Need help rigging up a spot welder for some 18650s

[VoltJesus]

Did not have time to rig it up today, but will sometime this week.
I did however pop the side cover off both my Schumacher and Sears battery charger/jumpers to have a look.
The transformer is identical in both, except for the secondary winding. The Sears unit has separated coils (4 terminals) on the secondary vs. what you can see on the Schumacher (photo attached).
Transformer is a little smaller than I was expecting, but looks bigger than any MOT I've ever worked on. That includes the Amana and Panasonic commercial units.

By stroke of luck, someone replied to my ad looking for an older MOT today. I will be going to pick that up tomorrow.

[Housedad]

This thread scares the crap outa me.  I've done welding for all of my adult life as a hobby.  GMAW, SMAW, Oy/Acet,  spot, Plasma. I have all the common types at my disposal.  But the current levels that you guys are talking about to weld on a nickle tab and some of the design ideas are, well,  not too kosher in my book.  They look dangerous as all hell.

[james_s]

There's really nothing unusual about them. A typical capacitive discharge spot welder will develop peak currents in the 10kA range but the voltage is relatively low and the pulse is very short. The idea is to heat the joint very quickly so it can cool before any significant heating occurs in the battery being welded. It's not particularly dangerous, the average power is low. A small CD spot welder is a heck of a lot safer than a MIG, TIG or stick welder, I use mine on the kitchen table.

[Housedad]

I guess I am definitely not used to this form of welding.

[james_s]

It's a similar concept to the nitrogen laser. Peak optical power can be in the kilowatts but due to the extremely short pulse width the average power is similar to a 99 cent laser pointer. I measured the output of mine years ago by scoping the drop across a piece of #4 copper wire and IIRC the pulse peaked at just under 10kA but was only about 5nS long.

Actually xenon flashes are another similar concept, the tiny little tube in a disposable camera can have a peak power of hundreds of watts, somewhat larger camera flashes can have peak currents of hundreds of Amps, but again it's a very short pulse so the average power is low.

[edpalmer42]

I have a 5V power supply that's rated for 250A @ 115VAC input or 360A @ 220 VAC.  It has remote sense and enable/disable capability.  Would it work as a spot welder?  Set up a timer to pulse the enable lead as required.  Current control would only be via selecting the appropriate lead size, but maybe?

Ed

[james_s]

If it's a linear supply it might work for light duty spot welding, but if it's a switchmode type it will almost certainly detect a short circuit and shut down. Spot welding is normally in the thousands of Amps at very low voltage. A friend of mine built a conventional transformer type spot welder and he used a microwave oven transformer core with only a couple turns of very heavy secondary. Only about 1V but lots of current.

[edpalmer42]

It's a switchmode power supply, but don't forget that full load for 5V @ 250A is only 20 milliohms.  5V @ 360A is about 15 milliohms.  So what kind of contact resistance do you have with a spot welder?  Don't forget that the only way to heat the spot is if there's resistance there.  I just used my millohmmeter (20 milliohm full scale, 0.01 milliohm resolution) and got 1-5 milliohms with two big copper electrodes pressed down onto a few typical battery strips.  So with appropriate lead selection I'll be able to limit the current to a 'safe' value.

A long time ago, I took about 20 cm of 20 ga wire and connected it across the power supply and plugged it in.  It just turned red and melted.  No drama at all!     Obviously, that isn't comparable to spot welding, but it was interesting to do.

I looked at the battery spot welders on ebay and saw values from 50 to 800 amps so 250 or 360 seems feasible.

I'll probably test this one of these days, but I have too many other toys to play with for now! 

Ed

[james_s]

Try it and see what happens, I'd love to hear the results. My friend used copper ground rod to form the electrodes for his spot welder.

[DBecker]

Also need a low-usage spot welder for cells.

The lowest cost approach is using a spare 12V car battery, jumper cables, and 8 AWG sold copper wires taped to a wooden handle.  I've seen it done successfully on YouTube, but it seems to require just the right battery age and lots of practice to get the contact timing right.

