On 2008-07-30 19:11:52 +0100, Conor said:

In article cc3c2337-405c-4e1c-9c7e-35359c976734
@b1g2000hsg.googlegroups.com, says...

That would explain your failure to see the spikes. Try repeatedly
switching off the rear window heater while measuring next time. Then
try it for real: switch off all accessories and waggle the loose
battery connection. Dont have your laptop connected

**** all happened. Difference is I had the night heater in the truck
instead of a heated window. A night heater is a bit of kit which has an
electrode which heats up diesel and a fan to blow the resulting hot air
into the cab. Works like central heating in the fact that you set a
temperature and it comes on and off to maintain that.

A night heater draws more current than a window heater and the
electrical noise from the fan far exceeds that of the window heater to
the point where it can be seen as RF interference on a TV.

And my laptop still works.

So again, you're talking out of your arse.

Really all that you can deduce from that is that nothing bad happens in
your environment. It doesn't give the data to say that it can never
happen in other cases.

In my early engineering career, I designed electronics, control and
communication systems that were often fitted into military vehicles of
various types.

In general it was necessary to incorporate various filtering and
protection into the DC supplies to the electronics, because of
electrical spikes and noise from the vehicle systems. Primarily,
this was to avoid damage to certain sensitive semiconductors in the
equipment and did so successfully.

The far harder problem was dealing with the sensitivity of the radio
receivers, that were working in the 2-30MHz range from being swamped by
the general electrical noise.

For example, on a tank, when the turret was rotated, one could find
sharp rising spikes of 600-800v on some of the wiring.

I suspect that in a typical domestic car and possibly even a commercial
truck, the potential for problems is not as great and certainly
electronics has been improved from the EMC perspective over the last
decade. Nonetheless, the mechanisms for bad things to happen are
certainly present in a motor vehicle.