VW Electrics Smooth 12v/5v supply

Covkid:

These days, we run laptops and other items that need a smoother or even reduced supply compared to the nominal 12.5V supply, and if the engine is running, the voltage can reach 14v. A raw supply is fine for some items but most modern electronics require a bit more precision than this. For instance, the dash clocks in a T25 use a fixed 10v regulated supply for part of the circuit and this is achieved by a voltage regulator fixed to the back of the clocks rated at 10v - LM7810.

Relatively cheap, voltage regulators have three legs and in various ratings (see last two numbers) including but not limited to:

LM7805 (5v)

LM7809 (9v)

LM7810 (10v)

LM7812 (12v)

With the addition of a few capacitors to further smooth out the supply, you can build a simple and effective power source at one or more voltage levels. They're cheap and easy to build and a whole lot less than ones you can buy - even on ebay. Check the amp rating will be suitable for your appliance.

Heres a simple circuit using a 12v regulator (for 5v you'd substitute with an LM7805):

'Input' refers to red wire from battery or other dash 12v power lead, 'output' to the item that needs the fixed supply. Earth (chassis) is common to both. I recently purchased a 12v notebook to make things simpler in the camper - no need for voltage increasers, and three components provide a perfect power source. These type of voltage regulators are less efficient when you're dropping 12.5v to 5v as more is lost in heat (hence the need for a heatsink, but dropping your battery supply to a fixed 12v is fine as the change is slight.

A great video explaining the principles can be found here: https://www.youtube.com/watch?v=GSzVs7_aW-Y

If you really want to go to town on this, you can create a really good, stable little power supply on hookup (240v) from an old computer ATX power supply as follows: https://www.youtube.com/watch?v=z2oSFpKh_Uw https://www.youtube.com/watch?v=GSzVs7_aW-Y