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R69 (and other) field coil repair?

Werner1111
Posts: 100
Joined: Fri Dec 16, 2016 6:39 pm
Location: Hollyweird, CA

Re: R69 (and other) field coil repair?

Post by Werner1111 »

Mal and Kurt,

Thanks for the input and the good suggestions. I haven't yet tried to unwind the coil only because it's got varnish on it and is still wrapped in field coil tape, but I'm definitely going to do that.

The magnet wire has a thin insulating coating on it so that it won't short out against itself when wrapped as a coil. As one increases the number of coils and/or the current running through the coils, the ability of the generator to create electricity increases. So, if you have a short(s) in the field coil, the current would take the easiest path, travel though fewer coils and decrease the ability of the generator to produce electricity. From the specs noted in my prior post, we can calculate what the resistance of the wire should be at a given length (or weight for that matter). If the resistance is too low, then the coil is likely shorted. There's a lot more behind that and I'm still learning about it, but that's the 30,000 foot view of how to determine whether a field coil has failed.

When I unwrap the coil, there would be no chance for a short and I would be able to determine the intended resistance of the magnet wire, and also determine the length of the coil. I'm ordering new magnet wire today, along with varnish and field coil wrap, so I'll be able to compare the resistance of the old magnet wire to the new.

Great ideas guys! Thanks! I'm on it and will post when I have updates.

Andrew
R69 R90/6 R100/7 R100S R1150GSA S2R1000

dougthatdoug
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Location: Zurich, Switzerland

Re: R69 (and other) field coil repair?

Post by dougthatdoug »

Hi Werner,

I'm currently emailing with someone else who is rewinding their coils as well, and they also get 1.8 Ohms through all four.

I suspect both Barrington and I have relied on a BMW source for the higher figure, so that gives me a bunch of checking to do to see if I can narrow down where that comes from! (This is super timely as I'm in the process of updating my book.)

I don't have a lot of information on field coil winding, but there is a document (in German) that might be helpful for you.

This one gives field coil winding information (number of windings, wire weight) for the R25 and R25/2 - https://cms.bmw-einzylinder.de/images/P ... chluss.pdf

Granted, you have a R69, but it shouldn't be a million miles out, and as long as you match the number of windings in your coils, you should be ok.

The "Hilfspule" in the diagram, wound around field coil #1, is the resistor, which on your bike is mounted on the generator.

One suggestion, that is a bit late now, is to number the coils before you remove them. They're not all the same, and the polarity needs to alternate. I don't have a unit with me that I can test at the moment, but when they're in the generator, if you put power through them, you should be able to use a compass to indicate the field direction, and make sure it alternates as you move it around the generator case.

I would love to know if a magnetic field sensor app on a smart phone works!
Doug Rinckes

dougthatdoug
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Re: R69 (and other) field coil repair?

Post by dougthatdoug »

The only R69 repair manual I can find (not R69S, see note below) has a test for the field coils.
Connect + pole of a 6-volt battery over ammeter to terminal 61 on (generator) housing, - pole of battery has to be connected with crankcase earth. Field windings are in order if ammeter indicates 2.2 amperes charging current and is further a piece of soft iron (screw driver) used for touching the poles is attracted to each of the 4 pole shoes with the same force.
OK so ignoring the slightly off translation, 6V battery through the field coils equals 2.2 A. Using Ohms's law, V=IR, this gives us 6=2.2/R, and unless I've forgotten everything that's R=6/2.2 and so the resistance should be 2.7 Ohms.

Your 1.8 Ohms will be causing a current draw of 3.3 A (at 6V) through the coil. I'm doubtful that that is enough to cause any damage, but the higher current will increase the field strength and therefore increase the generator output for the same engine speed. It could be argued this is a good thingTM.

This does assume that the lower resistance is not being caused by any internal short circuits!

It's possible the repair manuals were correct at one stage, but the part got changed and everyone just forgot to update the manual. It's also possible that everyone has been relying on some number that is common knowledge, and also incorrect.

