Power Inverter for Charging Laptop in the car? - Page 2 - Fiberglass RV


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Old 08-30-2007, 10:05 PM   #15
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Looks like everyone has tried something different that works, so there are a lot of good options out there--thanks, everyone, for the response!
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Old 08-31-2007, 03:04 PM   #16
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I doubt Belkin makes much of anything. Like Black Box, they're generally a brand name for stuff which they buy from the actual manufacturer. As a result, quality is inconsistent... but for all a power adapter has to do, I would guess that they would be fine.

Targus is a more common source for power adapters, especially universal output (use an interchangeable tip to match your device) and universal input (takes 12VDC, 120 to 240 VAC, 50 to 60 Hz) supplies intended for travelers. There are various other brands as well.

We used an older 120VAC input (only) Targus power adapter with a laptop for some time, and had no problems.

If you use the stock AC-to-DC supply that comes with the computer, and only need an inverter to get from 12VDC to 120VAC, I would expect just about any one with enough capacity to work fine. An inverter would only take as much power as it needs, so you can use one which is bigger than necessary... although it takes some "overhead" for itself so you don't want to go wildly big.
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Old 08-31-2007, 06:37 PM   #17
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The low-voltage shutoff or alarm with the larger inverters is as likely to be the wiring to the cigarette lighter as it is to be the load.

Very little equipment one would take RVing needs anything but the inexpensive inverters; as Darwin pointed out, something like a computer runs on DC and the brick or wall-wart can accept a lot of variation. Mine, for example, runs on 100-240Volts and 50-60 Hz. I do, however, take the precaution of unplugging the brick from the inverter before starting or stopping the engine to avoid spikes.

I keep a 75W Vector from Wally in the glove box for small stuf.
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Old 08-31-2007, 07:49 PM   #18
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I looked at the VAIO and it states only 19.5V DC, which is what in terms of watts, I wonder? Would a 160 watt DC to AC power inverter be enough?
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Old 08-31-2007, 10:54 PM   #19
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This is what I use Targus power adapter.

Need 2 values to figure watts. Volts and amps. On the AC power supply that came with the computer there are two sets of values. One set is input, should be 120 volt and ? amps. Important for getting the correct match is output. Will be 19.5 volts and ? amps.

A 160 watt inverter should be able to support all but the most power hungry laptop. I have a power hog and it needs 150 watts AC to supply 75 watts. DC. Lots of heat generated in the process. By going direct DC to DC I save much of the conversion loss. I haven't got my adapter handy, but it draws a couple extra amps at 12 volts and outputs 16.5 volts at 4.5 Amps or ~75 watts.


To figure the size inverter, you need to multiply input vots times amps. That will give you a number that is watts. Any inverter with a larger continuous output will work. Problems do develop because the power outlet ( used to be cigarette lighter ) is not wired to carry a heavy continuous load. It is very easy as others have indicated to attempt to draw too much power thru the small guage wire.

Curt
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Old 08-31-2007, 11:13 PM   #20
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Quote:
This is what I use Targus power adapter.

Need 2 values to figure watts. Volts and amps. On the AC power supply that came with the computer there are two sets of values. One set is input, should be 120 volt and ? amps. Important for getting the correct match is output. Will be 19.5 volts and ? amps.

To figure the size inverter, you need to multiply input vots times amps. That will give you a number that is watts. Any inverter with a larger continuous output will work. Problems do develop because the power outlet ( used to be cigarette lighter ) is not wired to carry a heavy continuous load. It is very easy as others have indicated to attempt to draw too much power thru the small guage wire.

Curt
Thanks, Curt,

The AC power supply states INPUT: 100V-240V 1.3A-O.6A 50-60Hz
So is it as easy as that being 130 watts-144 watts since there's a range given?

OUTPUT: 19.5V 4.7A

I would hope that just charging up the battery or trying to locate a campground won't overload the circuitry.
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Old 09-01-2007, 08:09 AM   #21
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Thanks, Curt,

The AC power supply states INPUT: 100V-240V 1.3A-O.6A 50-60Hz
So is it as easy as that being 130 watts-144 watts since there's a range given?

