Re: [ST] headlight relay

[Neil Lindsey <Neil.Lindsey@xxxxxxx>]

Frederic,

These relays are not driven by the ECU, and each relay only carries the
current associated of ONE headlight bulb (the other bulb of the pair is
not switched by any relay at all). If you don't believe me, try removing
BOTH relays, turn the ignition on and operate the dip switch.  One
headlight will illuminate in each position, one for low beam and one for
high beam.

The headlight cut-out relay is driven by the same voltage that is
applied to the starter solenoid, and when this switching voltage is
present (i.e. when the starter button is depressed) the cut-out relay
removes the ground connection for all filaments, preventing the
headlights from operating at all. The ECU plays no part in this.  I say
again, there are no 'drivers' involved, period.

The coil to which the switching voltage is applied has a fixed
resistance, and as long as the replacement relay is rated for 12V
operation, the relay should not get overly warm.
If it was rated for 6V operation then its resistance is lower and it
will draw more current when operated at 12V (not a good thing).

I had already mentioned that IF the switched (normally-open) contacts
are resistive (as might be the case if the relay is of overall poor
quality or not rated for the expected load current) then they will get
warm when the relay is closed.  This situation is not terribly likely.

The relay that is being added is activating only one low beam filament,
and it should therefore be cooler than the EXISTING relay, which is
handling the higher current associated with one high beam filament.  If
the relay that is being added seems hotter than the one that already
exists, then there is something else wrong.


----- Original Message ----- 
From: <Frederic.Nizery@xxxxxxxxxx>
To: "ST" <ST@xxxxxxxxxxxxxx>
Sent: Thursday, November 17, 2005 12:46 AM
Subject: Re: [ST] headlight relay


> Hello all,
>
> As the thread seems to be a long term one I finally have something to
add.
>
> I added whatever auto relayS to my sprint (2001) and to the one of my
> bro in law (2000)
> two years ago w/ no adverse effect. I took whatever I found in an
> autoshop providing
> that the contact numbers matches. The auto relays are obviously
> standardized and each
> pin has a number corresponding to its feature.
>
> The diode in a relay is for protecting the driving transistor from
> counter voltage impulse
> when switched off. Yes there is a driving transistor. It's in the ECU.
> Most common
> schematics for driving relays includes already the said diode. It's
most
> of the time even included
> in the transistor itself.
>
> I don't want to offend whoever but I can't see how a diode in such an
> assembly could overheat unless
> there is a deffect in which case it's more likely to burn a fuse.
>
> For protecting against spark we put a capacotor in parallel. But in
this
> range of use the contacts are supposed to be
> hard enought to stand the spark caused by the air being a little
ionized
> when the contact opens up.
>
> If a relay overheat either the contacts offer to much resistance given
> the current crossing it, or the driving voltage
> is too hight regarding the nominal voltage and the driving solenoid is
> getting hot.
>
> For the first possibility aparently on the bike it was spoken about,
> there is one relay instead of two, that is 110w instead of
> 55w that is close to 10 A. Remember that when the engine is reving,
the
> voltage is more 14v than 12v which is making us
> a 10.5A roughly. If the relay is of poor building, could be the cause.
>
> Regarding the second possibility, it's very unlikly that the founded
> relay has a nominal voltage of 6 volts but never know.
>
> Whatever, get gently the cap off the relay and put it back on the
bike.
> Then check by yourself what is hot, solenoid or contact.
>
> Hope this clarify.
>
> Fred 02 ST BRG
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