5 volt bus available ???
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Joined: Jul 2007
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5 volt bus available ???
I am a new owner of a 2002 A6 quattro sedan. I don't have the factory navigation system and would like to install my aftermarket GPS system which requires a 5 volt power supply. Is there a way to wire it in to the car's standard electrical system? I would rather not use a cigaret lighter adapter. Thanks in advance for any advice or pointers to other resources that might be able to help.
Audiworld Junior Member
Joined: Oct 2006
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I would use an LM7805
and build this simple regulator, assuming your GPS system won't draw more than an amp.<ul><li><a href="http://www.eidusa.com/Electronics_Voltage_Regulator.htm">click for link</a></li></ul>
AudiWorld Senior Member
Joined: Mar 2000
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It's a little more complicated than that....
An LM7805 can do an amp of current before it current limits to protect itself. However, since the input voltage is 12V from the battery, the part will be dropping 7V (12V input minus 5V output), and thus, its power dissipation will be equal to 7V multiplied by the current drawn by the load (the radar detector, etc). Since the LM7805 really shouldn't be asked to dissipate more than 1 Watt without a heatsink in an enclosed area with no airflow, the most current it can supply under these conditions would be equal to 1 Watt / 7 Volts = 140 milliamps. If you try to draw more current, the LM7805 will overheat and go into thermal shutdown, so you shouldn't start a fire, but it won't work too well.
AudiWorld Senior Member
Joined: Mar 2000
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I wouldn't eliminate the input capacitor as your link suggests.
The link from Chapaevsk2.7T6sp is a better approach. Too much inductance on the input pin of the LM7805 without a local capacitor can cause problems with the LM7805's operation.
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