The next step up is using a relay and pushbutton with the car battery.  The timing is easier and you can align everything rather than having to jab.  But the timing is still not repeatable.

My thought is to move the backyard scrap approach into the modern age.  Instead of a precisely-worn car battery, use a lithium jump start pack.  And instead of using an unpredictable  relay, use a MOSFET.   Lithium cells have significant intrinsic capacitance due to their structure, and the cells used in jump start packs are optimized for brief high discharge rates.

[VoltJesus]

Wow, so many questions! LoL     I'll try to get most of them in this one post. Look for your user name.

As has been mentioned, battery welding is a finicky process that needs EXCELLENT control to do it properly. And there is quite the risk if things go wrong. Exploding batteries is one.
I would say that as long as you understand the risks involved, protect yourself and nearby things accordingly, then you might be ok. Not meaning to downplay safety at all.
My example in the original post is NEITHER SAFE nor FINE CONTROL. So although I posted asking for advice/insight, I would otherwise not recommend what I am attempting to anyone.
That said, you are welcome to do whatever you wish. Just know what you are up against and the ramifications if you mess up (your fault or not).

@Housedad - Honestly there is danger everywhere. Driving a car on the road has very high risk, yet most of us do it every day. The best we can do is understand the risks and try our hardest to control the outcome.
I have a background in HVAC, so I am more aware of safety concerns than the average joe. I've be electrocuted, cut, fingers smashed, and had things go boom right in my face. Very few of those were my fault. My comment above should explain my position on this welder setup. Safe? No. Workable? Possibly.

@edpalmer42 - Just remember that welding is actually shorting the power supply. I do not know the design of your power supply, but there is always the chance something inside could burn up or go pop. Welding is getting the material hot enough to melt together as one, so when you melted that 20ga wire that's the same principal. Will it do battery spot welding? You need to understand that there are a multitude of battery tab strip thicknesses, and they all require different power levels to weld properly. Then there are different tab materials to consider. I am specifically working with (99% pure Nickel) what is considered to be quite thick strips at 0.2mm. Most common thicknesses are in the 0.1mm to 0.15mm range. A 0.2mm strip will need at least 2x the power to weld as the 0.1mm.
For 0.15mm strips, the avg. power needed to weld those is in the ~1100w range. However many Amps and Volts it takes to get there is depending on the application. Too high a voltage will cause too much spark, and will either blow holes in the material or stick your welding leads. Too low a voltage is not good either. Excessive heat at the weld could internally damage the battery, which just might make it explode. DO NOT kid yourself. This CAN and WILL happen if you do not have your settings right. Know your enemy.

@evb149 - See my reply to edpalmer42
About welding with a car lead-acid battery... The problem is that it is way too hard to control. Every time you put a load on that battery, you could get wildly different amounts of amps. This makes it unreliable for tab welding. See my original post. That was my last resort option with the bank of 4 solenoids. Not advisable and wont do a good job.
bout the battery tabs... I've yet to find a good source. Ordered mine on Ebay. You want Pure Nickel 99.6% strips. Many many listings on Ebay are flat out scams where they claim pure Ni, but are actually Ni coated steel. You do not want that because of higher resistance in steel, and it will rust. Nickel strip is the best for battery packs.
Different materials have different characteristics. Copper is the best conductively, but is hard to weld. Brass has much higher resistance. Sheets of Ni are fine, the thickness is key.
For chemical joining, I can promise you if a viable low-cost method existed, all the big name tool manufactures would be using it. So I assume no such beast exists.

@Dbecker - See my reply to evb149
Using lithium cells to weld can and has been done. The guys I bought my 18650s from are using old 123 cells and a control circuit to do spot welding on the packs they build and sell. The 123 cells they're using are 3.3v, but are capable of several 100 amps a piece and much safer that hobby grade LiPo packs.
I would not advise you use LiPo cells from things such as those jump-starter packs. The quality of LiPos in those things are horrible. Welding is a dead short, and not something you want to do to a low quality LiPo. If they managed to survive without blowing up, you would most likely damage them severely with repeated shorts.

