Newsgroups: sci.electronics.misc,sci.electronics.repair
Subject: Re: Inverter blew a fuse!!
References: <[email protected]>
"Jon Davis"  writes:

> I was using my new emachines M6811 laptop, which has an A/C adapter with a
> "90W" blue sticker on the end of it, with a 150W cigarette lighter DC/AC
> inverter, Tripp Lite brand, in a 2002 Toyota Echo. The car has a new battery
> and
> the cig lighter had never before been used. The first day, with about
> 7 or 8 hours on the road, there were no problems. Eventually, however, one
> day I plugged it in the inverter again and within about ten minutes the
> inverter alarm started sounding. 

This tells that there is something wrong... You should check things 
and not contonue to use the system unless you are sure that everything 
is right. 

> I kept resetting it and in another five
> minutes the inverter's fuse blew, and the car's fuse blew, too, but it was
> somehow delayed by a few hours I think for some reason because we didn't
> notice the stereo wasn't working until hours later).

You continued usign the thing even though you got warning that 
things were not right... You could have for example beign 
overheatign the inverter and then the overhatign caused 
a short-circuits..

Delayed fuse blowing sounds strange.... You either did not 
ntice it earlier, or the incident with the inverter almost blew 
the use, and later the starting power spike on the stereo burned 
it completely...

> A few dumb questions:
> 
> - Is it possible that the laptop adapter is already going bad, drawing more
> power than should be? (Every time I plug it into the wall while the laptop
> is running I get a VERY visible and loud spark.)

Sparking when pluggin in power supplies is quite normal. 
Many PC power supplies take quite high surge currents when 
they are started or plugged in. 
 
> - If I bought an inverter that supported more wattage--say, 250 watts--would
> that decrease the chances of the *car* fuse from blowing out, or does the
> car fuse not "care about" the power handling of the inverter? (I don't know
> much about electricity.)

Higher wattage converter would not (at least theoretically) 
decrease the chances of the *car* fuse from blowing out. 
The car fuse will blow when too much power is taken from 
the outlet protected by it. This to much power intake could 
happen because of high power inverter powering very high load 
or because of inverter malfunction (short circuit etc.). 

> - Would a direct DC-to-DC step-up converter be better? Any recommendations
> on a model of such an adapter for a laptop marked on the bottom with "18.5
> watts"?

I would quess that DC-to-DC step-up converter would be better 
suited in your applications. With this kind of device you get the 
power your laptop needs with less conversion steps in the way. 
Better efficiency and at least theoretically more reliable. 

Some inverters are not happy when feding power to devices 
like computer switched mode power supplies... They can take 
current in spikes while some inverters are designed for just 
pure resistive loads in their mind (this the load for what
their power rating is specified).  

Check carefully on the power rating and type of adapter you need. 
You are talking on the beginning of the mssage "90W" and now 
say "18.5 watts". Which one is correct figure. 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/