Charging Problem

[Warbucks]

My 1985 R65 has developed a charging problem. I've noticed since last October (when the temperature was warmer) when I resurrected the bike that at low RPM after the engine is started (but still cold), the red charge light was on. If I advanced the throttle to about 1200 RPM the light would go off. When the engine warmed up the red light would go out indicating that the battery was being charged. Back then I had absolutely no problems starting the engine, even if I didn't do that for two weeks.

Now that winter is approaching, I find that the battery is lacking the amps to start the engine if left for a few days, or in some cases overnight. I tested the battery when it was apparently drained and found that it only had about 12.5 volts. Trickle charging the battery will give it the juice to start the engine, but after a day or two of not using the bike the battery will drain back to 12.5 volts.

I went on a 350 km run last weekend cruising on 4500 RPM and the battery was adequately charged. The next day I started the engine without any problems. The day after that, the battery didn't have the amps to start the engine so I had to recharge it again from 12.5 volts. I then rode the 350 kms back home cruising on 4500 RPM. After an hour and a half into the trip I stopped to stretch my legs for 20 minutes, then resumed the trip without any problems.

The battery is about 6 months old. I know that its the older type, but it should last a lot longer than 6 months. The voltage regulator and everything else is all original (31 years old). For that reason and the fact that the battery does not seem to be charging at low RPM, I'm assuming that the charging system isn't working properly.

Can anyone give me some clues how to correct this issue?

[thrang]

The charging system on a standard R65 is not a complex system so pretty easy to fault find.

What voltage are you getting over the battery with motor running at 3500-4k rpm? You should be getting between (ish) 13.5 and 14.5v. If its low then have a look at your alternator- brushes are most likely issue and you can see if they are worn. If the brushes are fine, you can test the alternator but if you're unsure how to do it get a spark to do it for you.

If its reading over 14.5 then its over charging and I'd replace the regulator although if it was over charging an old lead acid you should have noticed low battery fluid levels.  

If the battery is charging fine on the bike then.

With the battery fully charged leave it disconnected from the bike and next morning check the voltage and ampage of battery in comparison to what you had after charge. If the batt has significantly discharged then you know its the batt, if the battery has held charge then its losing overnight on the bike this will probably be parasitic drain through a knackered diode board - replace it.

There are many people better at electrics than me on the forum but hopefully I've pointed you in the right direction.

[montmil]

You may also have the battery load tested at most any auto parts stores for no cost. Guessing by "older type" you mean a wet cell battery. Those batts can often sulfate and fail. You might try kicking it by charging at a higher amp rate than the usual three-quarter amp from the trickler.

And what gentleman Shaw says.

[Barry]

The battery is about 6 months old. I know that its the older type, but it should last a lot longer than 6 months. The voltage regulator and everything else is all original (31 years old). For that reason and the fact that the battery does not seem to be charging at low RPM, I'm assuming that the charging system isn't working properly.

Can anyone give me some clues how to correct this issue?

The lack of charging at low RPM is what you would expect after starting a bike with a partially discharged battery. Once it's been run long enough for the battery to be fully charged the charge light should go out at low revs and I think you are saying it does.

The real issue is why does the battery get discharged ?   It's either an inadequate charging voltage or the battery is being discharged some how.

You can easily check the charging system by measuring the voltage across a fully charged battery while revving the engine. Voltage should rise to 14 volts or close.

Assuming charging system is OK then only 2 possibilities:

The battery is self discharging which is normal for and end of life wet cell but very unusual for a 6 month old battery.    

Or the bike has a fault causing a permanent current draw.  A faulty diode board can do that.

First thing I would do is fully charge the battery and then disconnect it so that you can test for a current draw with everything switched off. Alternatively just leave the battery disconnected for a few dyas and see if it discharges.

[thrang]

And what gentleman Shaw says.

Gentleman Monte?  I don't know if I am offended or delighted.

[montmil]

And what gentleman Shaw says.

Gentleman Monte?  I don't know if I am offended or delighted.

Try harder, Tony. Either way.  

[Bob_Roller]

When the ' GEN ' light goes out, it doesn't mean the battery is being charged, it just indicates the charging system is working  .

Until the engine rpm's get to around the 3000-4000 rpm area, the charging system is just creating enough power to operate the electrical systems in use on the bike, usually not enough to do any real charging to the battery .

I have a voltmeter on my Guzzi, factory installed, it is a great source of information on how the charging system is operating, you can catch an issue, before it becomes a big problem .

When you can get around to it, if you haven't already, go through the electrical connections and check for security and corrosion, this seems to be a common problem among older bikes, depending on the environment the bike is operated in .

[jonathanrowley]

A 12 volt battery requires usually a minimum of 13.8 to 14.4 volts to achieve a complete charge.

This range depends on climactic conditions (temperature) and also the design and overall sulfation state of your battery.

An old sulfated battery with shorted cells will not re-charge to ~14.0 Volts !

Therefore the battery is the basic foundation to begin “tuning-up” the charging system’s to it’s optimum performance.