In order to run your car's 12 volt accessories, you'll need either a DC to DC converter or a separate "accessories" battery.

A DC to DC Converter taps into your main pack voltage and reduces it down to 12 volts so you can run your headlights etc. A separate accessories battery does the same but is separated from the main pack. There are basic pros and cons to each method.

• The advantage to a separate accessories battery is pure simplicity.
  The disadvantage is the inconvenience of having to manually charge this battery regularly.

• The advantage of having a DC to DC Converter is convenience. You can drive with all the accessories running - as long as you still have power in your main battery pack.
  The disadvantage of a DC to DC Converter is typically the cost

If you'd like a factory-made DC to DC converter you can expect to pay around $150 although with anything electronic the sky is the limit.

To reduce costs some EV converters are converting computer power supplies to act as a DC to DC converter instead.
For information on how to do this with a Thermaltake 450W Power Supply, check out this thread.

[skooler]

I've just read the article for the first time.

To be clear, you can run both a DCDC converter and an accessory battery together.

The advantages of both are then combined - if the DCDC fails, you are still able to use the 12v systems, as with the battery. The accessory battery can also keep the load off the DCDC converter effectively acting as a buffer between it and the 12V systems.

[kevin88]

That was a Pretty Informative article !
I want to add some information as well ; that , if you place an extra battery pack that means you also need to charge it along with the original one. Charging efficiency of your Alternator will reduced to half.
If some one is good at understanding (reading) circuit diagram and soldering then why not build a Personal DIY DC DC converter at low cost !!

Regards

[skooler]

Originally Posted by kevin88

If some one is good at understanding (reading) circuit diagram and soldering then why not build a Personal DIY DC DC converter at low cost !!

Because they're so bloody cheap it wouldn't be worthwhile!