Another Stupid Battery Question - BMW Luxury Touring Community
 
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post #1 of 6 Old Oct 23rd, 2008, 1:22 pm Thread Starter
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Another Stupid Battery Question

Does the battery start to charge when you turn it on or does the bike have to be moving? How about when you blip the throttle standing still?
Jim

Jim in Dublin, OH

2005 - LT Ocean Blue (Catuffalo - Part Cat / Part Buffalo)
2002 - Moto Guzzi Cal Spec Sport
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post #2 of 6 Old Oct 23rd, 2008, 2:08 pm
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Re: Another Stupid Battery Question

The amount of energy produced by the alternator is related to its rotational speed. At tick-over the chances are it isn't producing much more than is required to cover the basic outgoings. Blipping the throttle will increase the energy but only instantaneously so its effect is practically immaterial to the state of charge in the battery.

Although the alternator output is related to speed, it will normally be able to produce a lot more than the system requires, the maximum output being set to cope with the highest power draw. Early, permanent-magnet alternators (as on my 1950s and 1960s British bikes) had no internal regulation and the excess had to be literally burned off as heat. Modern control systems mean that alternators produce only what is required as it is required.

Keith


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post #3 of 6 Old Oct 23rd, 2008, 2:17 pm
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Re: Another Stupid Battery Question

The LT idles at approximately 1K RPMs. The alternator doesn't approach full output until somewhere between 1.5K - 2K RPMs, if I recall correctly. So basically, the battery is not getting charged until you are riding. That is why, so often, you will see your aux lights dim when you're sitting at a red light or stop sign. Blip the throttle = the lights get brighter. This especially happens when you put a lot more demand on the electrical system by adding farkle upon farkle. Halogen lights and heated gear are the worst offenders, obviously.
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post #4 of 6 Old Oct 23rd, 2008, 7:37 pm
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Re: Another Stupid Battery Question

Quote:
Originally Posted by messenger13
... That is why, so often, you will see your aux lights dim when you're sitting at a red light or stop sign. Blip the throttle = the lights get brighter. This especially happens when you put a lot more demand on the electrical system by adding farkle upon farkle. Halogen lights and heated gear are the worst offenders, obviously.
and that is why I have started turning everything off as we approach an interstate exit, for example. I turn off all the heated gear (rider and passenger), heated grips and seat(s), radio, etc. I'm doing that because my battery is acting like it's time to be replaced and I want to be able to pull away from the next rest stop without getting out the jumper cables.

Howard Schisler
2015 BMW K1600GTL
2009 BMW K1200LT - 60k miles
2012 BMW F650GS (sold)
2005 BMW K1200LT - "Gray Ghost", traded at 120k miles
2005 Honda Shadow 650 (sold)
AMA, IBA, BMW MOA. CCRs: Braselton 2006, Osage Beach 2007, Duluth 2012


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post #5 of 6 Old Oct 23rd, 2008, 9:48 pm
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Re: Another Stupid Battery Question

When the alternator light on the instrument panel just goes out the alternator voltage is the same as the battery voltage, so it is just keeping up with the current draw for the bike. Any RPM above that is charging the battery, slightly just after the light goes out to higher as the RPM increases.

The alternator light is a very important part of the alternator circuit. The current flow through the light before the engine starts running is used to "boot" the alternator. Without that small current through the rotor winding there may or may not be enough residual magnetism in the rotor to start the voltage producing process.

Some of us have had charging problems related to the wire from the indicator to the rear of the alternator getting loose or coming off, causing a no charge condition which you will not be aware of until it is too late since there will be no indicator light.

Always glance at that light when you turn on the ignition to be sure it is on before starting the ignition, and that it then goes out after start. If it never comes on, you have a problem.

I don't want to achieve immortality through my work...I want to achieve it through not dying.

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post #6 of 6 Old Oct 23rd, 2008, 10:41 pm
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Re: Another Stupid Battery Question

Quote:
Originally Posted by hschisler
and that is why I have started turning everything off as we approach an interstate exit, for example.
Or you could just put a PC680 in it and forget all that other nonsense.

Ken
Pacific NorthWet
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'09 Magnesium Beige Metallic K13GT, 63K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
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Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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