Electrical engineering question/problem. Auto power windows?

[Milford Cubicle II]

How do the auto power windows work? The type that go all the way up or down just by a single momentary push of the button. What turns off the motor? I doubt it's a limit switch set up. I suspect that it detects the increased current of when the window motor stalls, and cuts power. So my question is, what device do they use that senses the increased current and either opens the circuit itself, or powers an output that could be used to open up the circuit via an NC relay?

I've googled and haven't found much at all. I did however find a thing that I was previously unfamiliar with, resettable fuses. They seem like they would do exactly what I want. They allow current to pass, all the way to the threshold but if the current exceeds the threshold, the fuse "pops" opening the circuit. But then the fuse automatically resets once it stops receiving power (your finger lifts off the button).

The application is exhaust cutouts. I want to use a factory auto up/down window switch to open and close the electric exhaust cutouts. I've never had a cutout before but my friend does and it's sweet/fun. But I hate how you don't really *know* when the cutout is all the way open or more importantly, shut. You just kinda have to listen and hold the button for what is probably way too long for the durability of the motor. Not to mention how nice it would be to just push a button to open or close and not worry about it. And by using the window switch that does both momentary and auto, you will still be able to move the cutout from shut to wide open and everywhere in between.

I've been trying to make sense of the auto window wiring diagram for my LS on alldatadiy but I haven't cracked it yet. There are 7 wires going into the motor's wiring harness:
1. The "one touch" wire - grounded when pressed
2. Delayed accessory power (lets you roll your windows up after you've taken the key out of the ignition
3. Window up - hot when pressed
4. Window down - hot when pressed
5. "Global open/close" (lets you roll down all windows and sunroof from the remote) - PWM signal from the "door module"
6. Constant power from the PDC
7. Ground

Sounds like there's some logic going on between the motor harness and the motor. In the end, two wires power - or do not power - the motor; not seven. Also, I need to know what's going on in the door module since it's sending signals to the motor as well.

Input anyone?

 

[Milford Cubicle II]

Nothin?

 

[Milford Cubicle II]

I've called TI, they're supposedly "working on it" and are going to call me back. The tech's at mouser.com couldn't think of anything either.

I really didn't think that this would be very hard, I just figured I didn't know nearly enough about electrical engineering to figure it out.

Come on, there's gotta be someone in this crowd that can get this ball rollin!

 

[lazyxj]

The 2001 FSM only mentions that;
"In addition to the switches for its own door, the DDM houses .... circuitry
to support the one-touch down feature of the driver side front door power window."
The wiriing diagrams show no additional circuitry.

So, the control in in the Driver's Door Module (DDM).
Since there are no limits switches, current control is the only way this can work. This must be how all of the power windows work.
Now, can you use it to control a exhaust cutout? I doubt it unless the cutout motor has the same amperage draw.
You could find an old DDM and experiment with it, on the bench, using the cutout motor and a 12-volt battery.
Failing that, you will new to find or design a new circuit to control the motor.

Might be a lot easier to use a cable control, the way we used to do it 'back in the day'.

 

[Milford Cubicle II]

I'm not planning on stealing a body control module or door module cause you're right, it's unlikely that the current draw will be the same for the cutout.

I was planning on building a controller but using the same component/system as the body control modules use to monitor current and open the circuit accordingly.

The problem is that I don't know how they monitor the current and open the circuit. I've thought about using a comparator, but I wouldn't have a reference current to use since there's only one circuit.

 

[lazyxj]

The problem is that I don't know how they monitor the current and open the circuit. I've thought about using a comparator, but I wouldn't have a reference current to use since there's only one circuit.

Looks like an interesting project. I guess you would use a shunt to measure the amperage and then design an adjustable circuit that would shut the power off at a preset level.

