Electrical – Circuit to detect broken fuse

detectionfusessensor

Consider the following circuit:

Edited schematic with further information
[edited schematic]

DC_gen1 and DC_gen2 are two +28V dc ideal generators. Fuse is real component and it has a finite and small resistance (0.1 Ohm for instance).

I need to design a Sense circuit that detects that the fuse is broken. I have already considered a few possibilities:

  • A differential amplifier could sense a voltage across the fuse. Anyway, since the two generators have the same voltage, no current is flowing through the fuse and therefore there is no voltage drop on it.
  • A galvanically isolated power supply could inject a current in A point to B point to create a voltage drop across the fuse. Anyway, the injected current would flow through DC_gen1, ground and DC_gen2, and therefore no voltage drop would be createdo on the fuse.

Can you please suggest how to sense the broken fuse?

EDIT:
Following comments, I edited the circuit to add details:

  • The two generators are connected through a long power cable; the purpose of the fuse is to protect DC_gen2 from short circuits on the cable itself. DC_gen1 already implements its own protection so no fuse is required.

  • Due to physical constraints, the sense circuit must connect next to the fuse, at point A and B.

Best Answer

Banish your anxiety and shed your stress. Use a miniature circuit breaker with auxiliary contact.

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Figure 1. MCB with NO and NC auxiliary contacts.

Monitor the auxiliary contacts and enjoy the benefits of complete isolation of your monitoring circuit and the 28 V power. Fixing the fault is a matter of resetting the breaker. No fuse to stock.

Note that you'll need a DC-rated MCB. (The one in the photo is AC, I suspect.)