I am trying to chase down a problem with my Peugeot 306 electric windows and studying the wiring diagram (Haynes) has revealed a rather big gap in my
understanding.
I thought that relays were used to create a switching circuit and an operating circuit so that you could use switches that lower current. On this
diagram it appears that the switches and motors are on one side of the relay and there is just a loop from +ve to earth on the other.
I'd be really grateful if someone could point out what I am missing.
Thanks
Dave
[Edited on 15/12/12 by panichat]
The relay just switches the power on constantly to the window switches when the ignition is on (saves the ignition switch carrying all the current).
Then the motor current is switched directly by the window up/down switches.
Ian
Thanks - it makes sense
Dave
Think of a relay as a remotely operated switch.
You energise the coil, and it operates the contacts.
You are right, You can switch a larger current with a smaller one. But all will depend on the current (AMP) rating of the switching contacts and the
resistance of the coil.
Consider it as TWO circuits.
One to operate the relay (the Horn button).
One to Operate the Horn via the relay contacts.
A relay is a VERY simple device, It has a coil, and a set of contacts.
The cotact configuration can vary. eg Make, Break or Change-over contacts, and multiples or combinations
You operate the coil with a small current. The resistance of the coil causes only a small current to flow in the operating circuit.
The Relay Contacts will switch a heavier current (again depending on the load) to the device.
ALWAYS use a relay with higher rated set of contacts than the devices maximum current. This helps reduce arcing on the contacts, heat, and the relay
plastic case melting, and ultimately FIRE
.
SO:
You need 12v on one side of the coil, and an earth on the other to energise the coil.
It generally does not matter whether you switch the earth or the 12v to energise the coil, it usually depends on whats available at the operating
switch (eg Horn switch) end. Just wire the coil accordingly. ie the horn switch puts out and Earth, you then connect 12v to the coil and it will
operate. Or... Vice versa ie 12v from the horn button will need an earth on the other side of the relay coil to operate it.
As for the output side of the relay, Its just a set of switch contacts. Wire up as necessary to operate the device. Personally I prefer to switch
12v to the device, so that the device has an Earth on the end of it, as it leaves less of the wiring with 12V sitting on it when not in operation.
However a lot will depend on how the manufacturer as done their wiring, and this may be beyond your control.
Hope that helps.
Just as an aside, I spent nearly 10 years working on Strowger telephone exchanges, and they all operated with relays, or electro-mechanically switched
devices. Its amazing what you can achieve with a handful of relays!
Just think... 40 years ago, the entire worlds telephone system was just a bunch of relays, electromagnets, and switch contacts! Now its all chips and
transistors under control of processors and some very slick software.
There is nothing to watch go round or up and down anymore. It was fascinating to watch it in operation
Now its just a few blinking lights.
Just as an aside, I spent nearly 10 years working on Strowger telephone exchanges, and they all operated with relays, or electro-mechanically switched
devices. Its amazing what you can achieve with a handful of relays!
Couple of years for me 
Tunbridge Wells zone switching centre and a load of UAX 13 exchanges, they were really old.
Far more satisfying than electronics as long as you were not on bank cleaning
Assuming you're trying to diagnose knackered electric windows on a 306, check the plugs that connect the door to the chassis. They're
notorious for letting water in which corrodes the contacts and stops the door electrics from working.
Chris
Also check that the wires to those plugs haven't snapped off the pins. Had a bitch of a job with this on my mates Rover75. In the end I just cut the connector plug and socket off and hard wired the bloody thing, as he was selling it.
306's are also prone to electric window problems caused by broken wires where they run through from the body in to the door
If you are talking about relay 130 it is odd. The switching circuit seems separate from the ignition and supplied by a constant live. So as long as there is a battery in the car the relay is energised. The window motor power is shown routed via the ignition switch and passing through a relay which never can interrupt it. All the electrical load is on the ignition switch. This doesn't make sense to me unless perhaps the diagram is wrong and it's the switching current which should come through the ignition switch and the power supply from constant live.
Thanks for all the suggestions. Tomorrow I'm going to investigate further.
The wiring diagram and the role of the relay is a puzzle, but seeing as both front windows stopped working at the same time, the fault is intermittent
and swapping the relay doesn't make a difference it seems likely that it is a dodgy wire or driver's side switch.
Cheers
Dave
quote:
Originally posted by Dusty
If you are talking about relay 130 it is odd. The switching circuit seems separate from the ignition and supplied by a constant live. So as long as there is a battery in the car the relay is energised. The window motor power is shown routed via the ignition switch and passing through a relay which never can interrupt it. All the electrical load is on the ignition switch. This doesn't make sense to me unless perhaps the diagram is wrong and it's the switching current which should come through the ignition switch and the power supply from constant live.
