Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...
An Engineer in Wonderland – 180mA leakage
A friend of mine was having a car flat battery problem.
It turned out to be the car radio which, when ‘off’, drew 186mA.
The radio has both a permanent live connection, and a connection for the switched side of the ignition switch.
These had been wired together and connected to the permanent live to allow music to be played with the ignition off, under the assumption that over-night power consumption would be negligible and not 186mA.
After a bit of rewiring, using a spare dashboard switch in the ‘ignition’ leg of the circuit, the ‘off’ power drain dropped to a more respectable 8mA.
Surely, if the designer could get power consumption down to 8mA in one state, it could have been the same with both leads connected to +12V?
Another thing I learned was that the radio stores its settings as the ignition is switched off.
Some manufacturers, I think VW might be one, defy common usage and swap the permanent and ignition-switched feeds in their DIN loom connectors.
So this radio would never remember its settings in one of these cars, and would probably draw 180mA all night into the bargain.
Just for information: power consumption is around 500mA with just the radio on and the volume down, and an Amp or so with the CD operating.
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