Charging Question

174713 · Oct 2, 2017

Good morning electrical wizards-

I just replaced a failed battery and my voltmeter is showing no charging taking place. Readout is 12.8V after being on the battery tender all night the. It steadily drops to 12.1V while I’m riding. I shut it down at this point. The battery warning light never lights up indicating charging.

Ive checked and cleaned all connections, replaced the voltage regulator, checked brush’s and contacts on the alternator and diode board. I just noticed the battery warning light does not come on when I switch the key on so I’m suspecting a burned out bulb. Reading Snowbum’s site this should not prevent the battery from charging unless I’m reading this wrong.

Any ideas?
Thanks,
Charlie

1074 · Oct 2, 2017

Charge light

I think you're reading it wrong. If you turn the key on you should get a light. If you don't then you need to troubleshoot. Pull off the front cover and ground the rotor slip rings. If the light comes on while grounded then you have an open rotor to replace. If no light then take apart the instrument pod and check the light bulb. Do this in the socket because sometimes they corrode (the socket) so that you lose continuity.
Once you have the charge light coming on with the ignition start the engine. The light should go out around 1500-1800 rpm. indicating that the system is charging. Running a volt meter across the battery will tell you how well it is charging but that's an answer to another question.

174713 · Oct 2, 2017

174713 said:
Good morning electrical wizards-

I just replaced a failed battery and my voltmeter is showing no charging taking place. Readout is 12.8V after being on the battery tender all night the. It steadily drops to 12.1V while I’m riding. I shut it down at this point. The battery warning light never lights up indicating charging.

Ive checked and cleaned all connections, replaced the voltage regulator, checked brush’s and contacts on the alternator and diode board. I just noticed the battery warning light does not come on when I switch the key on so I’m suspecting a burned out bulb. Reading Snowbum’s site this should not prevent the battery from charging unless I’m reading this wrong.

Any ideas?
Thanks,
Charlie

Thanks for the quick response! I think the charge light just started not coming on so I checked the battery voltage at 3000 rpm, no charging taking place. Would the bulb/bulb holder malfunctioning prevent charging?

ebeeby · Oct 2, 2017

Yes, the bulb must be functional.

1074 · Oct 2, 2017

Check the rotor first! It is the easiest to do and is much more likely to be the problem.

174713 · Oct 2, 2017

1074 said:
Check the rotor first! It is the easiest to do and is much more likely to be the problem.

I checked the bulb, it’s good. I checked the bulb socket, also good. Connected the VOHM meter at the socket, turned the key on, got 12.6V. Put the bulb back in the socket, turned the key on, no light. Did this 3 times and got 12.6V at the socket but no light. Swapped out working bulbs to this socket, still no light.

Any other ideas?

20774 · Oct 2, 2017

Charlie -

Somewhere down the line, you should probably invest in the Boxer Charging book offered by Motorrad Elektrik. You can carry this with you to troubleshoot the charging system.

It sounds like your problem is downstream in the alternator. The rotor was mentioned...it is the weakest link. But you must take steps to isolate the problem rather than just throw money at it. Read this section from Snowbum's site:

http://bmwmotorcycletech.info/trbleshootALT.htm

This will step you through things to identify where the problem is.

174713 · Oct 2, 2017

20774 said:
Charlie -

Somewhere down the line, you should probably invest in the Boxer Charging book offered by Motorrad Elektrik. You can carry this with you to troubleshoot the charging system.

It sounds like your problem is downstream in the alternator. The rotor was mentioned...it is the weakest link. But you must take steps to isolate the problem rather than just throw money at it. Read this section from Snowbum's site:

http://bmwmotorcycletech.info/trbleshootALT.htm

This will step you through things to identify where the problem is.

Hi Kurt-

Thanks for the insight, I purchased Rick’s book then lost it in our last move. I’m ordering another copy today.

I’ve gone through Haynes’ troubleshooting steps, voltage regulator, alternator, diode board are all good. I’m down to the dash bulb and saw Snowbums comments about failures there.

