[Public-list] Notebook PC power in a boat... "Danger Will Robinson"

[Dan Sternglass]

Hi A-30 people,

I wrote an earlier reply to this post, but it was bounced for reasons 
that are not clear...

 > The answer to your question should probably be " Maybe
 > .......it depends on your laptop" The manufacturer usually
 > says you should buy there grossly overpriced DC adapter

As an electronic engineer who has worked on automotive electrical 
systems (and mobile phones and computers), I would strongly advise 
against that...

 > ......but here is my experience. I have a Toshiba Satellite
 > 1800 series.  It has an AC adapter that puts out 15VDC
 > so I don't worry about feeding it directly with 12vdc
 > even when the alternator is charging at  14.4.  Low voltage
 > is not a problem for the Toshiba either - it will not shut
 > itself down until the DC input falls below 11 volts and I
 > shouldn't be draining the battery further than that anyway.

Low voltage is not the problem, since the notebook PC has internal 
batteries and will switch to them if the external DC power drops out. 
The main problem is high voltage transients (short pulses). Transients 
happen when a charged coil (for example the alternator field winding, 
behaving like an electrical inductor, which stores energy) discharges 
rapidly when it is switched off. This happens frequently as the voltage 
regulator operates, and also when the engine stops or is stopped. All 
equipment designed for cars/boats withstands these 50 volt and higher 
transients, but there is no such filtering on the power plug of a laptop.

 > I would suggest you check the following and then you should
 > be able to decide for yourself it you want to try your computer
 > on direct DC power.

This may work for a while, but I think the $85 purchase price of a 
generic "travel" notebook PC power supply (or an inverter to go with the 
existing supply) that plugs into ship's power or a cigarette lighter 
plug is a much better way to go. These supplies accepts multiple "power 
tips," so they can run virtually any brand of notebook PC, cell phone or 
other DC device, and can be had at any electronics chain store like Best 
Buy.

Since the loss of data on a notebook PC is, at the very least, a big 
aggravation (if you didn't fry the hard drive electronics, so you can 
swap it into another computer, or if you have a recent backup), under 
$100 is cheap insurance. Also, some notebooks, like my HP, run on 18 
volts anyway...

EOR (end of rant),

--Dan S.
dans at stmktg.com
Watcher of the Skies, #201, 1966, Cayuga Lake, Ithaca, NY


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