Polarised Solar DC Circuit Breakers - Reverse Polarity
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange answerers and commenters link it as a visual demonstration of why polarity matters on magnet-assisted DC breakers and what can go wrong when current flows the wrong way.
Recommended by 0 people across 0 different months, 2022 to 2024.
What it is
A short video from an Australian solar installer showing what happens when a polarised DC circuit breaker is wired with reverse polarity and switched off under load. It explains that such breakers were used as solar isolators in Australia until 2010 and demonstrates the arcing failure.
What people said
Cites Sampath Liyanage · 2022-05 · Electrical Engineering Stack Exchange · on “Safety of a polarized DC breaker between the battery and the inverter”
DC breakers use a magnet to blow the arc into the quenching channel. If the current is flowing in the wrong directly, the arc is pulled into the guts of the breaker and can cause the arc to be sustained and melt/start a fire inside the breaker (as I understand). demo: [this video] When we install polarized DC breakers in between the battery and the inverter, we consider the battery as the source and set the polarity accordingly. But, when the battery is charging, the direction of the current flow is reversed and the breaker becomes reversely polarized. The ideal solution would be using a non polarized DC breaker. My question is how safe is it to use a polarized breaker in this case?
Cites Harper - Reinstate Monica · 2022-05 · Electrical Engineering Stack Exchange · on “Battery capacity and parallel vs. series battery connections”
Why wire batteries in series vs parallel? Series means higher voltage and lower current. Lower current is good because it means dramatically thinner wire on long distances, especially at low voltage. 2x voltage means 1/2x current for the same useful power. 4x voltage means 1/4x current for same useful power. However, higher voltage means danger. DC voltage starts being rather feisty as voltage gets higher, so switching it becomes much more complicated and dangerous. 24V is manageable but 48V starts to get interesting. Like this [this video] and this [LINK] . Once DC starts arcing, it cannot be reasoned with, it does not know pity or remorse or fear and absolutely will not stop, ever, unless kille
Cites Harper - Reinstate Monica · 2022-05 · Electrical Engineering Stack Exchange · on “What type of power supply is best for low resistance experiments?”
You could use a constant-current power supply. These give constant current at a variable voltage. But the most useful aspect of them is they are inherently current limited - they cannot give more current than spec. So you aren't going to have problems with a dead short, which by the way can explode any battery and throw chemicals everywhere. In fact, with the early (and very dangerous) transformer-based constant current supplies, placing a dead short on them is a Code requirement to render them safe! (they would make exactly X amps at any voltage; if shorted that was 0 volts). However if given an open circuit, then voltage would go clear up to infinity and you got the kind of blood-and-gore
Cites Russell McMahon · 2022-11 · Electrical Engineering Stack Exchange · on “Safety of a polarized DC breaker between the battery and the inverter”
@SolarMike See this video : [this video] from the question. Regardless of WHY the arc may vause catastrophoc failure, it evidently does.
Cites Russell McMahon · 2022-11 · Electrical Engineering Stack Exchange · on “Safety of a polarized DC breaker between the battery and the inverter”
The concept is good as far as it goes. The implementation may not be. It may work and may not. The video cited above [this video] shows a breaker being destroyed by reverse current arcing. There will quite possibly be a range of conditions where the reverse breaker arc is ahead of the fwd breaker arc and current is possibly reduced to the point where the fowrad breaker dows not function. While that involves several "maybes" it is still conceivable and as the result could be devastating it should be considered with due care. NOTE: I did NOT downvote your answer.
Cites Harper - Reinstate Monica · 2023-07 · Electrical Engineering Stack Exchange · on “Combining 2 DC battery banks INTO A 120V 150A PANEL?”
OK, you're actually going to need to learn a lot more stuff for this project to actually happen. But this can be fun learning, hanging out on solar power, off-grid lifestyle and VanLife forums, reading and asking questions. Remember, learning is for life. (well OK, skills can be perishable, but once you get good at learning, "learning them back" is easy.) So here's the problem with your question on this forum. Right now, you have skill gaps so large that an answer would pretty much have to be a book. That's not allowed in this forum. However, you're perfectly keen on buying the expensive bits , and you're all signed on with the idea of having large batteries. Most people make bad choices the
Cites Spehro 'speff' Pefhany · 2024-11 · Electrical Engineering Stack Exchange · on “DC breakers does polarity really matter?”
Yes, it very much matters if you care about the breaker opening, the arc quenching and it not bursting into flames. Image from here [this video] [LINK] A permanent magnet is used to help quench the arc, and that makes it polarity-sensitive. The marking are confusing IMO. Check your manufacturer's data. Here [LINK] is one such information page: [LINK] Polarized breakers may be prohibited by code in some jurisdictions, not so much because they don't work safely, but because installers can be knuckleheads and not install according to instructions. For a bonus, here [LINK] is a teardown from famed Youtuber Big Clive.