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post #1 of 8 (permalink) Old Dec 10th, 2008, 7:36 am Thread Starter
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Battery Charging Question

I have a new 08 GT, and the dealer installed the BMW pigtail directly to the battery so I could charge using BMW advanced Battery Charger II. Even after a long ride when I plug the charger in, it almost immediately goes to steady read with blinking green showing battery is at least 80% charged, but it takes 8 hours until I get a steady green light on the charger. I have no problems, starting is strong, just curious if this is normal, or a sign of problems to come. On my RT which has a Wescto AGM battery the light turns steady green in about 10 mins.

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post #2 of 8 (permalink) Old Dec 10th, 2008, 10:36 am
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Perfectly normal. It does the same on my bike. sometimes it takes an entire day to go through the full cycle.

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post #3 of 8 (permalink) Old Dec 10th, 2008, 11:28 am Thread Starter
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Thanks Larry!

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post #4 of 8 (permalink) Old Jun 1st, 2009, 12:24 am
 
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BAttery charging 2008 GT

I have an older BMW (Deltran) battery charger that I used on my 2003 GS. I put a pig tail directly on the battery and plugged it in. Works just fine. The voltage from my charger is just a shade over 14 volts like the alternator and right at 3 amps. I can charge with the ignition off and do not need to use the new $200 BMW charger that is "compatible" with the Canbus system. I always insure the iginition is off during charging and do not use the charger for a jump start. Works fine, tops off the battery and goes into the maintenance mode. I ride in the winter and this comes in real handy.
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post #5 of 8 (permalink) Old Nov 18th, 2010, 5:55 pm
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Hey all, trying to find out some info on charging. 2000 K1200RS
Good battery, 6 months old.
Ride 4-5 times a week at 100-200 miles each ride.
I can hook up my volt meter to the outlet jack, and it shows about 12.5 volts. Turn the starter and it drops to about 11 volts. When it idles it's about 14.2. Then when reved up to 3-4K it goes to 14.6-14.7. That's all it puts out. Is this the top voltage? Or does the power plug have a 14.5 v limit?
I haven't tried clipping straight to the battery posts.
There is not alot of info in Clymers about charging specs.
My Honda calls for increasing volts to a max of 15.5 v at 5,000 rpm. A gel cell battery.
Thanks ahead of the answer.

Sorry, we are talking the 19A wet cell battery on the RS..

Last edited by Brokerecord; Nov 18th, 2010 at 6:02 pm.
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post #6 of 8 (permalink) Old Nov 20th, 2010, 5:27 am
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This reply is for your early KRS bike, I don't know if they do things differently on later models:

The power outlet socket is nothing more than a socket connected through a fuse to the battery terminals. What you measure at the socket is what you get at the battery terminals and it saves you removing the seat - but it's easy to short it out with meter test prods and blow the fuse!

That's why it's a good idea to get a low current tender and plug it in there, nothing to remove when you get back from a ride then after leaving the bike standing a few days (clock draining battery) the bike will always start on the button with no flashing ABS llights afterwards.

What you measured is the battery terminal voltage when loaded with cranking - 11 volts so that is a good battery. Get a reading below 10 volts and start to think 'new battery' soon. 12.5 volts is a fully charged battery but this is a variable figure. If you did this first thing in the morning without running the bike it would probably have dropped to nearer 12 volts.

You got 14.2 volts when the bike was idling. This shows there was some charge going back into the battery, but not quite enough to put back what cranking took out, but the alternator is working ok. If you got 12-12.5 volts, same as bike not running then you would have a bad alternator!

When you got 14.6 to 14.7 at 3-4K that was probably the alternator now putting back the full charging current needed to make up the cranking loss. If you rode a long trip without lights, heated grips or high loads, stopped the bike and checked this again without cranking, it probably would have dropped a little showing the battery was now fully charged and didn't need more from the alternator.

Different battery technologies can produce slight differences in these voltages. But you have to remember that batteries are electro-chemical devices hooked up to a massive generator and charge controller design can vary, so you can't rely on the voltages you measure with decimal point accuracy. The alternator can at times be pulsing its charge and electronic voltmeters can be reading peaks instead of averages.

All you need to know is the battery voltage on cranking doesn't drop below about 10 volts, the battery voltage is around 14.2 on idle, possibly increasing a little with rpm and it doesn't measure much more than 15 volts. If it does then investigate possible battery overcharging, measurement errors, or battery if it fails the cranking voltage test.

The power plug has no limiting devices (except the fuse), as said it is the battery terminal voltage. Most accessories that plug into cars and bikes say they are 12 volts, but are actually designed for 14-15 volts. Actually all tungsten auto bulbs are the same. If they were designed and life spec'd for the 12 volts on the box, they wouldn't last very long.

Your battery and alternator charging seem fine and good to go.



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Last edited by voxmagna; Nov 20th, 2010 at 5:33 am.
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post #7 of 8 (permalink) Old Nov 20th, 2010, 6:36 pm
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Thanks Vox, was just wondering about it charging at such a low rpm, but, never getting to 15-15.5 v like the Japs do. I suppose the 19amp vs the 10 amp Jap could be why it charges so quickly. My trickle charger is 1.5 amps.
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post #8 of 8 (permalink) Old Nov 21st, 2010, 3:59 am
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Most alternators are charging from about 500 engine rpm upwards. It's not the max output that's really important, but what it gives out at idle. A rule of thumb is the alternator speed is about twice the max engine rpm. The japs must have some pretty good bearings in their alternators for the high engine rpm. Although generally the higher output alternators give out more at lower speeds which is more useful. It's a common Winter problem that high lighting and heated gear loads will pull a small battery down if riding is stop/start commute, so tendering in Winter is a must. I'm all in favor of ditching tungsten and going to HID.

There's a trend these days to produce vehicles, including our bikes, with high idle speeds. There are some other reasons like the Bosch efi not so good as carbs and aircon, but I think another is to get output from the alternator. Most of the older vehicles I ever owned idled at about 750 rpm, but you often got the fan belt slip and squeal problems in Winter.

I think you are confusing the higher battery terminal voltage with much greater charge and that's not necessarily the case or best thing for the battery and the life of light bulbs if it's real.

The real test is to switch on all the bike electrics load running at idle and watch the voltmeter. As soon as the engine rpm gives greater than 14 volts, your alternator has matched the load and has some left over for charging the battery. I bet you find that is around 3K.



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