The GEN lamp, before charging begins, is fed by current coming through the ignition switch from the battery. Due to the low resistance windings, common non-lab versions of ohmmeters tests on the three phases themselves are not usually or always indicative. High performance magnetic materials HAVE been available for some time now, at considerable cost (China is purchasing as many rare earth mines as it can, rare earths are needed), but the original rotor was never re-designed FOR THAT as there was no specific need. Once the voltage output is within the proper range again, the warning light will turn off. e. For /6 and later types: With the 3 phases & center-tap connections NOT connected to the bike wiring: GROUND the center-tap. Cars with an iDrive system will display alternator malfunction warning messages such as vehicle battery charge low or vehicle battery discharged while stopped. 2. Those wires pass 100% of the bike's electrical power (except the much larger wire at the + battery terminal that goes directly to the starter motor). DO NOT leave the transformer plugged-in to wall socket power for more than a few seconds, as it could be damaged by the high current drain of the windings. 01/30/2017: Add 4f. Diodes in the diode board are often tested (disconnect the bike battery first! The proper diode board, for any stator except the original /5, has an extra terminal, a center-tap on the stator windings, and was standard from /6 onwards. The following models come with metal mounts that are part of the timing chest casting and do NOT need to have 'solid diode board mounts' installed: /5; /6; 1978-1987 R65 and R80. Instead, a simple A.C. connection to a transformer and then reading all three phase voltages is a GOOD test. This contains basic electricity AND has all the schematic diagrams of the entire bike systems. In entire article add material & update things. (includes some troubleshooting & problems ...much more later in article). This small current must travel to electrical ground in order to have the lamp illuminate. The problem commonly seen is a major total complete lack of electrical power. The charging on later standard & Authorities models can be poor if the associated rotor is not the correct version. You don’t say where you obtained the voltage figure. The problem commonly seen is a major total complete lack of electrical power. Connect the wire for only a second or so. Similar symptom can occur if the very large battery wires which bolt to the battery are faulty, perhaps eaten away by battery acid (happens; at + connection), etc. Our team of experts provides the most accurate and detailed auto repair guides. The regulator receives the output of the SMALL diodes as previously described, and compares that to the VR internal reference zener diode (mechanical regulator does this with spring and solenoid coil which then operate the points). Update sources, links, etc. Usually this is blue/black and blue. If voltage reads in +14V range, alternator is OK; test resistance of charging circuit wiring per item 4(C.) below. As earlier described, the /5 model diode board did not have the extra diodes for the center-tap of the /6 and all later stator windings (there was no such stator center tap then). © 2020 YOUCANIC ® - All Rights Reserved. Further, the normal battery sketch has the small line being +, and the battery is thus shown reversed. Rubber mounts were a BAD IDEA! 15-B, This article is not a substitute for my other articles. You can use silicone dielectric grease or even Vaseline on these during re-plugging-in; it helps protect against environmental things that caused the original corrosion. SEE article #17: https://bmwmotorcycletech.info/altbrushrotor.htm. Do your bike a favor; install the inexpensive aftermarket diode board solid metal mounts if you have rubber mounts. Wait at least 15 seconds for the alternator output to rise. To determine which, remove the jumper wire or screwdriver. More often the rotor has opened electrically; or a brush, or both brushes, are very badly worn. That will properly de-polarize, re-polarize, and magnetize the rotor very faintly, in the correct direction/polarity. Batteries: Battery failures cause an enormous amount of problems & variable indications. The regulator is a solid state circuit built into the alternator. The rotor has a very low resistance compared to the lamp, particularly when the lamp is lit (even though lamp resistance rises when lit), so the magnetic field is quite small, but normally completely adequate. This is an OEM voltage regulator manufactured by Hella - an original supplier to BMW for many electrical parts. http://www.Euromotoelectrics.com has them reasonably priced ...see my references page: https://bmwmotorcycletech.info/references.htm. Any of these batteries will start and operate the engine. When the ignition key is ON (start/run position), a small amount of electricity flows from the battery, through the ignition switch, then through the GEN lamp, & then to the D+ terminal of the voltage regulator (blue wire). The stock Bosch rotor used on any of the Airheads, is not specifically designed to work as a residual magnet. The starter may not crank at all, or you will hear just a simple clunk, or small click noise. Check voltage across battery with key off. It is somewhat rare, but I have seen batteries that were temperature sensitive, regarding the opening & closing of an internal connection. Aftermarket rotors have been seen with different threads than the stock Bosch rotors have. See the Omega alternators, etc., here:
The alternator is charging at over 15 volts which is too much for the battery.
