Window relays

[Layne]

EDIT: Disregard most of the following, I didn't realize the difference between having a diode on the control circuit of the relay vs. the load circuit. The concept is identical, but applied in a different location.


I found many mentions of adding relays to the power windows with good results, so I decided to go for it. I found the diagram below in multiple threads. I wondered about the diodes, so I did some research. I learned a couple of things, 1) there's no need to add them separately since you can easily buy relays with diodes already in them (easily online anyway, not necessarily at autozone). 2) I don't think they're useful in this case. They are used to protect a digital circuit that is used to switch the relay, but in this case the switching is done by a very robust mechanical means, so there's no need for protection. This paper I found from TE Connectivity (one of the major manufacturers of relays) discourages their use when they aren't needed to protect a sensitive circuit. So I ordered standard relays for everything. About $3.50 each from Waytech Wire.

http://www.te.com/commerce/Document...v&DocNm=13C3264_AppNote&DocType=CS&DocLang=EN

 

[jmackro]

Diodes extend the life of the relay contacts. But if you chose not to install them, your relays will still probably outlive you. And if they don't, at $3.50 apiece, you can just replace them.

I did read that TE Connectivity application note. They seem to be talking about the inductive load of the relay coil and the damage that could do to a solid state driver. You're right: the e9 window switch isn't solid state, and the switch contacts can easily handle the inductive load of a relay coil. But that's not the purpose of the diodes shown in the schematic you posted - those diodes handle the inductive loads of the window motors. If the motor's back EMF isn't snubbed by a diode, it will certainly create a spark across your relay contacts whenever the motor is shut off. But even with that abuse, your relays will probably last a long time.

 

[Layne]

Ahhh ok, that makes sense. I guess we'll see. Can always buy the diode relays next time if these burn up. Actually in that case, I wonder if the diodes inside the relays are too small and that's why these are installed externally. (3 amp is a pretty big diode)

 

[aearch]

I TRIED TO WIRE UP THE E34 MOTORS THAT WAY AND COULDNT GET IT TO WORK
WHAT IM A DOING WRONG
IN THE 74 MODEL
ITS ACTUALLY A PLUG AND PLAY W/ THE NEW MOTORS

 

[Layne]

You can't wire two-wire motors using this three-wire schematic (the ground is not shown above). You would need 5-pin relays.

 

[coupedownunder]

perhaps a silly question but where do you put/ attach/place the relays ?

 

[Layne]

perhaps a silly question but where do you put/ attach/place the relays ?

Anywhere between the switches and motors is fine. Some put them inside the doors, but that means you need to add an additional wire through the door jamb. I'm going to put mine inside the hollow space just in front of the doors. There's plenty of space for the rear ones near the wire connections.

 

[aearch]

OK HOW DO I DO THAT

 

[Layne]

Ooooh I see now I overlooked the important difference, the relays with diodes in them have the diode parallel to the control coil, and this layout has the diode parallel to the load side. So using the diode relays is not the same thing and the paper I linked is not relevant. You do need to add them externally to get the effects desired here.

 

[Layne]

OK HOW DO I DO THAT

Basically something like this. You need the 5 pin relays so that both motor wires are connected to something at all times. In the above scenario (3-wire motors) you use 2 wires at a time and the unused wire is a dead end. With 2-wire motors both wires must be used to make the motor run. So in the schematic I've drawn here, both wires are grounded until you press the switch and then one or the other receives power, depending on the desired motor direction. I'm assuming that's how the switches in the '74 work. If that still doesn't make sense you may need someone with more electrical experience to help you in person. There's no full DIY for these motors that I've seen.