An Apparent Charging Problem

[MonoRT]

The bike: A 1985 R80RT with an over-5 year old Westco sealed battery, a Motorrad Elektrik diode board (same indeterminate age as the battery) and the Motorrad Elektrik ÔÇ£higher voltageÔÇØ regulator that is supposed to let the voltage peak at 14.2 volts.

The symptoms: at rest, the battery reads 12.77 volts. Flick the headlight on for 30 seconds and turn it off, still 12.77 volts. Bike starts and runs just fine (so far). GEN light comes on when ignition is switched on and it comes on at somewhere under 1,500 RPMs when the bike is running. Over 1,500 RPM, no GEN light.

As I got close to home after work, I noticed that the notoriously inaccurate Motometer relative voltage meter was indicating quite a bit lower than it normally does at freeway speeds. I got home, parked the bike and checked the battery at rest (12.7 volts) and then started the bike and locked the throttle at 4K RPM. Voltage across the battery terminals was 12.8 and it did not seem to vary much with RPM changes ÔÇô not so good. I noticed a lot of white powder built up on the negative battery terminal and connectors.

I disconnected the ground wires at the battery and cleaned off all of the white deposits. I also cleaned the main ground connection at the transmission breather. While the ground was disconnected, I pulled off the front cover and checked the brushes to be sure they had plenty of travel and made good contact with the rotor rings. I pulled up the brushes and checked for continuity across the slip rings. That was good. I checked all of the connections between the diode board and alternator (most of this is new compared to the bike since these wires were replaced when the ME diode board went in) and everything ÔÇ£lookedÔÇØ OK. The diode board has two paths to ground via a cable and the cast-in mounts in the timing case ÔÇô again, these ÔÇ£lookÔÇØ good (I get continuity with the meter).

I wondered about all of that crud on the battery terminal and since I was running out of time, I put the bike back together, started it and checked the voltage at 4K RPM across the battery terminals. 13.8 ÔÇô not great, but not so bad either. The bike had cooled down by the time I did the final test.

This morning, riding to work, the relative voltage meter was back to its old, ÔÇ£normalÔÇØ position at freeway speeds ÔÇô until I was about a mile from work (a 19 mile ride). Then, the needle dropped down to the position that worried me in the first place. I had the meter with me, so I checked the at rest battery voltage after I parked - 12.76 volts. IÔÇÖm not sure that IÔÇÖll be welcome to lock the throttle at 4K right in front of the office, so I did not do that, but I suspect that I'd have gotten a low reading.

So What do I go after first? I know that old batteries can cause all sorts of weird symptoms. Old wires are often culprits. Seems like the alternator rotor and GEN light are OK. Since the voltage appeared to drop at the end of a ride (last night and this morning), could it be a goofy voltage regulator responding to engine heat?

 

[m_stock10506]

The bike: A 1985 R80RT with an over-5 year old Westco sealed battery, a Motorrad Elektrik diode board (same indeterminate age as the battery) and the Motorrad Elektrik ÔÇ£higher voltageÔÇØ regulator that is supposed to let the voltage peak at 14.2 volts.

The symptoms ...... <big snip>

So What do I go after first? I know that old batteries can cause all sorts of weird symptoms. Old wires are often culprits. Seems like the alternator rotor and GEN light are OK. Since the voltage appeared to drop at the end of a ride (last night and this morning), could it be a goofy voltage regulator responding to engine heat?

At 5 years, I would replace the battery. You're really not going to get much more from that battery and it could have a cell going bad that is sucking up voltage. With a new battery you can eliminate that issue if you continue to have low voltage. You also could remove the voltage regulator and insert a jumper. You should see voltage continue to climb past 14 volts as RPMs climb. Don't overdo it.

 

[MonoRT]

The Battery is Near or at the Top of the List

Yes... I've seen a ton of posts here where strange electrical problems went away with a new battery. And... when I said that battery was older than 5 years, I meant considerably more than 5 years - I just can't recall - it's been that long.

I think that I'll double-check the positive cable up to the starter and also try to land a new battery.

 

[bikerfish1100]

In this situation- when you don't know how old the battery is, it's too old to bother with.

 

[20774]

What does the bike's voltmeter read at rest in comparison to the better handheld meter across the battery terminals? That will give you some indication of the offset in the bike's meter compared to what is really happening at the battery. Taking this a step further, I'd consider securing the handheld meter to the top of the tank, either in a tank bag or taped using the painters tape so as to not mess with the paint. Then run down the road...compare the two meters.

Before you get too deep, be sure that the grounds for the bike's meter are clean and secure. I had a voltmeter in my Lufty fairing that was giving me ulcers...in the end, the problem was that the ground attachment was fraying and coming loose.