@texaspyro - Not 2000 cells, 2000 welds. Packs I'm making will have strips across both series and parallel, needing at least 2 welds per strip. 4 welds per side of the 18650 for a total of 8 welds/cell. I'm trying to go for 3 welds per strip, making 12 welds per cell. If I do 12welds/cell that would add up to ~2000 welds.
Is my setup safe? No, not really. That is ok. Not afraid of a little risk. Guess all the things I've seen though my years of work has kind of dulled my senses a bit.

[jpanhalt]

Possibly off topic but maybe not.

Anyway I'm not seriously suggesting it for this particular application but it seems like some kind of "glue for metals" process shoud be possible for some combination of metals that leads to something about of the quality of a spot weld or soldering joint but is basically electro-chemical / chemical in origin.

1) There are many , low melting alloys that can  be used for "gluing" metals (think hot melts glues).  Wetting the surfaces can be a problem but some do wet well.  Many contain bismuth and/or indium.

2) A few years ago researchers announced a modified Tollen's reagent that deposits pure silver.  Original Tollen's was a very thin coating.  The new reagent sets at relatively low temperature and presumably can even be soldered.   Here's a link to the original: http://pubs.acs.org/doi/abs/10.1021/ja209267c  Unfortunately, the ACS (publisher of JACS) removed details from the abstract.  They are readily available on the internet.   Basically, the authors replaced glucose in the original Tollen's process with a reducing agent that gave gaseous products.  All of the reaction products in the revised procedure, except for the silver,  are gaseous.

3) If you do not need high currents, there are  variety of elastomers and paints that are conductive (zebra strips and window defroster repair paint).

4) Use a battery holder

The main problem with most of the alternatives just mentioned is mechanical strength.   Welds are very strong and relatively resistant to vibration.

John

[james_s]

I got the nickel strip I use from Sunstone Engineering, it seems to be quality stuff.

http://sunstonewelders.com/


I did blow a hole in a battery once, it happened because I bumped the foot pedal before I had pressed the electrodes down firmly. Didn't explode or anything but it did ruin the battery.

[DBecker]

@Dbecker - See my reply to evb149
Using lithium cells to weld can and has been done. The guys I bought my 18650s from are using old 123 cells and a control circuit to do spot welding on the packs they build and sell. The 123 cells they're using are 3.3v, but are capable of several 100 amps a piece and much safer that hobby grade LiPo packs.
I would not advise you use LiPo cells from things such as those jump-starter packs. The quality of LiPos in those things are horrible. Welding is a dead short, and not something you want to do to a low quality LiPo. If they managed to survive without blowing up, you would most likely damage them severely with repeated shorts.

The jump start boxes are using pouch cells.  I didn't believe the advertising at first, but tests show that they put out an amazing amount of power for a few seconds.  A 600 amp one might only deliver 300A, but that's still really impressive.  And a few years on the market shows that some models are reasonably long-lived.

The appeal for someone that only occasionally does a few dozen welds is that it can be "off-budget".  You can keep it in a car for its intended purpose, and hook it up only when needed.

Edit: fixed quote

[jpanhalt]

@Dbecker - See my reply to evb149
Using lithium cells to weld can and has been done. The guys I bought my 18650s from are using old 123 cells and a control circuit to do spot welding on the packs they build and sell. The 123 cells they're using are 3.3v, but are capable of several 100 amps a piece and much safer that hobby grade LiPo packs.
I would not advise you use LiPo cells from things such as those jump-starter packs. The quality of LiPos in those things are horrible. Welding is a dead short, and not something you want to do to a low quality LiPo. If they managed to survive without blowing up, you would most likely damage them severely with repeated shorts.

