12 VDC motor control?

First, some background. The headlamp door motor control module died
on my 1987 Buick Skyhawk. As a result, the doors covering the
headlamps had to be opened manually and left that way.

I checked with Buick, and the module is way out of my budget, and
there is some concern about whether or not it is even still available.
I've also called junkyards, but none has cars this old!

I could just leave it like this, with the doors always open, but I
really would like to get the doors opening and shutting again.

The motors seem to (me, at least) be typical DC motors. They have two
wires coming out of them. With 12V at one wire and ground at the
other, they spin one way. Reverse the polarity, and they spin the
opposite direction.

I've rigged things up using a switch (DPDT, I think) . With the
switch in the center position (of the three positions), there is no
power to the door motors. If you flip the switch up, the headlamp
doors will open. If you flip the switch down, the doors will close.

I don't have a momentary switch so I have to be careful to flip the
switch back to the center position quickly. Unfortunately, I am not
quick enough a lot of the time, so I am going through 2.5 amp fuses
like they are going out of style.

Does anyone know of a circuit that I could use that would be able to
control the headlamp doors to automatically open and shut when the
power to the headlamps is turned on or off?

Many, many thanks for any help!!

Rick

 

You need a limit switch that will open the circuit from the DPDT switch when the
door reaches the end of its travel.
The original module may have used some type of magnetic sensor to detect the
end-of-travel positions.
You can probably use some microswitches IF there's a place to mount them (so the
door mechanism can operate them at the proper point).

The easy alternative would be to use a circuit breaker instead of a fuse. The
circuit breaker can be reset ;-)

Another alternative would be to use a current sensor that detects when the motor
current increases steeply (at stall) and turns off the power.



More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter [email protected] mindspring dot.dot com. Fix the obvious to reply by email.

 

I do not know how they work, but have you tried looking at
the window drive circuitry of some more available car.
Mine seems to stall at the up and down ends and not blow any
fuse.
Just an idea to explore.

 

Yes, thought about this, but it would be a nightmare for me to mount
them such that they would operate reliably.

Nope, it senses the current spike in the motors like you mention
below.

Again, the mounting would be a nightmare!

I could really have used one, let me tell ya!

Now we're on to what I think is EXACTLY what I need. Unfortunately, I
have NO idea how to do it, or what devices accomplish this. Do you
have any more info on this type of thing?

Many, MANY thanks for your helpful reply!!!

Rick

 

Indeed! They probably operate in a very similar fashion. Thanks for
the idea! I would have never thought of that in a million years.

Thanks again!!

Rick

 

There are current operated relays, where the pull-in is based on current through
the winding instead of a fixed voltage applied to the winding. If you know (or
can determine) the operating and stall currents for the motor, you can get one
of these (probably not cheap).

There is also the "junk box" version of the current operated relay, where you
wind some turns of wire around a magnetic reed switch (used in burglar alarm
door/window sensors, probably still available from Radio Shack). Wind a number
of turns around the glass tube of the switch, then add or remove turns as needed
to have the switch operate at some point higher than normal running current.

The reed switch can't handle the current required by the motor, but it can
handle a small relay, which can control the power to the motor.

No diagram this time - it's a little too complex for an on-the-fly ASCII diagram

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter [email protected] mindspring dot.dot com. Fix the obvious to reply by email.

 

Hmm, I think I'd like to look into this despite the possible expense,
just to see how they work and exactly how much they are. The
operating current appears to be about 1.7 amps and the stall current
is around 2.5 amps, I would guess.

Any ideas where I could look for them, and what terms to search for?

While I'm not really clear on all of this, it does sound like a
possible solution as well. If it's not too much to ask, could you
point me to Radio Shack part numbers for what you think is exactly (or
as close as you can guess) what I'd need?

Completely understandable!

Many thanks for this! I hope to get these puppies working again!

Thanks again!!

Rick

 

Rick wrote;
"First, some background. The headlamp door motor control module died on
my 1987 Buick Skyhawk. As a result, the doors covering the headlamps had
to be opened manually and left that way.
I checked with Buick, and the module is way out of my budget, and there
is some concern about whether or not it is even still available. I've
also called junkyards, but none has cars this old!
I could just leave it like this, with the doors always open, but I
really would like to get the doors opening and shutting again.
The motors seem to (me, at least) be typical DC motors. They have two
wires coming out of them. With 12V at one wire and ground at the other,
they spin one way. Reverse the polarity, and they spin the opposite
direction.
I've rigged things up using a switch (DPDT, I think) . With the switch
in the center position (of the three positions), there is no power to
the door motors. If you flip the switch up, the headlamp doors will
open. If you flip the switch down, the doors will close."
_____________________________________
Re;
Hi Rick,
A simple solution might be to install a self-resetting thermal circuit
breaker in series with each motor. BUSS makes a variety of these for
automotive applications and you can find them in auto supply stores.
They basically consist of a thermal element that carries the load
current; when the current reaches the operating point of the device; the
contacts open. Subsequently the element cools and the contacts reclose
after a relatively short period of time.
But if I were you I'd revisit some more junk-yards. That unit was
probably installed in many GM models of that era with "winking" head
lamps...
No way to get into the module?? There's probably some sort of simple
relay arrangement to deliver a timed pulse to the motors and possibly a
hefty PTC (positive temperature coeffiecient) thermistor to limit any
sustained stall current.

-Dan Akers

 

Though I don't have any part numbers for radio shack I can tell you
how the relay system would work. When looking for a reed relay at
radio shack it will say on the package if is that type. It will also
tell you the current needed to operate it. I think radio shack has a
web site where you can look up part numbers and then go to the local
store to buy it. Anyway, the reed relay is a glass tube with the
contacts inside. There is a coil around it. You can remove this coil
but I bet you could just wrap wire around it as it is. You will need
to get one that is NC or normally closed. Then buy a relay with a 12
volt DC coil that has contacts rated at 5 amps DC or better. You will
need just one reed relay and one regular relay. The power from the
battery to the motors goes through the coil around the reed and then
to the NC contacts on the other relay and then to each switch and
finally to the motor. The power for the regular relay goes from the
battery, through the reed relay and then to the regular relay. I'm
sure someone here can tell you about how many turns of what guage wire
will activate the reed relay.
ERS

 

Radio Shack doesn't seem to have these any more. You might try a local alarm
supply shop. The standard door and window sensors use a reed relay and a magnet
(the pair of little "boxes" at the edge of the door.

Marlin P. Jones has three reed switches, one with SPDT contacts, the others with
SPST normally open contacts, they are 50 cents or less each.
http://www.mpja.com/listitems.asp?dept=69&main=117
They have a $15 minimum order; however, you might find other parts that you can
use that will reach that minimum. (Maybe just a bunch of switches in case you
destroy some in testing?)

If you want a sketch of some possible wiring configurations, send email (either
fix the address on this message or go to my web page - there's a webmaster link
there).

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter [email protected] mindspring dot.dot com. Fix the obvious to reply by email.

 

<snip>

Hi Dan!

Definitely gonna get one of the above. Thanks!

I certainly can't find any around here. Perhaps I will keep looking,
though.

First, thanks for spelling out what PTC meant.

Secondly, I downloaded some info from thermometrics.com and it does
look like one of these things might just help do the trick.

I'll have to dig into them a bit more and see if I can come up with
anything.

Also, should you come up with something that would help me out, I
would really appreciate anything you could pass along.

Many thanks!!

Rick

 

Many thanks for this! I'll see if I can work something out as you
mention!

Rick