How to make a cell spot welder in 5mins ... zero cost

ozz93666

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You need a short length of twin wire house wiring cable ...I used some twin 4mm square (each wire 4square mm)...thicker wire would be better ,but eventwin 2.5mm square might be OK ..

Removethe plastic insulation from one end,Only 10mm ...so now you have the cable with two wires protruding 10mm ..file the two wires into a more pointed shape in such a way that the points are as closetogether as possible ....now we have the plastic cable with two pointed wires protruding , held the correct distance apart by the plastic insulation, these are the electrodes ....

Connect the other end of the cable to the power source... I used 3s20p ... but I expect 2s20p would work .. perhaps even one 80p

That's it ...now place the nickel strip on the cell ...put the electrodes firmly on top... flash ...bang , it's done ... I get a much firmer welded than the commercial ones in videos I've seen .... I may have too much current ...

I did experiment with switching the current with a motor bike starter relay , but found it to be better not to have this ...just push the electrodes firmly , and pull away when the spots glow red hot.
 
I wouldn't use solid core household wiring as the cable, the constant bending will eventually cause the wire to fracture.
Fine to use solid core for the electrode, I'd use a terminal block to join the two cables, as it makes it easy to replace the electrode.

It's possible to have too much current for spot welding, which then involves burning a hole into the cell. This is why I've not even considered a rewound Microwave Transformer (potentially lethal project 'cause microwaves are 2,000V), to spot weld battery.
 
I have done some work to microwave and it works pretty good. Just rewire secondary side to get 4-7V depending on turns. Then you make sure to control it on AC side. Works decent... But yes its easy to burn hole in the cells without knowing it when just touch and go.. Been there done that :)
 
A true 1 Farad low ESR car audio capacitor charged to 10-12V works fairly well, it's fun watching the cables jump like twitchy snakes when you touch the electrodes. Anyone who hasn't seen it before will jump too, it makes an impressive flash crack.

The majority of car audio capacitors are worthless junk though, finding a good one is a matter of about three or four brand names, the Monster Cable version is good and there are a couple of others, Rockford Fosgate I think...


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I'm surprised powerwallers are talking about microwave transformers or capacitors to do this.

18650's are perfect for the job , and retain a fairly constant voltage over many welds ...capacitors need to be charged again each time to get consistent results ... no need for the danger of mains suply microwave transformers when you only want low volts ...

Just a few dozen cells works fine , now I see how quick and easy it is , I think I will be shifting over from soldering to spot welding.
 
1) The spot welders were being used to "create" the 18650 packs
2) the MOTs are not being used with Mains, but stepping the voltage from a DC source

and yes, it is easy to create these. But the problem with spot welding is the same as with soldering. If a cell goes bad, u have problems removing that cell. Actually, with spot welding, there's more of an issue as you can't just 'desolder' the connection. you have to cut, trim, and replace cell, and now you have at least 3 to re-spot weld the new piece of strip.

IMHO that is :p
 
The reason i dont use non controlled spot welder is the fact that when i started it i did it that way. And i destroyed plenty of cells due to going through... Or just not welding it good enough so the contact easily break loose.

In that sense the soldering will most likely feel safer for new people in the area. I though own a spot welder and that one does it "ok" but still not 100% happy with it. May be me that isnt good enough working with it.
 
Eh, I already had the capacitor when I started harvesting cells some years ago, I'm not a big fan of spot welding anyway and certainly not with used cells. Soldering is easier to do in the first place and as Korishan points out soldering is easier to reverse at a later date.

I welded a grand total of one smallish ebike pack and decided it wasn't worth the hassle in getting good nickle strip and setting up the welding apparatus to get good welds.
 
Korishan said:
.....If a cell goes bad, u have problems removing that cell. Actually, with spot welding, there's more of an issue as you can't just 'desolder' the connection....

There needs to be a thread on people's experiences of cells going bad ... I guess oldtimers here (over 9 months power walling experience) should have some tales to tell ...

My understanding is fuses don't help ... I guess you just wake up one morning and see one of your packs is low ,showing a cell is discharging the whole 3.7V pack ...

Then what's the plan??? how do you find the culprit cell ????
 
You'll find the pack needs to be balanced more and more often and the same parallel bank is the culprit, it's not common if you have done your culling well but it does happen that a cell becomes more and leaky over time.

It's why I'm not a particular fan of the "dumb" BMS that doesn't let you know what it's doing, that kind of BMS can cover up a cell or cells going bad for quite a while until it can't keep up any more and then you end up killing your entire pack when you aren't aware that the balance is not only getting further and further off but doing it faster too. That's a fairly common thing on ebikes and why BMS can also stand for Battery Murder Suspect.

I want a BMS that tells me, "Hey Rube, bank 3 is consistently needing more current to balance than any of the others, maybe you ought to get off your procrastinating keister and take a look at it".
 
I have had cells running for almost year now. Not on big system but on a very small test setup. I have active simple monitoring and i see when a bank getts lower or falls behind. Then its just matter of getting it out and retest them. Ie just volt monitoring on it.

So far i have no experience in fused cells since they only have been running for some months... And no fuses that had issues.

But i have retested banks on the above and then it was just to desolder them and put them into the tester again :)
 
daromer said:
I have had cells running for almost year now. Not on big system but on a very small test setup. I have active simple monitoring and i see when a bank getts lower or falls behind. Then its just matter of getting it out and retest them. Ie just volt monitoring on it.

So far i have no experience in fused cells since they only have been running for some months... And no fuses that had issues.

But i have retested banks on the above and then it was just to desolder them and put them into the tester again :)

Suppose you have an 80p pack which you know is self discharging .. does this mean you desolder the cells and test them all again !!??

I have one cell which seems to work fine up to 3.67V ... if I try to take it above that it turnsall the input into heatingthe cell !!!
If this cell was in a 80p pack it would slowly discharge the whole pack to 3.67 ... if the pack was above about 3.9 this bad cell would be warm ... if we pushed the pack up to 4.2 it would be noticeably hot to touch ..

This might be an easy wayof finding a bad cell in a pack that you knew was slowly discharging ... take the pack up to 4.2 and look for the hot cell.
 
Yes you have to desolder them all to find the culprit in worst case. in best case the fuse blown.. but not seen that yet.
And if im lucky i might spot it with the Flir gun if it gets hot.

Though have not had the oportunity to test that yet... but time will tell ...

But i agree. Cycle a pack fully from top to bottom and look for any excess heater may be 1 way to do it. And yes doing this size of packs makes it trickier to find the ones with issues.
 
Breaking the welds on the commercial packs isn't too hard, as they only have 2 or 4 small spot welds. I'd bet your not going to be that neat with every single weld on a homemade system.
I've considered if I could weld the copper wire/strip directly to the negative of the cell, as nickel has limitations for really high currents.
 
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