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Current sense - Circuit opening system
2

Current sense - Circuit opening system

Current sense - Circuit opening system

(OP)
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, called several companies, but 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 only problem is that after researching these more thoroughly, I don't believe that they actually open the circuit. I believe they simply increase their resistance thus limiting the current drawn by the circuit, which isn't what I want.

The application is electric 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 awesome. 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?  

RE: Current sense - Circuit opening system

Take your car to the dealer & say "my windows don't work", and if they reply "We'll have to order a pc board for that." You will know you are correct in your assessment.

Seems like everything goes through a box these days.

RE: Current sense - Circuit opening system

(OP)
Wow, that was fast. Thanks all!

As far as the PIC goes, wouldn't I still need a component to monitor current and send an input to the PIC?

RE: Current sense - Circuit opening system

2
Stick your hand in the window as it closes to test your "current limit" theory. Use your other hand to report back to us the results of the test. Safety regulations generally prohibit automatic closing of the windows. (Because there may not be a current limit to detect obstructions.)
A varistor changes resistance when it is hot. A circuit breaker opens the circuit completely. Automobiles use a lot of circuit breakers. Varistors are more used for control than for protection.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current sense - Circuit opening system

"Safety regulations generally prohibit automatic closing of the windows."

Almost all my cars have autoclose.  What's prohibited, sort of, is the inadvertent activation of the autoclose, which is why most window controls require you to lift the lever to close, so that you can't simply lean your elbow on the switch and get the window to close.  As far as I know, the only push for window control safety is the IIS, which routinely dings manufacturers that have poor switch design.

TTFN

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RE: Current sense - Circuit opening system

I've never seen autoclose. Auto open yes, but to close the window you must hold the switch.

RE: Current sense - Circuit opening system

My 1989 Honda Integra has auto close on the drivers window.

My step daughters 1990 Honda Integra has the same as does my 1988 Honda CRX, and my ex girlfriends 2002 Toyota RAV4.

My brother had it on a mid 1980s Nissan Skyline,It is on all 4 widows of my daughters Lexus IS250 and it is even on the drivers door of my brothers Nissan Navara work truck.

It is the RAV 4 where I replaced the window glass and lost indexing on the window winder motor so it wants to stop in the wrong place and requires manual over ride to park it fully closed.

Regards
Pat
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RE: Current sense - Circuit opening system

I stand corrected and indexed. grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current sense - Circuit opening system

Nonetheless, Bill, a reasonable question.  I think that because the switches cannot be accidentally activated, designers considered autoclose to be similar to a normal close.  I guess the trade between risk-averseness and convenience for the customer was swayed toward the latter.  Obviously, not every company or every car design group thinks quite the same way.

In a similar vein, some cars don't have a persistent cruise control enable, i.e., every time you start the car, you must re-enable the cruise controls.  Toyota tends toward that direction, with a momentary on switch for the enable, while Honda has a bistable switch for the enable.

TTFN

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