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Three-Step CBX Charging System Troubleshooting FAQ

Updated 24 December 2014

Mike Nixon


  1. Q: Why is this method called a 3-step method, when there are seemingly dozens of tests?
    A: There are actually only three tests of three functions Ė 1) rotor/regulator operation, 2) stator output, 3) and the final retest of charging output (amps). The tests mentioned in-between are part of the main tests and merely confirm them. Remember to think of this method as testing systems, and not just parts.

  2. Q: Why don't you use the official manual's test methods?
    A: Two reasons. Most importantly because there is no methodology in the manual -- it offers tests but no logic. Second, the tests offered are the least conclusive type, a fact borne out by the manual's inevitable recommendation to "replace with known good component." Whatever you call it, that is not troubleshooting.

  3. Q: Why do your charging system specifications differ so much from those in the official manual?
    A: Because the two output specs in the manual are incorrect, one being for loaded but unregulated output, and the other for the alternator by itself, without even the load of the motorcycle's electrical components (the manual's 24 A at 5000 rpm is not a charging specification).

  4. Q: Why donít you use industry-standard terminology in your explanation of the CBX charging system and its function?
    A: Because there is no standard terminology in the powersports (motorcycle, scooter, ATV, snowmobile, utility vehicle, recreational utility vehicle, and personal watercraft) industry. The industry has traditionally used confusing and contradictory terminology, and most change their terminology for the very same part from one year to the next. A generic, non brand-specific approach is the only way that makes sense.

  5. Q: Why do you speak of the rectifier and the regulator as if they were separate parts. Arenít they housed in the same container?
    A: Yes, they are contained in the same box, but they have separate functions, and, more importantly, separate failure modes. Unfortunately, the unitized construction means that when either fails, they both must be replaced.

  6. Q: You speak of the regulator as a supplying part, when most people assume it to be a limiting part. Can you reconcile this difference in descriptions?
    A: Sure. The regulator is both. It is a supplying part in that it supplies energy to the rotor to make it magnetized. But it is also a limiting part in that it monitors battery charge so as to control how much energy the rotor gets.

  7. Q: You say rotor failure is very common on the CBX. Could you expand on that?
    A: A shorted rotor is probably the most frequent cause of charging system trouble on the CBX, as well as on the other Hondas that use this system Ė all the 70s and 80s DOHC fours, for example. It is probably due to a design flaw in the wiring of the rotor's field coil. It would appear the insulation breaks down under constant heat and centrifugal force stress. The next most common problem is a "fried" regulator, and this is because it is usually caused by a bad rotor. The two parts usually fail together. A shorted rotor draws too much current through its babysitting part the regulator.

  8. Q: Explain about the alternator drive clutch problem you say all CBXs have.
    A: Here is a factory Honda engineerís memo outlining the problem. The engine side disc, the memo points out, was mistakenly made dish-shaped instead of flat, meaning that the discs touch only on their outer edges. The result is that the factory's carefully planned percentage of slip between the two discs is hugely multiplied Ė that is, the discs slip ten times as often as they should. These parts are not designed to slip continuously, and they quickly deteriorate. The fix is to simply make the drive disc's contact area flat like it is supposed to be. Why wasn't this problem the subject of a "recall"? Recalls are only for safety-related issues. As to a lessor sort of service campaign, the nearest guess as to why that wasn't done is that Honda decided that they could get away with doing nothing, which in fact the memo records was their decision. Motor vehicle manufacturers often do this, as the NHTSA is pretty busy with more serious concerns.

