Are microinverters really more reliable than large single inverters?

[Siwastaja]

there is no physical mechanism I'm aware of that is able to reduce the stress.

Bending PCBs crack MLCCs, potted PCBs don't bend easily.

Except when the internal stresses formed during curing, and simply different thermal coeffs of expansion, cause the potted assembly to bend more than a non-potted one.

[Kjelt]

https://www.solar-outlet.nl/solaredge-p401-power-optimizer.html
You might be right that it increased in price. I just don't like companies that overcharge customers.

I read that the P type optimizers from SE caused serious radio interference, the german Veron took action.

[tszaboo]

The problem is, when you assume that others know what they are doing, even if that assumption is true, you don't know why they are doing that. Your Occam's razor completely ignores all technical details, and details matter. The assumption they do it for MLCC cracking prevention is completely your invention and not explained by the billion dollar-ness of the company at all. I'm merely saying I don't share this assumption. I bet the potting is to hold the heavy inductors in place plus protect against moisture, simple as that.

The reason I am posting this is because I have seen reports on this forum and elsewhere, where adding a potting has caused significant levels of MLCC cracking failures. This is why I don't believe anyone tries to use potting to solve MLCC failures.

I talked with some potting compound experts, who actually encountered with the problem in the past. Stuff failing because a metal enclosure was used as the potting base, 100% filled. Then the thermal expansion was directed into the board. That's not how these are made, there is a separate block of potted electronics that is then fitted into the enclosure. If you make the PCB thicker, it will bend less. Similarly, if you pot it in a few cm of resin or urethane, it will bend less, and cracking will be lesser of a problem.
So I'm saying this, because it coincides with the info I get from the experts.

[Marco]

simply different thermal coeffs of expansion

If the potting has strong adhesion a thick rigid layer of it just wins, the PCB will have to expand/contract in thickness cause it isn't going to bend the potting. The tail does not wag the dog.

[Siwastaja]

simply different thermal coeffs of expansion

If the potting has strong adhesion a thick rigid layer of it just wins, the PCB will have to expand/contract in thickness cause it isn't going to bend the potting. The tail does not wag the dog.

Yes, and imagine the forces involved in making the resin "win". FR4 can take this no problem. Now apply this force to the MLCC body. Board did not flex, but MLCC failed anyway. This is why MLCC-compatible potting compounds are not that hard, they need to be somewhat flexible, reducing the forces. But the problem is here: MLCC bodies are surprisingly sensitive, even small forces from soft compounds are risky. This is why this shit is actually designed and evaluated by very experienced people.

I'm no expert on choosing the potting compounds, but I know enough to know it is far from trivial and have read stories of smaller companies wasting years with poor initial assumptions. Personally I just sidestep whenever possible, mounting heavy components using silicone or other types of glue, instructing sealed enclosures, possibly with a silica gel bag strapped inside.

I have also read about using a very soft intermediate layer just on the top of shear sensitive components (MLCCs), around which hard potting compound can be used. For small MLCC sizes, bog standard conformal coating alone might be enough, but small packages are lesser of a problem anyway.

I talked with some potting compound experts, who actually encountered with the problem in the past. Stuff failing because a metal enclosure was used as the potting base, 100% filled. Then the thermal expansion was directed into the board. That's not how these are made, there is a separate block of potted electronics that is then fitted into the enclosure. If you make the PCB thicker, it will bend less. Similarly, if you pot it in a few cm of resin or urethane, it will bend less, and cracking will be lesser of a problem.
So I'm saying this, because it coincides with the info I get from the experts.

Now I totally agree with this. Your story made full 180 degrees from: potting is used to reduce cracking, to: with correct potting, cracking [caused by potting] can be "lesser of a problem", exactly my original point.

[Siwastaja]

I read that the P type optimizers from SE caused serious radio interference, the german Veron took action.

I head from a local installer of SolarEdge that they have been banned in Sweden due to emissions interfering with some radio networks used by authorities. Don't know if this is true, so consider it a rumor.

EDIT: I can use Google! https://www.pv-magazine.com/2021/12/23/solaredge-growatt-found-in-breach-of-swedish-electromagnetic-rules-some-products-banned-from-sale/

[bdunham7]

I'm no expert on choosing the potting compounds, but I know enough to know it is far from trivial and have read stories of smaller companies wasting years with poor initial assumptions. Personally I just sidestep whenever possible, mounting heavy components using silicone or other types of glue, instructing sealed enclosures, possibly with a silica gel bag strapped inside.

I haven't done a study and can't claim causation from correlation, but in the specific field of automotive engine controllers the failure rate of potted types seemed to be much, much higher during the time that they were widely used.