The voltage regulator (that controls alternator output) is not part of the alternator brush assembly, as it is in nearly all more modern cars and motorcycles. What needs to be done to regulate the voltage back down to 14.6 volts which is normal? Be sure the D- and Df connections at the brushes assembly are connected. If it lights ...then go to the next step: Assuming the lamp DOES light up:
The diode board connections (via printed copper 'wires') have 3 of those large diodes connected to the chassis (negative side of battery). You can also check from the center-tap terminal (except /5 original alternator does not have this) to any of the three phases, check for equality. 05/13/2013: Go over article. Turn on Ignition. Sometimes a rotor winding will short to another winding, or short to the metal magnetic pole pieces material. These came in several varieties, the very last versions being slightly upgraded to better handle the possible increased rotor current of the 2.8 ohm rotors. This is typically confirmed by first measuring the battery terminal voltage with the ignition off. That AC current is rectified to DC by large diodes to do the primary charging, but the AC is also sent to the SMALL diodes on the diode board. AFAIK, 50-50 is sold only as a solid core...that is, it never comes with a flux core as does electronics 60/40 and other electronics solders. While the rare internal connection has failed, often annoyingly an intermittent failure because of a loose internal rivet or some such, MORE often the problem is one or two poor connections AT the SPADE CONNECTORS OR SCREW CONNECTIONS at that relay and its socket. Nicking/scratching across the steel laminations can reduce output slightly too, and this is difficult to analyze for the typical owner. document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
Miscellaneous items:
Electrically speaking, you can't measure the voltage output of the alternator properly if the battery is connected to the car since it is wired in parallel. Shop by Brand / Shop by Category. There is an article on this website about modifying the lamp circuit so even if a lamp fails, charging will occur. These are usually called Battery Load Testers. A failure to charge, in which the regulator is suspected, can be PROVEN, on BOTH the mechanical and electronics regulators, by bypassing the regulator. You can possibly obtain a digital multimeter for FREE from Harbor Freight Company ...they often give out quite adequate and accurate ones for FREE, upon ANY sale. Narrow the article, including adding more left edge justification(s) and increasing font size. Worn brushes frequently cause problems, but usually the lamp is then intermittent, especially with rotor RPM. Since the D- brush connection is always grounded (one hopes), it is unlikely to have a rotor wrongly magnetized from reversing the two connections, to D- and Df. I am pretty certain there is no "charging relay" whoever you spoke to at BMW is talking rubbish. With your alternator dissembled. The alternator should be tested with the engine idling and electrical accessories, such as the radio and headlights, turned off. Turn on the ignition. by using a higher temperature type of solder on cleaned-up copper pads on the stock boards, no drilling nor added wires was done. The high voltage output can even damage the battery. Read the resistance of the rotor AT the slip rings ...it should be as expected, under 5 ohms (/5 has 7 ohm rotor). I suggest you purchase the type which has TWO METERS. Troubleshooting a dead (not lighted or does so irregularly) GEN lamp:
The stators are typically 0.62 ohms per phase connection. This minimum charging voltage is 13.8 volts dc across the battery terminals, or at the output of the alternator. You can get an equivalent tool from aftermarket suppliers. The battery needs a higher applied voltage for reasonably quick re-charging. It is possible for a quite poor to bad starter motor to 'pull' ('draw') so much current from the battery, that the battery appears faulty. While you can use a test lamp if you know how to analyze things with it, use of a multimeter is probably easier, and you need to know how to use one. Update metacodes; fonts, layout, etc. For the most part, rotors are being rewound with the later lower resistances. If, when your ignition key is ON & the GEN lamp goes ON brightly, but it usually never goes out or only fades a bit when the engine is revv'd up, it usually indicates NO charging, or very little charging. That will produce maximum output from the alternator for any RPM that allows such, so do not let the voltage get too high at the battery, 14.6 is OK, absolute maximum is 14.9. There are a number of major symptoms of a bad motorcycle charging system. However, the best way to verify the problem is to use a digital multimeter. This flexible printed material can get microscopic cracks, and the lamp connection to the board can fail. 01/05/2017: Metas, scripts, colors, fonts, horizontal lines, excessive HTML, sketch details