Implement "auto zero" function in a wiper blade motor

[LinkZ]

Hi guys,
as said , the wiper blade motor of my car does not return automatically to "zero" position when i turn it off. I have to switch it of exactly in the "zero" position, which is really annoying. I've already opened the gear box and the motor does not have the mechanism that let it to do this function. Do you have any idea how to implement this function EXTERNALLY? Possibly with less parts as possible? The molex connector that comes from the car has three wires, but the wiper blade motor uses only two.

[Paul Price]

Something like this.

Use a relay that stays on,  it is turned on by the wiper switch in your car. Then, you need a way to detect the zero position of your motor. A mechanical leaf-type "micro-switch" that is actuated by the zero position could be used. It would open the power to cut power to the wiper motor, but only if the wiper on/off switch in your car is turned off. The leaf switch needs to be bypassed by the relay when your wiper on/off switch is in the on position.

[LinkZ]

The problem is "the way to detect the zero position"! I don't want to put anything inside the gear box of the motor, because is fully of oil and grease, so not the ideal place for a microswitch. I need something external and reliable enough that "detects" the damn zero position and switch off the motor

[Paul Price]

You have to find a way to attach a sensor not inside the motor, but to the arm that attaches it to the blade.

One easy way is to use a magnet super-glued to the rotating arm that actuates a hall-effect transistor or a reed switch.
Another way is to attach a small piece of dark plastic to the arm that is sensed by a optocoupler.  It is easy to find one or more of these optocoupler limit switches that works with a infrared diode/sensor in a discarded printer.

You can even mount a sensor on your dashboard that sees the rest position of your wiper arm through your windshield. It can "see" the position by sensing a small magnet on the wiper arm or a reflective  piece of metal/glass mirror.
Or else  a spring loaded nylon thread wound around the motor shaft  to your rotating wiper arm  to activate a switch a the "zero" point.  You could also attach a small  piece of plastic/metal to the rotating shaft of the wiper motor so it come into to position to be sensed at zero position by a micro-switch or an optocoupler.

[tautech]

Hi guys,
as said , the wiper blade motor of my car does not return automatically to "zero" position when i turn it off. I have to switch it of exactly in the "zero" position, which is really annoying. I've already opened the gear box and the motor does not have the mechanism that let it to do this function. Do you have any idea how to implement this function EXTERNALLY? Possibly with less parts as possible? The molex connector that comes from the car has three wires, but the wiper blade motor uses only two.

Quite a while since I had one apart, but as you say there a 3 wires, one of which should be live when the ignition is on.
IIRC there is a brass incomplete circle in the mechanisim with a "dead" spot and a sliding contact that continues to provide power until the "dead" spot is reached. This co-incides with the wiper "zero" position.
This description while not vividly clear should provide you with clues of what to look for to find a remedy.

[LinkZ]

I thought about hall transistor too. But I never worked with hall sensors, so can someone post a simple and reliable schematic? Of course this circuit should work as a NC switch, that opens only when the magnet face the hall sensor

[dfmischler]

Where are you located?  What kind of car do you have?  And what cheap aftermarket wiper motor is installed in your car?

[LinkZ]

Where are you located?  What kind of car do you have?  And what cheap aftermarket wiper motor is installed in your car?

Good that you asked. UNFORTUNATELY I live in ITALY, or to be exact in SICILY, CURSE LAND! and my car is a FIAT Cinquecento (1998). This place is a little different from USA or Germany, or any modern country: here the majority of youngs are JOBLESS and without a hope to become one in the near future, so in practice if you live in sicily you don't think about your future, because without job there is NO FUTURE. I can say that this is one of the worstest land in the world, and please DON'T SAY THAT THIS IS NOT TRUE, IF YOU ARE NOT SICILIAN! The only available jobs are (with a little help of mafia) in hotels or restaurants, because here the peoples are living with the money of the foreigners. So please if you plain a holiday, DON'T COME IN SICILY, and don't feed this mafia's business. Because of that i cannot buy a proper car, but before I go to Germany to build myself a proper life, I decided to stay another couple of mounths to try to find something one last time.

[max_torque]

Be warned, just turning off the motor at a certain point isn't enough!  What you'll find is that the mechanical inertia of the motor and wiper blades will result in the system slowing down, but not stopping, all the way past your "switch off" sensor, and then back to "on" again.  In most wiper motors, the "STOP" position switch also directly shorts the motor armature, and the resulting braking effect (full motor torque) stops the system rapidly.  Modern electronically switched systems use semiconductor switching to achieve the same result, and take a position switch input from a microswitch on the motor gear.

[Seekonk]

You could just add a switch and a resistor.  Switch to slow speed when you want to turn it off and it will be easier to time the off when it reaches the position.

[LinkZ]

I found this schematic (http://www.circuitstoday.com/wp-content/uploads/2010/02/hall-effect-switch.png) but I have some questions:

- I have only a UGN3503 sensor. Is OK?
- I have this normally open relay (http://www.futurlec.com/Relays/HORN12VDCSPSTpr.shtml). Can I change Q1 in the schematics with a NPN transistor to make the circuit work as normally closed?
- I need to make it work with 12V (the schematic says 6V)

[LinkZ]

Can somebody help me?

[Magicmushroom666]

I had a fiat cinquecento around the same age, and the wipers worked as you'd expect, they stopped at the bottom always regardless of where you turn them off. Are you sure its not just broken? fixing what's already there is bound to be easier than tacking on something extra.