Wiper circuit

[Mach1 Driver 560]

Could someone check my work please? I couldn't find a coherent description of how the wipers work, so I drew-up a schematic based on the wire diagram (what the hell- boy is that useless??) and guessed at the operation. The switching didn't make sense so I guessed that the RUN position of the motor switch must cycle to PARK when the wiper blades are down.
Thanks

WIPER.pdf

[Mach1 Driver 560]

maybe this is a simpler explanation

WIPERS.pdf

[det0326 179]

I think you are certainly on the right track Terry.  Don't know if you ever been into the motor/transmission or not but there's a limit switch  with a cam setup in the transmission part that is in series with the park wire and is opened when in the park position.

 

Dave  

[Mach1 Driver 560]

38 minutes ago, det0326 said:

I think you are certainly on the right track Terry.  Don't know if you ever been into the motor/transmission or not but there's a limit switch  with a cam setup in the transmission part that is in series with the park wire and is opened when in the park position.

 

Dave  

Thanks, that's what I figured. Fortunately I've never had to take mine apart. I guess some of the older Stangs have a foot switch for some reason!!

I'm converting the 37 pages of electrical diagrams and drawings from my FORD (Helm) manual to schematics. Diagrams certainly have their place, but jeez, they make it very difficult to figure out how something operates. The schematics will do that in a few pages, and you can actually see how it works. I don't have any problem with the electrical stuff but when something mechanical influences the electrical circuit (and I'm not familiar with it), then I'm in trouble. I believe this is one of those instances.

[danno 128]

If you are going to make real diagrams as you suggested, I think that will help  a lot of us. It also would help to show which wires bundles the wires are in, and which connectors they go through.   There are mistakes in the Ford schematics, and they also leave a lot of details out.  I can review some of these if you need them.

[Mach1 Driver 560]

1 hour ago, danno said:

If you are going to make real diagrams as you suggested, I think that will help  a lot of us. It also would help to show which wires bundles the wires are in, and which connectors they go through.   There are mistakes in the Ford schematics, and they also leave a lot of details out.  I can review some of these if you need them.

You misunderstand- I'm making schematics, not wire diagrams.  Diagrams are useful when you need to identify and connect wires. Schematics (which are not available) make it easier to figure out how the circuit works. They are quite different. I don't know the kilobyte limit for posting, but I'll try to do so when I'm finished. 

So does anyone know if the "motor position switch" in the wiper motor is in the "park" position when down, and in "run" at all other times?

[det0326 179]

21 hours ago, Mach1 Driver said:

 

So does anyone know if the "motor position switch" in the wiper motor is in the "park" position when down, and in "run" at all other times?

If I understand what you are asking the contact switch in the motor is always closed except when parked. It is closed when the motor is running but is independent from the run circuit and has nothing to do with run. When the wipers are running, then you turn the dash switch to off it energizes the park circuit that is tied to the low speed windings and drives the blades to park position . The limit switch opens and stops the motion. 

 

After looking at your dia. i think maybe what you are wanting to know is the state of the switch when parked. I think what is confussion is the switch is a spst does not switch to ground at any point just opens the supply to the motor.

[Mach1 Driver 560]

3 hours ago, det0326 said:

If I understand what you are asking the contact switch in the motor is always closed except when parked. It is closed when the motor is running but is independent from the run circuit and has nothing to do with run. When the wipers are running, then you turn the dash switch to off it energizes the park circuit that is tied to the low speed windings and drives the blades to park position . The limit switch opens and stops the motion. 

 

After looking at your dia. i think maybe what you are wanting to know is the state of the switch when parked. I think what is confussion is the switch is a spst does not switch to ground at any point just opens the supply to the motor.

Ahhh, the switch isn't SPDT!!! You are the only person on three forums that knew that!!! I knew the park contact and the ground were superfluous and I didn't understand why they were there. You provided the answer- they aren't there. The FORD drawing is wrong. The RUN switch is open when the wipers are down and closed at all other times, just as I suspected.

Thanks Dave, please see the attachment and let me know if it makes sense now.

