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Old 03-18-2008, 08:19 PM   #1
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Inverter Died

I hooked up a 400 watt inverter to run my laptop. The inverter did not last long. The laptop is a big one and draws ~ 7.5 amps. Per my after the fact calculation, thats almost 900 watts.
My son has a low power utilization laptop, but, it still draws 3.48 amp. Which I guess would be 400 watts at 115V. (amps X Volts =watts.) Is anyone successfully running good laptops on this size inverter or smaller?

Tom
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Old 03-18-2008, 08:21 PM   #2
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Quote:
Originally Posted by henw
I hooked up a 400 watt inverter to run my laptop. The inverter did not last long. The laptop is a big one and draws ~ 7.5 amps. Per my after the fact calculation, thats almost 900 watts.
My son has a low power utilization laptop, but, it still draws 3.48 amp. Which I guess would be 400 watts at 115V. (amps X Volts =watts.) Is anyone successfully running good laptops on this size inverter or smaller?

Tom
Tom,

I use a 12V DC cord directly from a power outlet on my laptop.

Bill
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Old 03-18-2008, 08:42 PM   #3
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"I use a 12V DC cord directly from a power outlet on my laptop."

Mine is actually 19.5 volts. Adapter built into cord. So i don't think I have a direct connect option. What confuses me is the difference in voltage and amps going into the adapter vs that going out from the adapter to the computer.

Tom
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Old 03-18-2008, 08:45 PM   #4
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Quote:
Originally Posted by henw
"I use a 12V DC cord directly from a power outlet on my laptop."

Mine is actually 19.5 volts. Adapter built into cord. So i don't think I have a direct connect option. What confuses me is the difference in voltage and amps going into the adapter vs that going out from the adapter to the computer.

Tom
Tom,

The 12V cord runs through the same transformer box at the 110V line. It must change the incoming voltage to match whatever the laptop needs. I have a Dell.

Bill
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Old 03-18-2008, 08:49 PM   #5
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That's a HUGE laptop! My P4 2.4 gigahertz with a widescreen 15" LCD only draws 1.6 amps at 120 volts.

Are you sure that's not 7.5 amps at a lower DC voltage? Mine draws 6.3 amps at 19 volts. 6.3 amps * 19 volts = 119.7 watts which is about 1 amp at 120 volts, which reasonably agrees with the inverter input I mentioned above if you factor in some inverter losses.

In any case, I think a better solution - if less flexible - is a DC-DC adaptor. I bought one on eBay for my laptop for like $30, and it also has the airline power adaptor. Unfortunately it does require a convenient 12 volt power outlet, and mine doesn't have a very long cord.
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Old 03-18-2008, 11:02 PM   #6
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Quote:
Originally Posted by henw
I hooked up a 400 watt inverter to run my laptop. The inverter did not last long. The laptop is a big one and draws ~ 7.5 amps. Per my after the fact calculation, thats almost 900 watts.
My son has a low power utilization laptop, but, it still draws 3.48 amp. Which I guess would be 400 watts at 115V. (amps X Volts =watts.) Is anyone successfully running good laptops on this size inverter or smaller?

Tom
Tom,
Something is wrong here. My desktop which has fast(read lots of pwer required) dual processors does not draw that much power. The UPS reports everything including the external drive enclosure to be less than 500W. 900W for a laptop is a LOT. How old is the thing?
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Old 03-18-2008, 11:05 PM   #7
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Targus makes laptop chargers that plug into a 12V cigarette lighter. They are smart adaptors. When you use the plug-in tip for your laptop, the output voltage should be correct. For my Toshiba, the output is 15v, 5amps. I don't know how it knows, but it knows.
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Old 03-19-2008, 04:50 AM   #8
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My laptop is a big Dell XPS. It uses 7.7 amps at 19.5 volts. The adapter is 150 watt, 2.5 amps, 115 volts in.

I'm wondering what the inverter sees out of this.
It claimed 320 watt sustained output with 3.48 amps.
Somehow the laptop load alone killed it after just a few seconds.

Tom
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Old 03-19-2008, 10:23 AM   #9
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Wow, that's a monster of a laptop. Personally, mine only runs at 65W max, more like 45W in practice. I use a 95W inverter with no problems. How do I know this? I use the Kill-A-Watt meter to measure consumption of devices around the home. This would be perfect for your trailer as well, since it measures line voltage, power factor, etc.

Take a look: P3 - Kill A Watt
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Old 03-19-2008, 02:23 PM   #10
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hi henw...

what brand and model inverter?

perhaps the inverter unit was/is defective.

most laptops are in the 100w range or less. mine are 85w and 90w.

and using a 150 or 175 w inverter i've had NO issues.

one other thought and i've not a clue if this is relevant...

was the laptop battery already DRAINED while u were using it?

in other words, IF the battery was charging AND the laptop was running...

would that bump up the energy consumption to nearly double?

cheers
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Old 03-19-2008, 04:35 PM   #11
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Did you try it more than once?

Quote:
Originally Posted by henw
... Somehow the laptop load alone killed it after just a few seconds.
The startup surge may have overwhelmed your inverter. I had a similar thing happen once with a small television.

The inverter's self-protection circuitry shut down the show.

Try plugging it in a few times. If the inverter's fuse does not blow, you are dealing with a startup surge. If the fuse blows, your laptop is, somwhat surprisingly, drawing too much current or the inverter is faulty.

Tom
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Old 03-19-2008, 10:58 PM   #12
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Quote:
Originally Posted by henw
My laptop is a big Dell XPS. It uses 7.7 amps at 19.5 volts. The adapter is 150 watt, 2.5 amps, 115 volts in.

I'm wondering what the inverter sees out of this.
It claimed 320 watt sustained output with 3.48 amps.
Somehow the laptop load alone killed it after just a few seconds.

Tom
Tom it is very likely that the high speed switching network used in the relatively low cost inverters didn't like or was not compatible with the high speed switching network in the 120 volt to 19.6 volt power supply for the laptop. We had the same thing happen using a 400 watt inverter on our flat panel TV. Many of the cheaper inverters, our was a 350 pr 400 watt Vector capable of peak load of either 700 or 800. Guess it couldn't handle a 40 watt flat panel TV!

I bought a higher quality inverter only rated for 175 wattt continuous and it works fine. The suggestion to get an adapter designed to let the laptop plug into a 12 volt cigarette lighter plug is the best solution. That's what I use for my work computer, a Dell Latitude 600.
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