☺
(+) (-)
| |
| ┌┐ |
| | | |
V V V V
========

Do you suggest series linked electrodes for getting 4 spot welds.
Sorry, you probably already have covered this.

Good point. The supplies I've used do have a constant-current limiting mode so are fine, but if someone was going to use something like a Meanwell type supply with hiccup limiting they'd probably have a problem (unless they modded it for constant current operation).

I've not tried anything other than a pair of electrodes. The only real problem I can see with four electrodes would be getting even pressure - I found this a challenge with the rig I made and reverted to hand-held electrodes.

Jeremy

 

[dannym]

OK, I did a bit more experimenting...
The aluminum bar I have (didn't try to brush it shiny, but it's basically clean), I couldn't weld it. It left some dots in it, that's all, no mechanical connection at all.

The A123 seems to have taken the 0.005" strip just fine! In fact I couldn't rip it off in one piece with pliers, I'm gonna have to carefully grind it off; the tab's not what I needed it was just a test . The top did seem to weld tighter than the bottom, the bottom's welds were smaller dots, but the bottom's weld dots did rip out of the nickel sheet before coming off the bottom.

 

[dannym]

Well you can't put them in series that I can see, because they'll be shorted out by the tab. You'll get a weld at the + and - and the two "in the middle" won't be connected to anything but each other and the tab so no significant current will flow through them.

If you tried each electrode having 2 tips connected together, I would expect an unpredictable ratio of current between them. Most likely one will get too little current and fail to weld properly, while the other may get too much, even blow apart.

You'd need two separate cap banks and two separate SCRs. Technically the cap banks need to be electrically isolated from each other but the way these high currents work, just like an ohm on each + and - (or diodes) between the banks and a common charging power supply would mean the currents won't affect each other and the currents will flow only between that bank's electrodes.

 

[dannym]

Huh. I tried brushing the 6061 aluminum scrap "bright".

The welder won't weld the nickel strip to it. Now the nickel strip falls right off, even though I applied plenty of pressure and there's like ~0.5mm pits on the underlying aluminum. So, it seems it was powerful enough to affect the aluminum. Is it just not possible to weld to aluminum? I know about the oxide layer problem and all, I don't need that explained.

Not that I NEED to be able to weld to aluminum right now. I'd just like to know if it can be done or not for future reference.

 

[amberwolf]

Based on what little I know of TIG and MIG welding of aluminum, doesn't aluminum oxidize instantly when molten? So maybe what's happening is it is turning the entire weld spot into oxidation, so it has no strength to hold, no bond to the rest of the bar?

Do you have any nonreactive gas there that you could "pool" around it? Nitrogen, argon, etc.? If you put the whole thing down into a deep pot in a room with no air currents or breezes, and put some liquid nitrogen into the bottom, it should fill up the pot with nitrogen gas as the liquid warms and sublimes. You should be able to tell when it has displaced the air by using a barbecue lighter or match dipped down into the pan very slowly, until the flame goes out from lack of oxygen.

Then try the weld right then, and see if it works. If so, then it is probably oxidation causing it to fail.

 

[7circle]

Thanks for replies, took me twelve hours to realise the voltage potential would be hard to balance to get good 4 spot welds from one power source with series electrodes on common base.

Understand discharge of isolated dual spot welding would be better.

On the Al'y spot welding, is the other side Nickel of Al'y?

The melting points are very different. Without considering burning of Aly to Oxides,

How thick are the two materials?

(Edit: would conducitve gue stop the gas reactions)

 

[texaspyro]

You pretty much cannot effectively spot weld to aluminum. What happens is you can get a weld nugget to form and the materials bond, but the aluminum at the bottom of the nugget is very brittle. Tug on the nickel and it breaks free of the aluminum base, leaving a divot in the aluminum and and an aluminum pimple firmly welded to the nickel (or copper) strip.