RELAYS; how they work and how to wire it up...

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Petrusd
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Thu Oct 07, 2010 3:03 pm

Oulike artikel wat ek op die net gekry het na ek die post viewtopic.php?f=14&t=14646" onclick="window.open(this.href);return false; gelees het..

Hoop dit help iemand

There seem to be many members who don't know what a relay is, or don't know how to wire one in. this guide is here to help solve that issue...

what is a relay?
-a relay is a device that allows you to control a high-current electrical load with a low-current electrical 'signal'. they are usually electro-magnetic, but are also available in solid-state forms. they can be used with a switch (to allow control of a high-current load with a small switch) or they can be hooked up to a switched power source in the car like the ignition or accessory power circuits (to allow power to be switched on/off automatically with the ignition key).

Why do I need a relay?
-when hooking anything up to a car's factory wiring, it's important to remember that factory wires are designed to carry the load of only the factory installed components. they are not 'general use' power circuits like the power outlets in your house. for example, the ignition (IGN) circuit is designed to power the car's ignition system and nothing else. hooking up a high-current device to this circuit can create a fire hazard. by using a relay, you can use the IGN circuit to control a high-current device without directly powering it from the IGN circuit itself.

Is a relay hard to hook up?
-no... most relays require only 4 wires.

Where can I buy a relay, and how much do they cost?
-you can buy standard automotive relays at radio shack, autozone, walmart, or at almost any electronics store or automotive store. a typical SPST relay will cost about $5(US).

I bought a relay, but I don't know how to hook it up. all I see are a few weird numbers and strange symbols, what do they mean?
-a standard bosch-style relay will have 4 or 5 numbered leads (30, 85, 86, 87, and sometimes 87a). why they picked those numbers, I have no clue; but I can tell what they hook up to.

-30 = constant [positive (+)] power (usually wired directly to car battery)
-85 = coil ground (wired to the negative (-) battery terminal or any grounded metal panel in the car)
-86 = coil power (wired to the control source. could be a switch, or it could be the car's IGN or ACC circuit.)
-87 = switched [positive (+)] power output. (when the relay coil is powered, lead/pin 87 is connected to lead/pin 30)
-87a = [on 5 lead/pin relays only] this lead/pin is connected to lead/pin 30 when the coil is NOT powered.

here is the bottom view of a standard 4-lead Bosch-style automotive SPST relay

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here is what happens inside the 4-lead/pin SPST relay. on the left, the coil is NOT powered. on the right, the coil IS powered. notice the switch changes positions when the coil is powered. when the coil is powered, pins 30 and 87 are connected. when the coil is NOT powered, then pin 30 is not connected to anything, therefore it is in the 'off' position.

Image

here is the bottom view of a standard 5-lead Bosch-style automotive SPDT relay. you'll notice that the only difference is the addition of the 87a lead/pin.

Image

here is what happens inside the 5-lead/pin SPDT relay. you'll notice that instead of an 'off' position, there is an electrical contact (87a). on the left the coil is NOT powered, and pins 30 and 87a are connected. on the right the coil IS powered, and pins 30 and 87 are connected.

Image

here is a typical setup to control power to a carPC via the car's ACC/IGN circuits. this is generally use for laptop installs or 'no-write' setups (not good for normal carPC because abruptly cutting power without proper shutdown can cause data corruption);

Image

I want to use the relay to turn on/off with the car. how do I hook that up?
-connect lead/pin 86 to the car's IGN, or ACC circuit. these circuits can be tapped into in the wiring harness that goes to your car's key switch. the ACC circuit can also be tapped into at the fuse box or in the stock radio harness.

What is the difference between the ignition (IGN) and the accessory (ACC) circuit?
-they are both powered when they key is in the 'RUN' position, and they are both not-powered when they key is in the 'OFF' position.

-the 'ACC' circuit is powered when the key is in the 'ACC' position, but is not powered when the key is in the 'START' position. when the key is turned, power to the relay will turn on as the key passes the 'ACC' and 'RUN' positions, then turn off in the 'START' position, then turn back on as the key is released (springs back to the 'RUN' position. this is not an issue if you're using a manual on/off switch, or have a delayed on startup controller.

