Laptop with Inverter in Car Question

[TeleTech1212]

Hi.

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?

Thanks in advance for your assistance.

 

[operator jay]

Hi.

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?

Thanks in advance for your assistance.

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.

j

 

[TeleTech1212]

What's the rating, in Watts, of your power inverter?

Rated for 50W

Can you see any
ratings on your laptop about power consumption (and/or voltage,
current rating)?
[...]

Maybe you are overloading your power inverter.

According to the label on the laptop's power supply:

120V, 1.5A in
19V, 3.16A out

[...]

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.

No difference, full battery, low battery...

Thanks.

 

[TeleTech1212]

DOH!

I just got it.

The thing is rated for 50W. The laptop is rated as follows:

120V, 1.5A in
19V, 3.16A out

120V x 1.5A = 180A
19V x 3.16A = 60.04A

Wheeeeeeeeeeee!

Sorry to waste your time, folks.

 

[repatch]

What's the rating, in Watts, of your power inverter?

Rated for 50W

Can you see any
ratings on your laptop about power consumption (and/or voltage, current
rating)?
[...]

Maybe you are overloading your power inverter.

According to the label on the laptop's power supply:

120V, 1.5A in
19V, 3.16A out

Well that right there proves things. The DC out of the adapter worst case
is more then 60W, and this is ignoring that the power adapter is probably
80-90% efficient (at best).

On top of that most inverter ratings are very "imaginative", i.e. a 50W
inverter will likely only be able to supply 40W.

You need a bigger inverter, get at least a 150W CONTINUOUS (ignore all
"peak" ratings) one. TTYL

 

[TeleTech1212]

DOH!

I just got it.

The thing is rated for 50W. The laptop is rated as follows:

120V, 1.5A in
19V, 3.16A out

120V x 1.5A = 180A
19V x 3.16A = 60.04A

Wheeeeeeeeeeee!

Sorry to waste your time, folks.

Make that 180W and 60.04W respectively.

 

[JohnR]

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

 

[Wayne R.]

Okay, please lay it out for me in simple terms what the difference is
between VA and watts...

 

[Palindr☻me]

Okay, please lay it out for me in simple terms what the difference is
between VA and watts...

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.

HTH

Sue

 

[Wayne R.]

I appreciate your explanation. Thank you very much!

 

[TeleTech1212]

Thanks, all of you, for the great advice as well as the thorough
explanations.

This always was a good group here...