How to calculate what mega fuse size you need in your van

Written By Bella Macchina

To determine the appropriate mega fuse size for your 200Ah GEL battery running a 2500W inverter, you need to calculate the maximum current draw and apply a safety margin.

1. Determine Current Draw

First, assume the lowest system voltage to be conservative - for example:

  • System voltage: 12V

  • Power: 2500W

  • Current = Power / Voltage = 2500W / 12V = ~208 Amps

2. Add a Safety Margin

Fuses should typically be rated at 125% of the maximum continuous current to avoid nuisance blowing:

• 208A × 1.25 = ~260A

3. Final Fuse Recommendation

V Install a 250A or 300A mega fuse

  • 250A is okay if your inverter has a soft start and you don't expect big surges.

  • 300A is safer to handle startup surge current.

Make sure your battery cables and lugs are rated for this current - 2/0 AWG or larger for these

amperages at 12V.

Bella Macchina
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