Topic: Electrical and Charging Issues

[fletcha221]

I finally got my CB350F finished. I installed a new Dyna-s ignition, put some gas in the tank, twisted the throttle twice, and with one push of the button she fired right up. (the amazing part is the bike last ran in 1983) I spent 30 minutes adjusting the timing and idle settings, then ran the bike around the block a few times. By the time I had made my final adjustments, the battery was completely dead. So, I decided to let the bike idle and charge the battery. After about 15 minutes, I stopped the bike and tried to retart......still dead. Any Ideas? ALSO, I noticed that all of my lights are dim at idle, and bright when the motor is rev'ed. Is this par for the course?

Some pics before I put the carbs back on: http://cb350fcafe.blogspot.com/

[number13]

Sounds like your battery may dead, but the
good news is your charging system is
in good shape!
How old is the battery?
Is it full of electrolyte?
Are the connections secure both
at the battery AND the frame ground?

[motorhead55]

Your bike won't charge much if any at all at idle. Besides you could overheat the engine idling it for that long unless you put a box fan in front of it. If the battery is new then charge it with a battery charger. Run the bike at 2500-3000rpm and put a volt meter across the battery. You want to see atleast 13.75 volts or more. My 550 seemed to be low on charging and as suggested to me, I went anf cleaned up ALL of my charging connections. It made a good difference.

[fletcha221]

Hey guys! I actually did have a fan in front of the bike when it was idling. To answer a few questions, the battery is brand new, all the connections have been cleaned. I went home during lunch today and kick started the bike. I spent a few minutes reving around 3-4 grand. The battery took a charge.....so I think the system is working properly, however, I will check the voltage.

My other other question about the headlight, lights, etc. Is this normal?

[TwoTired]

The alternator has a power output curve that peaks at 5000 RPM-ish.  The curve isn't flat, and when it spins at a low RPM, it makes much less power.
The SOHC4 with lights on draws about 10 AMPs or roughly 120W whenever the key switch is on.
The alternator can make about 150 Watts at 5000 RPM, and about 40-50 Watts at idle.  Bike still draws 120W at idle with lights on, meaning the battery is supplying the difference...until it is expended.

Your bike wasn't made to be sitting around idling, it was made to go out and ride around with some RPM on the clock.  Further, back when it was made, lighting was only used at night, allowing the battery to recharge much faster and not deplete as fast when idling.  Turn off the lights to get the battery to recharge faster.  But still, don't expect it to recharge at idle.

The lamps have a fixed resistive element in them.  The more voltage fed to them the brighter they get (until poof). 

A good battery at full charge (after resting) measures 12.6V.  A depleting battery reads less than that.  As it depletes the lights grow dimmer.
The bike will try to maintain the battery at about 13.8 -14.5v, if the alternator is spinning fast enough to do that.  This will have the lamps make more light.

[fletcha221]

Best reply ever. Thank you for your valuable input. I've spent a year building this bike, and you have put my fears to rest. Thank you!