[Ham-Computers] RE: Running laptop mobile?

[Hsu, Aaron (NBC Universal)]

OK, here's my 2 cents...

Most all laptops use 2 switching power supplies - the power "brick" that converts AC to some lower DC voltage (typ between 10v and 21v), and another internal DC-DC converter that further drops the voltage as required for the various components in the laptop.  Both are subject to causing "hash" in the RF spectrum, but the external "brick" (most of which are switching power supplies) is usually a worse offender.

A 12v DC to 120v AC inverter itself is a switching power supply, and, as such, can (and does) cause RF hash.  Even the "name brand" models can cause hash as they are designed for a typical laptop user, not an HF radio operator.  To the typical laptop user, they'll never experience the fustration of trying to work that "weak one" due to S9+ hash!

So, let's take a closer look at what we can do.  The laptop itself has a DC-DC converter which often works with an input as low as 10v DC.  With this in mind, it's entirely possible to work directly off a 12v battery or power supply.  This has the advantage of removing one source of hash - the external power brick!  Will it work?  Most likely - you'll need to check the specs of the laptop to be sure.

What's the catch?  Why not just run 12v all the time and forget the "brick"?  Well, the extra "juice" is usually used as overhead to charge the laptop's batteries.  Most laptop battery packs are rated between 10.8v and 14.4v.  And, if you're familiar with battery charging, you'll know that you actually need more voltage than the battery's rating in order to fully charge it.  So, the caveat of using 12v to power your laptop is...the batteries won't charge.  On my HP laptops, the charging circuit drops out of "charge" once the input voltage drops below 15 volts.  The "brick" supplies 18.5v @ 3.5A (65w) - sound familiar Phil?  Most small to medium laptops are designed around a 65w "standard".  Larger laptops will usually have a 90w adapter (such as 18.5v @ 5 amps) and the maximum I've seen designed for traveling is 120w (there are 135+ watt adapters, but they are usually "stationary" and power a docking station).

OK, should you get a "factory" 12v DC adapter.  If they have one, it's most likely a straight cord with a surge suppressor/noise filter - something you could probably builld yourself.  I actually have a "factory" 12v adapter cord for an older Compaq laptop - it's a cig lighter plug with a choke and cap inside connected to 3 feet of zip cord.  Pretty simple and a steal @ $30 bucks (really)!  Another option is to get a 3rd party "Auto/Air" adapter designed to work with a cigarette lighter or "Air Power" type socket - these come with different "tips" to match various laptops.  And, there are "universal" bricks that will work with an AC or DC input - I have one of these and it works great both overseas (240v) and in the car (12v).  And, yes, they are switching supplies and will cause hash.  So if this is of primary concern, they see if your laptop will run on 12v.  The 3rd party adapters usually run between $30 and $150, depending on brand and quality.  Targus is the leading 3rd party manufacturer (http://www.targus.com) and many places carry them, including office supply stores.

Anyways, hope there's some useful info in here.

73,

  - Aaron, NN6O



-----Original Message-----
Sent: Sunday, November 16, 2008 8:30 PM
Subject: [Ham-Computers] Running laptop mobile?

Here's my question.  Is it better to 'try' to get a 'factory' 12 Volt DC adapter for my Acer Laptop (not sure they offer one), or just get a 12V/110Volt inverter in the 100 Watt class?  The laptop's power supply is supposedly good from 95-230 Volts,inclusive, and draws 65 Watts, so I don't think regulation would be a problem.  Don't have an immediate need for portability, but just looking down the road. . .

What do the 'experts' say?

73 de Phil,  KO6BB
http://ko6bb1.multiply.com/
http://members.lycos.co.uk/ko6bb/

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