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Old 05-11-2020, 12:06 PM
Huskymaniac's Avatar
Huskymaniac Huskymaniac is offline
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Join Date: Jul 2010
Location: Corning, NY
Posts: 1,872
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Master window switch "fix" idea

I looked at the wiring diagram and there are two wires going to each window motor. The master switch either sends two grounds for off or a ground and 12V for on and which wire gets which depends on the desired motor direction (up or down).

The problem with the switch is that the contacts wear both electrically and mechanically. And the current has to travel through two contacts and two long wires so there is a lot of voltage drop. Since 12V and GND are not available at each window, we can't do much about the wire resistance. But we can do something about the contact resistance.

I am thinking of putting a single pole, double throw relay on each wire. So, 8 total relays. Each wire will get either 12V or GND depending on what voltage is driving the relay coil (or photodiode for a solid state relay). For a regular relay, the normally closed contact will be tied to ground and the active contact will be tied to 12V. The relay coil will be tied to GND on one end and the line coming from the master switch on the other. When it goes to 12V, the relay output will switch to 12V. There are 10 wires going to the master switch. 8 for the four window motors, 12V and GND. The wires can be cut and two connectors placed on the box with the new relays. One will go to the master switch and one will go to the window motors and the incoming 12V and GND lines. The 12V and GND will be used to provide the 12V and GND power for the relay outputs as well as the GNDs for the relay coils. 12V and GND will be passed to the master switch and the master switch will send out 12V or GND on the 8 lines between the relay box and the master switch.

The relay I am thinking of using is 551-EX2-2U1S from Mouser. Each has two SPDT relays so four would be needed. I can make the simple PCB on my board maker at work. This relay operates on only 75mA and switches at 6.5V so even the weakened contacts in our master switches should be fine to drive that. The relay contacts are made from a silver alloy and have a closed resistance of only 4 mOhm! Basically, the windows should respond like they did on day 1.

Am I missing anything?
__________________
Tony

1996 Polo Green Subaru SVX LSi, 168,XXX miles, Redline D4 ATF, Redline 75W90 gear oil, K&N HP-4001 Oil Filter, Mobil 1 5W50 FS (3qt) and 5W30 High Mileage (4qt) Oil Blend, Motul RBF600 Brake Fluid, AC Delco A975C Air Filter, NGK BKR6EIX-11 plugs, Centric Rotors, Power Stop Evolution Carbon Fiber Ceramic Brake Pads
2005 Gray Acura RL, 165,XXX miles, Redline D4 ATF with Lubegard Platinum Protectant, Mobil 1 5W20 High Mileage Extended Performance Oil
2009 Red Toyota Venza, 123,XXX, Mobil 1 5W30 High Mileage Oil
1992 Red Ferrari 348 ts, 82,XXX, Redline everything
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