Or you could order one of these and be done with it.
http://www.jegs.com/p/JEGS-Performance-Products/JEGS-Cast-Iron-Exhaust-Cutouts/1287065/10002/-1
It isn't nearly as sexy as the electric version but the price can't be beat- $57 vs. $170 (plus electronics).
Electric cutout
http://www.amazon.com/QTEC25-Electric-Exhaust-Cutout-Valve/dp/B003R2MSA8

 

[Milford Cubicle II]

A set of the QTP's is actually what I'm using. I got them for 60 bucks so... yea

QTP also has an electronic controller for them for like $180 complete with led display and the ability to set preset "stops" at any position between 0-100%.

Completely retarded IMO. I don't need to stop my cutouts at exactly 46% nor do I want a horribly gaudy led display tacked onto my interior and I certainly don't want to pay $180 for it.

I'm using a factory window switch to control this exactly how it controls the windows and it will be mounted right next to the factory traction control switch. It'll look like a factory option

And if I could just figured out what component to use that will convert current to a binary output to control a relay signal it can be done for a few dollars.

For what it's worth the cutout motors draw 110 milliamps each and stall out at .5 amp. So I need something to monitor current and at .5 amp it needs to output a signal.

 

[lazyxj]

For what it's worth the cutout motors draw 110 milliamps each and stall out at .5 amp. So I need something to monitor current and at .5 amp it needs to output a signal.

Have you measured what a power window motor draws?

 

[Milford Cubicle II]

Nope, unfortunately I haven't gotten to do that yet.

I'm hesitant to do that because of the work involved to back probe the motor, especially on my mint LS

And I'm afraid that even if I did, and even IF the window motor was close enough to the same that it could work, that the door control module would be ridiculously overpriced. Especially considering what I could build one for.

The logic is super simple. Simple enough that to use even a simple Picaxe or Arduino would be way overkill. Here's the logic:

if auto up switch is pressed then
power motor wire A
if auto sense is activated then
open motor wire A
if auto down switch is pressed then
power motor wire B
if auto sense is activated then
open motor wire B

I haven't worked out the specifics yet but that's the general scheme.

Also, I figured out how to open the circuit at a given amperage. Simple. Place a PTC fuse inline before the relay and make both the supply and coil for the relay feed through the PTC. That way, I can size the PTC fuse to allow the current for the relay coil as well as the running current for the motor but as the current quadruples from the motor stalling, the PTC will exponentially increase resistance which will limit the current to the relay far below the coil's drop out amperage, therefore releasing the switch in the relay and opening the circuit.

Make sense? :dunno:

I'll get something drawn up, it helps a LOT to be able to visualize it.

 

[O-Gauge Steamer]

Most auto windows work as follows:
The swich activates a small relay in the Window Control Module that is latched through what is essentialy a circuit breaker.

Once the window is all the way down the motor current exceeds the limit of the circuit breaker and the breaker opens resetting the relay. The ciruit breaker uses a bi-metallic arrangement so automatically resets itself once the metal has cooled down.

What usually fails in these devices is the bimetallic contacts. I repaired the one in my Son's Subaru by carefully taking it apart and refinishing the contacts to remove the amazing amount of pitting.

Hope this makes sense and helps...

 

[Milford Cubicle II]

That makes all kinds of sense and as usual, the solution is so simple I feel like a tard for not figuring it out sooner! Thank you so much.

Actually, what you said sounds like what I said except instead of circuit breaker, I said PTC fuse. Is the circuit breaker component you mentioned a PTC? Because in all of my research I've found that they don't actually open the circuit. Rather, they just increase their resistance to a ridiculous amount until they stop receiving power. And I've been unable to find an actual automatically resetting circuit breaker.

What did you think of my idea of placing a PTC in series before the relay, powering both the output of the relay as well as its coil? Then when the current exceeds the PTC's threshold, the PTC lowers current enough for the relay coil to drop out thus opening the relay. Sounds like we're talking about the same thing.

Thanks for chiming in! We'll figure this thing out soon.