Heated rear windscreen voltage drop

[Tom Brearley]

Just to update this thread from March a little --

Now we are in the winter, the rear screen has started fogging up on most trips out which makes testing functionality easier. With the engine at 1500 rpm, I'm getting 10.3V at the positive side of the HRW - and it clears well. Maybe not quite as good as our modern car, but still perfectly OK.

[Vic Butler]

Try running the engine at about 3,000 rpm. It's possible that at 1,500 engine rpm the alternator is not on full charge,
What's the reading across the battery terminals? It should be around 14v.
The alternator runs twice engine rpm.