-the IGN circuit is powered when the key is in the 'START' position, but is not powered when the key is in the 'ACC' position. this circuit avoids the issue stated above, but requires that the key is left in the 'RU' position if you want to use the carputer with the engine off. on some cars, this can burn out the ignition coil.

I bought a 5-pin relay, can I still use it as a simple on/off switch instead of a changeover switch?
-yes. simply leave pin 87a disconnected.

My relay has more than 5-leads/pins?
if your relay has more than 5-leads/pins then is is most likely a DPDT, MPDT, or MPMP relay (M=multiple). it will work the same way, it simply has two or more separate switched inputs/outputs inside it. regardless of the number of switched contacts, it will still use a single coil, so it will still be controlled by a single power source.

Are there others types of relays other than the standard 'bosch style automotive relay'?
yes, just like regular switches, there are several different types, sizes, and styles of relays. some have multiple switched contacts, some are circuit-board mountable, some have high-current capacity, some have low-current capacity, some use higher or lower voltage coil power (generally you would only use a 12v coil in a car).

What is a 'valet switch'?
-the 'valet switch' is a standard SPST switch wired between the coil power source and pin 86. it allows you to leave the relay turned off, so nobody (including a 'valet' driver) can turn your carPC on. how effective this will be depends on how well you hide the switch (it should be accessible, but hidden from plain sight).

does a relay take the place of a fuse?
-no! a relay provides no protection from overload or short-circuits.

do I need to use a fuse if I use a relay?
yes! you must still fuse your power wires!

Source:http://www.mp3car.com/vbulletin/faq-emp ... re-up.html

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CasKru
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Thu Oct 07, 2010 3:23 pm

Baie netjies
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Thu Oct 07, 2010 8:57 pm

nooit te oud om iets te leer nie. Baie nice
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Thu Oct 07, 2010 9:44 pm

Ek vote dat die n sticky gemaak word, vir quick reference.
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OOOOMS
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Fri Oct 08, 2010 7:07 am

My dogter se sucker is 'sticky' :wink2:

Stem saam, het ook al lekker gesukkel met 'n relay :!:

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Fri Apr 15, 2011 9:29 pm

Need some advice wiring 4 spotlights?
Each spot is 110w! What size wire, relay and fuse would I need?
I was thinking? 35A fuse with 6mm wire? with compatible relay.
Spots is going on the roof, with roof-rack.
It is 4 Ring spots I bought in the UK, maybe it is overkill :evil: :evil: :evil:

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Stef
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Fri Apr 15, 2011 9:47 pm

That 35A fuse might be a bit light, you're looking at 36.4A roughly. I would rather go with a 10mm^2 cable, 16mm^2 if the distance is longer than 2metres.

Look here for more info http://www.windsun.com/Hardware/Wire_Ta ... 0reference

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Fri Apr 15, 2011 10:02 pm

Thanks for the info

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Fri Apr 15, 2011 10:39 pm

Just be careful to buy the right relays, 4 pin relays come in 2 layouts...

First, the common one, 85 opposite 86... and 30 opposite 87 pin...

But then you get another 4 pin layout:

IIRC... 85 opposite the 87 and the 30 opposite 86.... generally a Hella relay

I helped a friend rewire his 5MGE SFA Hilux conversion and ran into these 'alternative pin layout' relays... they almost caught me out!

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Thu Jul 14, 2011 9:50 pm

Interesting, dankie vir die link.
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Sun Jan 15, 2012 8:20 am

Nou net terug van verlof en kom toe agter my ligte wil nie afskakel nie :-( Die enigste manier is om die hoofligte se Relay uit te haal. Ek het die Relay getoets en dit lyk nie of daar fout met die Relay is nie. Ek is egter nie 100% oortuig nie ! want dit lyk of die Relay se coil wel na ,n rukkie die relay oopmaak???. Wat my ook pla is dat daar self nadat ek die skakkelaar afgesit 'n spannings verskil oor die coil se terminale is op die voertuig met die Relay verwyder. As ek die skakellaar aansit styg dit met so 2V - Beteken dit die skakelaar is stukkend of daar is erns 'n kortsluiting in die stroombaan?

