In-Rush Current - Why Add Fuses Before Outputs

WARNING:  In-rush current can damage outputs.

Care needs to be taken as blowing outputs in this way is not covered by warranty.  

Any DC-DC should always be added prior to the power on the WatchMon and not after the output.

The output mosfet's from the supervisor cannot handle a large inrush surge current when first switching on the load ( fan). We had designed it with the view of small loads. The typical inrush current is 4X times the rating far beyond the capability of the supervisor. Whilst the surge is only for micro/milliseconds its still too much for too long for the FET's.

By adding the fusing, you prevent these surges causing damage and it protects your WatchMon.

Ratings of Outputs for Various Boards

WatchMon CORE

  • 1 relay outputs (5A/30VDC)

Expansion Board 3

  • 3 relay outputs (5A/30VDC)
  • 3 Solid State relay outputs  (5A/65VDC)

WatchMon 4

  • 2 digital switched mosfet outputs (3A/48V)


  • 2 digital switched mosfet outputs (3A/48V)

Expansion Board 12V

  • 6 digital switched mosfet outputs 4A (switched +ve 12v)
  • 4 relay outputs (30Vdc 5A) cont (10A peak)

Expansion Board 48V

  • 6 digital switched mosfet outputs 1.5A (switched +ve 48v)
  • 4 relay outputs (30Vdc 5A) cont (10A peak)

Expansion Board 2

  • 2 relay outputs 5A/30VDC
  • 2 Solid State relay outputs  2A/60VDC
  • 6 digital switched mosfet outputs (3A/48V)
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