  9. Q: Explain about the hydrometer and battery load tester.
    A: A hydrometer is a tool that measures the density of the electrolyte (fluid) inside your battery, which increases with charge and decreases with discharge, and as the battery ages. This density is therefore one of the surest ways to accurately determine the condition of a flooded cell type battery, if the battery has been charged first to ensure it is not merely discharged. As to the load tester, this is simply a coil of wire housed in a ventilated metal box. This tool is clamped onto the battery to stress it a given amount and a voltage reading is taken which indicates the batteryís health. It's rather like the stress test a cardiologist gives his heart patient, and it is the only 100 percent reliable way to test a battery. Battery load testers are available in many forms. You can simply go to a good automotive supply and buy an inexpensive wire coil based load tester. Or you can go all the way and spring for a professional carbon pile job such as a Sun VAT-60, Ferret, or Allen. For my money though, a wire wound ceramic resistor is all that is needed and works great. There are also ways to load test the battery without a load tester, and while usually fairly good, they are not as reliable as using the heavier external load. One of the classic easy ways is to disable the ignition system (turn the "kill" switch off) and crank the starter for 15 seconds while watching a voltmeter attached to the battery. The voltage will drop, but if it stays above 10 volts just before you let go of the starter button, the battery is probably in good shape.

  10. Q: You mention both analog and digital multimeters. Arenít digital test meters better than the old analog type?
    A: In the powersports world, the analog multimeter is far from obsolete, offering several advantages over the digital multimeter, among them the ability to display trends and transient inputs. The former is important in charging system checks, the latter in ignition system troubleshooting. Neither abilities are found in appreciable strength in digital multimeters, in the absence of special attachments, whereas analog meters display them very well as-is. Analog multimeters also more often come with the high current capacity needed for charging system output tests, whereas only the more expensive digitals have this capability, and usually it has to be added through an attachment. If you can buy only one, get a quality analog multimeter. If you already have a digital multimeter, then make sure it has a 10 or 20A capacity, or build yourself an external test shunt, and get a peak voltage attachment. These things will enable it to do what an analog does normally.

  11. Q: Why do you insist that charge to the battery be tested in amps and not volts?
    A: Volts is not charge. This is pretty important. First, let's understand the difference between amps and volts. Imagine a bucket under a water faucet. Water is rushing into the bucket -- that's amps. As a result of the water's flow, the level in the bucket is rising -- that's volts. The current is amps, the level is volts. Now, which of the two demonstrates activity more clearly, the torrent of water or the rising water level? The torrent, of course. Itís raw current, whereas the water level is merely the result of that current. The same is true when checking the charging system. When you check it with amps, you are seeing the actual movement of electrical current into the battery. When you check it using volts, you see only the delayed result of that currentís progress. Your information is second-hand, and therefore more susceptible to misinterpretation. Remember also that we talk about accessory loads, that is, the outflow of electrical energy, in terms of "current." Why then, when considering charge, which is simply the reverse, in-flow, of that same current, do some people all of a sudden insist on speaking in terms of volts? It's inconsistent, as well as unprofessional.

  12. Q: You say the CBX doesnít charge at idle. Are you sure, and why?
    A: Most if not all electromagnet based alternators ("excited field" is the formal name) have a slow but longish charging curve. That is, their output takes off slowly but builds pretty high at the end. The CBX alternator has such an alternator. Though the engine is running, because of three things, the battery is discharging, not charging. First, the rotorís magnetism is maximized at idle, which draws heavily on the battery, offsetting any potential charge. Second, at idle the rotor is spinning too slowly to induce very much current in the stator. Third, unlike cars and trucks, powersports charging systems have traditionally been pretty low output overall, meaning that even if as with a car the first two issues are overcome, the third makes the powersports-spec electromagnet alternator not charge its battery at idle.

  13. Q: Why does your troubleshooting system have two sides to it?
    A: Because dead batteries aren't always the alternatorís fault. Sometimes an electrical accessory or even the brake light switch is the problem. Two sides are needed because two problems are possible -- Either the battery isnít getting enough charge, or it is losing the charge that it gets, and both must be considered.

  14. Q: When doing the regulator bypass, you say that "fireworks" can result if the rotor is shorted. Why, and what kind of fireworks? Also, isn't this known in the automotive world as a "full field" test?
    A: Bypassing the regulator fully magnetizes the rotor, because it receives all the electricity from the battery it wants. Usually the amount of current it gets is limited by its own resistance to about 3 amps. When the rotor has a short however, it will pull ten times this amount, which will melt your jumper wire and throw all kinds of sparks all over the place. Despite this, the regulator bypass is too important a test to eliminate from troubleshooting, so avoid potential trouble by checking the rotorís resistance before bypassing the regulator. As to what the test is called, yes, regulator bypass on the CBX is identical to the automotive "full field" test. However, it isn't called a full field test in the powersports industry.

