928 seat switch repair: A different thought
Posted: Wed May 12, 2021 7:31 pm
So it's time to fix the seat switches on the 928S. I have the two sets of 4 way switches, and on the passenger seat the front switch works but the back one does not. It "tries", you can hear the motor try to engage on the rear lift "up" option but the seat recliner is out cold.
First step remove seat, which wasn't too bad once I got my 6mm Snap on 1/4 socket and tapped it on each bolt to seat it properly. Then with the seat up I was able to see that one of the front/back bearings is gone (checking with Rog to see if he has that part) but more importantly pulling the plug to the rear motor for seat recline allowed me to see a good 12 volts on the socket which means switch is "working". However when you plug the seat motor in, voltage drops to 2v. Which means voltage drop in the switch, makes sense.
Hooking a 12v battery up to the plug side allowed me to move the seat recliner back and forth without much effort, so the problem once again is high resistance in the switch. Time to take it apart?
Well.... Maybe not?
The problem I think is that Porsche put way too much current through these switches. The switch has to be haptic (user friendly) and deal with people pushing it hard, soft, etc. And it is driving a motor, which is the worst kind of inductive/reactive load. So the switch eventually fails.
Why not use relays? For the AC system I have a 20a relay under the hood that is switched by the little overloaded 2a relay in the climate box. That 20a relay then closes the magnetic load of the AC compressor clutch, removing the need to replace the dopey relay in the climate unit (it can close a 50ma load for the big relay forever). So what if we wire in a pair of relays for the seat back/forth?
I can see this: The two wires from the switch will supply either +12/gnd or gnd/+12 based on if the switch is commanding front or back recline. Have this switch two 20a DPST relays, each with a diode and the diodes in opposite directions. Thus when you command back, relay 1 closes and when you command front relay 2 closes. The relays are wired to the motor so that when 1 is closed the motor gets +12/gnd and when 2 is closed the motor gets gnd/+12.
Presto: No need to revamp the switch (it can switch the little load of the relay) and you can be assured that the motor will always get full power.
Thoughts? Before I build this myself is there a commercial relay product that does this? I could see it being used in a lot of places, windows, door locks, seats, all sorts of high current things.
Chris
First step remove seat, which wasn't too bad once I got my 6mm Snap on 1/4 socket and tapped it on each bolt to seat it properly. Then with the seat up I was able to see that one of the front/back bearings is gone (checking with Rog to see if he has that part) but more importantly pulling the plug to the rear motor for seat recline allowed me to see a good 12 volts on the socket which means switch is "working". However when you plug the seat motor in, voltage drops to 2v. Which means voltage drop in the switch, makes sense.
Hooking a 12v battery up to the plug side allowed me to move the seat recliner back and forth without much effort, so the problem once again is high resistance in the switch. Time to take it apart?
Well.... Maybe not?
The problem I think is that Porsche put way too much current through these switches. The switch has to be haptic (user friendly) and deal with people pushing it hard, soft, etc. And it is driving a motor, which is the worst kind of inductive/reactive load. So the switch eventually fails.
Why not use relays? For the AC system I have a 20a relay under the hood that is switched by the little overloaded 2a relay in the climate box. That 20a relay then closes the magnetic load of the AC compressor clutch, removing the need to replace the dopey relay in the climate unit (it can close a 50ma load for the big relay forever). So what if we wire in a pair of relays for the seat back/forth?
I can see this: The two wires from the switch will supply either +12/gnd or gnd/+12 based on if the switch is commanding front or back recline. Have this switch two 20a DPST relays, each with a diode and the diodes in opposite directions. Thus when you command back, relay 1 closes and when you command front relay 2 closes. The relays are wired to the motor so that when 1 is closed the motor gets +12/gnd and when 2 is closed the motor gets gnd/+12.
Presto: No need to revamp the switch (it can switch the little load of the relay) and you can be assured that the motor will always get full power.
Thoughts? Before I build this myself is there a commercial relay product that does this? I could see it being used in a lot of places, windows, door locks, seats, all sorts of high current things.
Chris