Date: Sun, 6 May 2007 21:03:03 -0500
Reply-To: Matt Roberds <mattroberds@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Roberds <mattroberds@COX.NET>
Subject: Re: another power window question
In-Reply-To: <20070506235432.HHSF24694.eastrmmtai105.cox.net@eastrmimpi04.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
> From: Raymond Paquette <raymondpaquette@GMAIL.COM>
> Date: Sun, 6 May 2007 10:18:48 -0700
>
> Anyway, I'm thinking of putting the windows on an unswitched circuit,
> so I can raise and lower them any time, key or not.
I think the main concern with power windows is small kids and/or
animals. Having them only work with the key in the ignition is a
minimal check on there being a responsible adult person around to stop
little Timmy from trying to roll up the window on his sister's head, or
to stop Fido from standing on the switch and rolling up the window on
his own head.
A secondary reason is theft resistance. I've seen a locksmith open the
doors on a car by using one of those professional-grade bent coat
hangers to get in past the gasket and push the power lock button. If
the windows work even with the key off, the same trick would lower the
window. (Someone that good could _probably_ just slim-jim the door
latch, but the always-on windows woul provide another way in.)
Another possible reason is a fault in the window motors draining the
battery. A dead short should blow the fuse or open the breaker, but
there are some failure modes that will draw enough current to kill your
battery after a few hours but not enough to blow the fuse or open the
breaker.
The low-tech approach is probably to install a pushbutton that allows
you to temporarily power the windows - push and hold the button, then
push and hold the window switch. Put the pushbutton somewhere where the
kids and critters are unlikely to find it and it can even be reasonably
secure. You can use a big pushbutton that can handle the window motor
current by itself, or use a tiny one (easier to mount and hide) to
trigger a relay that does the heavy lifting. Using a SPDT relay
(separate 87 and 87a contacts) will also allow you to avoid powering
everything else that runs from circuit 15 (hot with key on) when you
push the button.
Newer cars have "retained accessory power". The first version of this
was that certain "accessory" things, like the radio and power windows,
were on a timer and remained powered for 3 to 5 minutes after the
ignition was shut off. A refinement is to also cut the power when a
door opens, regardless of timer status. You might be able to buy a
ready-made timer to do this from somebody like JC Whipme.
Really new cars allow tricks like: Put the key in the driver's door lock.
Flick it to "unlock" and the driver's door unlocks. Hold it on "unlock"
and all the doors unlock. Keep holding it and the driver's window rolls
down. The "lock" position does the same thing in reverse. The official
way to do this is to have a body computer; the low-down way is to get
creative with hiding microswitches inside the door on the lock linkage.
Newer cars also claim to have stall protection and/or reversing on the
power window motors. If the window is going up and encounters too much
resistance, it either stops, or reverses to full open. The windows on
my T@y@t@ are said to do this, but I don't have a calibrated reference
kid's head to try it out with.
Matt Roberds