  15. Q: Why must the alternator connector stay connected to check stator output?
    A: Because the magnet's (rotor's) wires are in the same connector as the stator's. Disconnecting one disconnects the other. No magnetism, no output.

  16. Q: Arenít some feeler gauges stainless steel and therefore not attracted by the rotorís magnetism?
    A: All feeler gauges (except those used in electronic relay work, which are brass) are stainless steel. But itís not the same kind as in your dinnerware, and as such still has a lot of iron in it to be attracted by magnetism. I have never had any trouble getting a magnetic field to attract a feeler gauge.

  17. Q: Why is the feeler gauge test done with the engine not running?
    A: The regulator energizes the rotor the most (producing the most magnetism) at very low rpm. This includes zero rpm (keyswitch on but engine is not running).

  18. Q: I have never heard of your way of testing a stator. Why must the stator be loaded, and what is wrong with testing it the way in the official manual?
    A: The manual offers two methods, the first of which is a resistance test. Resistance tests are not used by professional techs. They vary considerably with temperature, and the test values are relevant only when using the factory-recommended test meter. Resistance tests, if used at all, should be used only for double-checking, that is, to backup dynamic tests. The second method offered by the manual is a more realistic loaded output test -- the stator is best tested under a load because wire coils often exhibit good condition when relaxed but when put under a strain they fail. However, the manual's loaded stator test has a fault in that the load is the vehicle's own electrical system. Problems in the system (such as a shorted diode in the rectifier) can reduce stator voltage and give inaccurate readings. Therefore the best stator test is a loaded test using an external load.

  19. Q: What is "a 2 ohm, 100 watt resistor," and why is it necessary?
    A: This is a so-called "power resistor" often used in experimental radio work, and as such, is easy to find. This resistor happens to be a good test load for stators, as it simulates the bikeís electrical loads very well, yet keeps the stator isolated from the bike for accurate testing.

  20. Q: Where do I find a this resistor?
    A: Try Allied Electronics. Ohmite Solder Lug Power Resistor 2 OHM, 100 WATT.

  21. Q: How could there still be a problem when the charging system shows there is good charge?
    A: See the answer to number 13 above. Two things are responsible for chronic low batteries, given a good battery to begin with. Either the battery isnít getting enough charge, or itís losing the charge that it gets. One is just as common as the other in charging system diagnosis.

  22. Q: Explain dynamic and static leaks.
    A: A leak is merely excessive or unaccounted-for discharge. A dynamic leak is simply where the battery is losing charge faster than it should. A static leak is where the battery is losing charge when it shouldn't, when the keyswitch is turned off and the engine isn't even running. Labeling leaks either "dynamic" or "static" merely calls attention to whether the keyswitch is on or off, because for each case the troubleshooting steps are different.

  23. Q: How does the breakeven rpm test tell you whether you have a dynamic or static leak?
    A: The CBX discharges its battery at idle. It therefore has an rpm point at which the battery begins to charge -- that is, output and input "break even". This breakeven point is supposed to happen at a fairly low rpm (below 1700 is spec). Higher than normal breakeven therefore indicates an excesssive discharge problem, for which more engine rpm is needed to compensate. On the other hand, normal breakeven rpm would normally indicate good charging system health, but it doesn't necessarily. Coupled with a chronically low (but tested) battery, normal breakeven indicates a static (key off) leak precisely because nothing in the charging systemís or accessoryís function appears abnormal. The leak therefore has to be happening when everything is turned off.

  24. Q: How can the brake light affect charge?
    A: Older vehicles like the CBX have fairly low-powered charging systems (the CBX's 350 watts is puny alongside today's 1100-watt and higher systems). As a result, the current going out due to the brake light is rather high compared with the charging current going in. A stuck or misadjusted brake light switch can therefore raise the breakeven rpm so high that at normal road speeds the battery will receive too little charge and get weaker and weaker.