 

[MonoRT]

I wish it was just the Motometer

Actually, I am pretty familiar with the Motometer vs. Fluke meter offsets - they are not linear. At 12 volts indicated and below, the ol Motometer is a bit low, but reasonably close to correct. When the Motometer reads 13 volts, actual voltage is a little above 14, so between 12 and 13 indicated (and probably above) things get screwy.

Taking a ride with the Fluke meter connected is a good idea. I have a tank bag and map case that the meter could be stuffed into. Sadly, I only brought the probe leads with me today. The aligator clip leads are at home. It would be "fun" to get a more accurate read on what the charging system is doing while I'm under way.

I rode the bike to get some lunch and the Motometer read low the whole way. I parked a little out of the way and checked the running voltage at 4K RPM and got 12.2 volts. Things are not getting any better. I do have a line on a new battery and I'll pick it up tomorrow. If the current problem is not the battery, the next one surely will be.

Riding to work today is not looking like the brightest idea I've ever had. I hope I don't have to spend any quality time on the side of the 405 freeway.

 

[ISAMEMON]

battery, alt brushes, thats my two guesses
i bet youll make it home ok
easy for me to say sitting here at my laptop

 

[40401]

Last summer I had an intermittant low charge condition on my '82. After a BUNCH of searching it turned out to be a broken solder connection between one stator wire and the plug on the alternator. Two minutes with the soldering gun and all was well.

 

[MonoRT]

New Battery, Still Low Charging Voltage

Well, I got home OK yesterday evening. I may have been lane-splitting a little more aggressively than usual, just to keep moving.

Today, I put in a new WestCo battery. I still get 12.8 volts across the battery terminals at 4K RPM.

Rick Jones at Motorrad Elektrik suggested checking the heavy wire that runs up to the positive terminal on the starter, so I'll take a look at that and the rest of the wires (in daylight this time). Rick said that sometimes the later airheads don't ground really well through the timing case and that running a heavy gauge wire from a ground lug on the diode board to the negative battery terminal can fix poor charging. I'll experiment with that if I don't find anything else, but having a ground wire right from the battery to the diode board would mean that I'd always have to disconnect the battery ground at the terminal instead of at the breather bolt.

 

[35303]

Intermittent rotor?

http://bmwmotorcycletech.info/trbleshootALT.htm

 

[Bobmws]

Some the wiring gets some internal corrosion. My 74 90S was experiencing slow starter turn over, flaky turn signal operation even when hooked to a charger. This in '87 at an age of 13 years. I found corrosion in the positive lead to the starter a full 8" in from the battery end of the cable, similar on the ground. Replaced both cables and cured the problem.
Note, my bike spent most winters at that time in an unheated dirt floor garage in PA.

 

[GeorgeRyals]

Isn't 13.8 volts kind of to standard peak voltage for the factory regulators?

If you are a commuter/short trip rider and adjustable/high output regulator may be helpful to keep the bat charged. The high output (over 14 volts) regulators will over-charge the bat on long trips where you drone on for hours at 4000 rpm.

 

[35303]

An adjustable regulator lets you set charging voltage.

http://www.beemershop.com/catalog/p...d=246&osCsid=f8876036dabc1f8b502e562a183c6490

 

[MonoRT]

It "Works" Now...

Thanks for all of the ideas everyone!

In response to some of the recent posts: I still work for "the man", so most of my riding is commuting and in heavy traffic at that. I'm running the 14.2 volt regulator because I don't get to do much of anything beyond urban riding.

So, the 13.8 volts I'm getting now at 4k RPM is lower that what I ought to see, but better that 12.8 volts.

This is a fun problem. As several have noted, with old wiring, everything is suspect from the start. I know that there is a maddening difference between good continuity and good current carrying capacity. Here's what I've messed with:

Battery - replaced, but at first, charging remained at 12.8 volts at 4K RPM.
B+ wire from the diode board to the positive terminal on the starter. Checked and cleaned. This is newer as it was replaced when the ME diode board went in a few years ago.
Brushes - seem plenty long, they can wear quite a bit more before running out of spring of hanging up on their braided leads. I replaced the brushes a couple of years ago.
Wiring from regulator to brushes. Lots of cracked insulation once it goes under the front cover. I think I'll replace these, but I can get good continuity from the voltage regulator plug through these two wires, the brushes, slip rings and rotor windings all at once. This circuit can't possibly carry much current, but still, if it is weak, the rotor won't be as strong a magnet as it ought to be.
Negative battery wire. First thing that I cleaned - both ends.
Positive battery wire. Clean, but there are cracks in the insulation once it gets under the starter cover (HOT in there). That big old bosch starter has always been able to spin the motor over quickly, without any hesitation, so I'm not really suspecting this wire yet... I figure that the current needed to start the bike is far beyond anything the charging system can produce (note the difference in guage between the main battery cables and the B+30 wire), so, I'm not too worried about those primary cables.
Wires between the alternator and diode board - all new-ish, replaced with the diode board. They check out OK...

