12v Power Supply
You have 2 ways of getting the 12v power supply you need to power your computer
with car batteries. You can either use the same type of conventional mains power
supply you would use in your desktop PC, or use a power supply specifically
designed to run on 12 volts.
use a normal mains power supply, you require a DC to AC
inverter, to take the 12
volts DC from your car battery, and convert it into either 110v AC, or 220/240v AC.
Your mains power supply then converts it back to 12v DC.
That seems a bit pointless doesn't it?
As you would expect, this is a very inefficient way of supplying the power (in
some cases, the efficiency can be as low as 30%). You need to keep the power
requirement as low as you can. For this reason alone you should
choose a car computer power supply specifically designed to work with a 12v system.
There are several other reasons why a DC DC converter is the better choice.
- A properly designed DC-DC power supply, with voltage regulation, will be
able to power up the PC automatically when the car is started.
- It will completely power off the PC when the car battery voltage falls to a
certain level. This ensures there will always be sufficient power in the battery
to start the car. However, if you anticipate regularly using your carputer with
the engine off, you need to consider fitting a deep cycle battery to protect your SLI battery.
- It will tolerate battery voltages from as low as 6 to 8 volts. The battery
voltage will drop when the car is being started. A DC-DC supply will continue to
supply power to the car PC even while the car is being started.
- Car voltages can vary widely between 6/8 volts when operating the starter,
and spikes as high as 16 volts, from the alternator or other electrical
equipment. A DC DC PSU will cope with this and supply a regulated 12v DC (as
well as 5v and 3.3v) to the car PC.
- The conversion process generates a lot of heat. The more inefficient the
process, the greater the heat generated. Depending on the location of the
inverter, this could be a safety hazard.
- Inverters are prone to generating electrical "noise" which interferes with
audio appliations. They can also generate electromagnetic interference which
shows up as hum in audio signals. A 12v power supply does not give this problem.