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Home PowerDrive V2 - Germany ** 33+ kWh ** Big Power ++
#51
(06-03-2020, 10:08 PM)ajw22 Wrote: No particular recommendation for breakers from me.  But from my understanding, all DC breakers that have marked (+) and (-) terminals are probably not suitable for bi-directional DC current.

So while it may function correctly when the battery short circuits (stopping charger->battery current flow), it may fail when the charger short circuits ( battery->charger flow).
Or vice versa, depending on which device is wired to the top/bottom side of the breaker.
And it may just work fine if the voltage is low enough to not cause any major arcing issues in the first place.

I can't fully understand what you are saying. In the house electricity network I also have fuses that can do two ways and my car fuses can also do two ways. So far it is unknown to me that fuses only work in one direction.

Maybe others have an opinion about it. Would love to hear that the subject of security is important.

Huh
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#52
For home AC circuits, the arcing-on-trip problem is very small, because the voltage drops to zero every 100Hz/120Hz, at which point the arcing naturally dies off.

Polarity doesn't matter to DC Fuses - both ends are generally the same design.  But beware that fuses also have maximum voltage ratings, above which arcing can become an issue.


Here is a DC breaker from a very respected manufacturer.  "DANGER: Correct voltage polarity required"!
It's got the clearest diagram and markings I could find.  Most polarized DC breakers have similar, but far less clear markings.



My poor attempt at trying to illustrate the problem when connecting a battery with such a breaker.  The solar panel was perhaps a poor choice... imagine a charger or a hybrid inverter instead.
Normal operation: 



When there is a short circuit on the battery side, the breaker trips successfully, as it was designed to do.  So far so good.



But when there is a short circuit on the PV(/charger/hybrid inverter) side, things can get ugly.  The power is now at the bottom, and current through the breaker is now flowing in the wrong direction.  It's not designed to trip safely in this configuration, and could start to burning like in the YouTube video I posted earlier.




Here's another video showing the dangers of wiring a polarized DC breaker the wrong way.
https://www.youtube.com/watch?v=Cup5fMGaE2g

Now, personally, I assume that a polarized DC breaker rated for 600V will work correctly bi-directionally when running at less than 60V.  But nobody will guarantee that.
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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