What's wrong with my truck's power inverter?

September 11, 2004 3:03 PM

I have a Vector MAXXsst 225 Watt DC to AC power inverter that I run in my truck. Problem is, it keeps blowing the truck fuses... It's gotta be a short, right? What am I missing?
posted by ajpresto to travel & transportation (5 comments total)

The inverter is drawing more current than the fused circuit allows, perhaps?

Does it plug into the cigarette lighter?
posted by Kwantsar at 3:35 PM on September 11, 2004

225 watts = 18.75 amps @ 12 volts. Assuming it's about 80% efficient (it'd have to be pretty good for that), it will draw about 280 watts at full load, and perhaps 400 watts at peak. That's an actual draw of 23 1/3 Amps steady (maximum) and 33 1/3 Amps (surge).

Your cigarette lighter socket is going to be fused at about 10, maybe 15 amps. 20 amps if you're really lucky. Very few circuits in your car that you would be willing to hook this device up to will be good for over 23 Amps.

There's your problem. Try wiring it through a larger fuse (say... 30 Amp, or, better yet, 25 Amp slow blow) directly to your battery. An on/off switch would be a good idea too. To keep power dissipation in the wire reasonable, you should use wire as thick as, or thicker than, 10 AWG in this case. That will drop 0.36 volts at full load and dissipate 8 watts of heat energy. Thinner wire, all the way up to 18 AWG will work, but the wire will get hot, and that could (will) mean bad things. Here's an AWG table for reference. 20 AWG wire and thinner will cause a voltage drop low enough to stop your inverter from working.

Your alternator shouldn't have a problem with the load.
posted by shepd at 4:22 PM on September 11, 2004

Yes, it plugs into the cigarette lighter.

So, my question is, why isn't it stepped down or something? Why would they sell something (and this is on the low end of these things, FWIW) that would blow out fuses?
posted by ajpresto at 3:23 AM on September 12, 2004

>Why would they sell something (and this is on the low end of these things, FWIW) that would blow out fuses?

Because people will buy it? :-D

Some vehicles have more "powerful" cigarette lighter sockets than others. It's all caveat emptor and "check your lighter socket first", you know.

All of the 300+ Watt inverters I've seen sold had battery clips and battery cables...

>So, my question is, why isn't it stepped down or something?

You mean like giving a lower output voltage when the load is too high...

That's not going to work all that well. :-)
posted by shepd at 3:38 AM on September 12, 2004

also, ajpresto, you may be able to find a custom auto electric shop that will either rewire the cigarette lighter with a heavier gauge wire or create a new socket with a fusible link.

As to why they would sell it (no need for a conspiracy), I've seen full-size trucks that have cigarette-lighter style power ports fused with 30A fuses.
posted by Kwantsar at 9:46 AM on September 12, 2004