Struggling with alternator on R100GS (1990)

[Lewis1965]

Hi Folks,

Basically the battery is not getting charged.
I have been a carer for my step dad for the last 8 months full on shared time with my wife 12 hour shifts...It was a toughie...He died 4 weeks ago...So now I have time for my bike again...My bike hasn't been on the road for 8 months...I put it to bed for the winter after the battery went flat last year which it shouldn't have been as the battery was only 12 months old...So...I took the old battery out and it was dry which was a surprise but I got a new battery and fired it up...I checked the battery with a multimeter while the bike was running and the multimeter doesn't change so nothing going into the battery...I checked the rotor with the multimeter (following one of Moto Pheonix videos) and I'm getting a reading on it so that means it is ok...The brushes are still good...but now I am at a loss as to what the next process of elimination is...

Electrics are same as fairies and elves to me...Wizardry!...Hence the cry for help

Thanks for any help fellas...

 

[DrFarkoff]

Condolences on loss of your Dad Fair play for undertaking such a task I am not sure I would be capable

Did you slip plastic under or lift the brushes when doing the rotor continuity test

Do you have a Battery lamp with Ignition on ?

These older systems need some current to energise the rotor so if no continuity in the rotor or no battery lamp it cant do its stuff
if the battery lamp is always lit Check the blue wire all the way down for grounding out (Chafed)

Start with the easy and work up to the difficult

What was the last work that you did to the bike before this happened ??

 

[theoneandonly]

i check rotor resistance ,(3.6-4.2 ? ) THEN check through the brushes @ the terminals , and allow 0.5 ohms for each side =4.6-5.6 ohms.
quite often the 2nd reading is sky high.
as it has stood , i would go and , break and make, all the connections as a start point , and check earth point on rectifier .

 

[Santa-2512]

What voltage does the battery have at rest, and running

if i recall anything less than 9v no load it's toast and running should be 12-14V

Check your earth connections - if there corroded, they can cause high resistance - less current to flow

 

[Gelandestrasse]

Condolences for your loss.

As your battery died before you laid it up you have had the snag for a while. To make electrics less wizardry, I recommend Rick Jones's "Classic Boxer Charging" book available from Motorworks or sometimes on ebay and maybe other places.

To help you we need a little more info. However, if your battery is not getting charged then that narrows down a few things - I would start with checking for corrosion on the 3 pin plug for the voltage regulator. If ok, the regulator may itself be suspect. There are ways of checking this, easiest is fit a spare.

But, now for the info. Assuming your battery is not getting charged by the bike, does your red charge light come on when you switch the ign on? If not, it's most likely the regulator. Does it come on and then go out when engine running? Again, regulator problem. If the light stays on it indicates you have an alternator or wiring issue. All this I have paraphrased from the mighty Rick Jones's book.

 

[Lewis1965]

Wow...Thanks for all the input fellas...I am going to have another go at things this weekend and will get back to the forums after...I am still learning (albeit I have had the bike for nearly 30 years) and I tend to figure out how to deal with issues when they happen...

Thanks again fellas

Lew

 

[Lewis1965]

A thing I noticed is that I have 2 coils for the 4 spark plugs as the bike was twin plugged about 10 years ago...When I took the tank off the other day to check after I got the new battery I saw some brown tar residue that had come from one of the coils as if it had overheated at some point...Given that the battery had run dry I am wondering if there had been too much power coming out of the alternator and frying things?...

Maybe buy a voltage rectifier from Motorworks and a new coil...would do the trick?

Thanks again

 

[Gelandestrasse]

Lewis, although the VR is a very likely cause, and having a spare one is always a good idea, your latest thought does not fit the symptoms in your first post.

However, over-volting (VR not working and allowing alternator output to 'touch' all bike systems including the battery) would kill a battery (ask me how I know) if not picked up very soon, and (if my transformer theory is correct) seriously overload your coils (my standard coil survived a couple of days of over-volting and is still working but now I am worried!).

But then, to fit your (first post) symptoms, the VR would need to then fail (again) open circuit - unlikely? So many other things could contribute to this, it is wise to work through the 'light on/light off - ignition on/off - engine running' process outlined in my last (from Rick's book) as that will pinpoint your issue. It takes seconds.

 

[Lewis1965]

Had another look today...The red battery light comes on (nice and bright) when I turn the ignition key and 'neutral' light comes on...Then I turned the engine over and both lights go out on dash...but I am not getting any spark now from any of the 4 spark plugs...so bike doesn't start...

I checked the 2 connectors coming out of the 2 coils and I'm getting no reading from one and the other one (that had some discharge out of it) the connector came out of the coil (below)...So I think both coils have been blown...I'll get 2 new coils...but I'm reluctant to replace both of them immediately because there must be an underlying cause that will blow 2 new coils should I fit them

I'm thinking that somewhere along the line the bike has drained a battery over a short time and blown 2 coils too...so what part of the electrics would do that?

I bought a spare diode board (used) from Motorworks....I'll fit that

Sent off for 'Classic Boxer Charging Book' by Rick Jones....

Thanks again

 

[Gelandestrasse]

The most likely answer to your question is the voltage regulator. The next most likely is the diode pack and the VR. If you are buying coils a VR is not much on top.

The fact that both lights go out when trying to start is nothing to do with the state of charging system. You need to observe the off condition and the running condition to diagnose the charging system. I think there is a load-shedding relay that turns most things off (apart from the starter and ignition) when you try to start the bike, for obvious reasons.

 

[Lewis1965]

It lives....IT LIVES!

Bought a used diode board from Motorworks...Got a couple coils...and fired the bike up...Fired straight away and ticked over without much fuss

I'm now getting a reading on the battery that goes up to 13 plus on tickover....so I guess that is now charging...Hopefully all is good...

Big thanks for the help here...Reassuring to know there's folks who know what they are doing with these old steeds and are happy to give advice...

Regards

Lew

 

[Gelandestrasse]

Glad you got it started. Put the multimeter on the battery and rev the engine to 3000-4000rpm and make sure you don't go about 14.5VDC. If you do, the VR is up the swanny.