Experiment: How much power can the 12V system produce?

[tmorrowus]

I just did some experiments with the Prius 12V system, and indirectly I think I discovered a ballpark experimental answer to how much power the prius 12V system can produce to power aftermarket accessories.

Here's what I did: I connected a 12V->120V inverter (300w continuous, 800w "surge") directly to the 12V battery. Into the inverter I plugged a Wattsup (Kill-a-watt) electrical power meter, and plugged a 500W halogen light with dimmer into that. The Wattsup let me see how many watts were actually being delivered into the lamp.

I turned the dimmer slowly up with the Prius in "Ready", and right when the Wattsup said 275 to 280 watts, the 12V system voltage dropped below the 10.5V that causes the inverter to turn off (I verified independently with a voltmeter to make sure this was the car's limitation rather than that of the inverter). This was totally repeatable; every time I tried it, it petered out in that 275-280 range.

Now the 12V->120V inverter itself is probably not completely efficient, so the actual amount of power the car was delivering was more than 275 Watts, probably in the ballpark of the 400 Watts that has been previously estimated.

On another note, my wattsup meter died in the middle of this experiment, so don't try this at home. I'm still not sure exactly why it died.

[tochatihu]

If the outboard inverter you used produces modified sine wave power, then this experiment may not give accurate results, and might have damaged the wattsup.

For the 12 volt line dropping to 10.5, I must wonder if the connections to the battery were adequate. Small resistances matter a lot with high power at low voltage.

[tmorrowus]

The voltage drop when the system was pushed to the limits was a sudden and dramatic drop off a shelf, not a gradual fall off, so I'm confident it wasn't a result of resistance.

[Presto]

I'm confident that the 12V system can produce at least 1000 watts sustained, without breaking a sweat. I can never remember who, but there's a PC member running 1500 watts without any problems. I've been running ~600 watts for the last few years without any problems. Voltage stays at a solid 13.9V when the music is blasting with the car in READY mode.

[tochatihu]

We certainly want to make sure there is not something wrong causing your Prius to be different from others that have been tapped for big watts from the 12 volt system.

You know about the voltage sensing line that runs from battery to the DC/DC converter, yes? Everything OK there?

Maybe you could post some pictures of the setup. And again, is the inverter modified sine wave? MSW into a triac dimmer might not be such a good idea.

[wlai]

I noticed that, when plugged into the center console outlet, that my inverter sounds an alarm when the ignition is on ACC mode, but is fine if engine is running. It's a Xantrex Xpower 400, a Modified Sine Wave inverter.

Any one knows if this is a limitation of the center console outlet vs. the one under the glove box?