180 capacitor swapout

[MattH]

Yes the connections are push fit, I will keep an eye on them and the banks temperature when I give the Mig some serious use to make certain I don't get any nasty surprises! If the connections are rated 15-20A each I have 150-200A rating, the Mig is 180A max so I hope I won't have a problem.

You will. One or to will arc, overheat and cause all sorts of issues. Solder the leads to the caps.
I used to build 1000w amplifiers with banks of 20 10,000uf 100v caps to smooth the DC. I always used copper busbars and that was at nowhere near the current you will be pulling per cap.

 

[normspanners]

20 10,000uf 100v caps to smooth the DC.

Hi matth was the banks of caps to facilitate the instantaneous big bass draw's/ pulses? 'sucking' on the system.

 

[MattH]

Hi matth was the banks of caps to facilitate the instantaneous big bass draw's/ pulses? 'sucking' on the system.

Yes, it's all about keeping the ripple on the DC rails as small as possible. Ripple on the rails equals higher THD (total harmonic distortion).

 

[wilbur]

Like other people have said, the 'one big vs many small' question is unanswerable without knowing the actual spec of the capacitors involved - it might be better, it might not, either way I doubt you'd see it in the arc.

But just to add further doubt and concern, you also should not hugely increase the amount of capacitance in the system beyond what it was designed for, in a 'more is always better' quest. That Scott Henion quote says the bigger caps increase the 'surge when the contactor turns on' - that's true, but it neglects another important issue which is that as you make the output smoother and smoother by increasing the capacitance, the rectifier diodes have to deliver the output power in a smaller and smaller fraction of the mains cycle. This means that their peak current gets higher as the capacitors get bigger, even though their average does not. I'm too lazy to draw the pictures to illustrate that, but I'm sure Googling 'rectifier conduction angle' will show something relevant.

There are lots of good Far Eastern (Japanese) brands of electrolytic cap, searching for British ones is almost certainly just giving yourself pain.

 

[GW8IZR]

This means that their peak current gets higher as the capacitors get bigger, even though their average does not.

Absolutely correct - its an unintended consequence of modifying a design, one bit of performance seems to improve but at an unseen cost to another component.

 

[normspanners]

Absolutely correct - its an unintended consequence of modifying a design, one bit of performance seems to improve but at an unseen cost to another component.

We are getting away from the original POST here,
The op has not changed the design capacitance, that is the same, so therefore the design is the same, apart from his connection array which has doubled I believe, So from my original statement that more caps is not a bad thing, having more smaller caps actually reduces the equivalent series resistance (ESR), by having more cables and connections to each cap to distribute the current and therefore heat, AS LONG as those connections are equivalent to the original design, which I doubt they are, after seeing the array used before, and now, the connections used to modify the system.

As I said originally it helps having more connections to try to emulate that array, to make the system efficient but the sum of those connections have to be equal to the original spec,
A similar capacitance single cap to do the same job would have to have truly HUGE connections to reliably handle the the expected current without burning itself or it's buzzrail .

To save yourself problems in the future it might be better to solder each, because the weak spot in most electrical systems is the actual connections not the component, it's usually the connection that goes on to damage the componant. IMO

 

[normspanners]

And...

Sorry I didnt reply to this and I assume it was a question as to why I showed the picture
it was in answer to your statement

They also don't have individual connections,

I think the photo proves that they do.

 

[normspanners]

Really interesting , so it needs someone who is a bona fida top dog welder to take a machine and rig it with various caps of differant sizes and ratings to see which is best ? my geuss would be you would find differant machines(plant) would be better with differant set ups,so surely if you replace with multiple and it works better,or indeed single and it works better, thats the point isnt it ,end result is all that matters .
Will bear it in mind if I change any in future thats for sure, my monies would be on multiples though!

I dont believe there will be any difference in the welding ability it is just the efficiency of that current transfer that makes a difference in the overall reliability of the system, IMO
but with a sound system which uses a similar array that difference can be 'heard' that is what has been explained to me.

 

[GW8IZR]

We are getting away from the original POST here,
The op has not changed the design capacitance, that is the same, so therefore the design is the same,

Ah but somewhere further up the thread there was a suggestion that adding more capacitance and changing the design on other welders would be worth trying, IMO thats dangerous territory particularly if the sugestion was followed by someone who didn't understand the design.

<snip> having more smaller caps actually reduces the equivalent series resistance (ESR),

<snip> So from my original statement that more caps is not a bad thing,

Its important that subsequent readers who may selectively choose the bits of information to read -


I've measured a lot of capacitors in my life and sorry but you are incorrect in saying that more caps will have a lower ESR, unless you know the actual capacitor specification.

Anyway thats my last on this as the OP has done the job and it should be fine.

 

[Rig Pig]

Thanks for the advice gents, next time I'm kicking my heels I'll solder the joints to save any heartache.

 

[GW8IZR]

Thanks for the advice gents, next time I'm kicking my heels I'll solder the joints to save any heartache.

Here is my 'other' last on this :-)

I was thinking about the heating effects of the current connected to the spiral while eating my boiled egg for lunch. It (the heat) is concentrated in the middle, with smaller caps there is less foil to connect too which means the current density is greater and the heat has less area to dissipate over, however the heat will be pretty much the inverse square of the current so reducing the current per capacitor, on balance, is probably better for reliability.