for current flow direction & a.c. on 4 connections. Now and then a diode board is fried by someone installing a wrong type of battery (reversed polarity terminals). Models after the /5 had that mentioned kill switch located on the right side controls assembly on the handlebars. The GEN lamp, necessary in the stock system to properly initiate charging, does not fail often. The alternator can crank out 170A which is more than most fuses can handle. This puts + 12 volts from the battery into the rotor. Problems with the small diodes in the diode board rarely occur, and can usually be seen by poor charging or 'funny' GEN lamp indications, and sometimes strange radio noises. June 1999 was a most comprehensive article, but there are many others. as shown in the photo ....you may BEND or CANT the tool inside of the rotor, & then you are in SERIOUSLY DEEP trouble. The VR can be serviced, article on this website. For a /6 or later motorcycle, wiggle, a bit, the umbilical cord that goes into the back of the instrument pod. The final changes to the Airheads alternators used slightly lower power output alternators; that is, instead of the 280 watt alternators, they had 240 watt alternators, but the charging began earlier, just like the Authorities models. The red wires at the starter relay go to different starter relay connections. First check that the D- terminal is electrically the same as engine case ground, and that the Df terminal is insulated from the case. Plumbers use a type of solder that is 50-50 mixture of tin and lead. Available from Euromotoelectrics; Motorrad Electrik; & Thunderchild. The mechanical regulator regulates by separating two contacts in the regulator to reduce the charging. No matter what starter you install, be sure it has the proper 8 or 9 tooth drive gear. Another common failure is a shorted cell, usually only one fully shorts; but, it can be partial for one or more cells. k. Occasionally there is a problem with the POD CABLE PLUG, or the pod side of it. Connect the secondary to ANY two of the three phases male spades. Some late 1974 & early 1975 models did have the larger 107 mm stator, which will not fit the stock /5 timing case. Testing with an ohmmeter, D- and Df wires OFF, & paper under the brushes so they do not contact the slip rings of the rotor, are a quick method of determining things. If the charging is now good, and voltage keeps rising with increased RPM (do NOT let it go over ~14.6 or so, absolute maximum 14.9), then the VR is almost for sure bad. Something in the diode board has failed. Alternators; Alternator Pulleys; Alternator Support Parts; Voltage Regulators; … However, I will list various tests below. http://www.Euromotoelectrics.com has them reasonably priced ...see my references page: https://bmwmotorcycletech.info/references.htm. Do your bike a favor; install the inexpensive aftermarket diode board solid metal mounts if you have rubber mounts. Check charging system wires. Extra heat was in this area on the faired (RS and RT) models, making things even worse. I have personally seen up to a .5 voltage drop caused by a maintenance-free battery installed in a BMW. BE SURE to use a large mass type of soldering tip on your soldering iron. NO proof, and to my knowledge, no one has produced such a rotor for the Bosch system. You may have to add more rosin from a separate container. As a final measurement, slide a piece of paper under the brushes so the brushes do not contact the slip rings. Over the years there have been various problems with diode boards, grounding, the rubber mounts, etc. Do NOT forget to disconnect the battery before replacing the front cover. It is on sale now and then, and you may be lucky & combine it with a 20% off coupon! Update the alternator sketch so /5 era version is more clearly shown as to details on Y and diodes. & QUICK fix, if the external spade connections are the problem, is to UNplug the relay & plug it back in. The resistances are hard to read accurately, & hence only gross changes or differences may mean anything. The battery will act as if there is a resistance inserted in series, & may even charge up to the correct voltage at the battery terminals, yet be unable to properly crank the engine. If you want to make a tool,
diode boards. The rotor needs to be magnetized in the correct direction (or, not magnetized in the wrong direction). 11-14-2005: Add hyperlink for additional schematic. Now and then a rotor solder joint fails. I suggest you use a very sharp thin blade on a very flat angle. If the battery voltage is OK, yet the lights are turned-on but do not light-up (usually the starter motor will not actuate either), you may have a relay plug/socket problem, or a problem inside the relay. Attach the two probes from the digital multimeter to the positive and negative battery terminals and turn the selector switch to DC voltage. The diode board was modified for an extra connection in the 1974 transition period to the /6 series, and there were various types of voltage regulators; both early mechanical and later electronic types. Nerdy paragraph:
