Topic: 1980 CB650 charging issues

[Mentch171]

The brushes showed up today and the springs were noticeably stiffer than the old ones presently in the bike. I though that’s it, not making reliable contact with the rotor. I swapped them out, fired the bike up and no change. Only 12v ac on the yellow leads before the rectifier and low 13’s dc at the battery at 4000 rpm.

[TwoTired]

The battery's ( lead acid) normal voltage at full charge is 12.6v.  Anything higher than that and the battery is accepting charge.
 However, if the battery is not at full charge, the low charge current available from a working alternator. Won't raise the voltage to 14.5 v very quickly.

Are you checking charge voltage with a known good fully charged battery?  Are you willing to run the bike at 4000 rpm for 10 hours to charge a depleted battery?

Cheers,

[Mentch171]

Yes I totally agree but can you explain this to me?  After I changed the failed rotor, one ohm restistance, and saw 13.x volts at the battery while running why did the battery discharge and leave him sitting along the road?  I’m reluctant to return this bike to him since I’m seeing the same readings after the latest work I’ve done and have him sitting along the road again.

[Mentch171]

I tried an experiment, maybe it’s valid. I drained the battery (new lithium battery) down from full charge by leaving the key on for a bit. I brought it back to 30% charge according to my Pro-Logix charger, then fired the bike up. At 4000 rpm I still only see 12.9v at the battery. It’s not charging.

New regulator is marked 14.5-14.8v. Reinstalling the old regulator which tests good doesn’t change voltage either.

[TwoTired]

A discharged battery will hold the system voltage down until it is charged. 
The battery can sink and supply 200-300 amps instantaneously. The bike charging system can supply 14-20 amps tops.

This is why you test the charging system with a known good, fully charged battery.  The bike charging system is a slow battery refill device, not a device that will operate a starting motor all by itself, or dominate the system voltage incorporating a depleted battery..

When you have your off bike charger on the battery,what voltage does it have while reporting 30% charge state?

Alternately what is your battery voltage before and after adding your alternator output into the bike systems with it spinning?  And, if you watch the voltage of a depleted battery, does the voltage trend slowly rise indicating charging, or slowly fall indicating a discharge trend, while spinning at 4000 rpm?
Intananeous v readings give a momentary snapshot.  That voltage can be voltage trending higher or voltage trending lower.  This is why you test charging systems with a known good fully charged battery, as the battery should hold full voltage while under normal system loads, indicating that the charging system is supplying bike system power as well as a bit extra to keep the battery restored. 

Are you aware that depleting LiFePO4 batteries below a minimum voltage can damage them?  Has the battery you've been testing with been subjected to depletion abuse?  Can you test the charging system with a known good lead acid type that the charging system was originally designed to maintain?

Cheers,

[scottly]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

[Mentch171]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

That’s exactly what I did after replacing the brushes. No change from previous readings. I’m really starting to believe the stator is bad.

[Mentch171]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

Fully charged battery bike off 13.56v.  Bike running at idle 12.79v.

What ac voltage should I see coming back to the rectifier?  75v?

[scottly]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

Fully charged battery bike off 13.56v.  Bike running at idle 12.79v.

What is the voltage at 4000 RPM, starting with a fully charged battery?

[scottly]

What ac voltage should I see coming back to the rectifier?  75v?

Are you reading 75v with the stator connected to the rectifier?

[Mentch171]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

Fully charged battery bike off 13.56v.  Bike running at idle 12.79v.

What is the voltage at 4000 RPM, starting with a fully charged battery?

13.5v fully charged at 4000rpm

[Mentch171]

What ac voltage should I see coming back to the rectifier?  75v?

Are you reading 75v with the stator connected to the rectifier?

No. I’m only seeing 10-12v ac. That’s why I’m wondering.

[TwoTired]

Mentch, charge the battery to 100%, then check the battery voltage with the bike running.

Fully charged battery bike off 13.56v.  Bike running at idle 12.79v.

What is the voltage at 4000 RPM, starting with a fully charged battery?

13.5v fully charged at 4000rpm

If the battery isn't charging, how did its voltage get higher when you revved the alternator?

The spinning revs have an output relationship.
Not sure about the 650 but other SOHC4 alternators make about 1/3 of their max output at idle.
That's why the voltage sags at idle because the alternator can't overcome bike system load at idle rpm.  When the bike revs it can make more than the bike uses and the extra is used to recharge the battery. 

