DIY: Relay wiring
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Joined: Mar 2004
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From: B.C., Canada
Rep Power: 786 
DIY: Relay wiring
So I haven't seen this on here anywhere yet. Relays are great resources in 12v wiring. Although they might seem complicated at first, they are very simple once you get acquainted with them. Some people, including myself, might shy away from them at first as they seem too complicated, but the purpose of this little DIY is to show you that they aren't.
First of all, what is a relay? There are many kinds, the variety most often used in car audio is the SPDT (single pole, dual throw) type. This means they have a single source (the pole) and two outputs (the throws) that are either open or closed based on whether or not the relay is energized or not.
The most common style is known as the Bosch style, pictured below. There are five terminals, all serving different, but different functions. The terminals are as follows (for the example, I will be assuming you are tapping off an accessory power wire)
30 - The terminal for the power source to be switched. This would usually be a power wire coming from your battery.
85 - The input for your switching source. You would normally tap an accessory or ignition wire and connect it here. This is what will trigger the relay into opening or closing pins 87 and 87a. This is where the accessory power wire that you tapped into would connect to.
86 - Ground. Relay coils do not have polarity, therefore pins 85 and 86 can be hooked up either way (either one could be power or ground). I use 86 for ground, for no particular reason.
87 - Normally open terminal. When the coil is not energized (key is out of the ignition, accessory wire isn't live), no current will flow through this terminal. When you turn the key on (accessory wire becomes live), the coil will energized and terminal 87 will become live. If you for example, wanted a power inverter to turn on when you turn the key, you would turn the key to acc and the coil would energize, turning the inverter on.
87a - Normally closed terminal. When the coil is not energized, this terminal will have power.
So, between 87 and 87a, only one can have power at a time. Think of the coil as being able to route the power between the two terminals.
EXAMPLE: Say I wanted to wire up some neon lights in my trunk so that they come on whenever my amps are turned on. I don't want to wire them right to the remote line, I want them to get power directly from a distro block mounted in my trunk.
I would tap the remote wire going to the amplifier and connect it to terminal 85 on the relay. Terminal 86 would go ground. I would run a wire from the distro block to terminal 30. Finally, the neon lights would be connected to terminal 86. Simple as that, the neon lights will turn on with the amplifiers.
I guess this was a bit longer than I wanted it to be, but hopefully it's simple enough for a beginner to understand, I've explained everything with as little writing as possible, but with enough for you to get a good idea how everything works.
If there's any other questions or comments, post em in the thread
.
And for further reference, a drawing of what the pinout on the bottom of a Bosch relay looks like.
First of all, what is a relay? There are many kinds, the variety most often used in car audio is the SPDT (single pole, dual throw) type. This means they have a single source (the pole) and two outputs (the throws) that are either open or closed based on whether or not the relay is energized or not.
The most common style is known as the Bosch style, pictured below. There are five terminals, all serving different, but different functions. The terminals are as follows (for the example, I will be assuming you are tapping off an accessory power wire)
30 - The terminal for the power source to be switched. This would usually be a power wire coming from your battery.
85 - The input for your switching source. You would normally tap an accessory or ignition wire and connect it here. This is what will trigger the relay into opening or closing pins 87 and 87a. This is where the accessory power wire that you tapped into would connect to.
86 - Ground. Relay coils do not have polarity, therefore pins 85 and 86 can be hooked up either way (either one could be power or ground). I use 86 for ground, for no particular reason.
87 - Normally open terminal. When the coil is not energized (key is out of the ignition, accessory wire isn't live), no current will flow through this terminal. When you turn the key on (accessory wire becomes live), the coil will energized and terminal 87 will become live. If you for example, wanted a power inverter to turn on when you turn the key, you would turn the key to acc and the coil would energize, turning the inverter on.
87a - Normally closed terminal. When the coil is not energized, this terminal will have power.
So, between 87 and 87a, only one can have power at a time. Think of the coil as being able to route the power between the two terminals.
EXAMPLE: Say I wanted to wire up some neon lights in my trunk so that they come on whenever my amps are turned on. I don't want to wire them right to the remote line, I want them to get power directly from a distro block mounted in my trunk.
I would tap the remote wire going to the amplifier and connect it to terminal 85 on the relay. Terminal 86 would go ground. I would run a wire from the distro block to terminal 30. Finally, the neon lights would be connected to terminal 86. Simple as that, the neon lights will turn on with the amplifiers.
I guess this was a bit longer than I wanted it to be, but hopefully it's simple enough for a beginner to understand, I've explained everything with as little writing as possible, but with enough for you to get a good idea how everything works.
If there's any other questions or comments, post em in the thread
. And for further reference, a drawing of what the pinout on the bottom of a Bosch relay looks like.
Thread Starter
Joined: Mar 2004
Posts: 51,077
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From: B.C., Canada
Rep Power: 786 I always use 30 pin as my power source. reason being is that if I DID want to use both 87a and 87, then it would need to be on pin 30, so I do it that way anyway 
but other than that, of course it can be reversed
but other than that, of course it can be reversed
Good writeup. As he mentioned too, relays can be used for all sorts of things, especially when you get into alarms and such. One of the best 12v pieces to play with. Ohh so many possibilities.
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Rep Power: 0 hey, have been wondering if any of you know if you can use the relays to switch residential (120 Volts). I would still use 12 volts for the relay coil, but would put a 120 volts line to pin 30, 87a & 87? cause i know the coil needs to be 12 volts, but the switch (30, 87a & 87) is not connected to the coil. The only problem i see is the AC line will interfere with the coils magnetic action of pulling the switch. anybody here tried it or knows if it is possible. if it is possible, endless possibilitys for the house too. I know they sell relays for house that run off 24 volt AC, but looked everywhere on net and can't find any
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Rep Power: 0 Aside from the ability to allow a relatively small electric signal to switch a relatively large electric signal, relays also offer electrical isolation between coil and contact circuits. This means that the coil circuit and contact circuit(s) are electrically insulated from one another. One circuit may be DC and the other AC (such as in the example circuit shown earlier), and/or they may be at completely different voltage levels, across the connections or from connections to ground.
(from http://www.allaboutcircuits.com/vol_4/chpt_5/1.html)
seems like it could work. Worst comes to worse you blow a few fuses and trip a circuit breaker.
(from http://www.allaboutcircuits.com/vol_4/chpt_5/1.html)
seems like it could work. Worst comes to worse you blow a few fuses and trip a circuit breaker.
Thread Starter
Joined: Mar 2004
Posts: 51,077
Likes: 4
From: B.C., Canada
Rep Power: 786 To put it in simple kinda terms, a relay is an switch that is triggered electronically. There are 5 pins, the trigger (85), which can be something like an accessory wire or any other non-constant wire, ground (86), the input (30), the normally closed (NC) output (87a) and the normally open (NO) output (87). When there is no voltage in the input, there is continuity between pins 30 and 87a. When there is voltage, there is continuity between 30 and 87. It lets current flow based on an electronic event, which would be the trigger wire becoming live. They could be used for example to power neon lights in your trunk. If you wanted the lights to come on with your amp, you could run the remote line from your amp into pin 85, ground pin 86, put a small power wire coming from your amp on pin 87, and have pin 87a going out to your lights. Turn the amps on, relay coil becomes energized, and the lights turn on.
In that application, I'm just referring to a basic single pole, dual throw (SPDT) relay, which are the most common, but there are a million other types as well, but not to confuse you.
In that application, I'm just referring to a basic single pole, dual throw (SPDT) relay, which are the most common, but there are a million other types as well, but not to confuse you.
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