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Russ 09-20-2009 10:31 PM

Electric cars and Power inverters
Random topic number 4:

In this electric car I'm trying to brain storm thru I'll need AC power for the occasional accessory. Specifically a laptop in my case. In my present GAS car I plug my little inverter into the cigarette lighter, and I get AC enough to run/charge the laptop. This is heavily dependent on the inverter. A brief search turns up inverters up to 3000 watts.

Clearly the devices I've seen mentioned to step down to 12V would work. I'll need one for the cigarette lighter. But am I wasting energy doing that? Would some other method of getting AC be more efficient?

I had assumed I'd be creating a DC vehicle but I'd certainly like to hear about AC motor options too as I'm trying to educate myself.

Perhaps I'm over-complicating things.


NiHaoMike 09-20-2009 11:21 PM

If the pack voltage range is between about 140 and 370, you can just use the existing laptop power supply.
PriUPS update 08 Jan 2006

Ryland 09-21-2009 12:08 AM

every time you add a step you get a loss, a/c motors tend to be more efficient because all motors in the end run off a/c, with a d/c motor it is being mechanically changed to a/c as the motor rotates, this is the job that the carbon brushes have, sad thing is carbon is not very conductive but it is used because it is self lubricating and wears well without welding it's self to to commutator or creating many other problems.
With an a/c brush less motor you do away with the brushes... of course and rely on the switching of the a/c, because the motor has to vary in speed you need an inverter that is designed for this, if you want to run a regular 120v motor in your electric car and run it off a/c it is going to get more complex and less efficient, granted I only described a few of the many options but if really, you just want to run your lap top off an electric car, get a d/c to d/c converter and a 12 volt cord for your lap top, it is basically going to be a switching power supply, pretty efficient.

NiHaoMike 09-21-2009 12:47 AM

If the pack voltage is between about 140 and 370, the existing laptop power supply will work as the DC/DC converter. And if it's a recent one, it will also be surprisingly efficient.

Just make sure to set cpufreq or whatever to use power saving even on external power. Power management is often limited on external power in order to increase performance. In particular, it takes a short time for the PMS* (Power Management System) to sense the increased load and a little more time for the PLL to adjust.

*PMS has been referred to as "power management stress" due to the annoyance of the clock adjustment lag. My solution is to use a KDE applet (PowerDevil or something like that) to manually change the power management setting. It defaults to aggressive power saving on battery, normal power saving on external power, and I can manually force full CPU speed when I need it.

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