Relays

Post by **Sven** » 19 Dec 2007, 09:04

Probably a stupid question but what exactly is the purpose of a relay?
Sven

Post by **Ye Olde Syncrospares** » 19 Dec 2007, 09:11

its a switch.

Post by **Titus A Duxass** » 19 Dec 2007, 09:23

A relay allows the switching of high current without loading the switch itself.

If you measure the current flow when you e.g. toot a set of horns you should get somewhere around 7 - 9 amps. This is okay through your switch gear (horn button) but only for a very short time. If you were to toot your horn for say 10 minutes your switch gear would get very hot because of the current flow, which could cause damage and more importantly the switch itself will limit the current flow to the horn.

By using the horn button to switch a relay on (to energise) you channel the high current flow through the relay contacts (which are normally around 30 amps.) instead of the horn button. This equals less heat for your switch and more horn! (ooe'r missus!).

Post by **ermie571** » 19 Dec 2007, 09:55

This equals less heat for your switch and more horn! (ooe'r missus!).

Kinda viagra for busses then??

E

Post by **Rozzo** » 19 Dec 2007, 19:23

Titus A Duxass wrote:A relay allows the switching of high current without loading the switch itself.

If you measure the current flow when you e.g. toot a set of horns you should get somewhere around 7 - 9 amps. This is okay through your switch gear (horn button) but only for a very short time. If you were to toot your horn for say 10 minutes your switch gear would get very hot because of the current flow, which could cause damage and more importantly the switch itself will limit the current flow to the horn.

By using the horn button to switch a relay on (to energise) you channel the high current flow through the relay contacts (which are normally around 30 amps.) instead of the horn button. This equals less heat for your switch and more horn! (ooe'r missus!).

thats a good description

if you think of a starter motor in the same way you switch a low current coil with a very thin wire which in turn bridges the 2 massive teminals which turn your engine thru the fat red wire. the coil you energise at low current is actually a powerful electro magnet once energised, which pulls magnetically the 2 contacts together for high current (thats the click you hear from either a relay or a starter motor)
you could do without them if you were prepared to use the massive clunk switches you see in the old frankenstein movies