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Old 06-03-2010, 03:37 PM   #1
ashrubbery OP
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Charging problems -R100RS

Hello,
Sorry for having to introduce myself by having to ask for help! I am a new airhead owner having recently bought a '82 R100RS. The bike is in good condition, no dents, paint was perfect, engine sounds great etc. etc. It had done about 8500km (53000 miles) when I bought it.

Anyway, the guy I bought it from had been plugging the bike and charging it in every day because he didnt use it much. While it was charging the Voltmeter showed about 11 -12v which is low, but he said the battery and everything was fine...mmm...

Well I had done about a week of riding, a lot of it slow , low revving riding when the bike wouldnt start. Just that click click click click click sound. So we check the battery its one of those closed batteries with out easy access. But we got the rubber seal on each of the cells off and found that the battery was completely empty. So we filled the battery up with distilled water and charged it up overnight. The voltmeter showed 13v yay! It also looked like the bike was charging when it got good rpm.

So i continue to ride it but I also notice each time the voltmeter is slowly getting less and less until it went below 11v, and well, I couldnt start my bike. This was four days later. I admit while riding the rpm would often be around 3-4, sometimes over 4rpm, and sometimes id be in slow traffic. Upon closer inspection, when the bike is revving the charging light does not completely go away but remains dimly lit!!
When I checked the voltage across the battery while revving the engine it was about 12. something volts and not increasing very much even with increased rpm. Isnt it supposed to be 14?

So what are my options and what is the most likely culprit? Alternator? Regulator? corrosion? loose wires? If it is corrosion and loose/broken wires where should I look?

What steps do I need to tack to be absolutely sure the battery is charging well? So it wont fail on me again! (planning on long trip...soon...)

Ill also check if the battery is able to keep a charge since it is a bit shady....

Thank you
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Old 06-03-2010, 03:53 PM   #2
SOLO LOBO
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First, replace the battery.... if it is even the slightest but shady go new!

Second, someone is going to tell you to head over to Motorrad Elektric and buy Rick's book titled "Classic Boxer Charging"... unfortunately Rick doesn't have any left and isn't planning on printing a new edition any time soon.

12v is way too low, and you do have something wrong other than the battery for absolute certain... there are a number of things to check and methods to check them... my own voyage of discover his here...

"OK charging system Guru's.. WTF is up with my GS"

I would say to start by checking the rotor.... that's my guess. Although when my former R100RS had a similar issue, it was the brushes.

My current R80G/S throws about 13.7 volts at 4K rpm's.... all on the stock charging system
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Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 06-03-2010, 03:53 PM   #3
puncar thogoole
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Start with a new battery.

Go through the wiring & clean & solder connections as necessary, bad connections can cause the charge light to glow.

After cranking the bike to start it, it'll probably take somewhere around 10-20 minutes at medium to high revs to put the charge back in, so if you are doing a lot of short runs, re-starting often or riding at low revs the battery will not have a chance to charge & eventually won't start the bike.

If the above fails, then start checking components.
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Old 06-03-2010, 03:58 PM   #4
SOLO LOBO
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Quote:
Originally Posted by puncar thogoole
.

After cranking the bike to start it, it'll probably take somewhere around 10-20 minutes at medium to high revs to put the charge back in, so if you are doing a lot of short runs, re-starting often or riding at low revs the battery will not have a chance to charge & eventually won't start the bike.
I would disagree.... he says that while reving the engine the charging voltage is <12v... that means there is a charging issue (most likely along with a battery issue)

If the charging was fine and the battery poor, the charging voltage would be closer to 14v than 12v
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Quote:
Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 06-03-2010, 04:23 PM   #5
Wirespokes
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Good advice. Also, don't allow the starter to do the click click click click click click click click thing. Serious arcing occurs in the starter solenoid and it'll stop working.
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Old 06-04-2010, 03:53 AM   #6
ashrubbery OP
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Thanks for all your replies

So I charged my bike up overnight again (i needed to get somewhere) and it was all good.
The wierd thing is I found out that riding in 3rd gear around 4000 rpm the voltmeter shows a nice 14volts. 2nd gear will only sometimes go over 13volts at 4000rpm. So i guess maybe I just needed to push the bike a little more. Shouldnt the bike charge the same based on rpm not on different gears? Im a complete novice to the motorycle/mechanical world.
For the battery to be charging where should the voltmeter read?

Im going to get a new battery for sure, and hopefully I can have a look at the brushes as well....

