How do I wire in power inverter?

[jjones0377]

I want a 400w power inverter for our 2012 edge. Will probat never Max it out. What is the best way to run the power source to the inverter? I want it to come on and off with the ignition. And my Ford Explorer I installed a toggle switch for a power inverter. I do not want a toggle switch for this one. Would rather have it switched with the ignition. Is it okay to use a switched to use in the fuse box with a 20 amp fuse?

[TheWizard]

Install a relay. The relay is basically an electronic switch that switches a high power circuit on and off under the control of a low power circuit. They are quite inexpensive ($5 - $10) and available from any auto parts store and even Walmart (as well as countless online vendors). You connect the main power of the inverter through the relay to the battery and then connect the relay switching coil to an ignition-switched circuit from the fuse box. The current draw of the relay on the ignition-switched circuit is very small so you don't risk overloading a factory circuit.

 

That will give you an inverter that gets its power directly from the battery but is switched on and off by the ignition.

Edited November 4, 2014 by TheWizard

[akirby]

And that's the ONLY safe way to do it.

[Depiry]

A 400 watt inverter will draw about 33.33 amps at fulloutput it needs at least 30 amp relay,and fuse off the battery if you dont intend to use it at full output, as the wizard says thats your best hook up,

a Bosch relay rated at 30 amps should work well,Marty

Edited November 5, 2014 by Depiry

[jjones0377]

Does my fuse need to be rated at 30amps too? I'm assuming so

[akirby]

The fuse is based on the wire size. Since your inverter could potentially pull 33 amps I'd use a 35 amp fuse and 8 gauge copper wire. 10 gauge wire would require a 30 amp fuse but the fuse would blow if you maxed out the inverter.

[TheWizard]

Fuses don't protect electrical accessories - they protect your car from burning to the ground. Electrical circuits don't push power through the accessory or device, the device draws whatever power it needs from the circuit. Fuses are not there to protect a device from drawing too much current because if it does, it's already broken. Fuses are there to make sure they don't allow more current to be drawn by the device (or by a short circuit) than the wire can handle. The idea is that the fuse will blow and stop current flow before it can cause the wiring to overheat and possibly cause a disastrous fire.

 

So that means you want to select a fuse that is rated at less than the amount of current the connecting wire can safely handle. You also want to select a large enough gauge of wire that can safely pass the amount of current expected to be drawn by the device - in this case about 30 amps for the inverter. An extreme example would be to use a 30 amp fuse (because the inverter might draw that much current) connected with 18-gauge speaker wire. Normal operation would allow the inverter to draw up to 30 amps (actually 33 amps due to normal fuse tolerance) without blowing the fuse but that small wire would quickly overheat, melt its insulation and possibly start a fire if it was touching something flammable.

 

What you want to do is connect the relay using at least 10-gauge wire (8-gauge would be even better especially if the wire is long) and a 30-amp fuse or fusible link. A normal ATO or ATC 30-amp fuse will run 33 amps for up to an hour before blowing so unless you max the inverter for an extended period, you shouldn't find yourself blowing fuses.

 

You should also get a 40-amp relay because Bosch-style NO (normally open) relays rated at a nominal 30-amps aren't designed to carry that current for long periods (their NC - normally closed - rating is even lower). A 40-amp relay won't cost much more but will last much longer.

Edited November 5, 2014 by TheWizard