[Spridgets] Relays

[Mark A. O'Neil]

> From: Kirk Hargreaves <khargreaves2 at gmail.com>
>
> I am in the "dark" about this - relays, why are they effective?
>
> My ignition dash switch went out on me about a year ago.  In the  
> wait time
> to get a new switch, lock, keys, etc I wired my lights up to a  
> simple off /
> on switch on my dash.
>
> My ignition switch is wired under the dash to a place that would not  
> be
> obvious.  I reach under the dash to turn the car on before I pull the
> starter (which is wired to an off / on switch behind the dash).
>
> Did I need a relay to do this?  The car has been running fine like  
> this for
> a good while now.
>
> Are relays used when you want two things to turn on together?  Ok,  
> stupid
> question. . . but I am curious regarding the application or the  
> reason for
> relays?

Hi Kirk,

Relays are useful for separating a high load circuit eg lights from a  
low load controlling circuit eg the switch. The relay switch only  
powers a low current coil which throws the relay closing the high  
current portion of the circuit. The lower current required for the  
switch side is generally safer for the user and easier on that side of  
the circuit - switches last longer.

I believe in the case of our cars the reason the light switches fail  
is that the newer ones simply cannot hold up to the amps pushed  
through for extended night driving. Placing a relay in the circuit  
puts the load for the switch more around 30mA instead of ?20A? so the  
switch lasts longer. The reason lights are brighter is less voltage  
drops in the loop means more action at the lights.

Okay that is all I've got/can remember from 1979 electronics 101.

-m