At this point, I've done a bunch of poking around and cleaning. I was going to check each of the 3 phases out of the alternator, but the darn thing started charging again. I've now ridden 20 miles with 13.8 volt charging. If it stays there, I'll be happy, but I'll still replace the wiring between the VR and the brushes.

If problems return... There are a bunch of things I can still check...

 

[jerulator]

Resolved ?

Did you ever come to a conclusion on this ? Or is it still operating good. I have the exact same problem on my 1980 R100RT. Although mine was intermittent at first, it has now become a "hard" failure. I can start, ride, idle the bike and the battery voltage is at a consistent 12.7 volts, but it is not charging at any rpm range. I have removed the ignition system cover for a mechanical inspection with inconclusive results. Going to be checking everything mentioned in this thread and will post any results (good or bad) here.
Jerry

 

[MonoRT]

I thought the problem was resolved. However...

Funny you should ask.

The charging system had been working OK, but last week it went back to so-so. At 4K RPM, I'm getting 12.8 to 13.2 volts across the battery terminals. The voltage does go up and down with RPMs, but NEVER over 13.2V. I have a "high" voltage 14.2 volt regulator, but you'd never guess it from the indicated voltage.

The readings that I'm giving are what my multi-meter shows - not what the volt meter shows. BTW, I did replace the Motometer VM with a VDO unit that seems to agree with my Fluke meter most of the time.

I do have a new "wiring harness" for the wires that carry current from the regulator to the brushes. The old wires have cracks in the insulation that I don't like the look of. I've not had time to swap those wires out yet and, perhaps there's hope for a fix there.

Also, Rick Jones had suggested running a heavy guage wire from the diode board back to the negative terminal on the battery instead of relying on a good ground path back through the timing case. I have not tried that yet, but if this continues, I will.

 

[MonoRT]

I have more data, but it is confusing

So, IÔÇÖve changed the battery and the wiring harness that connects the voltage regulator to the brushes.

IÔÇÖve been through most everything else that I can think of, but my Fluke meter tells me that the voltage across the battery terminals is either 12.7 or 13.18 volts at freeway speeds (my ÔÇÖ85 has a ÔÇÿshortÔÇÖ final drive, so freeway speeds require more than 4K RPMs). Most of the time, IÔÇÖm seeing 12.7 volts with occasional 13.18 volt readings ÔÇô never more than 13.18 volts.

Last night, I did what I should have done MUCH earlier. I pulled the tank, pulled off the VR plug and jumped the opposing (not Brown!) wires. I started the bike and ran up the revs. With the tach showing 4K, the meter was about to go over 16 volts when I shut the bike down. I thought ÔÇô OK, so the alternator can put out some juice and it was a bad regulator all along (I have a TRANSPO brand 14.2 volt regulator from Motorrad Electrik).

I ran down to the local auto parts store and got a (U.S. made!) regulator for a VW bug that was close enough to my current unit. The included paperwork said that I should see something between 13.8 and 14.8 volts if everything was working correctly. HowÔÇÖs that for precision?

I installed the new regulator, fired her up and got 12.7 volts at 4K RPM. On the ride to work today, I was getting 12.7 volts mostly but did see 13.2 a couple of times.

Now, IÔÇÖm really stumped. Clearly, the alternator and diode board can put out some power, but it appears to be over regulated. Should I buy one of those adjustable VRs and run it at the ÔÇ£boil your batteryÔÇØ setting?

 

[20774]

You've shown it's probably not the alternator or diode board...also a brand new regulator didn't help. An adjustable regulator is not going to solve the problem either.

I believe Snowbum talks about monitoring the voltage as it leaves the diode board. What is the voltage at the B+ terminal at the diode board? Clip the voltmeter negative to ground and see what's at the B+ termina. The wire at the end of the B+ terminal goes to the starter solenoid...what does the probe read there? Then finally, put the probe on the +terminal on the battery. Is the voltage the same at all three of those points? If not, then you have figured out where the loss is. If it is and it's only 12.7v at B+, then you really do have a problem with the alternator/diode board.

 

[42906]

 

[lmo1131]

Clearly, the alternator and diode board can put out some power, but it appears to be over regulated.

deja vu, I knew this thread seemed painfully familiar....

Read the last page of this thread > http://forums.bmwmoa.org/showthread.php?t=60764&page=3

You mentioned that you changed the battery... did you fully charge the battery? As I found out, just because it is a new battery doesn't mean it's a "good" battery (mine had a defective cell). A dead cell will affect the amount of voltage the alternator will put out.

I also added a 12ga. ground cable from the diode board to the frame ground at the coil mount, and then continued it onto the battery; ideally, I suppose it should have run continuously, unbroken (by a soldered ring connector) from the diode board to the battery, but ....