The jump start boxes are using pouch cells.  I didn't believe the advertising at first, but tests show that they put out an amazing amount of power for a few seconds.  A 600 amp one might only deliver 300A, but that's still really impressive.  And a few years on the market shows that some models are reasonably long-lived.

The appeal for someone that only occasionally does a few dozen welds is that it can be "off-budget".  You can keep it in a car for its intended purpose, and hook it up only when needed.

Your quote is screwed up.

John

[james_s]

I use LiPo packs in my RC aircraft and I can say from experience that if you abuse them they will puff and the internal resistance rises. Sure you may get huge current from them, a few times, then they'll quickly degrade.

[VoltJesus]

The jump start boxes are using pouch cells.  I didn't believe the advertising at first, but tests show that they put out an amazing amount of power for a few seconds.  A 600 amp one might only deliver 300A, but that's still really impressive.  And a few years on the market shows that some models are reasonably long-lived.

The appeal for someone that only occasionally does a few dozen welds is that it can be "off-budget".  You can keep it in a car for its intended purpose, and hook it up only when needed.

Yes, those pouch cells are LiPo packs. Essentially RC car/plane battery packs. Most of the companies making these jump-packs are buying the lowest grade "no name" LiPos they can get their hands on and stuffing them into plastic cases.
There are many brands and qualities of hobby LiPos. Have a look at HobbyKing and see just how many different variants of the same 3s1p LiPo they sell.

Also, very very few of these jump-packs offer any real protection. When you flip the little flap up to attach your jumper cables, you are looking right at the battery connector. There is no circuitry between that connector and the LiPo cells. Only the box on the jumper cable attachment has any kind of protection. And most are very poor, to say the least.
The only jump-pack I have seen that offers built in protection in the actual pack is the Noco Genius Boost.

Bottom line, using those to weld would be more dangerous than my retarded setup. 18650s are much safer than pouch cells (the good quality 18650s at least).
By design an 18650 is a steel shell, with gaskets, and a vent under the positive terminal to release excess pressure should something go wrong internally. LiPo pouch cells just keep swelling until they go BOOM.
I see james_s also has experience with these. So there are 2 guys that can tell you first hand not to play with pouch cells. I don't mind toeing the line on safety when it only involves myself, and others are not in harms way. That said, I do not play around with pouch cells. Too high a risk.

[Ian.M]

Even the humble Lead Acid battery can be unsafe for welding  or other applications that draw an extremely high current.  All it takes is a cracked or loosened internal strap between the cells and if its recently been fully charged, you risk internal sparking resulting in a hydrogen explosion.  Its also possible for them to short internally if the links are corroded or otherwise weakened and they are grossly overloaded.  Chunks of lead and boiling sulphuric acid being thrown everywhere is not something you want to be complacent about.   It doesn't happen often, but when it does it ruins equipment and if anyone is in the way, even lives.

The hazards of a mistreated LiPO pouch cell mAH for mAH are probably less than a mistreated 18650.  The stored energy is the same but without rigid confinement all it can do is burst and burn.  An 18650 with blocked vents can explode like a grenade or launch its casing like a rocket, and do comparable damage similar to being shot with a shotgun slug.  A 2600mAH 18650 cell has about 31KJ of stored energy.  For comparison that's about double the maximum muzzle energy of a .50 BMG round, and if even 5% of it is converted into kinetic energy of the casing or fragments, that's equivalent to a .22LR round.

[mc172]

Just buy one. You will spend more money messing about building your own or buying and bodging up some other contraption not intended to do welding.

http://www.ebay.com/itm/US-Shipping-18650-Battery-Charger-800-A-0-1-0-2-mm-36V-60A-788H-Spot-Welder-/171866427579?hash=item28040990bb:g:ZEsAAOSwPCVX9kTw

$138 shipped.