Separation of those contacts occurs as voltage rises enough & thus increases the mechanical relay's magnetic field in its coil enough to cause the contacts to open, which turns the rotor current OFF (or reduces, considerably but not entirely, the rotor current, depending on the type of mechanical regulator). Remove the grounding wire you added. The D- terminal is the one that should have the SOLID BROWN WIRE. One thing old /5s — and just about every airhead from 1970-1994 — can really benefit from is a charging system upgrade. The BMW Airhead charging system is basically the same; with only modest variations, on all models from the introduction of the 1970 /5 series, to the end of production in 1995-1996. The Airheads that already should have solid metal diode board mounts cast into the timing chest (check your bike, no matter the model, as I have seen anomalies) are: /5 models; /6 models; 1978-1987 R65 and R80 models. This one’s the big, obvious one. The HF unit is ADJUSTABLE to match battery capacity size. Another common problem that causes BMW battery and alternator warning is a faulty BSD BMW module, typically mounted on the alternator. 11/07/2017: Commentary about the sketch improved. have had the diode board out of the bike, & when replaced, there is no charging. I usually use de-soldering braid to join the wires, but a wrap of common lamp cord (insulation removed & wires look shiny, not corroded from age) will do. https://bmwmotorcycletech.info/genlampresistor.htm. The charge indicator lamp does not light up. I have never done formal testing to find out, as I was not curious enough. It is possible for a quite poor to bad starter motor to 'pull' ('draw') so much current from the battery, that the battery appears faulty. An alternator should put out between 13.5 and 15 volts of power. This is an especially good test, and HIGHLY recommended. The details. With all electrical connections and battery cables in good shape, the voltage output should be anywhere from 13 to 14 volts. If the connector is quite poor, replace it. That almost always works, might even last. In some instances, once the engine IS started and run, the battery MAY seem to act OK ....until the next cold startup. Note that electricaly speaking as a nerdy engineer, current flow is from negative to positive, not as shown in the sketch. I've even used a propane torch soldering tip (BUT, you must very carefully avoid side-flame damage). To test for that, either install another one; or, UNPLUG the VR, & in the PLUG, connect a paper clip or other item, between the opposing female connections. Used with relatively brightly cleaned male and female spade connections, this will likely be a 100% permanent fix. Because of the potential problems, I DO NOT APPROVE that sort of tool. If you would like to test the system maximum possible output, you can leave that jumpering in the plug, and start the engine and monitor the battery voltage as you raise RPM. You can also use a formal Load Tester on the battery for confirmation, after trying to fully charge the battery. A considerable current is possible, as much as 5 amperes on the much later low ohms rotors, and it would unnecessarily also heat the rotor. The load test is done by reading the voltage accurately at ~15 seconds of loading time. If voltage reads in +14V range, alternator is OK; test resistance of charging circuit wiring per item 4(C.) below. The /5 era 6.9 ohm rotor can not be energized by the battery, nor by the alternator after charging begins, to as high a current as later models with lower resistance rotors; the restriction is based, if curious, on Ohms Law. We participate in the Amazon, Advance Auto Parts, and eBay affiliate programs. The starter relay has RED wires going to it. Charging System & Battery for BMW Z3 (1996-2002): Alternators. The copper printed area, with no enamel coating left, MUST be clean and shiny!! As of 05/17/2018, my most recent check, Buchanan's errors were STILL not fixed, after many years of him knowing about this. How to determine if the voltage regulator is bad:
Do not disconnect a battery cable while the engine is running to test the alternator. DO NOT jumper to the brown wire. BROWN is ALWAYS ground, which is always D-. Nerdy: Replacing 1 or more large diodes is possible, should one or two fail. It is usually NOT seen at the center tap of the stator windings (/6 and later). You have mixed up the two wires going to D- and Df of the brushholder. Here is a link to my article covering the various starters, including aftermarket ones like the Valeo & Denso ....and the article also covers the fitting problems:
