Folks at world,
Christmas cheer has dulled my senses - but surely a relay will not
compensate for wiring intended for only one lamp - and allow two current
sucking lamps to be put on a wire intended for one only one. Doubling
amperage on the wire may just run it a bit hot.
While mumbling on....I have to confess that I am puzzled over the use of a
relay. It does not change the voltage, it does not change the draw of the
electrical device, it does not make wires carry more current
(devices). What it does do is allow a power circuit drawing big amps to be
controlled by a low amp circuit (switch). Obviously this saves on thick
wire and heavy duty switches but this is negated by the cost of a relay. As
to the drop in voltage, the use of slightly thicker wire would help the PD
which surely does not drop all that much - or does it? Never worked it out
or measured it, but I suspect the resistance of connecting wire is very
small. I am missing something as manufacturers would not use relays
especially as they are comparatively expensive. So can anyone explain in
engineering terms what their advantage(s) is(are) please?
At 02:26 PM 12/22/2002 -0600, Bullwinkle wrote:
>On the MGA and earlier, the original wiring for the fog lamp
>was intended for only one fog lamp. If two lamps are fitted
>then a relay is needed as the wiring is not heavy enough for
>two. The MGA parts book lists the relay as for "USA only."
>My guess is that at this time it was permissable in England,
>and maybe Europe, to run with only one "head" lamp. Thus in
>fog conditions the heads were shut off and only the fog
>used. In the US, probably most states had laws requiring
>two "heads." Thus if one were to shut of the low beams, you
>needed two fogs to comply with state regulations.
>There is and added advantage to using a relay in that the
>wiring may be shorter depending on the battery location.
>Thus there may be less "line loss."
>The wiring of the relay may be done in such a manner that
>the fogs only operate when the heads are on low beam only,
>work only with no heads, etc.
>My driving lamp is wired into a two position switch. In one
>position the lamp is aways on. The other position the lamp
>is only on when the high beams are up. Thus putting the
>heads on low beam causes the driving lamp to go off.
Barrie Robinson - firstname.lastname@example.org
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