What I can’t understand is why I’m getting voltage at the dash bulb socket when I turn the key on but the bulb does not light up. Next thing is to call Rick.

1074 · Oct 2, 2017

dash socket

Often you'll get power on the board but no light. This usually means that the bulb socket is not making full contact with the thin metal tape that fits in the hole that the socket fits into. Sometimes it is corrosion on the metal tabs on the socket where they contact the thin metal from the board. Sometimes the thin metal from the board isn't stuck down the hole that the socket fits into. Sometimes there is a hairline crack on that thin metal tab and the contact point with the socket tabs is not through to the rest of the board.

174713 · Oct 2, 2017

1074 said:
Often you'll get power on the board but no light. This usually means that the bulb socket is not making full contact with the thin metal tape that fits in the hole that the socket fits into. Sometimes it is corrosion on the metal tabs on the socket where they contact the thin metal from the board. Sometimes the thin metal from the board isn't stuck down the hole that the socket fits into. Sometimes there is a hairline crack on that thin metal tab and the contact point with the socket tabs is not through to the rest of the board.

Thanks Bruce. In talking with Rick Jones I realized I had not retested the rotor after correcting the socket connection to the bulb. Once I tested the rotor again, the light came on so bad rotor. One is on it's way!
Thanks to all for the input,
Charlie

174713 · Oct 20, 2017

Round 2

174713 said:
Thanks Bruce. In talking with Rick Jones I realized I had not retested the rotor after correcting the socket connection to the bulb. Once I tested the rotor again, the light came on so bad rotor. One is on it's way!
Thanks to all for the input,
Charlie

OK, new rotor from Rick is now installed and his charging book is on backorder. So turned on the key and charging dashlight is now lit. Then went for a ride and the dashlight stayed on and got brighter as the revs increased. The voltmeter shows 14.3-14.4v just like it did before the rotor failed.

I just went through Snowbums guide but couldn’t find a “light staying on while having 14.xx volts”. I swapped out the voltage regulator, same problem with light staying on.

Any ideas to troubleshoot this?
Thanks, Charlie

20774 · Oct 20, 2017

When you say voltmeter, what is that? Does the bike have a built-in voltmeter or are you measuring the voltage across the battery terminals? A built-in voltmeter is ball-parkish...it would be nice to know what is reading at the battery, say at 3500 RPM.

For the gen light to be lit, that's an indication that the voltage on either side of the gen light is different. If the voltage is the same, then no current flows and the gen light is off. One side of the gen light basically reflects the battery voltage while the other side of the gen light is an indication of the output voltage of the alternator. Sounds like the alternator output is pretty high.

To install the rotor, you had to remove the stator. Are you positive that the stator and connections are back correctly?

174713 · Oct 20, 2017

20774 said:
When you say voltmeter, what is that? Does the bike have a built-in voltmeter or are you measuring the voltage across the battery terminals? A built-in voltmeter is ball-parkish...it would be nice to know what is reading at the battery, say at 3500 RPM.

For the gen light to be lit, that's an indication that the voltage on either side of the gen light is different. If the voltage is the same, then no current flows and the gen light is off. One side of the gen light basically reflects the battery voltage while the other side of the gen light is an indication of the output voltage of the alternator. Sounds like the alternator output is pretty high.

To install the rotor, you had to remove the stator. Are you positive that the stator and connections are back correctly?

Thanks for the feedback. The voltmeter is a digital “Bug” unit (no longer made but known for their reliability for use with motorcycles and snowmobiles) across the battery terminals. I confirmed this reading with v-ohm meter across the battery terminals. The voltage at 3500rpm is 14.1v.

Good thought about the connections being the same, I’ll confirm that tomorrow. I also thought one of the brushes may need replaced as it is 1-2mm shorter than the other brush but I don’t believe this should impact anything, only if there was no charging present.
Thanks,
Charlie

James.A · Oct 20, 2017

In certain, odd circumstances, a single diode can fail but the system will still supply the electrical system but not charge the battery. I/we saw an example of this at Air Central at the national rally in Minnesota a few years back.