 

WIPERS.pdf

[RPM 1,190]

Good info, glad you found it and hope I never need to use it :)

[69RavenConv 286]

I thought I had some notes on this but I can't find them so I'm going from memory here. I don't claim this is 100% accurate schematically but I think it's close. Smarter folks than me will correct me if I'm wrong.

The motor runs when voltage is applied across it, and stops when it's removed (obviously)

In the HIGH position, a full 12V is applied across the motor, causing it to run at top speed.

In the LOW position, a resistor in series drops the voltage applied to the motor, causing it to run at a slower speed.

When RUNNING, a cam opens and closes the PARK SWITCH, applying 12V to slow position on the motor. When the switch is in HIGH or LOW, this is redundant and has no effect. When the switch is moved to OFF, however, the PARK switch continues to provide juice to the motor until it hits the PARK position. where the cam opens the switch, removing power, and the wipers stop. 

When the switch is in the OFF position and the cam is in the PARK position, no power is applied

[det0326 179]

Makes perfect sense to me Terry.   I had mine apart one time to replace a gear that had broken and that is how I knew otherwise I would not. 

That is good info for troubleshooting in the future if needed, I have it stored away. Thanks for the time u put into it.

 

Dave

[Mach1 Driver 560]

9 hours ago, 69RavenConv said:

I thought I had some notes on this but I can't find them so I'm going from memory here. I don't claim this is 100% accurate schematically but I think it's close. Smarter folks than me will correct me if I'm wrong.

The motor runs when voltage is applied across it, and stops when it's removed (obviously)

In the HIGH position, a full 12V is applied across the motor, causing it to run at top speed.

In the LOW position, a resistor in series drops the voltage applied to the motor, causing it to run at a slower speed.

When RUNNING, a cam opens and closes the PARK SWITCH, applying 12V to slow position on the motor. When the switch is in HIGH or LOW, this is redundant and has no effect. When the switch is moved to OFF, however, the PARK switch continues to provide juice to the motor until it hits the PARK position. where the cam opens the switch, removing power, and the wipers stop. 

When the switch is in the OFF position and the cam is in the PARK position, no power is applied

Ok good, you have verified what Dave is saying about the Park switch in the motor, on several counts.

We have similar circuits. Yours works and is actually simpler than the Ford circuit shown on their diagram.

In the FORD drawing there isn't a resistor, and instead it is drawn to indicate that there are two motor windings, one Hi and one Lo. Since you wouldn't want both windings on at the same time they separate the circuits by adding another Park switch, only the added switch is in the dash switch. 

I'll never know for certain unless I open up the motor, but I feel fairly certain that the latest version of my schematic is how it operates, and that is shown above in the thread. BTW, the FORD version does work as drawn, it just has an extra throw on the motor Park switch (the Run contact) that doesn't do anything and is unneeded, SPDT instead of SPST.

Thanks.

[69RavenConv 286]

2 hours ago, Mach1 Driver said:

Ok good, you have verified what Dave is saying about the Park switch in the motor, on several counts.

We have similar circuits. Yours works and is actually simpler than the Ford circuit shown on their diagram.

In the FORD drawing there isn't a resistor, and instead it is drawn to indicate that there are two motor windings, one Hi and one Lo. Since you wouldn't want both windings on at the same time they separate the circuits by adding another Park switch, only the added switch is in the dash switch. 

I'll never know for certain unless I open up the motor, but I feel fairly certain that the latest version of my schematic is how it operates, and that is shown above in the thread. BTW, the FORD version does work as drawn, it just has an extra throw on the motor Park switch (the Run contact) that doesn't do anything and is unneeded, SPDT instead of SPST.

Thanks.

I agree, your version is correct - 2 windings, high and low. Nice work, reference material like this is valuable.

[Mach1 Driver 560]

Thanks, this is one of the pieces of a whole car (69) schematic. I condensed 37 pages of diagram down to about 3.5. I've got a few more things to check and I'll try to post the entire thing

[bigmal 225]

This will be very helpful. Looking forward to seeing the completed schematics.

