how relay works ? Options

[jimkelly]

and can some describe how a relay works?

is it that HIGH AMPERAGE thru 85 and 86 operate a switch, and when switched send LOW AMPERAGE thru 30 and 87? what is 87A's purpose?

[914itis]

How relay works Have fun

[arcadeforever]

from what I can see.... oddly enough it appears 87a has no purpose, its a pole for whatever event 85 and 86 do to 30 that make 30 switch to 87 (85,86 could be the grid for a rear defroster system(just a wild guess)). Im not sure WHY 87a has nothing hooked to it. I guess Id have to see the rest of the schematic.

this is a SPST (Single Pole Single throw) switch/relay. relays have tons of applications, this is a pretty smart relay where the sensor within the relay switches the load, typically, what they pretty much do is use a low power circuit to turn on a high power circuit. A relay in a fog light scenario, where, when two terminals are connected via a switch will actuate a high current switch that turns on the lights.

You cant eliminate the relay in this type of circuit or you will watch the switch in your dash melt into a puddle (IMG:style_emoticons/default/smile.gif) The relays' high current contacts are made of MUCH thicker metal so it can handle the current/heat.

The double relay for the FI system is an amazing little relay that gets switched on when the key turns to on and ALSO has a set of inputs from the AFM that turn on the fuel pump, so basically the fuel pump gets turned on with the AFM is actuated meaning the engine is creating vacuum. Of course it does more than that...

and can some describe how a relay works?

is it that HIGH AMPERAGE thru 85 and 86 operate a switch, and when switched send LOW AMPERAGE thru 30 and 87? what is 87A's purpose?

[arcadeforever]

wow, thats a great document!

How relay works Have fun

[arcadeforever]

Shows how much of a newb I am, lol, I just saw in another post that this is one of the relays on the relay board. Im sure I will grow to know them (IMG:style_emoticons/default/smile.gif)

from what I can see.... oddly enough it appears 87a has no purpose, its a pole for whatever event 85 and 86 do to 30 that make 30 switch to 87 (85,86 could be the grid for a rear defroster system(just a wild guess)). Im not sure WHY 87a has nothing hooked to it. I guess Id have to see the rest of the schematic.

this is a SPST (Single Pole Single throw) switch/relay. relays have tons of applications, this is a pretty smart relay where the sensor within the relay switches the load, typically, what they pretty much do is use a low power circuit to turn on a high power circuit. A relay in a fog light scenario, where, when two terminals are connected via a switch will actuate a high current switch that turns on the lights.

You cant eliminate the relay in this type of circuit or you will watch the switch in your dash melt into a puddle (IMG:style_emoticons/default/smile.gif) The relays' high current contacts are made of MUCH thicker metal so it can handle the current/heat.

The double relay for the FI system is an amazing little relay that gets switched on when the key turns to on and ALSO has a set of inputs from the AFM that turn on the fuel pump, so basically the fuel pump gets turned on with the AFM is actuated meaning the engine is creating vacuum. Of course it does more than that...

and can some describe how a relay works?

is it that HIGH AMPERAGE thru 85 and 86 operate a switch, and when switched send LOW AMPERAGE thru 30 and 87? what is 87A's purpose?

[pcar916]

To answer in short...

When the circuit is completed (low current like a switch) between 85 and 86,

1. 87 is grounded on a (high current) circuit separate from the 85/86 circuit
2. whatever device it's attached to will be provided with a ground at that point.

- The device grounded by 87 gets it's power (+12v) separately from this relay.

- 87a is unused in this application, but could used to ground another device when 87 is not grounded. For instance it could ground anything from another device to a simple indicator light that shines when 87 is not grounded.

30 is always a hard, rather than the switched ground indicated by number 15.

Good luck

[JStroud]

How relay works Have fun

Nice link, where did you find that, you're link shows a 914world address, but I couldn't find a section of the site that has that kind of info....unless I use your link (IMG:style_emoticons/default/confused24.gif)
Am I missing something.

