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Cliff
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I am having a charging problem with my 69 R50. I replaced the armature, brushes and springs but it will not charge unless I put voltage across the field windings for a second. I tried to magnetize the field windings by running 6 volts through them but I get no output unless I excite the windings. I am about to give up and install a 12 volt conversion but the bike is very original and I would prefer to keep it that way.

schrader7032
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VBMWMO #7032
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Was the generator working

Was the generator working prior to the replacements? I'm DC-challenged to a great degree, but the fact that you have to excite the winding certainly suggests something. Not sure if it's the same thing on the /2, but on the /5-on bikes, the charge light is a critical element of the charge circuit. Current has to flow through the light in order to provide the excitation voltage for the rotor. If the bulb burns out, the alternator won't charge. Since the /2 has a similar charge light, I'm wondering of the same thing is needed. Does your charge light work?

There is a PDF file online by Doug Rinckes called "Understanding and Maintaining the BMW /2 Electrical System". I would find that and see what info is there for troubleshooting. Vech sells version 2.0 of this book which is much better with the troubleshooting and has wiring diagrams for all models of bikes. You might be able to keep the current system with some decent troubleshooting.

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'78 R100/7 '69 R69S '52 R25/2

Cliff
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I replied one but it

I replied one but it disappeared so if this is a duplicate I apologize. I did check the bulb and it does light although I did not check to see if the correct bulb was installed. I believe that the generator is a self excited shunt type. This type uses residue magnetism in the field coils to start the process. The symptom I am experiencing sounds like a loss of magatisum in the field coils but I magnetized the coils and it did not help.

schrader7032
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VBMWMO #7032
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Cliff -Again, I'm

Cliff -

Again, I'm DC-challenged, but are you sure about the magnetism of the generator coils? Certainly, the magneto is a magnet but that is part of the ignition system...separate from the charging system.

From the diagram, connections 30/51 are directly connected to the battery so there should be +voltage here relative to ground. Terminal 61 is connected to the charge light. Terminal 31 is a connection through the ignition switch...the color being ground seems to indicate that it should be a ground wire at some point. Not sure if any of that helps...

There's a regulator also which is important to charging.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

butch housman
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Here's a link to a useful

Here's a link to a useful manual on ur electrical system:

http://www.snafu.org/restore/uandm_bmw_v1.pdf

Please don't make a rash decision to abandon a potentially good 6 V system. I would suggest u call Vech at 662-465-6444 & ask for help. He will give u more info than u will be able to quickly digest.

Biker Butch

PS. I know nothing !

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Cliff
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Thanks for the encouragement,

Thanks for the encouragement, I will give him a call. They were very nice when I ordered the brushes and springs. It is very frustrating that I can't find the problem. I have electrical training and work in a technical field. This is a very simple circuit, It should be easy.

butch housman
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Hah.....ur singing my song

Hah.....ur singing my song exactly....SHOULD BE SIMPLE !

Many things on these bikes r deceptively simple, I think this is where u ad, "The Devil is in the details".

I have always heard abt the "windings" loosing their magnetism & how u have to do some kinda voo doo ceremony involving batteries & wires to help them get their juice back. It has never happened to me so I can't give u any advice based on experience but it does sound like this could be ur based on ur having to excite the field to get output. However, I would think once it was working it would keep working. I n use I believe the field coil is energized by the voltage relay so maybe the problem is there. Have u done the voltage relay test ?

Armatures can only be checked effectively by a machine called a "glowler". Continuity tests don't work. Agn, how that works exactly is also a mystery to me & decades into the era of alternators I doubt that growlers or the skills to use them r easily found. The simple way to see if a generator is good is to just hook it up to a battery & see if it runs like a motor but there agn ur stuck in this application.

Vech should be around tomorrow I suspect he will be able to get u on track.
good luck,
b

PS. Another approach would be to abandon all hope & buy a Harley, chicks love 'em & they're WAY cheaper to work on than these Vintage Machines Wink

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butch housman
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Cliff
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I think I may have fixed it.

I think I may have fixed it. I took the the generator out and magnetized the field coils with a 12 volt car battery. It now self excites. Thanks for all of the help and support.

butch housman
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Hot damn !

Hot damn !

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butch housman
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Cliff, Exactly how did u

Cliff,
Exactly how did u remagnitize it ?

Cliff
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I removed the outer half of

I removed the outer half of the generator that has the field coils attached. I connected ground of my 12 volt car battery to the ground side of the field coils and positive to the plus side of the coils. I did that for about 5 seconds. I had tried this several times with the 6 volt battery but it did not fix it. The 6 volt battery may be weak.

butch housman
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did u make a solid connection

did u make a solid connection & leave it connected for 5 seconds or did u do it intermittently ? Did it spark much ???

I've seen my Dad magnetize big screwdrivers by wrapping a coil of wire around the blade & stroking the battery terminals. What could go wrong there Wink

It worked on the screwdrivers & glad u solved ur own problem. Good goin'
+ tnx for the info
b

schrader7032
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VBMWMO #7032
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I'm still having trouble

I'm still having trouble wrapping my head around the field coil "charging". My limited understanding is that the brushes bring current into the rotor which has an iron core and windings all around it. When the rotor is turned inside the stator windings, the energized rotor induces current to flow in the field coils which is what we get out to power the bike, charge the battery, etc. I'm not aware of any permanent magnet situation with the field coils...it's just a long length of wire. I don't see how hooking it up to a 12v battery does any good.

As I mentioned before, the only permanent magnet I was aware of was the magneto rotor.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

ScottA
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I'm no expert

but AFAIK no permanent magnet is required. We flash the field to get all the electrons lined up.
https://en.wikipedia.org/wiki/Excitation_(magnetic)

and if an iron bar is magnetized this way, something as simple as dropping it on a hard surface can cause the electrons' polarity to jumble-up again.

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'61 R27, '63 R60/2 etc.

schrader7032
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VBMWMO #7032
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Electrons lined up?? I feel

Electrons lined up?? I feel my leg being pulled... D Oh

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

wa1nca
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yes this is real

yes this is real

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Tommy Byrnes
54 R51/3 55 R50 64 R27 68 R69US 68 Sears Allstate 250 (Puch)

butch housman
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For my birthday last year my

For my birthday last year my wife bought me a basic "Quantum Mechanics" tool set. I has a QM screwdriver, a QM hammer, a QM adjustable wrench, a pair of QM pliers & a tiny pair of tweezers to get everything out of the box with. At first I too thought she was pulling my leg too because the box appeared to be empty except for the tweezers. The whole set only cost $3.99 from Edward Scientific. It's gotta be a rip....RIGHT ?

As it turned out it was on the level but the catch was the tools were SO small u need an electron microscope to use them, an additional $33,999,999.99 !

No wonder the Iranians r having so much trouble Sticking out tongue

REALLY ! I would NEVER BS u guys.............................

Biker Butch

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