Power supplies

[Herald1360]

I should think most of the noise on a modern will be from all the other electronics in the system. You may well get a kick from the starter, but that's once per journey. The alternator control, not to mention output ripple, could be pretty noisy, and stuff like injector drivers (petrol and common rail diesel) takes large gobs of current for short intervals with an audio range prf.

[davegsm82]

Originally Posted by Sean Williams

Inductive spikes from glow plugs? How - they are a resistance, not an inductance......

They are spiral wound heating elements (usually, other types do exist such as PTC) and the fact that a set of 4 plugs will draw about 56 AMPS means that the wiring to them becomes a high current 1-turn inductive loop.

I've got a secondary heater (peugeot 306) in the coolant hoses on my golf, the arc from the original relay that I used was quite impressive!

Dave.

[MichaelR]

I have used this device on some pic based designs that I did a few years ago. The propulsion system was as noisy as you get in typical automotive sytems and they behaved perfectly. These devices are designed for these harsh environments.

http://www.onsemi.com/pub_link/Collateral/LM2931-D.PDF

Mike