Topic: CB650 battery or charging issue

[ballinchestr]

I read a lot of threads about this, seems like a common problem, but I want to make sure that I've diagnosed it correctly. The bike is a 1981 CB650C. I replaced the battery almost 2 years ago, and when I pulled the bike out for the season last week, I topped up the cells with distilled water. (a couple were an inch or so under the mark. I took decent care of the battery, and it's not too old, but all the evidence points to it. Starting with a fully charged battery, riding the bike for pretty much any distance will kill the battery.

Before testing battery voltage, I tested resistances at the rotor and stator.

between sliprings: between 3 and 3.5 ohms, no continuity to ground
between yellow stator wires: two were around 0.8 ohm, the other around 1 ohm, none have continuity to ground

After charging, the battery will read between 12.7 and 13 volts. It drops to about 9.5V while starting, and read the following voltages at different RPM.
(headlight on low-beam)

idle: 11.7
2000: 13.0
3000: 14.3
4000: 14.5
5000: 13.5 to 14 (was hard to get a solid reading here)

Then I turned off the bike and immediately read the battery voltage, coming out at 12.19, and the bike failed to crank over.

The resistances seemed okay to me, the rotor's was a little low, and the stator's a little high
The running voltages seem okay? Since it cut off around 14.5, does that indicate my regulator is okay?
It seems that I just need to replace the battery, but I want to make sure I don't need anything else before I drop any money on it.

[scunny]

yes your rotor readings look a bit low, but that could be the accuracy of your meter.
Looks like it's charging.
The battery isn't holding a charge.
The important bit... I topped up the cells with distilled water. (a couple were an inch or so under the mark)
I would replace the battery.
 

[ballinchestr]

Glad I included that bit, thanks for the tip. I think I'll hook up some battery tender leads to keep the next one in better shape. Why do you think it died so fast? It could be my weak rotor, but still, I've heard batteries typically last a lot longer.

[scunny]

from your voltage readings, I see no problems in the charging circuit.
I have been using Mottobat AGM batteries for a few years now and I have no problems, no long winter storage tho.
Just a concern over some of the cells being low on fluid, some batteries don't like that.
For a no cost play to see if things get better, clean all the eletrical connections on the bike, especially the ignition and charging cicuits. also make sure your battery connections are clean and tight.
as a fwiw, years ago on a 500/4, my bike started acting up and losing power, I was riding at night with the headlight on. turned light off and bike ran better, so limped home in the dark. the wiring from the alternator was corroded and so no charging.
I think points are more forgiving of low voltage than the ignition system on the 650 ( I stand to be corrected on that)

[ckahleer]

I have the same bike as yours. and have the same issue. Probably the nature of the beast.
A week or so ago, I had the bike idling for a long time while setting ignition timing and syncing the carbs. The battery was close to dead by the time I got done.
At 11.5 volts while idling, the battery is being drained quickly. It really does not start charging until above 2K rpm.
I guess my solution will be to keep idling to a minimum.

[Flyin900]

If you can afford the extra for the AGM battery then go that route for sure. The fact that your cells were down a full inch possibly indicates the charging system maybe overcharging the battery at some point and boiling off the water. Clean up all your connectors associated with your regulator and rectifier, since the regulator may not be telling the electrical system to stop charging the battery when it is already fully charged.

 Once a flooded style battery gets low on water, or has suffered a discharge from sitting over 30 days or more without a trickle charger to maintain them, they will almost always give up the 👻 sooner that expected.

The AGM’s hold their charge better over long storage periods vs a flooded style and are maintenance free. As an added bonus they usually have better CCA vs a flooded one and last usually much longer. I have a older NAPA AGM battery in one bike that is 8 years old and still working. No lead acid flooded one has ever lasted that long for me, so I now always buy AGM when replacing the old style ones in my other bikes.

[ballinchestr]

I bought a standard Yuasa battery yesterday, and installed a lead for my battery maintainer on it. I will definitely be cleaning my connections, but I don't think it's an overcharging issue, as I only noticed the low levels after the bike sat for several months. Not sure what could've caused that, don't have too much experience with flooded batteries like this.

Oh well, it fired right up, and held its charge after riding for a while. Hopefully I'll get some more out of this one, as ill be plugging it in every time its sitting.

[scunny]

That's good news. Sometimes it's to easy to over think things, and you end up will a new rotor, rectifier, and still got a #$%* battery.