The CDI must use considerably less than 1 amp. INSULATE the results with electrical tape or self-sealing tape...neatly!!. These are usually called Battery Load Testers. This is better than depending on the brown wire to be grounded at the VR, which it may not be connected for. It is fairly rare for a stator to be bad. The snail spring on the brush usually can be seen to be "bottoming" on the white plastic brush holder. Female spade connectors can be carefully squeezed just a wee bit with pliers, and thus made to fit much tighter. A BETTER TEST is with the diode board OUT OF THE BIKE using a 6 or 12 volt brake or turn signal light bulb and a 5 to 15 volt AC transformer. If the problem is inside the cable plug, it can be fixed, but you must try to do neat work here. Leakage current can be measured at that same + output terminal of the board, by putting a current-reading meter in SERIES between the mentioned terminal and the red to-battery wire that you pulled off it. A shorted turn makes a rather gross difference in output from a phase. This booklet also has very detailed individual parts and systems drawings, schematics, descriptions and operations, etc. There is a modification that can help (for the plug-in type starter relay). 11/05/2014: Entire article: Simplify some testing for ease in understanding & speed. Rebecca Jane. And, as a coolant pump will not work as well, the engine may overheat in a short time. While any well-used & worn starter motor can exhibit this problem, it is especially egregious on early Valeo starters (which were installed by BMW instead of the Bosch starters, in the later eighties) in which the permanent magnet pole pieces, which were glued in place, came loose and mechanically locked up the starter. Tightly wrap some shiny copper wire around the removed insulation area. Your Bosch alternator requires a rotating magnetic field which is supplied by the rotor when energized through the GEN lamp and battery. The alternator is held in place with mounting bolts. Many problems show up by the GEN lamp lighting up at the wrong time, or not lighting up, or it is irregular or dim. Three phase stator windings (most any alternator, generally) are actually three separate windings, so there are six wires. What has been needed is a simple, easy (& cheap) method of repairing the overheated diode board solder joints at one or more of the 6 large diodes. VR failure is hardly the only failure to cause these problems. I have seen rewound rotors improperly tested before sale, that were shorted to the steel of the rotor. The parts. I removed it, gave up trying to get him to fix his. With a bad battery, the voltage will drop off a huge amount. There is a simple modification that allows the system to start up even if the lamp fails (depending on how the modification is done it may make a very slight improvement on rpm at which charging begins); it is in this website as article #19:
Everything in the alternator area should look good, including the diode board. This fault could point to a faulty alternator or voltage regulator. Use the one below! This is probably too expensive to seriously consider, considering the labor ....and cost to purchase a large power diode, ....and remove & replace it. If you have a plug-in starter relay, UNplug it, then clean the male and female connectors as best you can, then re-plug-in the relay. Once in a while a rotor will short circuit between turns of the wire, and this may or may not be such that your ohmmeter can show a short. If the lamp does NOT light up, the wiring from the VR to the pod or its large rear plug, or internal wiring or lamp or lamp connection in the pod is at fault. The charging device now supplies the electrical system's load requirements and recharges the battery. There is a chart available for the lower voltage limit, versus temperature ....and the load tester comes with the chart and it is printed on the meter, and in 'good', 'no-good', colors. There are also other sources for starters. AFAIK, IMO, there are NO problems caused by this external jumpering, if done neatly. Either testing method can be used; but best to do it at the diode board connection. This alternator uses the same Bosch design with an electromagnetic rotor. & QUICK fix, if the external spade connections are the problem, is to UNplug the relay & plug it back in. DO NOT touch the D- terminal, nor ground, shell of stator, etc, with this jumper wire, or sparks will fly. IF partial, the battery might charge up to the correct voltage, yet after standing a half hour or hour, have its 'open terminal' voltage fall towards 12, rather than maybe 12.5 to 12.7. When the rotor rpm rises, its rotating magnetic field induces a voltage in the STATOR windings, first very tiny, then more as RPM rises, and if the rpm is enough, and the system needs the electricity by the system voltage being lower than VR-set optimum, more electricity is produced and becomes a substantial current flow. I usually use de-soldering braid to join the wires, but a wrap of common lamp cord (insulation removed & wires look shiny, not corroded from age) will do. THAT would be nice for commuters, that is, city riding, stop and go folks. That almost always works, might even last. This is where reading article 14A and 15A may help in understanding.
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