July 7, 2016 | By Jeff King
We all know that it pays to keep up on the basic maintenance of our motorcycles. Conducting pre-ride safety inspections, checking oil and coolant levels, adjusting the chain, inspecting our brakes and tires for wear… but when is the last time you checked the health of your charging system?
OK, I know it can be a little intimidating poking around your bike’s electrical system, but keeping tabs on the health of your motorcycle’s charging system is easily accomplished with just a basic understanding of the system’s components, their role in the overall health of your motorcycle, and only one specialized tool every motorcyclist should have anyway… a $20 voltmeter. Checking on the health of you charging system should be in every rider’s skillset.
OK, there’s just a touch of science involved here, but NO MATH, I promise you. Let’s define some terms:
Alternating Current (AC) is a type of electrical current in which the direction of the flow of electrons switches back and forth. (The electricity coming out of the three-prong outlets in our home is AC.)
Direct Current (DC) is the unidirectional flow of electric charge. Electricity flows from positive to negative only. Simply put, anything that runs on a battery is using DC, including our cars and motorcycles.
Let’s start with a rundown of your motorcycle's charging system, its role and components:
On modern bikes the charging system consists of a battery, a stator, and a regulator/rectifier. I say “modern,” because bikes manufactured pre-1970s can be different, as they often utilized separate components for the regulator and rectifier. (Usually when charging problems are encountered on bikes with a separate regulator and rectifier, they are in fact replaced with a modern all-in-one regulator/rectifier.) For the scope of this article, we will focus on motorcycles that have the regulator and rectifier combined into one unit (often abbreviated Reg/Rec).
Your motorcycle runs on a 12-volt DC system. All electrical components on the motorcycle are designed to run on (or around) 12 volts DC. There is some tolerance built into the system, but suffice it to say, our bikes need a minimum of 12 to 13 volts to run properly.
A stator is an AC (alternating current) generator attached to the crankshaft of your engine. It uses the rotational energy from your running engine to generate electricity (It’s a basically a mini electric power plant on your motorcycle). This electricity is later processed and harnessed to power the bike’s ignition, lights, accessories, and charge the battery. The output of the stator is Alternating Current (remember our bike’s electrical system runs on DC), and the voltage output of the stator varies also with the engine speed (the faster the engine spins, the higher the voltage output). Because of this, we need a way to convert (or rectify) the stator’s AC output to usable DC, and also limit (regulate) the voltage to a usable range … enter the Reg/Rec.
The regulator rectifier’s job is two fold. Convert the AC output of the stator to usable DC, and regulate the voltage to a safe range (usually 12.5 to 14.8 volts). Any excess voltage generated by the stator is dumped (or shunted) to ground. The by-product of this conversion is heat buildup. (This is why the regulator rectifier has cooling fins and is best located in a spot that gets maximum airflow.)
Now that we know the major players, how does the charging system actually work?
Well, the Reader’s Digest version of the charging system function goes like this:
When the engine is running, the stator generates AC voltage; the Reg/Rec converts this voltage to usable DC and limits (regulates) the voltage to around 12 to 14.8 volts. This voltage powers the bike while running, and used to recharge the battery.
So what can go wrong with your charging system?
Problems come in two basic flavors, undercharging and overcharging. There are also areas in between, where our systems may be functioning at somewhat less than optimal levels, slowly failing toward one extreme or the other. It could be one single component of the system failing (or beginning to fail), dirty electrical connections, or a combination of several under performing components resulting in a less than robust charging system.
Although there are specific guidelines, oftentimes it’s a gradual slide into charging system failure. Regular testing and monitoring will help you identify a failing system before it leaves you with a dead motorcycle, scratching your head on the side of the road. (I don’t know what happened, it started this morning!)
INSPECTING YOUR CHARGING SYSTEM
Let’s start with the heart of the charging system, by checking the battery. With your trusty voltmeter set to read DC voltage, and with the IGNITION OFF, put the RED voltmeter lead to the positive (+) battery terminal and the BLACK lead to the negative (-) battery terminal.
Read the voltage on the voltmeter. You should see a reading above 12.0 volts. (Although we commonly call it a “12- volt battery”, a healthy 12-volt battery should test around 12.5 volts).
If your battery reads less than 12.5 volts, put it on a trickle charger overnight and see if it comes back to a healthy voltage. If this doesn’t bring the voltage to around 12.4 to 12.9 volts, then it’s time for a new battery.
Without a healthy battery installed, the following charging system check will produce inaccurate results. Make sure you are starting with a healthy battery!
Now that we know we have a healthy battery installed, let’s get down to the nitty-gritty and see how our charging system is performing.
1.) With a healthy battery installed, START THE BIKE and again check the battery’s voltage at engine idle -- RED lead to positive (+), BLACK to negative (-). A healthy charging system should read somewhere between 12.4 and 13 volts at idle. Readings in this range mean (at least at idle) that your charging system is able to generate enough electricity to run the bike at low RPMs. This is good! If it reads lower than 12.3v or higher than 13v, this is evidence that there may be an issue. Make note of the results and continue to the next test.
2.) With the voltmeter leads still attached to the battery -- RED lead to positive (+), BLACK to negative (-) -- slowly increase the engine RPM to 3500-4500 RPM. With a properly functioning charging system you should see the battery voltage gradually rise as engine RPM increases. The maximum battery voltage you would like to see is 14.8 volts @ 3500-4500 RPM. This means that at high RPMs, the charging system is indeed producing enough electricity to recharge that battery, but not overcharge it.
If there is little to no voltage rise as engine RPM increases, your system is no longer capable of producing enough electricity to run the bike and charge the battery effectively. Any reading over 14.8 volts and the charging system is in danger of overcharging the battery (also not good!). If the charging system is overcharging or vastly undercharging the battery, it’s time to have the bike checked out by your trusted local mechanic.
If the voltage does rise, but not quite to the full 14.8 volts, you are in that grey area where the system is still functioning, but not to it’s fullest. A less than robust charging system could be caused by a slowly failing component, a bad battery or as simple as dirty electrical connections. If your charging system is producing results outside of the guidelines of this article, look on the bright side, as you’ve found a potential problem before it found you! Troubleshooting the separate components in the charging system is beyond the scope of this article, but suffice it to say, if your system is performing sub par, further investigation is warranted.
If you do find an issue, there are many resources on the web to help you track down the problem component. One of the best is ElectroSport’s Motorcycle Fault Finding Electrical Chart (PDF). Again, just a voltmeter is required, but the testing can get pretty technical (Ohms and stuff!). They say fortune favors the bold ... you already have the tools, so why not give it a shot?
If you don’t feel confident in chasing down the problem yourself, probably the best option will be taking your bike to your local repair shop. Ask them if they have experience in troubleshooting charging systems. If they answer anything other than an enthusiastic “YES!”, maybe look into finding a more experienced repair shop. Diagnosing troubled charging systems is where experience really matters. An experienced mechanic has encountered all types of charging system troubles (classic failures and downright oddball ones as well) and will save you time, money and probably a tow or two.
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DISCLAIMER: The methods in this article are guidelines, provided and performed by a trained mechanic. If you are not comfortable performing routine maintenance on your bike, it is recommended you get a trained mechanic to complete these and more difficult tasks on your bike.
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