I have these same black box motors and one of them appears to be dead. It's getting power but not moving or showing any signs of life, and the window is stuck in the closed position. Wondering if the motor (only) can be removed for testing in this state, and what my replacement options are before removing same. Crazy, windows are "hot" when the ignition is off. Better pay attention to the position of the rocker switch when parking car!!!
A few tips on installing e28 window motors
- Thread starter jmackro
- Start date
I’ve encountered a small issue that I don’t see written up here. While the replacement E28 motors have the same bolt pattern and gear as the original black motors in my ‘74, there’s not enough clearance between the new motor housing and the moving regular arm. The regulator arm rotates around freely with the big gear until its elbow pin interferes with the motor housing, thereby prematurely stopping the window movement. The interference seems worse with the mechanism under load. I tried adding a washer or two as a spacer under each motor mount so the arm is free to rotate, however the motor and regulator gears then don’t have enough contact with one another.
Before I go ahead and grind the regular arm pin and the E28 motor case to create some clearance, has anyone else run into this issue?
Before I go ahead and grind the regular arm pin and the E28 motor case to create some clearance, has anyone else run into this issue?
dbower
Well-Known Member
I installed 4 E28 window motors a few years ago. Now, two have "died," according to my technician. I need to know if these motors are repairable, and if so, by whom. These were hard to find a few years ago and I assume are even rarer now. My situation sounds similar to 2002turbo's post above (#81). We all may need to start scavenging Euro cars for manual winders. Thanks for any tips.
Don
Don
If its only the motor that has failed it can be replaced with one from an e28 front window motor assembly
I assume this is the front and not the rear motors?
Responding to an old post on a thread that just got bumped up.
The black motors shown in Storage Andy's photo are the same as are in the E12 based E24s (I know this from comparing them to the window motors in my 1980 Euro E24, which has the black motors).
I believe that the classic E28 rear window motors are the same as the rear window motors on the E28 based E24s.
I just removed some of those from some mid '80s E24 rear window mechanisms I had sitting around. I have not checked to see if they are 8 or 10 tooth drives.
SO this may open up a new source for the later style motors. I also wonder if the drive gear coudl be replaced in the much later motors to go from 10 to 8 teeth.
The diode is called a "flyback" or "freewheeling" diode. Coils behave rather strangely. When they are first energized current rushes in (since it is just a wire connected to ground). However, as the current flows in the wire, the magnetic field from the current induces a reverse current in the adjacent coil windings (this effect is called "back emf, since it represents a voltage applied in the opposite polarity). Eventually the coil is fully energized, so the magnetic field is not changing, and the back EMF dies away, leaving just the coil resistance to control the current. All the while the magnetic field from the coil closes or opens the relay contacts. This is all good until you go to de-energize the coil. At that point the falling magnetic field causes a current to flow in the coil, except there is no opposing current fromthe battery (because the coil has been disconnected. The result is a huge (but short) negative voltage spike. The diode across the coil simply grounds this spike preventing it from disrupting other electronics in the vehicle.I had a question about the use of the diode in the diagram provided by m5bb. If I don’t use one will the system short out? It seems that way because the diagram appears to show pins 87a 86 and 30 of both relays all connect together, the only thing that would be stopping positive coming in contact with the ground would be the diode?
As you can tell I have no idea what i am doing
Any help is appreciated!
This spike is similar to the spike that produces the spark in a coil based ignition.
So, now ya know..
I think he means the motor can be removed from the front window housing only and swapped to the rear casing.
This may have been answered before, but here is how that circuit works:
The two-wire motors turn one way when current is applied in one direction, and turn the other way when the current is reversed. The three wire motors have one common terminal, and two windings, one that turn the motor one way, and another that turns it the other way.
For the two wire motor, then, you need to reverse the current flow. This is done by grounding both ends of the motor via pins 87a on the relays when they are OFF.
When the window switch is moved one way, it activates ONE of the relays, causing pin 30 (the one connected to the window motor wire) to connect to 12 volts. Since the other relay is OFF the other motor wire is still connected to ground through the other relay pin 87a. So the motor turns one way. If the switch is moved the other way, the opposite happens (the first relay goes OFF, thereby grounding that motor wire, and the other really goes ON routing power to the other motor wire, and the motor turns the other way.
jmackro
Well-Known Member
Scott explains the functioning of this circuit very well. Perhaps it's worth saying that this circuit is intended for 2-wire, e28 motors. A different circuit would be used with 3-wire, "sardine can" motors.
Perhaps the inclusion of the "flyback" diodes is confusing people. The circuit will work OK without them, but the life of the relay contacts will be shortened because they will spark each time the circuit is interrupted. The diodes simply suppress these sparks.
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Actually, to explain a bit further. Some circuits show the diode across the relay COIL, which is what I was talking about with a "flyback diode". The circuit in question, however shows diodes across the motor contacts. This basically reduced arcing of the contacts as @jmackro states. In a CSI or Megasquirt car I'd add the flyback diodes, since you definitely do not want the window relay spike taking out an ECU. In all cars, the snubber diode is a good idea because these motors do draw a lot of current. But this is really just belt and suspenders for longevity. There is no risk of burning anything out with out he snubber diodes.
So this shows how you would add relays? The two wire motors have no relays.
