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R69 (and other) field coil repair?

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

R69 (and other) field coil repair?

Post by Werner1111 »

Hi All,

I've been a member for a few years, but believe this might be my first post. I'm working on my 1960 R69, which has a charging issue. Has anyone had any success repairing the field coils, either yourself or by sending the part out for service?

I've already done a significant amount of web research and gathered up what documents I could about the issue, including the free version of Doug Rinckes /2 manual and I already own the Barrington Motor Works /2 manual. I also found a fantastic resource about aircraft 6V generator systems. While the setup is different, it's a great introduction to all of the principals of a 6V generator and regulator (https://www.flight-mechanic.com/airfram ... al-system/). The DC Generators sections (Parts 1 and 2) and Generator Controls (Parts 1 and 2) are very helpful.

I have a situation where I am getting almost no charge from the generator. The brushes have plenty of life and I have done the tests prescribed in the Barrington manual to check my armature and field coils. The armature tests AOK, and I believe my field coils are the primary issue. I checked resistance through my coils and it is 1.8 ohms (should be between 2.5 and 4.0). I also did the next step which is to run 6V DC through the field coils with an ammeter in series. A healthy field coil should draw 2.7 amps, however mine only draws 0.7 amps. Healthy field coils should each provide equal magnetic attraction to a screwdriver, however only two of my four coils have a magnetic attraction. The last test is to push in the contactor arm on the voltage regulator during this setup and the amps should decrease. Mine instead increase slightly from 0.7 to 0.8 and a 3rd coil starts to energize, tested by the magnetic attraction of a screw driver.

The bike seems to be all original and I'd prefer to keep it that way, rather than upgrade to a 12V charging system. I might go with an electronic voltage regulator, once I get the generator working.

So, I ask again, after the explanation,Has anyone had any success repairing the field coils, either yourself or by sending the part out for service? Are there other options besides trying your luck with a used set on eBay. My go-to has always been Benchmark, but as you may or may not know, Vech recently retired, closed the shop, and sold the stock to Max BMW, so that resource is no longer available. I'm not quite sure where else to go for that kind of assistance.

Thanks for any help.

Best regards,

Andrew
Los Angeles
R69 R90/6 R100/7 R100S R1150GSA S2R1000

sorbo1
Posts: 50
Joined: Fri May 16, 2014 6:45 pm

Re: R69 (and other) field coil repair?

Post by sorbo1 »

Andrew
Although I live in Australia , I have visited Los Angles on several occasions and can recommend you contact Mr Evan Bell of Irv Seaver Motorcycles in Orange County . He was very helpful with parts on one of my trips and also is very knowledgeable on early BMWs . He has a collection of BMWs including a Rennsport. Address is 607 W. Katella Ave. Orange CA 92887 , Phone 714 532 3700 . He was President of the company but may have retired since I was last in LA . Hope this is of some help .

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

Re: R69 (and other) field coil repair?

Post by Werner1111 »

Thanks mate! I've been to that shop before and the museum is pretty spectacular. I'm stoked you got to see it on your visit.

Thanks for reminding me about the Irv Seaver shop. Good advice. I'll give them a call.

I get stuck in my groove sometimes and forget that there are some really great resources right under my nose. My wife suggested I look for ads in the Vintage BMW Owners magazine and the Airheads magazines. Doh! She's right, of course!
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Re: R69 (and other) field coil repair?

Post by Micha »

The wife is always right, even when she's wrong.
Michael Steinmann
R51/3 1952
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Werner1111
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Joined: Fri Dec 16, 2016 6:39 pm
Location: Hollyweird, CA

Re: R69 (and other) field coil repair?

Post by Werner1111 »

Just a quick update. I broadened my web search from BMW specific generator charging issues to "field coil rebuild" and started to find some results. This video, while of a starter motor, gives me hope that rebuilding my coils is doable in my home shop:

https://www.youtube.com/watch?v=pc6BYNp ... ngsOfficial

I'm having a few conversations via email about this and will update when I find out more.

Cheers!
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Re: R69 (and other) field coil repair?

Post by wa1nca »

Salis has replacement field coils
All 4 coils have a different part number

https://www.bmwclassicmotorcycles.com/p ... generator/

Tommy
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
Ashfield, Ma
USA

Werner1111
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Location: Hollyweird, CA

Re: R69 (and other) field coil repair?

Post by Werner1111 »

Thanks so much Tommy. I was remotely aware of Salis, but did not know they stocked so many parts for the older BMWs. What a great resource. And fairly priced too, it seems.

I'm still contemplating rewinding my original coils, but haven't done quite enough research to really be sure which way to go. I think I will take apart one of the bad coils to see what's going on in there.
R69 R90/6 R100/7 R100S R1150GSA S2R1000

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

Re: R69 (and other) field coil repair?

Post by Werner1111 »

In spite of the coils being available from Salis, I've been doing some research and talking with a few friends to learn how to rewind my own coils. You never know when you might need the skills necessary to create an electromagnet and I'll now be prepared for that day...

Per my prior post, I already took some measurements on the Armature (OK) and the field coils (not OK). The resistance across all four field coils is 1.8 ohms, however several sources (Doug Rinckes, Barrington) suggest it should be between 2.5 to 4.0 ohms measured between the 61 D+ and F(-) terminals. I then removed the four field coils from the stator and measured the resistance across each coil and found #1 = 0.5 ohms, #2 = 0.5 ohms, #3 = 0.4 ohms, #4 = 0.4 ohms. In my nomenclature (which is the same as Salis), #1 is on the right (3 o'clock), when facing towards the generator, and # 4 is on the top.