A person might endeavor to learn how to test the diodes in the board individually.

Depending on which diode in the board is failed, the V.O.M meter can show a positive result, but the output will be alternating current. That will not charge a battery. If you have a V.O.M. that indicates alternating current in the Direct Current mode, this can be ruled out. On some meters, this displays as a flashing L.E.D on the meter. I do not own a meter as sophisticated as that, but I have seen one or two of them in the kit of heavy equipment mechanics that I know.

Another thing to consider is this, In my experience, the failed diode board allows the battery to fall down slowly depending on the rate of drain on the battery. If the diode board is supplying A.C., the bikes lights and ignition will still still still function but the battery slowly dis-charges. With a failed diode board on my /5, the red discharge light actually gets brighter as the battery voltage drops.

Please do not buy a diode board based on my recommendation. I would be willing to send you a known, good spare to "fluke" it out. Send me a P.M. to explore this further.

ebeeby · Oct 21, 2017

James.A said:
In certain, odd circumstances, a single diode can fail but the system will still supply the electrical system but not charge the battery. I/we saw an example of this at Air Central at the national rally in Minnesota a few years back.

A person might endeavor to learn how to test the diodes in the board individually.

Depending on which diode in the board is failed, the V.O.M meter can show a positive result, but the output will be alternating current. That will not charge a battery. If you have a V.O.M. that indicates alternating current in the Direct Current mode, this can be ruled out. On some meters, this displays as a flashing L.E.D on the meter. I do not own a meter as sophisticated as that, but I have seen one or two of them in the kit of heavy equipment mechanics that I know.

Another thing to consider is this, In my experience, the failed diode board allows the battery to fall down slowly depending on the rate of drain on the battery. If the diode board is supplying A.C., the bikes lights and ignition will still still still function but the battery slowly dis-charges. With a failed diode board on my /5, the red discharge light actually gets brighter as the battery voltage drops.

Please do not buy a diode board based on my recommendation. I would be willing to send you a known, good spare to "fluke" it out. Send me a P.M. to explore this further.

I think you just nailed it....

James.A · Oct 21, 2017

ebeeby said:
That doesn't necessarily mean that I'm right. I still do not fully understand the theory behind these things.

To quote the Grateful Dead; "answers a plenty in the bye and bye".

20774 · Oct 21, 2017

James.A said:
To quote the Grateful Dead; "answers a plenty in the bye and bye".

From St. Stephen, one of my favorites!

guenner · Oct 21, 2017

I think James theory is close. But if any of the BIG diodes (to B+ and from ground) would fail the output to the battery would be LOWER because the failed diode would not add its share of its alternator phase to the DC output at B+/battery.

But there are three LITLE diodes (to D+) which independently from the big diodes should produce about the same voltage. Their output is connected to the voltage regulators input and also to one side of the GEN light. If one of these little diodes fail there would be a lower output voltage on D+. Hence the regulator 'thinks' we are below 14.0V and increases the current (DF) through the rotor. Now the big diodes (all working) generate an even higher voltage at the battery. This higher voltage on B+ is also present at the other end of the GEN light. Now we have a difference between the two sides of the GEN light and the GEN light comes on.

And bottom line: The diode board has a fault.

Btw. with a stock voltage regulator (like from Hellas) and a good voltmeter you normally don't get 14+ Volts at the battery. Typically 13.70-13.85 Volts because of a voltage loss in the wire and connectors to the battery.

/Guenther

174713 · Oct 22, 2017

Broken connection

Took the cover off this morning and it turns out one of the 3 alternator wires had a broken connection on the stator. Resoldered this wire and the problem went away. Thanks to all for your help!

guenner · Oct 22, 2017

Thanks for reporting back the problem and fix. A disconnected phase cable of the alternator - same symptom as a dead big diode on the diode board.

/Guenther

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