Your battery is depleting at idle because the bike is either using too much power or the alternator is too weak at idle rpm to make bike load power and charge the battery.

What has been altered on the bike to use more power than the stock one used?
Higher watt headlight perhaps?

If your particular 650 spends more time at or near idle with full electrical load, then yes, your battery will eventually deplete to exhaustion.  That is what your reported numbers show, and what is fairly typical of the entire SOHC4 fleet.  If you have selected a battery that has too little storage capacity, it will deplete quicker than a stock one when the alternator isn't being revved as expected.

Watch the voltage at the battery change from idle and increase the rpm slowly to 4000. At some point the battery volts will begin to rise off that low number.  That will tell at what rpm the alternator makes enough power to begin battery restoration.  If you must operate at too low an rpm, get a bigger battery.  You aren't going to change the alternator design characteristics with a replacement stator.

Cheers,

[Mentch171]

If the battery isn't charging, how did its voltage get higher when you revved the alternator?

The spinning revs have an output relationship.
Not sure about the 650 but other SOHC4 alternators make about 1/3 of their max output at idle.
That's why the voltage sags at idle because the alternator can't overcome bike system load at idle rpm.  When the bike revs it can make more than the bike uses and the extra is used to recharge the battery. 

Your battery is depleting at idle because the bike is either using too much power or the alternator is too weak at idle rpm to make bike load power and charge the battery.

What has been altered on the bike to use more power than the stock one used?
Higher watt headlight perhaps?

If your particular 650 spends more time at or near idle with full electrical load, then yes, your battery will eventually deplete to exhaustion.  That is what your reported numbers show, and what is fairly typical of the entire SOHC4 fleet.  If you have selected a battery that has too little storage capacity, it will deplete quicker than a stock one when the alternator isn't being revved as expected.

Watch the voltage at the battery change from idle and increase the rpm slowly to 4000. At some point the battery volts will begin to rise off that low number.  That will tell at what rpm the alternator makes enough power to begin battery restoration.  If you must operate at too low an rpm, get a bigger battery.  You aren't going to change the alternator design characteristics with a replacement stator.

Cheers,

Well I thought it was charging when I changed the bad rotor (1 ohm) for him because I saw 13.something volts at the battery back then. It didn't work out because it let him sit along the road again.  He was convinced other components failed too, regulator and stator.  I told him we'll try the regulator but stators rarely fail and his stator tests ok.

Absolutely nothing has been altered on this bike. It's as stock as they get. 

Maybe you're onto something with the bike being run too "easy", never getting the rpm's up enough to charge the battery. I don't ride it, it's not mine. I don't have, never have had this issue with my bikes not being run hard enough to keep a battery charged. Maybe the lead acid battery was on its way out combined with a failing rotor not charging. He replaced the battery with a small lithium battery. You might be right that the new battery doesn't have enough capacity.

I still question two things though. Why don't I see more ac voltage before the rectifier and also when the regulator is marked 14.5-14.8v I never see anything close to that voltage at the battery?

I have a lead acid battery in my shop that might fit. Maybe I'll see if that works better.

[scottly]

Temporarily remove the 7 amp headlight and 5 amp taillight fuses and check the battery voltage at 4000 RPM.

[Mentch171]

Temporarily remove the 7 amp headlight and 5 amp taillight fuses and check the battery voltage at 4000 RPM.

Two fuses pulled and I’m seeing over 13v at idle and 14.0v at 4000rpm.

[TwoTired]

Where does the rpm charging "knee" occur, with and without fuses?

The knee is the point where the alternator takes up the bike's operating load.

Below the knee the battery voltage falls, above the knee, it rises.

Cheers,

[scottly]

Temporarily remove the 7 amp headlight and 5 amp taillight fuses and check the battery voltage at 4000 RPM.

Two fuses pulled and I’m seeing over 13v at idle and 14.0v at 4000rpm.

Sounds like you've fixed the charging system. How long did it take at 4000 RPM to reach 14.0V? The electric starter draws over 100 amps of current, and even though it's only for a short amount of time, that power needs to be replaced. With the fuses removed, there is more power available to "pump" the battery voltage up in a shorter amount of time. 

[Mentch171]

Well I finally got around to putting this bike back together. The owner brought me a good lead-acid battery and I swapped it out with the small lithium unit. I had high 13’s to low 14v at the battery while running now. I’ll give it back to him to put some miles on and hopefully the problem is solved. Thanks for your advice guys.