[Mach1 Driver 560]

This is the straight scoop, the real deal, the unvarnished truth, the real skinny, and gospel. I know “how” and “why” the wiper circuit works. I think you’ll find this surprising. There is real science going on here.

I have received so many versions of how the wiper circuit functions (from 3 forums) that I still had doubts. So I took the perfectly good wiper motor out of my completely stock 69 Mach and investigated. BTW, I’m the original owner so I know its completely stock. I disassembled the motor and found that it agrees 100% with the FORD diagram (printed by Helm).

I had misgivings about the diagram because the Park to chassis contact in the motor seemed superfluous. I disconnected the park contact, reassembled the motor and hooked it up to the car.

Some background: the motor has a SPDT switch that is in Park for about 15 degrees of its rotation. The rest of the time this switch is in the Run position.

It is important to note that stopping is a two stage process, and stage one occurs when the circuit is switched off via the dash switch. The motor is prepared to stop by switching it to LO for the remainder of its rotation. A slower motor is less likely to coast too far.

I started the motor but when I turned the dash switch off the motor wouldn’t stop spinning. The Run switch would open and you could hear the motor turn off, but it would coast right through the 15 degrees until it switched to Run and started going again. It did this repeatedly, every time tested.

I wondered why this was happening and a light bulb went off. I looked at the schematic to verify and confirmed my suspicion. Both Park switches close, connecting the ends of the motor coil together. Without this connection the motor would never stop, at least not within the allotted 15 degrees of rotation.

So here's what happens: when the motor is turned off, the magnetic field in the motor coil collapses causing a reverse voltage, called a Back EMF. Connecting both ends of the coil together causes the motor to “reverse” for the instant that the magnetic field is collapsing, and the motor stops before coasting into the Run position.

I reconnected the Park contact in the motor and it operated normally, stopping when it should. Isn’t that cool? It momentarily puts on the brakes. Betcha didn’t see that coming! Please see the attached operating sequence.

WIPERS.pdf

[RPM 1,190]

Say what???

Kidding, sorry of. Thanks again to the brainiac kind of guys.

[det0326 179]

Yes that is called a dynamic brake. In my line of work (before I retired) I was an electronic tech troubleshooting CNC equipment that had permanent magnet motors driving the axis and as the saying goes they would stop on a dime when the leads where connected together by relays.  When I had my motor apart I sure don't remember a spdt but I am getting old. Sorry for the confusion. 

[Mach1 Driver 560]

5 hours ago, det0326 said:

Yes that is called a dynamic brake. In my line of work (before I retired) I was an electronic tech troubleshooting CNC equipment that had permanent magnet motors driving the axis and as the saying goes they would stop on a dime when the leads where connected together by relays.  When I had my motor apart I sure don't remember a spdt but I am getting old. Sorry for the confusion. 

Wow we've got a really diverse group here. Well there ya go, I had no idea such a thing existed until I took the motor apart. Now I've learned it's name and something new. BTW, the switch was on the motor side with a pin that poked it every revolution coming from the transmission side. Maybe that's why you missed it. Anyway thanks Dave for the confirmation of the technique.

[danno 128]

Mach1, that is interesting, I wonder why they bothered?  They maybe could have started the cutoff at 20 degrees so it would not coast through.  I wonder if a flyback diode would do the same thing. The same thing is used in relays to collapse the coil voltage when it shuts off, but that is a little different purpose.  It is a diode hooked up with the anode to ground, cathode to the + side of the motor. During operation it is never conducting, only for a few milliseconds when the motor voltage is shut off. 

[Mach1 Driver 560]

Well, remember it was 1969, semiconductors were fairly new and starting to creep into car designs. They opted for a reliable electro-mechanical design that is still used today. Besides, what you are describing is meant to stop the the reverse emf, not employ it. Flyback diodes are typically used on relays driven by electronics. When the relay is turned off the collapsing magnetic field tries to reverse, but the diode prevents the reverse surge that would destroy the relay's delicate electronic driver circuit.

I can only assume that they wanted to stop the motor within a narrow range and be assured that it would indeed stop. When the Park contact is disconnected the motor shows no sign of stopping anytime soon- it coasts through the 15 degrees quite readily.