Jeff

[pcar916]

Bowlsby has a lot of information on his site.

https://bowlsby.net/914/Classic/

[Dave_Darling]

I also have a write-up, about halfway down in this page:

http://members.rennlist.org/damp_dave/electric.html

--DD

[pcar916]

Forgot about this! That's a great write-up Dave.

[914itis]

How relay works Have fun

Nice link, where did you find that, you're link shows a 914world address, but I couldn't find a section of the site that has that kind of info....unless I use your link (IMG:style_emoticons/default/confused24.gif)
Am I missing something.

Jeff

It was a PDF attached to a thread, I copied the link to the PDF instead of the thread.

[jimkelly]

freakin ingenious.

since our cars are run from a 12v battery, how does current know to be high or low, simply by the diameter of the wire it passes thru, or the draw of the item being run?

I assume running a circuit with a relay is cheaper than running a circuit thru a switch that can handle more current because of the cost of a better switch and the cost of running more heavy wire throughout the car?

I think I am beigining to understand the purpose of a relay, visually.

thanks guys (IMG:style_emoticons/default/idea.gif)

i think image is correct?

[Mike Bellis]

Current is limited by the fuse size and to some extent by the wire size.

[Mike Bellis]

By the way current is stupid and don't know shit.

87a is a normally closed contact and has a million uses.

Are you guys for reals??? (IMG:style_emoticons/default/confused24.gif)

[Spoke]

freakin ingenious.

since our cars are run from a 12v battery, how does current know to be high or low, simply by the diameter of the wire it passes thru, or the draw of the item being run?

I assume running a circuit with a relay is cheaper than running a circuit thru a switch that can handle more current because of the cost of a better switch and the cost of running more heavy wire throughout the car?

I think I am beigining to understand the purpose of a relay, visually.

thanks guys (IMG:style_emoticons/default/idea.gif)

The thickness of the wire is determined by the load. Heavy load needs thick wire; light load needs thinner wires.

Cost and practicality determine minimum wire size. For example running battery cable thick wires through the car would be very expensive and would not fit under the dash.

The current draw is determined by the type of load for example:
1) A side marker light might draw 1AMP and only needs a small diameter wire.
2) A headlamp might draw 5-10AMP will need a heavier wire.
3) A starter might draw 60-100AMP will need a real heavy wire.

You are correct about the relay. It allows a small switch to switch a large current.

Think about a 914 with 2 headlights, 2 heater fans, the ECU, and FP. Even a large switch couldn't turn all these on/off. Each is run by relays where the ignition switch turns on the relays and the relay contacts carry the high currents.

[Tom]

Relays use a small current to control a much larger current. The round relays in our cars draw about 150 mili Amps, or 0.150 amps. Their contacts can control upwards of 30 Amps. Relay contacts are made out of an alloy that resists arcing when being switched/un-switched, unlike our other switches used in the car. Other switches can have their contacts damaged by switching high current. That is why it is better to have a low current thru your switch and higher current thru the relay.
Tom

[r_towle]

Current or load is always dictated by the device calling for the power.
Sizing the circuit (wire, fuse, relay) is always dependent upon the device being driven by the power.
Power is not pushed, power is pulled by the device.

Starter motor is a very simple example.
The motor needs 600 CCA (cold cranking amps) so there is no fuse, just a fat wire directly connected to the battery.
The relay for that motor (starter solenoid) needs 20 amps to flip the switch.

So trigger amps requirements are fairly small, while the device amp requirements could be huge.

All electricity is this way...

[Mike Bellis]

Read this...

 BoschGuide.pdf ( 3.2mb ) Number of downloads: 85

[pcar916]

...
i think image is correct?

30 is always a permanent ground. You can check it with an ohmmeter to a chassis ground point.

[underdog]

...
i think image is correct?

30 is always a permanent ground. You can check it with an ohmmeter to a chassis ground point.

On Kelly's fog light diagram if pin 30 is ground does the high current come in to 85? I really need this info to hook up my fogs.