  25. Q: Why do some electrical components draw current even when the keyswitch is turned off?
    A: Alarms, radios, clocks, (and in modern vehicles, electronic fuel and engine management circuits) are wired directly to the battery, bypassing the keyswitch, because these components have memory and logic circuits that require full-time power. Nothing on your bike should draw more than 40 mA (1/25 amp) full-time.

  26. Q: Why is the static leak test performed at the battery instead of at the fuse terminals like the amps charge and dynamic leak tests? And, why the negative battery terminal?
    A: This test must be performed at the battery simply because a leaky rectifier, the most common reason for static leakage (leakage with the key off, remember), would not be picked up at the fuse terminals. As for the negative side, this is for safety. It is the traditional way to avoid the sparks that can result in battery explosions.

  27. Q: What is meant by a "leaky" rectifier?
    A: The rectifier has a unique connection in the electrical system. It is the only DC carrying component not controlled by any switches. This connection is potentially troublesome. The rectifier's internal diodes are supposed to permit current flow in one direction only -- stator to battery. You do not ever want it to allow flow the other way -- battery to stator. However, when one or more of those diodes short, the battery's current can then reverse-flow into the stator, depleting the battery while the vehicle is parked. This is not an unknown phenomenon, and will result in chronic battery discharge while showing very little sign of charging system malfunction.

  28. Q: Why doesn't your method include the traditional regulator/rectifier resistance checks?
    A: Because "ohmming" the regulator/rectifier is an archaic procedure, and even Honda admits that it rarely works. More importantly, it is unnecessary when using live, dynamic tests. For the rectifier side, the best test is a stator output test. If current to the battery is low, but the stator outputs strongly, the rectifier is bad. What could be simpler? The rectifier is also tested in the reverse direction in the key-off drain test. As for the regulator side, it is tested dynamically by the bypass test.

  29. Q: Why is the traditional stator test missing in this method, and why isn't it tested first?
    A: The stator is tested dynamically in Step Two. As for not being the first test, stators don't fail as often as people think. Although it does happen, especially on certain models such as early Suzukis, Yamahas, and Honda V4s and GoldWings, stator failure is the rarest of all charging system parts failures on the majority of motorcycles, including the CBX.


    Additional questions are welcome.
    carbrebuilder@gmail.com
    www.motorcycleproject.com
    www.cbxcarbs.com


Please don't overlook the fact that I have written a booklet covering troubleshooting the CBX charging systems. I think you'll find it comprehensive and resourceful.

Servicing the CBX Charging System
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The CBX charging booklet is a very special book. Servicing the CBX Charging System offers a close-up look at testing the CBX charging system. A bit more technical than the others, but like the rest, systematic and laid out in everyday terms. This book includes testing for bad wires and connectors, and checking common failure points in the system such as the rotor and brushes. There is also quite a bit about the use of the digial VOM and other special equipment, some of which you can make yourself. Also included are simple drawings of the charging system, and an easy-to-follow 3-Step Troubleshooting flowchart. Like the others, this is an 8 1/2" by 11" booklet, running to about 30 pages, and contains over 100 clear illustrations, many of them close-ups. And, except for the location of the alternator rotor, all the steps are equally applicable to the very similarly-equipped early DOHC CB750, CB900/1000 and CB1100 Honda Fours, as well as the SOHC CB650. For the Honda SOHC Fours, check out another booklet I have available. Don't just throw parts at the problem until it's fixed. Do it right. All this for just $27.95 plus $5.75 domestic, $20.55 Canada, $24.75 everywhere else, for fast USPS Priority Mail shipping. Combined shipping on multiple purchases. PayPal will automatically adjust the shipping amount when you check out. Be sure you don't click a button twice unless you mean it. Can be on your doorstep in just 3~4 days. Check or money order okay also. Contact me for more information. Here's a sample page.