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

[posplayr]

Thanks to jwegman for finding this and FusionFanatic the original author for writting it;
I made no contribution other than reviewing and posting here. It looks like a nice explaination.

http://www.mp3car.com/vbulletin/faq-emporium/117895-faq-relays-how-they-work-how-wire-up.html

For anybody in the US these Tyco Relays (formerly Bosch) are apparently environmentally sealed and really are only marginally more expensive.

http://www.parts-express.com/pe/show...number=330-070

http://www.weltronics.com.cn/pdf/pline/TycoElectronics/12434032588960.pdf

Some more background on Relays; (it is a little more advanced).
http://www.parts-express.com/resources/relays.html

And a cross link to my flavor of Coil Mod relay
http://www.thegsresources.com/_forum/showthread.php?t=141055

Now to our normally scheduled programming ...................shhhhhh lights down


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

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.

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.

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.

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);

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!

__________________
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Fusion Carputer [1.0]
Last edited by FusionFanatic; 04-27-2008 at 09:23 PM.

 

[Guest]

Good work Jim.
This should help alot of folks.
I think it's good to mention that he writes these himself and doesn't copy and paste.

 

[posplayr]

I think it's good to mention that he writes these himself and doesn't copy and paste.

Huh? Who is "He"?

 

[Steve]

Huh? Who is "He"?

"He" is the middle of "they".

You know the guys, "they say that ...", etc. :-\\\

.

 

[posplayr]

"He" is the middle of "they".

You know the guys, "they say that ...", etc. :-\\\

.

I see them now

 

[fgrable@sbcglobal.net]

5 tab socket with lead wires for Bosch 5 tab relays:


http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=330-075&scqty=3

 

[Steve]

5 tab socket with lead wires for Bosch 5 tab relays:
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=330-075&scqty=3

The sockets work quite well, but they add about an inch or so to the space that is required to mount the relay.

There is no electrical advantage because you still need to connect to the wire that goes to the socket.
The only real advantage is that the wires stay in the same location if you happen to remove the relay.

.

 

[posplayr]

The sockets work quite well, but they add about an inch or so to the space that is required to mount the relay.

There is no electrical advantage because you still need to connect to the wire that goes to the socket.
The only real advantage is that the wires stay in the same location if you happen to remove the relay.

.

I think the real advantage is in gas milage and handling. You dont have to trailer a portable generator behind the bike, so you can run your 120 VAC soldering iron to remove the relay at road side :-\\\.

Pulling the relay to swap in a new one is a distict advantage over soldering direct to the relay.

 

[bonanzadave]

so you can run your 120 VAC soldering iron to remove the relay at road side :-\\\.

Gotta have one of these in the survival kit.

http://www.radioshack.com/product/index.jsp?productId=3086616

 

[posplayr]

Gotta have one of these in the survival kit.

http://www.radioshack.com/product/index.jsp?productId=3086616

Never seen one of those

 

[cowboyup3371]

Great read POS but can we now put it all into perspective from the viewpoint of something like my bike? What types of modifications would I want to use this for? Something like running lights as well as my turn signals? Or could I do much where I would need one on a GS550?

Also, when does adding something on become too much for both the battery and stator for these bikes?

 

[posplayr]

Great read POS but can we now put it all into perspective from the viewpoint of something like my bike? What types of modifications would I want to use this for? Something like running lights as well as my turn signals? Or could I do much where I would need one on a GS550?

Also, when does adding something on become too much for both the battery and stator for these bikes?

Cowboy,
This thread was intended as a tutorial on relays only as relay mods for various components are covered elsewhere. BassCliff's website has several or search here. This is just ABC's or relays.

The first and most importnat is Coil Relay mod (actually ignition circuit).

next maybe horn or lights depending if you have outfitted your bike with extra power consuming units.

Jim

 

[Nessism]

Nice write up by Jim. Bumping this back up to the top. This diagram would have helped me when wiring up the coil relay mod on my bike...

 

[Steve]

Pulling the relay to swap in a new one is a distict advantage over soldering direct to the relay.

True enough, but I have never soldered directly to the relay. I have always used spade terminals to the relay contacts.

There is an advantage of doing it that way, too. If you use a socket, you have to overcome the tension of all 4 or 5 terminals, all at the same time.
By just using spade connectors, you can do one at a time.


Another thing to remember for anyone comtemplating a relay "upgrade", ...
there is nothing fancy or exotic about a relay. It's only a remote-controlled switch.

.

 

[850GT_Rider]

Personally, I would never solder to relay terminals. Too great of a chance you could overheat the connection and melt the solder connections on the INSIDE of the relay.

For our applications with limited space, and vibration being an issue, I use spade terminals, crimped & soldered to the wire end and covered all the way to the end with heat shrink tubing. If you want to use a socket, I'd ty-wrap the relay to the socket.

 

[posplayr]

True enough, but I have never soldered directly to the relay. I have always used spade terminals to the relay contacts.

There is an advantage of doing it that way, too. If you use a socket, you have to overcome the tension of all 4 or 5 terminals, all at the same time.
By just using spade connectors, you can do one at a time.


Another thing to remember for anyone comtemplating a relay "upgrade", ...
there is nothing fancy or exotic about a relay. It's only a remote-controlled switch.

.

Steve, I was not suggesting soldering directly to a relay.

 

[posplayr]

Nice write up by Jim. Bumping this back up to the top. This diagram would have helped me when wiring up the coil relay mod on my bike...

that is kinda nice :dancing:;

 

[Steve]

Steve, I was not suggesting soldering directly to a relay.

No, but you did mention it back in post #8.

And I was just pointing out the advantage of individual spades instead of a socket.

.

 

[posplayr]

No, but you did mention it back in post #8.

And I was just pointing out the advantage of individual spades instead of a socket.

.

If you want to be difficult about it, I specifically pointed out that there was an advantage to using a relay connector in direct contrast to your comment that there was none.

 

[Nessism]

I used individual spade terminals but would have preferred to use a socket. Either way though the connections are not water proof. I'd like to find a boot of some sort to cover the relay and wires to provide some protection. Any ideas?