OUTPUT: 19.5V 4.7A

I would hope that just charging up the battery or trying to locate a campground won't overload the circuitry.
I have a Dell Notebook PC and its AC Power Supply that says INPUT: 100V - 240V 1.5A 50-60 Hz

I have a 300 Watt DC to AC converter that I use to power a portable TV. It will only power the Dell for about 10 minutes, then the converter trips its thermal overload protector. I would suggest that you get something greater than 500 watts. Or better yet purchase a DC to DC converter. The one I purchased from Dell is only a 75 Watt converter and it runs the Dell PC all day when plugged into the Escalade.
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Old 09-01-2007, 12:02 PM   #22
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The AC power supply states INPUT: 100V-240V 1.3A-O.6A 50-60Hz
So is it as easy as that being 130 watts-144 watts since there's a range given?
Yes, that's how I would interpret these ratings.

Quote:
OUTPUT: 19.5V 4.7A
That's 19.5 x 4.7 or about 91 watts, typical of modern laptops (but not enough for the largest screens and biggest processors). A perfectly efficient power adapter would then need only 91 watts of input power (less than 8 amps), but as the AC input spec shows, they do waste a significant amount of the input power as heat (the extra 40 to 50 W)... if you get the AC power from an inverter, it's wasting power too. A DC-to-DC supply as Curtis uses might be more efficient, which would mean less current drawn from the battery, but we're still talking about less than 10 amps in the worst case.
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Old 09-01-2007, 12:59 PM   #23
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Okay, sounds like the VAIO is a powerhog like the Dell and that getting a DC-to-DC will reduce the amount of power wasted that would occur with a DC-to-AC conversion. With DC-to-AC I might have to go as high as 500 watts to avoid tripping the overload and those power inverters are quite expensive and bulky, so a DC-to-DC auto adapter will actually be less expensive and waste less energy.

Thanks for the input, everyone!
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Old 09-02-2007, 07:12 PM   #24
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Don't forget that an equipment-specific adapter of any kind becomes instantly worthless when the equipment is replaced by a newer whatever, whereas an inverter continues to be useful.

My laptop's brick has a output power spec (3.16A@19VDC) which is 60Watts (19x3.16), but the input spec of 1.5A is unclear as to which voltage is used (100-240VAC), so I dunno if it is 360W or 190W (Probably the latter). The brick gets pretty warm in use, so input energy is being wasted creating heat. In fact, there's a lot of wasted energy because the CPU gets hot also.

Also, because the laptops may require higher voltages than a home unit (to recharge the battery, I would guess), we don't really know how inefficient the DC-DC adapters may be. They can't just drop the voltage because it needs to be higher than 12VDC.
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Old 09-03-2007, 11:28 AM   #25
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Don't forget that an equipment-specific adapter of any kind becomes instantly worthless when the equipment is replaced by a newer whatever...
...which is a good reason to use a universal adapter, which just needs a different output tip to fit the next computer. The tips not only physically fit the equipment, but also signal the adapter to put out the right voltage.

Quote:
The brick gets pretty warm in use, so input energy is being wasted creating heat. In fact, there's a lot of wasted energy because the CPU gets hot also.
Other than the bit of light coming out of the screen, essentially all of the energy going into a computer comes out as heat - they don't really do physical work. I'd rather not waste too much before it even gets to the computing electronics!

Quote:
Also, because the laptops may require higher voltages than a home unit (to recharge the battery, I would guess), we don't really know how inefficient the DC-DC adapters may be. They can't just drop the voltage because it needs to be higher than 12VDC.
True; the nominal voltage of laptop batteries is routinely more than 12V... my Compaq and HP machines have used 19V inputs. A DC-to-DC converter putting out more than 12V is doing some of the same things as a 12VDC-to-120VAC inverter, but not inverting. On the other hand, it's still more efficient to do fewer conversions, and a good converter (stepping up or down in voltage) is much more efficient than a simple "throttle" which passes current while throwing away excess voltage, like an old 12V to lower voltage car power adapter.

I'm not currently using a DC-to-DC converter for the computer, and have used the 12VDC to 120VAC to computer-required DC path. It works, it's just not the ultimate in efficiency or simplicity.
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