Post by Davey
On Fri, 02 Jun 2017 00:42:42 +0100
Post by Dave Plowman (News)
It's something like 20 amps. Cheaper to use a relay than a meaty horn push.
Yikes! 20A each? My DMM won't even measure that high!
I can't remember a horn relay on my Rover (but I didn't look for the
presence or absence of one either), but I do remember that the internals
of a horn are configured like an old-fashioned bell or buzzer. The
electromagnet attracted an arm connected to the diaphragm, and as the
diaphragm moved it broke the electrical contact so that the diaphragm
returned to its resting position which made the circuit again and the
electromagnet was energised again. The cycle repeated while the horn
was pushed. The diameter of each diaphragm and the length of the
(coiled) sound trumpet determined the note of the horn.
The wire to the horn was reasonably thick, and would probably carry 20A
if necessary, but because of the intermittent use of the power, it would
only need to do so for half of the time the horn was sounding.
Averaging current over time, you are probably looking at 20A the pair,
with a few instantaneous higher readings. Also, given that the wiring
used in the 1960s tended to be over-engineered, a wire looking capable
of passing 20A was probably only be required to pass 15A max because the
manufacturer wouldn't want the wiring loom to carry a warm wire.