If they operate (satisfactorily) with DC, then the voltage of the circuit is obviously irrelevant - a SP MCB knows only about current, and hasn't a clue as to what voltages exist within the circuit.
Kind Regards, John
12v system
- Thread starter Maybedaisy
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Kind Regards, John
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In some MCBs ( so I am told ) the use of AC creates a slight vibration in the mechanism which is an "essential" part of the tripping action.
Others use a current transformer and these will NOT work at all on DC
Some years ago the magnetic over protection devices used in electronic equipment were either DC or AC and not interchangable. Using the wrong type meant it would not operate at its rated current.
Have you looked at a vehicle type fuse box for your distribution "board" ? These are designed for blade fuses and some fit on the battery terminal making a very compact fuse board with terminals for charging leads and supply leads.
Others use a current transformer and these will NOT work at all on DC
Some years ago the magnetic over protection devices used in electronic equipment were either DC or AC and not interchangable. Using the wrong type meant it would not operate at its rated current.
Have you looked at a vehicle type fuse box for your distribution "board" ? These are designed for blade fuses and some fit on the battery terminal making a very compact fuse board with terminals for charging leads and supply leads.
I think it is virtually inevitable that any electro-mechanical device which trips at a current of X amps DC will trip at some AC current other than X amps RMS (which is what we normally think in terms of). If the AC were extremely low frequency, or were square wave (or some other waveform which was close to peak for a substantial portion of the cycle), then I would expect it to trip roughly when the peak current of the AC corresponded to the DC trip current. With sine wave AC, however, I don't really know what the trip current would be. I might guess that it might trip when the average (about 64% of peak) current corresponded to the DC trip current, but that may well be wrong. It certainly unlikely to be related to RMS, since that is a concept used because of its relevance to power, not generation of an electric field.
Kind Regards, John
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Also, don't forget that the contacts inside a regular breaker will not be designed to break a DC current.
Yes, I thought of that, and it's well illustrated by the range of MCBs to which you linked, many of which talk of much lower DC voltage 'ratings' than AC ones. Having said that, a standard MCB is capable of breaking at least 6kA (if not 10kA or 15kA) of AC current, so I imagine that it would probably be able to break a reasonably high DC current.
Kind Regards, John
Breaking DC current requires that the contacts are separated far enough to break the arc rapidly, or magnets can be fitted to bend the arc to extend its length beyond the sustain distance.
With AC the arc goes out when the current goes to zero as the voltage goes through the zero crossing point.
With AC the arc goes out when the current goes to zero as the voltage goes through the zero crossing point.
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