Re: [ST] Spastic turn signals

[Neil Lindsey <Neil.Lindsey@xxxxxxx>]

If our flashers were of the bi-metallic type, the flash rate would slow
down when a bulb burned out or otherwise became disconnected.  This is
because less current would flow, and it would take more time for the
bi-metallic strip to heat up.

With semi-conductors it is easy to sense a change in current flow (in
this case a decrease).  It would also be easy to cause the flash rate to
speed up as a result.  It was probably decided that an increased flash
rate alerts the user more reliably.

Neil

----- Original Message ----- 
From: "Chris Harwood" <Chris@xxxxxxxxxxxxxxxxxx>
To: <ST@xxxxxxxxxxxxxx>
Sent: Saturday, September 10, 2005 9:00 AM
Subject: Re: [ST] Spastic turn signals


> Historically, flasher units were an electro-thermal oscillator.  The
> load current flowed though a heater that bent a bi-metal strip that
> broke the circuit after a delay while it warmed-up.  When the circuit
> broke, it all cooled and re-made.  Hence the current drawn affected
the
> speed of oscillation.  The fact that it flashed fast when a bulb blew
> was seen as a usefull diagnostic feature.
> With modern power semiconductors, it is possible to provide the same
> functionality without the naff side-effects.
> Chris Harwood
> 00 RS
>
> >>> Neil.Lindsey@xxxxxxx 10/09/2005 00:27:00 >>>
> I just HAD to jump in here.
>
> For starters, the typical function of a relay is to allow the
> controlling/low-current switch (in this case the turnsignal switch) to
> avoid having to carry the higher current drawn by the LOAD (in this
> case
> the LEDs or lightbulbs) and this allows the controlling switch to the
> be
> mounted relatively far away from the relay and the load itself.  The
> only thing that varies when you change from lightbulbs to LEDs is the
> load current
> (nothing changes on the controlling/input side).  So if the new load
> is
> LESS (as it will be for LEDs only), then the existing relay is, in
> fact,
> now MORE THAN ADEQUATE to handle the load and there is no need for a
> change to the relay. Just as an aside, when you add additional
> turnsignal bulbs to the circuit, as you would be doing, for example,
> by
> wiring in trailer turnsignals, you will be increasing the load
> current.
> Only then is it possible that you could conceivably exceed the
> current-carrying capability of the output side of a relay.
>
> However, as has been pointed out, the decrease in load current caused
> by
> replacing turnsignals with LEDs, can upset the flash rate.  That's why
> you add more load (suitable resistors added in parallel to the LEDs to
> increase the current back to what it was before the lightbulbs were
> replaced.
>
> I had a look at the schematic of the Sprint RS and here's what I
> found:
>
> There is no relay.  There is an Indicator Unit and no, this is not
> just
> a case of semantics. It is the OUTPUT of this flasher unit that is
> directed (by way of the turn signal switch) to either the left- or
> right-side indicators depending on which way you throw the switch.
> Therefore the entire load current drawn by the signals IS passing
> through the turnsignal switch.  Any decrease in this load current can
> change the flash rate.  So you would need the additional 'load
> equalizing' resistors to increase the total current drawn from the
> flasher unit.
>
> Neil
>
> ----- Original Message ----- 
> From: "Paul English" <tallpaul@xxxxxxxxxxxxx>
> To: <ST@xxxxxxxxxxxxxx>; <rgalea@xxxxxxxxx>
> Cc: <brian@xxxxxxxxxx>
> Sent: Friday, September 09, 2005 12:28 PM
> Subject: Re: [ST] Spastic turn signals
>
>
> >
> >
> > On Fri, 9 Sep 2005, Rupert Galea wrote:
> >
> > > On 9/9/05, Brian Nobles <thenobles@xxxxxxxxx> wrote:
> > > > I bought some Lockhart Phillips Short Stalk III LED turn signals
> (like
> > > > these:
>
http://www.newportcycleparts.com/categories/electrical/turn_sigs-short.htm).
> > > >
> > > > They work great but... now my signals flash at about a rate of
> 3x's per second.
> > > >
> > > > Anybody know how I can get them to slow down?
> > > >
> > > > I assume it has something to do with resistance or ohms or watts
> or
> > > > volts or something else like that (I can barely spell
> elektrickle
> let
> > > > alone speak intelligently about it).
> > >
> > > You need to add a resistor
> > > http://www.customdynamics.com/led_motorcycle_lighting_faqs.htm
> >
> > Bringing the resistance (and wattage) of your LED signals back up to
> the
> > same as your original bulbs in order for the original flasher relay
> to
> > work. Thus destroying any possible value of going to LEDs in the
> first
> > place (power savings) and then you get to live with the reduced
> viewing angle that the LEDS have.
> >
> > What you *really* want to do is replace the turn signal relay with
> one
> > sized for the lower power draw of the LEDs. This is a pretty common
> > problem on 4-wheeled vehicles when you ad a trailer and suddenly
> you've
> > got twice the power draw on your turn signals - the original relay
> doesn't
> > work any more.
> >
> > Unless of course it is just a matter of having a separate wire
> controlling
> > flash and the original relay *can* handle the power difference & the
> > "flash" signal just isn't getting through. In that case the fix
> referred
> > to by others will work.
> > _______________________________________________
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> >
> >
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