[Flyin900]

Only two things boil off the water and that is excessive heat in a very hot climate, or overcharging of the system. I still run a few flooded ones that are still working and they can run more than a season with no change to the fluid level. I live in a moderate climate and every connector on the bike has been taken apart and fully cleaned when I do a rebuild/refresh of any bike I purchase.

Just a suggestion to keep an eye on the battery fluid level over the season to see if it drops below the low level mark on the case.

Apparently the CB650's do have a rep for rotor issues over time with heat as the culprit. The Yamaha XS 650 rotor will fit the Honda crank as a replacement and bolt right up and is apparently more robust. It is certainly a lot cheaper to buy vs a used or new Honda one.

[ballinchestr]

Good insights, I'll definitely keep an eye on the fluid levels. I don't think I'm out of the woods yet though, unfortunately.

I rode the bike for a while today, stopping several times. Each time I started, I did notice that the crank-over wasn't very strong, even though it started. I rode it hard on the way home, and after shutting it off, I thumbed the starter, and it started but just barely. The ride was around 20 miles, and I started it with a fully charged, brand new battery. Something is definitely still wrong. Given that my charging system seems to be okay, could it be shorting somewhere, or something wrong with the starter motor? I'm gonna start tomorrow with inspecting / cleaning the connections in the starter, charging, and ignition circuits.

[scunny]

What state of charge (volts) is your battery now ?
One thing that can upset starting the 650 when warm is the solenoid. Had that happen a few years ago. managed to pull it apart enough to dress the large starter contacts. The next time it happened I bought a cheap replacement , cost about $35 NZed. No problems since.

[scottly]

4000: 14.5
5000: 13.5 to 14 (was hard to get a solid reading here)

The "hard to get a solid reading may be a clue. The 650 has brushes and slip rings to energize the rotating field coil, just like a normal car alternator. Failing brushes can cause intermittent charging. Also, you mentioned the reading at the was low. What is the normal resistance for the field? Too low of resistance can overheat the brush holders.

[ballinchestr]

I think you could be right about the solenoid. I measured the battery voltage at 12.69 today, rode for about 10 miles, and it came back at 13.01 afterwards. I then started and stopped the engine three times (without trouble), and it measured 12.7 afterwards, going up 0.01 every ten seconds or so with the engine off. I think this means my battery and charging system are both okay.

Last summer the solenoid wasn't working smoothly (it was the original one) so I replaced it with a cheap one from ebay. I would have bridged it to see what was up, but the bike was starting fine so I don't think it would have been a conclusive test. I guess I'll just have to keep an eye on it, and keep the battery on the tender just to be safe.

[Flyin900]

Just a FYI on your solenoid replacement if you chose a cheap Chinese EBay one with the build in blade main fuse you may want to reconsider that choice. There have been reports on various forums of some of them sticking closed when activated and ruining both the battery and starter on the bike.
Aparrently they are not up to carrying the cranking amp load and weld themselves closed and won’t disengage when the starter button is released.

In regards the your electrical system possibly overcharging the battery. There is a sensing circuit built in that is supposed to sense when battery is fully charged and shunt the excess current away from continuing to charge the battery. So doing a test to confirm your getting a lower voltage at idle and a increased output at 4K rpm does nothing to confirm that circuit is working. It just shows your system is capable of charging.
So keep and eye on the fluid level in the battery over the season and if it’s evaporating off regularly, it could be a sign your system isn’t working as intended.

[ballinchestr]

In regards the your electrical system possibly overcharging the battery. There is a sensing circuit built in that is supposed to sense when battery is fully charged and shunt the excess current away from continuing to charge the battery. So doing a test to confirm your getting a lower voltage at idle and a increased output at 4K rpm does nothing to confirm that circuit is working. It just shows your system is capable of charging.
So keep and eye on the fluid level in the battery over the season and if it’s evaporating off regularly, it could be a sign your system isn’t working as intended.

In this case, if my battery is regularly evaporating its electrolyte, would replacing the regulator/rectifier be the best course of action? (Since everything else in the charging system seems to be working ok).

[scottly]

In regards the your electrical system possibly overcharging the battery. There is a sensing circuit built in that is supposed to sense when battery is fully charged and shunt the excess current away from continuing to charge the battery.

That's not quite how it works on these bikes. When the regulator reads a certain voltage, say 14.5 for lead acid, it starts reducing the current to the field coil to limit the voltage from going higher.
Permanent magnet charging systems use a shunt type regulator.

[scottly]

I guess I'll just have to keep an eye on it, and keep the battery on the tender just to be safe.

Keeping a battery on some "tenders" can slowly boil off electrolyte...