Topic: CB500 charging - what is normal?

[CBKY]

Hey guys,

It would appear that I have some issues with my '72 CB500 electrical system. After charging to full with a trickle charger, I will lose all power after about 100 miles worth of 10-20 mile trips around town. Most trips involve relatively frequent stops for lights, etc., and cruising RPM generally stay between 4,000-5,000. Low beam headlight is always on.

I've searched and found some very helpful information for diagnostic testing (especially from TwoTired here http://forums.sohc4.net/index.php?topic=134465.msg1510391#msg1510391 ), but want to make sure I understand what I should be expecting before I get to work on fixing the issue.

I am assuming this is irregular, but I am new to motorcycles and especially new to 40+ year old machinery. Should the bike be expected to stay charged indefinitely with frequent riding? How often should it need to be placed on the charger?

I apologize if this a frequent question, but I appreciate any help in advance!

[flybox1]

How good/new is your battery?
Run thru the battery tests/@ the various rpm's and report back...

Begin with problem verification and characterization with recorded data.
A -- Fully charge a known good battery.  Let it rest for 2 hours, off the charger, and measure the battery voltage.  (Target is 12.6-12.8V.)
B -- Start the bike and measure the battery voltage at idle, 2000, 3000, 4000, and 5000 rpm.
C -- Repeat the measurements of B with lighting off.

[CBKY]

It looks like the battery may be part of the problem. It came with the bike when I bought it a few months ago, so I'm not really sure how long it has been in there. Here are the results I got from running the tests:

A: Battery isn't known to be good, and hadn't rested off the charger for two hours. Nonetheless, the voltage read 12.24 originally and then 12.01 after running long enough for the tests.

B/C:

lights off:
idle: 12.14
2000: 12.70
3000: 12.98
4000: 13.38
5000: 13.70

lights on:
idle: 12.19
2000: 12.41
3000: 12.55
4000: 12.60
5000: 12.70

high beam:
idle: 12.07
2000: 12.26
3000: 12.38
4000: 12.47
5000: 12.48

Additional information that might be of interest: When the electrics died while I was riding yesterday, I was able to switch the lights off, kickstart it, and it ran perfectly fine without lights. When I warmed it up today and disconnected the negative from the battery, it died immediately.

[TwoTired]

The stock battery is rated for 12AH.  It's no coincidence the the charging system is rated for about 12.5 Amps.

@ 3000 RPM and above, the bike should run indefinitely, keeping the battery at full charge (assuming it started off nearly so).
The stock bike normally draws about 10 amps with everything turned on.  At idle speed, the charging system can only make about 1/3 of full power. which means the bike draws power from the battery during times of deficit production from the alternator.
If the charging system can only make 4 amps and the bike demands 10A, the voltage falls, and the spark stops.  This is why the bike dies when disconnect the battery while the bike is idling.

It also matters if your headlight uses the stock 40/50 watt consumption and not some higher watts(brighter) replacement.  It matter if you have replace ignition components with low ohm coils that draw more power, and/or a dyna-s that doubles the power draw of any coil installed on the bike.


The numbers show your battery is certainly unknown and began the test in a dodgy condition with no more than 50% charge state.  Even a good charging system will take 5-6 Hours to peak that puppy up to full and will depress the charging system readings until, the battery has increased it's voltage.

Garbage in = garbage out.

Take your battery in to be load tested.

But, either your system is drawing more power than stock battery consumption and components, or your alternator isn't making more power than the battery and bike are consuming.

[cadman]

You are fairly good with the headlight off. Many of these bike were built before the requirement for "headlight on all the time requirement" which was about 1978.

[iron_worker]

TT is right that 12.24V to begin with is not "fully charged." You may have prematurely killed your battery by fully discharging it several times. Lead acid batteries tend to like to stay at 80% charge or above (which is why the alternators are designed to charge all the time).

Try charging your battery one more time. After it's done, unhook it from the charger and let it sit for 2 or 3 hours and then measure the voltage. The voltage should be between 12.6 and 12.8V and shouldn't drop below that over the next 24hr. Otherwise, you could take your battery to be load tested as TT mentioned which is a better indicator of actual condition.

Your voltage should come up to at least 14.2V at the higher rev ranges and the regulator should limit it to 14.6-14.8v, however, if your battery is low to begin with then your charging system is working double time to catch up and the voltage readings won't come up as high as they should ... As TT mentioned.

So ya, basically 2x what TT said. lol

IW

[CBKY]

Thanks for the replies everyone. I left for vacation a couple of days ago so I am not near the bike right now. As soon as I get back, I'll check the battery out and see what I'm dealing with.

[CBKY]

Back from vacation (and a few busy days at work) now, so I apologize for dragging up a thread from a couple of weeks ago. I took the battery in and had it tested - it checked out fine. Next step then is to repeat the voltage tests with the battery fully charged, correct? I am not sure what exactly the electrical system has gone through in the last 42 years worth of ownership, so it is very possible that it is drawing more than the stock bike would have. I have been looking into replacing my headlight and taillight with LEDs to get the power draw down as well as increase the brightness of my lights a little bit, which I think would at least lessen the issue.

[strynboen]

normaly there goes abaut 2 years betveen extern tharting...and then only after i have worked on the bike ..and used a lot of power vith engine off..
they can support them self even with 55w front light..used inn/aut of city

[Deltarider]

they can support them self even with 55w front light..used inn/aut of city

Easily, later models were standard equipped in Europe with 55/60 Watts halogen.

[Airborne 82nd]

Back from vacation (and a few busy days at work) now, so I apologize for dragging up a thread from a couple of weeks ago. I took the battery in and had it tested - it checked out fine. Next step then is to repeat the voltage tests with the battery fully charged, correct? I am not sure what exactly the electrical system has gone through in the last 42 years worth of ownership, so it is very possible that it is drawing more than the stock bike would have. I have been looking into replacing my headlight and taillight with LEDs to get the power draw down as well as increase the brightness of my lights a little bit, which I think would at least lessen the issue.

Yes see reply #1 or do this again (Battery isn't known to be good, and hadn't rested off the charger for two hours. Nonetheless) and get nowhere.

[Jerry Rxman Griffin aka MuthaF'er]

You had the battery 'tested'. For voltage or load testing? Load testing is imperative. I use Advance Auto Parts for this. Many/most places don't have the proper equipment to Load Test one of these small batteries.

KY, huh?! Red or Blue?

[Spanner 1]

Hey Griffin, no politics... lol!
OP seems for sure the system is not charging at the proper ( full ) rate.... historically this is usually caused by poor and failing electrical connections in the charging circuit. That big old 8-way connector ( has yellow, yellow, yellow, white. green , purple/red ) is often the culprit and sometimes the connection under the alternator cover...... mostly fixed by attention to connections........ good luck !

[CBKY]

Honestly, I'm not sure what test they ran on the battery. I took it into an O'Reilly's. I'll rerun tests and look into the connections in the charging circuit. Thanks for sticking with me as I try to figure this out, guys!