F800 Electrical System

[Daboo]

So I have a question that has been running through my head recently. How does the F800 Electrical system work? I think it is different than a car's electrical system, but I'm really vague on this.

My radar detector has a voltage readout. How accurate it is, is up for debate. But the numbers show a high of 14.2V, and a low of 12.5V. I also have a Clearwater Voltage Sentry that shows a blinking green light, which indicates all is good.

But why the variance? Does the voltage regulator vary output based on need?

Thanks.
Chris

[Richard230]

I think the voltage regulator keeps the voltage around 14.2 volts and varies the current output based upon the the needs of the battery. That is my guess from watching the voltmeter on both my F650GS and my R1200RS. Both stay at 14.2 volts all the time. But then I never let my battery charge drop so it might be different if the battery is discharged and the charging system is doing its best to recharge it. However, with other motorcycles that I have owned I have seen the voltage rise when the battery is charging and drop when the battery seems to be fully charged. So it may depend upon how the charging system is designed.

[Runmyownlife]

My feeble understanding is that the stator puts out a current as long as the engine is running. How much current depends on engine speed. The stator is a fancy coil placed around a magnet that rotates along with the crank shaft. The coil plus rotating magnet produce AC current.

The rectifier unit converts AC to DC. The regulator ensures voltage is delivered within certain limits. Excess voltage (because the stator provides current whether it's needed or not) is converted to heat. If the demand on the system (heated gear, lights) is greater than the output, voltage drops.

[emlevy]

Better to monitor the amperage draw (current). This will tell you if your electrical system is a net producer or a net user.

[ccramerusc]

Richard and Andrew are both correct. The system will put out as much as it can based on rpm (speed of rotor around stator). The R/R converts it to DC and controls how much gets put into to system.

14.2v DC is ideal. Once the battery provides enough amps to start the motor, the charging system will run everything and the R/R will continue to add what is needed up to 14.2v. If the drain on the system is more than the charging system can produce, then the battery will provide the amps to keep things working until it is drained. This is when you will start to see voltage drop.

Remember that amps times volts equals watts (Ohm's law). A certain number of watts is what everything requires. As long as there are enough amps, voltage will remain steady. It's only when available amps drop that voltage ends up dropping. That's when you get into trouble.

Imagine water and pipes. Think of watts as the total volume of water coming out of the end of the pipe. Volts would be the size of the pipe and amps would be the water pressure (flow). More amps in a steady 14.2 volt system will yield more watts at the end of the pipe. Too many amps through too skinny a wire (pipe) would create too much resistance, leading to heat and possibly a fire.

So it works the same as a car system, just much weaker since it can only produce about 400 watts. At 14.2 volts, that's only about 28 amps. My VW GTI puts out about 2000 watts for perspective.

Sent from my SAMSUNG-SM-G891A using Tapatalk

[rcb78]

Your water analogy is skewed. Voltage is the difference in pressure between inlet and outlet, current is flow rate and wattage is your flow volume per unit time.
People too often interchange amps and watts when trying to determine system load. They are related by a time factor but they have unique definitions. Amps is a measure of how much current you can flow, watts are how fast you flow it. The reverse is looking at the requirements of accessories where amps are how much current a part will draw and current is how fast it will draw that current. Ohms law just connects it all with resistance and give more depth to what a watt means for each application.
Our systems have more moving parts than cars, so to speak. They are much lower capacity to limit parasitic power loss and reduce system weight, both of which we pay very close attention to. Stators, and full system alternators (stator combined with R/R) are rated to put out a specific voltage at a specific rpm, this is a value provided for a known resistance, but is usually given for each vehicle. So you will often see lower voltages at idle that will then ramp up and stabilize with added rpms. Load on the system will draw down the voltage when you exceed the limitations of the charging system. This is easy to see with stators, R/Rs and batteries nearing end of life. Turn on your high beams and you can easily see a voltage drop if one component is weak. Heated grips that turn themselves off and on are a dead giveaway for compromised charging systems as the ZFE will shut them off when the system voltage dips too low. The ZFE itself also adds to the complexity as the bike will report a different voltage than what you may measure at the battery terminals.
So in short, the system design as a whole is very similar to a car, but on the edge of being underpowered which will lead to a voltage that can often vary by .5vdc and still be considered normal.
My wifes bike, a Kawasaki Vulcan S, specifically calls out that there is only 2 extra amps (25w) available for accessories above what the bike itself needs to run, that's one of the tightest margins I've seen yet.

[Richard230]

I bet there are no end of videos and blogs on the internet that will really give you an education regarding motorcycle charging and electrical systems and how they function better than any of us could.

You think discussion about politics are bad? You should see the fights over electrical problems by (apparently) electrical engineers and electricians on one of my electric motorcycle forums. Who knew that electricity and how it functions could be so controversial?

[Runmyownlife]

I bet there are no end of videos and blogs on the internet that will really give you an education regarding motorcycle charging and electrical systems and how they function better than any of us could.

You think discussion about politics are bad? You should see the fights over electrical problems by (apparently) electrical engineers and electricians on one of my electric motorcycle forums. Who knew that electricity and how it functions could be so controversial?

Tesla and Edison.

[rcb78]

I think you're just describing engineers in general

[Royce]

All i know about my bike's charging system is that it does not produce enough power to legitimately be called a "touring" or "sport touring" motorcycle. I believe any bike with touring in its name should produce enough power to easily accommodate a full suite of heated gear (jacket, vest, pants, socks, gloves, etc), plus auxiliary lighting as desired and plus add-on electronic do-dads (GPS, noisemakers, etc). Our F800s will run some of those, but not all of them.

[ccramerusc]

Royce, I completely agree. My ST won't keep up at idle with my heated gear going. I installed a volt meter which has been very helpful. I'm constantly turning down and switching off stuff while sitting at a stop light in cold weather. Very frustrating!

Sent from my SAMSUNG-SM-G891A using Tapatalk