OK, I'll go through this one more time, then, I'm afraid, I'm out of this thread, as you seem to be intent on going down a path which is wholly unproven and fraught with problems, rather than follow the advice of the many on here who have worked out the best way to build one of these things..
The ignored advice given so far:
The capacitor needs to be around 2 to 6F, probably 2 or 3F is optimum if you have high quality capacitors. It needs to have as low an ESR as possible, preferably much less than the remainder of the circuit resistance, or else large amounts of power will be wasted in the capacitor (which may not be able to cope with the heat build up over time as you do multiple welds). It needs to be charged to around 15V, with a variable voltage supply to allow for weld power adjustment. Car audio capacitors have been proven to work well, as have big commercial grade low ESR electrolytic capacitors.
You seem to be intent on using capacitors that are quite clearly unsuited to the job and which have never (as far as I'm aware) been used in this way. The capacitors you've pointed out could be connected in series, but you would need to find a means to ensure that they each stayed within their voltage limits. This may well mean using some form of shunt system to limit the voltage across each capacitor. Let's do some very simple arithmetic on your choice:
The Maxwell BCAP0005-P270-T01 is rated at 2.7V, 5F, 0.2ohms ESR.
Let's say you put 7 in series; that gives you a capacitor with a capacitance of 0.714F with a voltage rating of 18.9V and an ESR of 1.4ohms.
Assuming that you can charge and discharge these safely when connected in a series string like this, and assuming that you use a 15V charge voltage, the peak current that you could get from this set up would be just 10.64 amps (15 / 1.41) when discharged into a typical weld circuit resistance of around 10mohms. You need hundreds, perhaps over a thousand, amps to make a good weld.
Around 99% of your weld energy would be dissipated inside the capacitor with this set up, due to the very high ESR, with only around 1% actually going into the work piece.
Now, let's compare this with all the good advice from here that you keep ignoring:
Take a good car audio capacitor. It will typically have an ESR of around 5mohms or so, maybe less. Charged to the same 15V and discharged into a circuit with a resistance of around 10mohms, it will deliver a peak current of around 1000 amps (15 / 0.015) and only waste around 30% of the weld energy inside the capacitor. What's more, we know beyond any doubt that this set up will work and make good welds.
Please feel free to experiment, all we're trying to do here is save you from making mistakes, wasting money and perhaps having an accident by pointing you towards what we know works.
Jeremy