I've laid them out on my bench per the picture, below, with 1 through 4 from left to right.

Image

If you look at the coils, you'll see that the wires exit from #1 and #3 in the opposite direction compared to #2 and #4, which I think suggests reversed polarity. Other than that, it looks pretty straight forward. I believe I need to use the same size wire and mimic the number of wraps using the same ID, OD and depth of the wrapped coil.

The magnet wire in my coils has a diameter of about 0.95mm, which works out to 19 awg magnet wire. Magnet wire is copper wire with a very thin coating of insulation around it and is used for winding coils, among other things. I also weighed the four coils and got about 15 oz. I found some basic specs on 19 AWG magnet wire including:
  • 2.04 ohms/lb.
  • 3.95 lb/1000 ft
  • 253 ft/lb
Doing some simple math, I've determined that the four coils together, weighing 15 oz, should have a total resistance of 1.88 ohms and have a length of about 237 ft. Recall that the reading on my coils combined is 1.80 ohms, which is not too far off. Considering that my coils still have the added weight of the wrapping tape, the difference is even smaller.

As I mentioned earlier, the Doug Rinckes book and the Barrington book both indicate the four coils together should have a total resistance ranging from 2.5 to 4.0 ohms when measured between the 61 D+ and F terminals. I'm not sure how to reconcile the difference here. I don't believe that there would be 0.7 to 1.2 ohms of additional resistance added by the connectors, but maybe I'm wrong. I'm not a EE, just a hobbyist. Actually, I believe I took the original measurement of 1.8 ohms between those two terminals, before removing the generator from the bike.

I'd appreciate any input on this last issue. 1.80 ohms, as on my unit, should be out of spec and it was the reason I believed my bike wasn't charging. However, after researching the specs of the magnet wire, I'm now not sure what to think.

I also hooked up my F-type Voltage Regulator to a variable DC power supply and ran it through its paces from 5V to 8V and back to 5V. While the two sets of points are opening and closing as I'd expect, the voltage that triggers the movement of the coil differs a bit each time, so I will need to address that issue as well.
Last edited by Werner1111 on Fri Jan 07, 2022 8:34 pm, edited 1 time in total.
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malmac
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Re: R69 (and other) field coil repair?

Post by malmac »

Werner1111 wrote:
Thu Jan 06, 2022 8:23 pm
In spite of the coils being available from Salis, I've been doing some research and talking with a few friends to learn how to rewind my own coils. You never know when you might need the skills necessary to create an electromagnet and I'll now be prepared for that day...

Per my prior post, I already took some measurements on the Armature (OK) and the field coils (not OK). The resistance across all four field coils is 1.8 ohms, however several sources (Doug Rinckes, Barrington) suggest it should be between 2.5 to 4.0 ohms measured between the 61 D+ and F(-) terminals. I then removed the four field coils from the stator and measured the resistance across each coil and found #1 = 0.5 ohms, #2 = 0.5 ohms, #3 = 0.4 ohms, #4 = 0.4 ohms. In my nomenclature (which is the same as Salis), #1 is on the right (3 o'clock), when facing towards the generator, and # 4 is on the top.

I've laid them out on my bench per the picture, below, with 1 through 4 from left to right.

Image

If you look at the coils, you'll see that the wires exit from #1 and #3 in the opposite direction compared to #2 and #4, which I think suggests reversed polarity. Other than that, it looks pretty straight forward. I believe I need to use the same size wire and mimic the number of wraps using the same ID, OD and depth of the wrapped coil.

The magnet wire in my coils has a diameter of about 0.95mm, which works out to 19 awg magnet wire. Magnet wire is copper wire with a very thin coating of insulation around it and is used for winding coils, among other things. I also weighed the four coils and got about 15 oz. I found some basic specs on 19 AWG magnet wire including:
  • 2.04 ohms/lb.
  • 3.95 lb/1000 ft
  • 253 ft/lb
Doing some simple math, I've determined that the four coils together, weighing 15 oz, should have a total resistance of 1.88 ohms and have a length of about 237 ft. Recall that the reading on my coils combined is 1.80 ohms, which is not too far off. Considering that my coils still have the added weight of the wrapping tape, the difference is even smaller.

As I mentioned earlier, the Doug Rinckes book and the Barrington book both indicate the four coils together should have a total resistance ranging from 2.5 to 4.0 ohms when measured between the 61 D+ and F(-) terminals. I'm not sure how to reconcile the difference here. I don't believe that there would be 0.7 to 1.2 ohms of additional resistance added by the connectors, but maybe I'm wrong. I'm not a EE, just a hobbyist. Actually, I believe I took the original measurement of 1.8 ohms between those two terminals, before removing the generator from the bike.

I'd appreciate any input on this last issue. 1.80 ohms, as on my unit, should be out of spec and it was the reason I believed my bike wasn't charging. However, after researching the specs of the magnet wire, I'm now not sure what to think.

I also hooked up my F-type Voltage Regulator to a variable DC power supply and ran it through its paces from 5V to 8V and back to 5V. While the two sets of points are opening and closing as I'd expect, the voltage that triggers the movement of the coil differs a bit each time, so I will need to address that issue as well.
On the assumption you are going to rewind the coils, would it be a good idea to unwind a coil and measure the length of wire that was used, as a double check on your calculated length of wire.
I am sure you have already planned to do this, but I just wanted to show that I had read your post with much interest. Please keep us posted as you progress.


Mal
mal - R69s
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Re: R69 (and other) field coil repair?

Post by schrader7032 »

After checking your math as Mal suggested, what about buying the same length of replacement wire you had planned to use and measure the resistance of the new wire.
Kurt in S.A.
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