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I'm hard wiring an inverter into my automobile. Tapping into a 15a fuse in the fuse box. To hard wire it I had to remove the "cigarette plug" and in so doing removed a 12a fuse. I have an inline fuse connector which only takes "bladed" automotive fuses and none of them appear to be 12a, everything I see online for this type of fuse seems to go from 10a to 15a. And I am having a very hard time finding simple 12a inline fuses designed for 12v systems and 12g wire.

So, can I replace the 12a "cigarette lighter" connector fuse with a 15a inline fuse? Or could this endanger the inverter, since it's designed to be protected with a smaller fuse?

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  • \$\begingroup\$ What is the surge current on the inverter? and VA rating? It might be not enough \$\endgroup\$ Dec 13 '19 at 20:58
  • \$\begingroup\$ 12Amps? To an inverter? I hope it is a very small inverter. I am sure you can find a 12A inline fuse at digikey or mouser or a similar place in the country where you live (if it is not the US). I just looked and found dozens of 3AG type fuses with DC rating at digikey. \$\endgroup\$
    – mkeith
    Dec 14 '19 at 5:08
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Never replace a fuse with one rated for a higher current. If you can't find a 12A fuse try a 10A fuse.

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The fuses are to protect the wiring, not the downstream devices. In the case of an electrical fault, you want the fuse to melt before the wiring does :)

If the device is taking more current than it was designed for, the damage has already been done.

If you are sure that all the circuit wiring is #12AWG (on either side of the fuse), and you're sure that the wiring connectors and harnesses are rated for 15A, then you could feel safe about increasing the fuse size. I personally wouldn't take the chance that I had missed something.

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It's your car, but the whole point of fuses is to protect the wiring in the car. If this were wiring in a house or structure, I'd be standing on the table yelling. But I'll stand down since you're likely to confine the damage to the car itself. But still, melting a fuse block or wiring harness sucks.

I would either get a tube-type fuse holder (which are cheap), or downfuse to 10A.

Your better plan, really, is to install a dedicated circuit for that inverter, with a better plug than a cigarette lighter. That way you can pull more than 100 watts. Try coming off an appropriate (provided) high-amperage hot-in-run terminal on your car. (or from an always-hot terminal via a relay whose coil is hot-in-run).

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