Polymer aluminium vs traditional electrolytic caps

[fryingpan]

Polymer caps promise much longer lifespans and somewhat greater linearity, with the drawback of higher leakage currents. Can they effectively replace electrolytics in most applications?

[Bunkey]

https://www.rs-online.com/designspark/aluminum-electrolytic-vs-aluminum-polymer-capacitor-and-how-its-benefits-are-used-properly

Seems to be the case but the implication is that the leakage current is less favourable for battery powered devices as it will contribute to draining the battery when used for decoupling / supply filtering. A typical leakage value for a single cap looks looks to be in the region >500uA, which is more than some classic circuits in their entirity, so yes a few of these in a more complex pedal is going to munch the battery somewhat.

Might be an interesting choice for large-value stage coupling and AC bypass though.

[fryingpan]

The fact that there is some leakage doesn't negate the cap's decoupling effects?

[Rob Strand]

The fact that there is some leakage doesn't negate the cap's decoupling effects?

It's not related.  The ability to decouple is the impedance.   The polymer "electros" have a very low impedance
better than standard electrolytic.   Given it's fairly new technology you will find a lot of articles on the web.

One thing though, a lot of power supplies required a certain range of capacitor ESR to remain stable.  If
you take an existing power supply design and substitute a polymer cap in place of an electro you could
be in for a nasty surprise because the power supply could become unstable (ie. oscillate).   One way
around that is to add a series resistance (!), so you gain the reliability of the polymer cap without affecting
the design.

The leakage issue is a good point as well.

[amptramp]

It sounds like you are looking at these:

https://industrial.panasonic.com/ww/products/capacitors/polymer-capacitors/os-con

They have some application notes there including one where they don't know how to spell "summary".

[phasetrans]

Polymer caps promise much longer lifespans and somewhat greater linearity, with the drawback of higher leakage currents. Can they effectively replace electrolytics in most applications?

For high temperature, long life applications, they are a substantial improvement. We used them in high performance LED drivers.