I don't even know which automotive group would handle such a question, but surely somebody here can shed some light.
I have a power inverter which plugs into my car's cigarette adapter. When I switch it on, the "power" LED stays lit just fine. As soon as I try to run my laptop off of the AC outlet, the LED comes off an on (without any pattern to it) and the computer indicates it's on battery power, then back to AC, then back to battery, etc.
My guess is that the computer is not drawing a steady load as would a light bulb or motor, (Is that what is called a "non-linear load?") I think that's where a building's AC system would have power harmonics, etc. All of that is a bit over my head, though.
My question is, does anybody know of an easy solution for this? Is it possible that something is not grounded properly to the car's chassis or would a toroid coil help or some other "secret" that would fix this?
What's the rating, in Watts, of your power inverter? Can you see any ratings on your laptop about power consumption (and/or voltage, current rating)? Maybe you are overloading your power inverter. Note that the laptop will draw a lot more power if it is recharging it's battery in addition to running. I suspect your laptop would normally draw a pretty steady load. It would be non-linear, and that does involve harmonics, but it doesn't mean the load would not be steady with time, and we might not have to get concerned with all that here.
For (my) interest, you could run the battery down a little on your laptop, then plug it in your inverter, with the laptop powered off, so that the inverter is used to charge the laptop's battery. Is the power LED steady in this case? How about the opposite ... run the laptop off the power inverter but start with a fully charged battery.
You may just have an inverter that is not big enough for the load. I have been running a P166 on a 135w inverter for several years as an MP3 player but it is a bare system unit, no display.
Well... Technically, the input would be 180 volt-amps, not watts. It draws too much current and causes the inverter to trip on over current. A typical inverter should have be able to deal with a momentary power surge but at
180w, this is probably way too much for it.
My inverter is rated at 140W continuous, 200w 10 min @ 50% duty cycles and
250 watts at instant shut down. I believe they make some note that this is actually VA in the manual. John
VA is simply the reading of a voltmeter connected across the supply multiplied by the reading of an ammeter wired in series with the supply. It is handy for all sorts of reasons - current and voltage are easy to measure and the cable, for instance, has to handle the specified current at the specified voltage - so you need to know the current and voltage.
For DC, this /will/ give you the power flowing, as volts x amps = watts for a dc system. So, if the power source can produce 10V at 10A, it can drive a 100W load.
For AC it gets more complicated as things like capacitors and inductors in the load screw things up and can easily make the current higher than if the load was just plain resistance, for a given power transfer. So, if the load needs 100W, it may need 11A rather than 10A. Thus you would need a 110VA power source to drive the 100W load.
Now, a laptop has a thing called a switching power unit. This further complicated things because, although well designed ones have special circuitry, they can draw far, far more current when they start up than they use when running normally.
So a power supply that would be quite happy supplying the normal load just can't cope with the start up load. It typically has a go, lights the power on light briefly and then safety ciruitry trip it out to protect it. A typical inverter will do that, then try again a few seconds later, and then again and so on. This is very bad for everything and a badly designed inverter may get damaged quite quickly under these conditions. Also, the laptop power unit wasn't designed to cope with a supply that comes on and off every few seconds - its internal protection circuitry may trigger to save the rest of the laptop and the laptop power unit become permanently damaged.
Now a general purpose inverter with a lot more VA rating than the watts the load required becomes a good idea. It can cope with the VA needed by the load being greater than the watts. It can also cope with the startup demands. Using a
300VA inverter for a 100W load is quite common.
Alternatively, an inverter designed specifically for laptops typically has protection circuitry designed to cope with the starting demands and so gives a bit more time for the load to stabilise before calling time out. So, a relatively modestly rated one will do. So a 120VA specially designed inverter will do for that 100W load.
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