 Use of relay for the electronic guru'st |
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| 914itis |
 Mar 5 2013, 01:56 PM
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#1
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Advanced Member  Group: Members Posts: 2,892 Joined: 9-October 10 From: New York City Member No.: 12,256 Region Association: North East States  |
Lets say I am hooking up a horn or a a light with an on -off switch, why not just connect to power source with the switch? Why use a relay ?.
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| 914GT |
Mar 5 2013, 02:02 PM
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#2
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Senior Member Group: Members Posts: 1,100 Joined: 11-October 04 From: Tucson Member No.: 2,923 Region Association: Southwest Region |
A couple of reasons .... it takes the high current load off your ignition switch or whatever controlling it. Second, reduces voltage drops from wiring resistance.
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| PDXMike |
Mar 5 2013, 02:05 PM
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#3
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Slowly Learning Group: Members Posts: 111 Joined: 20-December 10 From: Portland, OR Member No.: 12,501 Region Association: Pacific Northwest |
Usually a relay is used so that the high power needed to run the accessory doesn't need run through the entire switch circuit. Either the total length would be too long (too much resistance and loss) or the switch itself wouldn't handle the current.
The best example is the starter. The starter pulls a LOT of current. The switch in the steering column couldn't handle all that current, and running all that power from the battery to the dash and back would add up to a lot of loss simply because of the length of the wires. |
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| SirAndy |
Mar 5 2013, 02:17 PM
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#4
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Resident German Group: Admin Posts: 41,637 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
QUOTE(914GT @ Mar 5 2013, 12:02 PM)  it takes the high current load off your ignition switch or whatever controlling it. Second, reduces voltage drops from wiring resistance. (IMG:style_emoticons/default/agree.gif) |
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| Cupomeat |
Mar 5 2013, 02:19 PM
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#5
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missing my NY 914 in VA Group: Members Posts: 1,336 Joined: 26-November 07 From: Oakton VA Member No.: 8,376 Region Association: MidAtlantic Region |
QUOTE(SirAndy @ Mar 5 2013, 03:17 PM) QUOTE(914GT @ Mar 5 2013, 12:02 PM) it takes the high current load off your ignition switch or whatever controlling it. Second, reduces voltage drops from wiring resistance. (IMG:style_emoticons/default/agree.gif) AND, any voltage drop result in a corresponding increase in current for the same load, which burns things out faster. |
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| 914itis |
Mar 5 2013, 02:45 PM
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#6
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Advanced Member Group: Members Posts: 2,892 Joined: 9-October 10 From: New York City Member No.: 12,256 Region Association: North East States |
Thanks guys .
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| Mike Bellis |
Mar 5 2013, 07:25 PM
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#7
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None 
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