I said there was a note about the R69S. The R50, R60 and R69 are supposed to draw 2.2A through the coil, so should have 2.7 Ohm resistance. The R26, R27 and /2 twins all draw 2.7A, so should have 2.2 Ohm resistance, and the R25 to R68 draw 1.6A, so should have 3.8 Ohm resistance.

If anyone is able to check any of these figures, either by measuring the current through the coil, or just throwing an ohmmeter across it (measure resistance from D+ to ground should do it), please post your model and reading!
Doug Rinckes

dougthatdoug
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Re: R69 (and other) field coil repair?

Post by dougthatdoug »

Two more things. I see you have some suspicions about your F-type regulator. Fortunately there's a super document all about the F-regulator, unfortunately it's all in German and whoever wrote it doesn't believe in paragraphs.

Together with Google Translate I've made a translation.

Secondly, there's an Android app called Pole Detector by Webcraft AG. You can use this on your phone to point to a magnet (or field coil with power) and it will tell you the orientation, N or S, so you can confirm that the coils have alternating orientation.

You might even be able to use that on your field coil shoes, to make sure you install them in the correct order.

Good luck!
Doug Rinckes

Werner1111
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Re: R69 (and other) field coil repair?

Post by Werner1111 »

dougthatdoug wrote:
Sun Jan 09, 2022 8:27 am
Hi Werner,

I'm currently emailing with someone else who is rewinding their coils as well, and they also get 1.8 Ohms through all four.

Doug, that's also me emailing with you. I started this post and then found some info about you while searching the forums here. Thanks for your help here and via email. Everything you've shared thus far has be super helpful and I really appreciate it!
R69 R90/6 R100/7 R100S R1150GSA S2R1000

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Re: R69 (and other) field coil repair?

Post by schrader7032 »

Welcome to the forum "dougthatdoug"! Took me a while before I realized who that Doug was!! :lol: Finally, someone who knows /2 electrics!!
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
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vechorik1373
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Re: R69 (and other) field coil repair?

Post by vechorik1373 »

A procedural important hint about replacing field coils.
After you install the steel shoes in each winding, and install the windings in the housing, when you install the screws that hold the steel shoes in the housing, do not tighten them! Install them finger tight, and then take your armature(If you have not removed it from the crankshaft, do so now), and wrap layers of paper around it, and carefully work the wrapped armature into the 4 shoes that are in the housing. You see, there is a degree of slop, in the way the steel shoes fit the housing, and if you blindly just tighten the screws, the curve of steel shoes will NOT be accurately lined up with the armature, and you will destroy the armature when you start the engine. You must fool around with the layer of paper, to get the thickest layer you can, and still get the armature to go into the space. Only then, when you have a snug fit of the armature inside the armature inside of the steel shoes, can you tighten the 4 bolts that hold the windings in the housing.

I hate to say this, but I learned this method the hard way, at least 35 years ago, when replacing field coils.
Vech
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Re: R69 (and other) field coil repair?

Post by wa1nca »

More good info
Thanks Vech
Tommy
Tommy Byrnes
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Werner1111
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Location: Hollyweird, CA

Re: R69 (and other) field coil repair?

Post by Werner1111 »

vechorik1373 wrote:
Tue Jan 11, 2022 8:47 am
You must fool around with the layer of paper, to get the thickest layer you can, and still get the armature to go into the space. Only then, when you have a snug fit of the armature inside the armature inside of the steel shoes, can you tighten the 4 bolts that hold the windings in the housing.
Thank you Vech. I suspect I may have had the same learning experience without that advice. Is the clearance that tight - ie a couple of paper widths? I have already thought to myself while doing all this, "man those field coils are really stuffed in there. I'm going to have think about that when winding/shaping the coils." I didn't realize the spacing between the armature and shoe is so close as well. Glad you mentioned this.
R69 R90/6 R100/7 R100S R1150GSA S2R1000

dougthatdoug
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Re: R69 (and other) field coil repair?

Post by dougthatdoug »

Yeah, Vech is right.

The pole shoes were made slightly oversized, fitted into the housing and then machined down to provide the clearance to the armature.

Treat em like the field coils - number them before you remove them, put them back in the same positions, and use Vech's trick to make sure there's clearance to the armature.
Doug Rinckes

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