Calculating Inverter Wattage Needed

**brucedog** · 01-11-2008, 07:33 AM

Hi All,

I have a Compaq SR5350F desktop that I plan to install in the cargo compt. in my Saturn wagon.

I opened the PC; it has a 250 psu. I chatted online with a Compaq tech; he says a 250 watt 12 vdc to 120 vac inverter will be ok...

But, looking at the nameplate near the ac cord on the Compaq, it says "120 volts, 6 amps." If one does the basic (dc) calc P = I*E, then:

P = 6 x 120
P = 720 watts.

Could someone correct me or comment on my thought process here?

By the way, I am aware that I would be converting from dc to ac to dc...
...and that inverters can be noisy, and that I may be using a lot of power, and of the existance of the Opus 320 w psu... Butr for now, I would like to play with getting this project up probably using an inverter.

**DarquePervert** · 01-11-2008, 08:28 AM

The general rule for inverters is to use one rated for 1.5 to 2 times the output rating of your PSU.
for your compaq, 375-500w woudl be sufficient.

Understand that inverters have their own set of issues. Most folks will recommend a DC-DC power supply over an inverter any day of the week. They cost more, but are decidedly worth it!

**brucedog** · 01-11-2008, 12:24 PM

Thanks, Darque

I read your usually helpful posts regularly.

I'll continue to post to update (as follows)

>I'm currently ripping my cd's into Compaq as .wav files; adequate for what my amps can reproduce
>Installing programs such as Office, Street Deck, Griffin volume ctl., etc, etc driver
>Installed bluetooth dongle for when on the road
>Installed PCI wireless card for at home and for getting on networks where I can...
>Ruggedizing case baseplate for vibration damping and stability

More to come on appropriate projects, etc forums..

**MatrixPC** · 01-11-2008, 06:40 PM

Depend on the inverter you buy, some can do a decent job while saving money for a DC-DC PSU. Just shop around for an inverter than can still function for a short time while voltage drop during cranking.
So basically, you have to find out how low voltage drop while cranking and get an inverter that work at least at that voltage for short period.
But I think you better off just not buying it and start saving for a DSATX or Opus 250. You can get a used DSATX some time for sale for about 125-150 in the classify section.

**brucedog** · 01-11-2008, 09:30 PM

Thanks Matrix,

Yep, you watch this newbie. I'll use the inverter for however long, dicover it's latent deficiencies for myself, then in a few months convert to a dsatx, opus or some such - and become one of the stauchest and loudest supporters of 'em!!

...but for now, it's a lot of fun - this learning and growing phase...

Thanks. CU in the forums.

**crzyjoker13** · 01-13-2008, 08:18 PM

simple befor you buy your inverter check to see how many amps it will put out and not the max they usally have two rateings one for countinous and one for surge or max, which is momentary.