Suitability of "CBB15" Welder Capacitors for Pulsed Applications

[Benbmw]

Hello,

I am curious if anyone has experience with these Chinese made "CBB15" welder capacitors for pulsed applications. They have nice lug terminals which bodes well for their current handling capability and they are at a nice price point for fairly high voltage unpolarized capacitors. I might buy a few and could do some testing to destruction if folks think they could be promising.

https://www.ebay.com/itm/192586693166?chn=ps&mkevt=1&mkcid=28&var=493995973465

[Twospoons]

The longevity in pulse applications has little to do with the size of the terminal, and a lot more to do with the construction of the attachment to the metalized film inside.  This attachment is the failure point, which I know from experience building electric fence energisers.
Realistically you wont know if they're any good until you try them, unless you can contact the manufacturer for advice.

[Benbmw]

The longevity in pulse applications has little to do with the size of the terminal, and a lot more to do with the construction of the attachment to the metalized film inside.

Fair point, although I am hoping that the end terminal, along with the general geometry of the capacitor, is somewhat of a proxy for:

1. The intended current
2. The construction method

The cylindrical shape and axial connections indicates a fairly direct connection from the terminals to the end spray on the metalized polypropylene roll inside. Which is preferred to something like this which would have more complex internal connections:


Like you say, the only real way to know is to test!

-Ben

[Twospoons]

The failure point is between the film metallization and the metal spray. Excess current appears to burn away the metallization.  I had some 20uF 1200V pulse capacitors that showed this failure mode after a week of abuse at one pulse every 1.5 seconds. Could have failed earlier, I wasn't keeping a close eye on the test.  This was operating within the published I²t rating of the caps - but that rating was only for 20ms half sine, not for the 100us pulses I was doing.

[Benbmw]

The failure point is between the film metallization and the metal spray. Excess current appears to burn away the metallization.

I see, that is good to know. Thanks for sharing your experience!

-Ben

[Mads Barnkob]

Be careful with any kind of capacitor, that does not have any specifications! No current ratings, no derating information, no heat loss information and not a single datasheet in sight.

Compare them to the Chinese "cheap" Dawncap and you can see that they are way cheaper than the cheap-but-still-good-from-china products.

One of the parameters killing most capacitors in pulse operation, is the reverse-voltage capability. If you have a inductive load, that is not exploded open circuit, you will have a large negative reverse voltage from the inductive ring down, which can kill even a good pulse Maxwell capacitor.

You would be better off with building your own capacitor bank from a cheap bulk auction like these 23x 40uF/900V caps: https://www.ebay.com/itm/403432601273?hash=item5dee74f6b9:g:ydAAAOSwMtxXtF-q