OEM Inverter 400watts vs Cobra CPI880 800watts

Recently purchased, a Rigid Vacuum from home depot. (http://www.homedepot.com/p/RIDGID-3...ERCH=RV-_-rv_homepage_rr-_-NA-_-202078667-_-N)
Rated at 7 amps.

When plugged into OEM inverter.(2012 DoubleCab TRD OffRd Towing)
400Watts enabled, the vacuum turns on and operated fine.

Meanwhile when hooked up to a Cobra CPI880(800 continuous watts, peak 1600)
The vacuum would only turn on for half a second before tripping the inverters shutdown. When I leave the vacuum on it cycles on and off every few seconds. The Cobra is hooked up directly to the battery alligator clips and the truck is running.

 

That is interesting. If the motor indeed draws 7 amps, you are grossly overstressing the OEM inverter. Motors typically draw more current when starting (2 to 3 times normal run current is typical, as I recall). The Cobra inverter is acting like I would expect with such an overload.

 

Right. 7 amps at 120vac = 840 watts continuous draw. more than the OEM produces by a factor of 2. And barely more than the 800w inverter. Must have a pretty sensitive over-current circuit. Either one is really below what you need for that motor.

 

Agreed, I understand why the aftermarket inverter wouldn't function. But why would the OEM inverter work. Does anyone really know it's power rating? Because it's definitely not 400watts.

 

Tough to answer. They obviously rate things conservatively to avoid problems. And probably to keep your battery hot enough to get you home. 400 watts is a constant 30 amp draw. That can flatten your battery in 3-4 hours with no problems. 400 watts is chickenfeed at 120volts, but it is 30 amps (assuming 100% inverter efficiency, when it is more like 80% in reality, 400 watts / 12v =30+ amps).

Beware however. That thing is in a bad place. I had one I used to power my computer on long trips. It physically burned up as in melting the case and smoking like crazy, with no warning. That inverter, buried in the bottom of the console, is not something you want to flame up.