POWERING A COMPUTER ONBOARD
The two basic power sources for any electronics onboard are 12 volts DC from a battery bank and 120/240 volts AC from a generator
All computers onboard whether laptop or desktop require 12vdc, 5vdc and 3.3vdc closely regulated to operate. A power
supply inside the computer case provides these regulated voltages to the computer motherboard and its peripherals. This internal
power supply requires input power from the vessels power system which is either unregulated 12vdc or 120/240vac. Your computers
internal power supply will require its input voltage to be regulated also for proper operation. This regulation is provided
by the inverter circuitry or generator regulator in the case of AC input and usually by an external power brick either AC/DC
or DC/DC if you are using a laptop or other computer using DC input to the internal power supply.
Getting the required input power to your computer involves two concerns for most cruisers; first, energy losses and second,
electrical noise (RFI). No form of energy conversion is 100% efficient nor is it electrically quiet so the less conversions
between your power source and computer, the less RFI and less power loss. The worst case situation involves using an inverter
to run a power brick which provides power to a laptop. The noise on an SSB from the inverter and power brick is usually enough
to wipe out all but the strongest fax and pactor signals and you can easily loose 25% of the power taken from your batteries
in the conversions. If you have a Pentium 4, 1.6 ghz, laptop it could typically require 75 watts to the internal power supply.
Most power bricks and small inverters are usually around 85-90% efficient so the 75 watts used by the computer could require
around 100 watts from the batteries. This is a loss of at least 2 amps at a nominal 12 volts.
Using a DC/DC power brick (sometimes called an auto-air adapter) to convert 12vdc into the voltage required by your computer
would increase efficiency and reduce RFI but the most efficient, quiet way to power your computer is to use the unregulated
12vdc from your battery system to power a desktop or in the case of a laptop, its internal batteries. With the IslandTime
PC, which is a small form factor desktop computer, we use internal power supplies designed to handle input voltages from either
6-24 vdc or 10.5-30 vdc depending on the case choice. These power supplies can absorb higher voltage spikes without damage
although they will shut down the computer and the 6-24vdc model can keep your computer running during engine cranking.
Some laptops will run off of the unregulated 12vdc from your batteries. These are generally the older Pentium III models
although the new Pentium M machines may take 12vdc input. Check your power brick output voltage. If it is above 12vdc you
can expect your laptop batteries to discharge if left in the machine. Most laptops that can run off of 12vdc directly still
cannot take the voltage variation found in a boats 12 volt system. Don't experiment with your laptop power unless you're
willing to give up the warranty or the machine. It's much easier to replace the power supply in a desktop than a laptop.
Onboard WiFi Primer
WiFi operates at 2.4 Ghz with relatively weak transmit power. Two important facts to know about radio signals in this frequency
range are that water and most solid objects absorb considerable amounts of any signal and long coaxial cable runs to antennas
can reduce power output at the antenna by half or reduce the incoming signal strength to the point that the signal is not
All onboard WiFi systems have a computer connected to a WiFi transceiver which is connected to an antenna.
The connection to the computer can be through a PCMCIA port, PCI port, mini-pci, USB port or LAN port. The first 3 connections
are internal to the computer with the transceiver either totally within the computer or partially accessible to the user.
A USB transceiver can be directly plugged in the computer or connected by an extension cord. The LAN connection uses CAT5
network cable to connect the transceiver to the computer.
The WiFi antenna can be either internal to the computer, USB device or PCMCIA card or it can be an external antenna which
attaches directly to the transceiver housing or to the transceiver using coaxial cable.
The best system for onboard WiFi reception will use an antenna deployed so that it has a 360 degree view of its surroundings
not blocked by any vessel structure other than the mast & rigging. The transceiver should be mounted as close to the
antenna as possible to minimize or eliminate the coaxial cable run. The best types of transceivers to use to achieve these
goals are ones that use USB cable or LAN cable to connect to the computer.
Any transceiver that can connect with an AP (access point) is operating as a "client device".
USB based adapters are the least expensive way to set up an onboard system. They can be placed up to 15 feet from the
computer by using a passive extension cable. Additional extensions of 15 feet can be achieved using active extension cables.
One computer can be used per adapter.
The client bridge provides the most flexible WiFi system. These adapters use POE (power over ethernet) which allows 1
CAT5 cable to carry both data and power. This allows for unrestricted placement of the adapter. A client bridge can provide
input to an access point on the interior of the boat so that any wireless equipped computer onboard can access the internet.
You end up with a network similar to what you may have used onshore except that the client bridge takes the place of the
DSL or cable modem.
How Many Serial Ports Do I Need?
I use 3 com ports to run my navigation and communication software. One port takes the GPS nmea data, one port takes my Pactor
Modem and one port controls the SSB.
USB ports are another type of serial port. Most types of peripheral equipment can be operated off of the USB ports. I
keep an RF transceiver for a wheel mouse, a WIFI transceiver, an infrared dongle for internet over the cell phone and a printer
plugged in all the time. In addition I use the USB ports for a floppy drive, external hard drive and power for an amplified
pair of speakers. If you run MaxSea or Nobletec software you'll probably have a USB dongle with a software key plugged in
all the time. You'll use as many ports as you have. You can never have too many ports.
I've just hooked up my GPS to my new PC and the mouse pointer goes crazy when I boot up the computer. What's going on?
If NMEA input is present on your com port when Microsoft XP starts up XP recognizes this input as a Serial Ballpoint Mouse
and loads a driver for it. The following steps will cure the problem. IslandTime PC's are modified before shipment to prevent
this problem on any of the COM ports.
1. With the GPS connected and running boot the computer.
2. After the machine is up and running regain control of the mouse pointer by turning off the GPS or otherwise
removing the input signal.
3. Select START>CONTROL PANEL> SYSTEM>HARDWARE TAB>DEVICE MANAGER BUTTON>
4. Find "Mice and other Pointing Devices" and expand it.
5. There should be an entry for "Microsoft Serial BallPoint". Right click and select "Properties".
6. At the bottom of the Properties window there is a drop down list. Click the arrow to open this list and select
"Do Not Use This Device (Disable)".
7. Click OK to close the window.
8. It's best to restart your computer immediately to save your changes.
IslandTime PC * 243 W. Orange
Ave. * Wewahitchka, FL 32465 * USA