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Sun Jan 15, 2012 8:29 am

mtbbiker wrote:Nou net terug van verlof en kom toe agter my ligte wil nie afskakel nie :-( Die enigste manier is om die hoofligte se Relay uit te haal. Ek het die Relay getoets en dit lyk nie of daar fout met die Relay is nie. Ek is egter nie 100% oortuig nie ! want dit lyk of die Relay se coil wel na ,n rukkie die relay oopmaak???. Wat my ook pla is dat daar self nadat ek die skakkelaar afgesit 'n spannings verskil oor die coil se terminale is op die voertuig met die Relay verwyder. As ek die skakellaar aansit styg dit met so 2V - Beteken dit die skakelaar is stukkend of daar is erns 'n kortsluiting in die stroombaan?
Vir my klink dit so. :think:
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Sun Jan 15, 2012 8:44 am

Mud Dog wrote:
mtbbiker wrote:Nou net terug van verlof en kom toe agter my ligte wil nie afskakel nie :-( Die enigste manier is om die hoofligte se Relay uit te haal. Ek het die Relay getoets en dit lyk nie of daar fout met die Relay is nie. Ek is egter nie 100% oortuig nie ! want dit lyk of die Relay se coil wel na ,n rukkie die relay oopmaak???. Wat my ook pla is dat daar self nadat ek die skakkelaar afgesit 'n spannings verskil oor die coil se terminale is op die voertuig met die Relay verwyder. As ek die skakellaar aansit styg dit met so 2V - Beteken dit die skakelaar is stukkend of daar is erns 'n kortsluiting in die stroombaan?
Vir my klink dit so. :think:
Dankie, ek sal maar na Auto Elektrisien gaan want die parkeer ligte werk nog 100%. Ek sien om die skakelaar te vervang moet die stuurwiel en lugsakke ontkoppel word. :thumbdown:

PS: Ek sien nou jy is van Oos Londen. Ek was daar naby laas week (Cintsa). Ons het soontoe natuurlik die "scenic" toete gevolg :shh: via die Lapa Munnik pas (Bastevoetpad). Julle omgewing het ons betower :thumbup:

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Sun Jan 15, 2012 10:09 am

Hi, moontlik is jou voertuig positief bedraad, doodeenvoudig beteken die dat jou + kragdraad direk na jou applikasie, in die geval jou ligte gaan. Vanaf die neg. vanaf die lig gaan die draad na jou kontrole of skakelaar. In jou geval is die neg draad van die ligte iewers deurgeskuur en short direk op die bakwerk wat die ligte aanskakel sonder jou kontrole. As dit ''n hilux is, kyk links voor in die engine bay onder die aircleaner loop 'n dik string drade. Verwyder die aircleaner en inspekteur baie mooi vir skaafmerke. As die fout nie daar is nie, gaan die hele harnas na in die engine bay, kyk ook mooi waar die harnas voor die radiator onder die bonnet catch aangele is. Sterkte

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Sun Jan 15, 2012 1:08 pm

doppies wrote:Hi, moontlik is jou voertuig positief bedraad, doodeenvoudig beteken die dat jou + kragdraad direk na jou applikasie, in die geval jou ligte gaan. Vanaf die neg. vanaf die lig gaan die draad na jou kontrole of skakelaar. In jou geval is die neg draad van die ligte iewers deurgeskuur en short direk op die bakwerk wat die ligte aanskakel sonder jou kontrole. As dit ''n hilux is, kyk links voor in die engine bay onder die aircleaner loop 'n dik string drade. Verwyder die aircleaner en inspekteur baie mooi vir skaafmerke. As die fout nie daar is nie, gaan die hele harnas na in die engine bay, kyk ook mooi waar die harnas voor die radiator onder die bonnet catch aangele is. Sterkte
Dankie,

Dit klink moontlik toe ek vanoggend alles weer toet to is daardie spanning oor die coil van die relay weg ??. Wat vir my se daar is oop drade erens, aangesien hierdie probleem begin het nadat ons deur hengse reen gery het oppad terug. Dit klink ek gaan soek vir 'n naald in 'n hooimied :think:

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Frontier 320
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Sat Jun 21, 2014 4:21 pm

always wanted to know why we need them :)

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