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Discussion Starter #1
Howdy-
I'm in the process of resurrecting my bike that I have owned for >30 years. I am trying to wake her up slowly. I already hit a big bump. I got it running and blew every bulb on the bike out. I checked the battery, it was long gone, dead beyond dead. I expected that, but what I'm wondering is, if the battery was so dead that it essentially opened from a circuit standpoint, would that cause a voltage spike to blow out all my bulbs? I put a new battery in and when the bike is running, I'm getting close to 9V on the battery. This seems a bit high to me. I would be much obliged if anyone out there with an old CB125S 6V system could do me the favor of measuring the voltage on the battery while it's running. Otherwise, I'm spending money on voltage regulator. Bad enough that headlight is gonna cost me some big $. Just want to make sure before I burn out everything again. I also don't want to burn the points while I'm at it.
I appreciate any and all information
Jim A
 

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Before you replace the regulator, verify all its connections are clean and tight, especially the ground connection. Without special equipment, they are hard to test. To save bulbs, just unplug them - a working regulator should stop the battery voltage at about 7.4V, with or without the lights on.
 

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If you've got an alternator or generator running, and either DISCONNECT the battery, or induce an open circuit, that alt/genset is going to spike the voltage attempting to keep current flowing. That's called INDUCTANCE, the desire of flowing electricity to KEEP flowing. It's the same reason you have a condesnor with a set of points -- to accept/suppress the ARC that comes with interrupting the flow of current to the coil.

So if your battery was open circuit, and you started your bike by jump-starting it off another battery, the moment you disconnected those jumper cables, ka-pow!

I wouldn't be panicked about seeing 9V on a 6V system while charging. It's a bit high, but on a 12.6 (nominal) battery charging of 13.8 or MORE is required to actually make the battery accept a charge. That's a 1.2 volt differential. You've got 3V, a bit high....perhaps worth replacing the voltage regulator, but...

If you've got dirty / corroded connections, it may be that the voltage regulator is only SEEING some of that 3V differential you've got. A bad ground, for instance, between the battery N frame, will make the alternator work harder, BELIVING it's only seeing 7V instead of the 9 it's actually putting out, because you've got a 2V voltage drop.

I've written a treatise (posted elsewhere here on MCForum) about voltage dropping, but the bottom line is clean all your grounds, battery connections, alternator connections, connectors, fuse holders, etc. andyour problem is likely to go away.

Hope this helps.
 

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Discussion Starter #4
Thanks guys, I appreciate the feedback. I can tell you that I have cleaned up some grounds (not all) and they were bad. So now I know where to start. I appreciate the feedback.
Hope to get to this by the end of the week, I'll let you know how I make out. I appreciate both of you taking the time to reply.

Jim A
:thumbsup:
 
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