[m.k]

I built my MOT one as a simplified version of this: http://www.avdweb.nl/arduino/hardware-interfacing/spot-welder-controller.html
Quite a nice circuit, you get very repeatable results with it. One thing i learned is you need current, as much as possible, i don't think mine does have more than 3 or 4 volts open circuit voltage on the secondary. So if you use the transformer above you would have to replace the secondary. But it seems big enough. I definitely needed a thick cable from a welder for the secondary, a 10 mm² car jumper cable did not do the trick.
And if you use a MOT: remove the magnetic shunts. I skipped this step in the first place but the welding times were too high.
Costs were about 10€ for the components and 25 for the copper Pins

[VoltJesus]

So if you use the transformer above you would have to replace the secondary. But it seems big enough. I definitely needed a thick cable from a welder for the secondary, a 10 mm² car jumper cable did not do the trick.

Cool. I am working on something similar. Picked up that microwave yesterday, and got it torn down today. Mine is a Sharp 1100w MOT from 2000.
Removed the secondary and replaced it with a piece of 2awg I had laying around. Hope that is big enough? I see most people end up using 4awg and can just barely get that to fit. I had quite a time getting the #2 in there. Nothing bigger will fit without some major modifications.
I had to use my framing hammer, if that puts it in perspective.     I'll post pics up later.

The hazards of a mistreated LiPO pouch cell mAH for mAH are probably less than a mistreated 18650.

Good info Ian. Scientifically speaking, an 18650 would be more dangerous than a pouch cell.
I was mostly addressing using the LiPo as your power source for welding. Dead shorting a LiPo accidentally is scary enough. The reason I would consider them more dangerous is because they are notorious for being tempermental. That and the astonishing lack of quality control with all the various brands running amok.
You are correct in regards to the info you posted, however.

[james_s]

I have personally seen LiPo pouch batteries erupt into surprisingly large fireballs. It happens occasionally when an electric RC plane or helicopter suffers a severe crash.

18650 cells are relatively safe, they can blow the end out and flame in a really severe case, stored energy is dangerous, no way around that but I've never seen one make a fireball.

[Conrad Hoffman]

I've seen schematics for thermocouple welders, which are the same or similar to what's needed here. They start with a small isolation transformer (I think) and then a Variac. The output of that is rectified and charges a large cap through a big limit resistor to whatever voltage is set by the Variac, 0-400 VDC for the one I looked at. The limit resistor is such that you can discharge (essentially short) the cap without having to disconnect the charge circuit.

A mercury relay is used to discharge the cap through a transformer having one or two turns as the secondary. That gives you a low voltage pulse capable of hundreds of amps, depending on the Variac setting.

Pretty simple device and easily built, save for the mercury relay. You'd probably want something like a big contactor relay with a snubber, even if it had to be cleaned now and then. I don't know if the newer units have replaced the mercury relay with something solid state but it would be surprising if they still used the mercury devices.

[james_s]

That's certainly a valid approach. When I built mine I decided the stored energy was already dangerous enough so I didn't want high voltage too. I went with a lot of capacitance, around 1F charged by a variable voltage of up to about 22V.

[VoltJesus]

Which Arduino is suitable for this task? Uno, Leonardo, Mini Pro, Mega... ??
I was at the store just a few days ago and was planning to pick one up, however I could not find an answer online while in the store. Didn't get one.
Got an open box Rpi 3 model B for $24, but it has WiFi issues. The Rpi Zero W I got a few weeks back wont stay connected to bluetooth. I'm just going to return them both.

I will still setup the first design in the OP just for kicks, using the microswitch to manually actuate the pulse, to see if it would work.
But I want a more precise setup with the MOT I am building, and an Ardrino circuit seems like the easiest/cheapest option.

One more thing I am curious about. What makes a SSR "zero cross switching" ?  I have worked with a few different types, but have never come across this terminology. At least not "zero cross switch" printed on the SSRs I've messed with. I might even have one of these laying around in all my stuff.
There is this particular type of multi-pin relay used in Hobart equipment that we refer to as "Ice Cube" relays. I am wondering if these are zero cross switching.