Quote:
After cranking the bike to start it, it'll probably take somewhere around 10-20 minutes at medium to high revs to put the charge back in, so if you are doing a lot of short runs, re-starting often or riding at low revs the battery will not have a chance to charge & eventually won't start the bike.
10-20 mins for each start up? If youre doing a lot of inner city travel/lots of stops how do you guys compensate for the loss of battery power?
thanks
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Old 06-04-2010, 05:01 AM   #7
bmwloco
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+1 on visiting Rick's site. He is "The Man" when it comes to BMW electrical issues and undoubtedly has the fix.

> Second, someone is going to tell you to head over to Motorrad Elektric and
> buy Rick's book titled "Classic Boxer Charging"... unfortunately Rick
>doesn't have any left and isn't planning on printing a new edition any time
> soon.

The current version is 2.0, and it is light years away from the first edition when we shot photos with a QuickCam... (look it up, early, basic digital technology... my avatar to the right is a 20 year old shot taken with a QuickCam and hand colored with PhotoShop). A lot of the information is just basic knowledge.

BMW hasn't changed airheads in a decade or more. I will bring up the issue of updating the book at the Gathering of the Clans with him next week.
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Old 06-04-2010, 06:12 AM   #8
Jasper ST4
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Quote:
Originally Posted by ashrubbery
10-20 mins for each start up? If youre doing a lot of inner city travel/lots of stops how do you guys compensate for the loss of battery power? thanks
Battery charger and longer rides.
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Old 06-04-2010, 01:17 PM   #9
ashrubbery OP
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After spending all day on the bike trying to figure out what was wrong, we have come to the conclusion that everything (except the battery) is in working order. We checked the brushes, made sure that the coil was good and nothing was shorting, that that thing that changes AC to DC (cant remember what that was called) was working properly. Also, tested the bike with the new battery we found it to be charging. With a voltemter at the battery terminals it would slowly climb to 13volts and above with a max of 14.

Though when we tested the bike with the lights on, even with revving the light did not get brighter. (isnt the light supposed to get slightly brighter when you increase RPM? does your bike do this?)

The consensus of the mechanic who checked much of the bike was that the bike was fine and charging as it should.

Anyways, even with a working battery the little voltmeter on the dashboard shows it to be at 11v when idling. Why then did it show 13v right after charging the old battery up? The only thing I can think of to explain what the voltmeter on the dashboard is telling me when I ride is that it isnt working right. (dont think it came with the origional bmw but was replaced sometime with a cheap one).

Having said all this, should I be worried? Is there something we missed?
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Old 06-04-2010, 01:35 PM   #10
Jasper ST4
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Quote:
Originally Posted by ashrubbery
Anyways, even with a working battery the little voltmeter on the dashboard shows it to be at 11v when idling. Why then did it show 13v right after charging the old battery up?
It will drop when starting, especially if the lights are on and it isn't charging while idling. Plus the voltmeter could be wrong, I'd check it with a known good VOM.
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Old 06-04-2010, 01:41 PM   #11
puncar thogoole
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Once again, new battery & go through your wiring cleaning & replacing suspect connections.
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Old 06-04-2010, 04:03 PM   #12
mcma111
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Battery

It's ALWAYS the battery. Replace it and start from there.
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Old 06-04-2010, 11:40 PM   #13
boxerboy81
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The dash vm is renowned for being inaccurate. The trick to knowing its usefulness is to know what it normally displays and to recognise when it changes from that.
Removing it's connections and cleaning them well can also improve its performance. I use a dremel to deglaze the connections. It does help.
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Old 06-05-2010, 03:58 AM   #14
Twinz
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Quote:
Originally Posted by SOLO LOBO
First, replace the battery.... if it is even the slightest but shady go new! I would say to start by checking the rotor.... that's my guess. Although when my former R100RS had a similar issue, it was the brushes.
+1

When my riding buddy's R100RS had charging issues, eventually after checking everything it turned out to be the brushes.
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Old 06-05-2010, 04:45 AM   #15
Wirespokes
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When the system is busy recharging the battery (like after a start-up) it'll read a lower voltage than when it's all topped up. And as everyone says, the volt meter tends to show a different voltage than actual - usually a volt or so less - being several connections removed from the battery, plus inaccuracies in the meter itself.

It's not the high voltage reading that matters so much as the current. But we don't use current meters so can't monitor that. I've had a system that charged at 13.5 without problems because it had very good connections with plenty of current flowing. Remember that Voltage is the potential, but Current is how much can flow. For example, a cup of water dropped from 176 feet has the same potential as Niagara Falls, but nowhere near the same current.
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