No, this explains how the circuit using relays for two-wire motors works. You expressed confusion about how the circuit posted back at #47 (?) or so worked.. this is how that works,
To add to the mix, aren’t some of the relays available built with a built-in diode to specifically prevent the issue described above? I have a CSi but had not put in the diodes since it didn’t seem that they were truly necessary for the functioning. I used 12v relays that I purchased that were labelled as “with built-in diode”
jmackro
Well-Known Member
e9Leveque said:
Yes, some circuits show the diode across the relay coil and some relays are available with a built-in diode. However, diodes across the relay coils do nothing to prevent arcing across the relay's contacts. Those diodes across the relay coils are also "flyback" diodes, but they are there to absorb the energy generated when the relay coil is shut off, protecting the device that switches the relays. In an automotive window application, the switch on the console is the device that switches the relay coils and those switches have beefy contacts relative to the inductance of the little relay coil; you don't really need a diode there (though it wouldn't hurt anything). When a relay is switched by a transistor, the relay coil's flyback voltage can fry the transistor, so in that application, a "flyback" diode is necessary.
Taking a step back, anything with a coil wound around a steel core will generate a "kickback" voltage when it is abruptly shut off. That's how your ignition coil works, but in it's case, the kickback voltage is routed to the sparkplug where you want a spark. But when shutting off a motor, you generally want that "kickback" voltage to be absorbed so that the switching device doesn't get fried. Window motors have a lot more inductance than a relay coil, and as such, generate a much higher "kickback" voltage when the relay contacts open to shut the motor off. So the schematic in post #90 has diodes in it to absorb the motor's "kickback" voltage and protect the relay contacts. You could also put diodes across the relay coils, but as I wrote above, relay coils have too little inductance to generate enough energy to materially damage the console switches.
HBChris said:
Yes, that's true. And the schematic that I reference in post #1, originally published by kdelimin, shows no relays in the circuit. So sure, 2-wire motors (and 3-wire motors) will work just fine without relays - heck, that's how BMW built these cars. Adding the relays delivers more current to the motors by eliminating the resistance from the console switches and all the associated connectors, while the "flyback" diodes improve the relays' longevity. I thought those additions where worthwhile doing while I was installing the e28 window motors, but admittedly, they were optional.
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Not sure what HBChris was referring to. AFAIK none of the motors originally had relays.
The two wire motors require reversing the current direction to make the motor run the other direction. The three wire motors simply require energizing one wire relative to ground for one direction, and the other wire relative to ground for the other direction.
Both types can benefit from relays.
The primary rationale behind the use of relays is:
- Reduces circuit losses. Since the motors draw a lot of current, and the original wires must go from the fuses, to the console switches and then out to the window motors, the combination of wire length, wire size, and small switches means there are resistance losses that reduce the current in the motors, slowing them down*.
- Reduces the current controlled by the switches, causing them to last longer and operate more reliably (and less loss/resistance)
- Allows for a larger gauge wire carrying the drive current, reducing resistance (lower wire resistance, shorter wire).
* For those who may not understand the mechanism: As current flows across a resistance, the voltage across the resistance drops. Here isa simple circuit called a voltage divider. I have drawn this as a battery, a switch, a resistance and a motor. Consider the resistance to represent all of the resistances in the chain from the battery to the motor (switch losses, wire losses, connector losses, fuse losses, etc). Since all of these are in series, we can just bundle them all together, and then assume a perfect battery and a perfect switch.
Now, if we assume the motor, if attached to the battery directly draws 10 Amps. By Ohm's Law we can determine that the "resistance" of the motor is 1.2 ohms (I put resistance of the motor in quotes because it is technically not a "resistor"...). If the circuit resistance R is zero then the voltage at the motor (Vmotor) will be 12 volts. But watch what happens to the motor voltage and the motor current as the resistance goes up.
So, you can see that even small amounts of resistance in the circuit will cause the voltage at the motor to drop significantly, and this causes the current through the motor to drop, reducing the power and torque of the motor. If we assume that torque is proportional ti current, then 0.5 ohms of resistance in the wires, fuse, and switch will cause the current (and this the motor torque) to drop by 30%. If the resistance is 1 Ohm then the current and torque will drop by nearly 50%...
Yes
I ran 8mm2 (~8AWG) cable to a new fuse box inside the car, and then 4mm2 (~12AWG) to the door relays. I saw about a 0.5v drop in voltage at the door relays with a 20A fuse inline.
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jmackro
Well-Known Member
I just saw your most recent post, but had missed your original question last year. By now, you have probably long since solved your problem. But just out of curiosity, what was interfering? Sorry, but "elbow pin interferes with the motor housing" didn't mean much to me. What is an "elbow pin"? Where on the motor housing did it encounter interference? I don't suppose you have pictures.
I have put e28 motors into both the F and R window regulators on my e9 and don't think that I encountered the sort of interference that you refer to. But then, since I don't really understand your issue, I can't say much more than that I didn't need any washers to space the motor back from the regulator frame.
That seems about right, although 8 Ga wire is pretty huge!!
Looking at the wire resistances, 8 Ga wire has about 4X lower resistance than 14 Ga wire (which is about what is used inthe stock setup. That said, however, there's not all that much wire length, so the wire resistance is probably not a huge factor here. 14 Ga wire is about 2.5 Ohms/1000 ft, vs 8 Ga, which is about 0.6 Ohms/1000 ft. If there is 10 feet of wire between the battery and the motor, then this is only a difference of 0.019 ohms...
So, I suspect that the relay contacts are the real source of improvement.