Vintage BMW Motorcycle Owners

Great post
Qoute:
Doug Rinckes

Sometimes when the generator has been disassembled or the battery has been connected the wrong way
around, the generator won't work. When you start the engine, there is no voltage coming from the
generator, so the field windings get no current. This would prevent the generator from working, except for
the small amount of residual magnetism left in the field, which is enough to start up the generator.
When this residual magnetism is lost, or has the wrong polarity, you must repolarise the generator (send a
current through the field windings). Just connect battery positive to D+ for a few seconds - you can do
this by closing the circuit breaker contacts with your fingers

Tommy, that's a good reminder. Thank you. I will definitely need to polarize the generator as part of the process. Thanks for mentioning that.

I'm going to delay winding the coils. I would like to use yellow heat shrink so I can make my coils look factory fresh, but I don't keep that around usually. So, I'll order some and delay winding until next weekend. Believe me, it's not easy for me to do!

After four less than acceptable attempts, I was finally able to produce a couple of coils that were satisfactory (to me). I have continued to play with the dimensions of the spool until the width allowed solid seating of the winds and the ID would fit over the shoe, after pressing/bending the coil into shape. I have two more to do, however I ran out of magnet wire and have ordered some more to make the last two coils. In the interim, pretty pictures.

I measured the resistance of these new coils and they seem to be between 0.3 and 0.5 ohms each, so a set of four would be between 1.2 and 2.0 ohms. Still not quite getting up to that 2.6 to 4.0 range. I tested the coils by applying 6V via a variable DC power supply while mounted on a shoe, and they're certainly capable of being electromagnets, when juiced.

Winding the coils with even distribution of each wrap is tricky. This was the final layer, hence it does not create an entire layer.


I place three small bands of super glue after each completed layer. You can see the superglue in this profile picture, once 1/2 of the spool is removed


I add a little more super glue after removing the coil from the spool to ensure it doesn't unravel, however it may not be good to wear nitrile gloves at this time. I've added yellow heat shrink for the factory fresh look.


Finally, the coil wrapped in tape. There are a few more steps before the coil is mounted onto the stator. I will share more photos after making the other two coils.

looks great
Tommy

But you'll still never know now if all you really needed was a new regulator? I admire your abilities though.

Dave

Daves79x wrote: ↑

Wed Feb 16, 2022 10:11 am

But you'll still never know now if all you really needed was a new regulator? I admire your abilities though.

Dave

I'm pretty sure that was all I needed! I sure hope these new coils work and that this wasn't a 3-month trip to nowhere. Well, I've been learning a lot along the way at least and having fun.

When I first tested the coils for magnetism by placing my screwdriver against the inside of the shoe, two were very strong and two were very weak. I thought this was a bad sign. However, I now realize that the two "weak" coils have their poles oriented in the opposite direction of the other two, as is normally the case, hence the stronger magnetic attraction for the screwdriver would have been on the outside of the coil. I didn't try that. Now I know how it works. "One learns by doing".

congratulations, I see you did well, you printed with a 3D printer tool and wound a new spool, of course it will work nicely like new, well done ,TOP

years ago we developed a new ignition coil, there are many old non-functioning electrical windings, as oxidation occurs between the winding threads and the breakthrough of electricity - green oxidation in the picture

oldtimers.si wrote: ↑

Wed Feb 16, 2022 12:40 pm

congratulations, I see you did well, you printed with a 3D printer tool and wound a new spool, of course it will work nicely like new, well done ,TOP

Thank you TOP. I appreciate the encouragement. And thank you for sharing the pictures too.

It's interesting to think about how these old electronics were made. There must have been a lot of trial and error to get the manufacturing tools dialed in.

Werner1111 wrote: ↑

Wed Feb 16, 2022 11:26 am

When I first tested the coils for magnetism by placing my screwdriver against the inside of the shoe, two were very strong and two were very weak. I thought this was a bad sign. However, I now realize that the two "weak" coils have their poles oriented in the opposite direction of the other two, as is normally the case, hence the stronger magnetic attraction for the screwdriver would have been on the outside of the coil. I didn't try that. Now I know how it works. "One learns by doing".

Hmm. I don't think that's how magnets work, unless your screwdriver is also magnetised. All four coils should have the same field strength, just with alternating polarities.

The repair manual states that putting 6V through the field coils should result in current draw of 2.7A, and "a piece of soft iron (screwdriver) used for touching the poles is attracted to each of the four pole shoes with the same force".

You should be able to confirm the polarities alternate using a compass, or using a smartphone app like Pole Detector that can tell you if it is pointing at the north or south pole of a magnet. I suspect that at least one of your coils is connected the wrong way around, and is combining with the opposite coil to create a single, stronger magnetic field. See the attached diagram.