Topic: Charging system and shorts (read 3rd, 4th posts )

[kawazacky]

Hey y'all,

My CB550/650 was running relatively fine until last week, when the battery decided to die on a road trip. Now, I haven't had opportunity to check the system out because I've been in the middle of moving. I have a question though - can a short in the system kill the battery while the bike is running? I assumed that the charging system would keep the battery topped up while the bike was running, no matter what kind of a short I have, but the bike is NOT charging and something with the taillight circuit seems screwed up, because bulbs and fuses are blowing. So, could that be the charging problem too, or is it more likely they are unrelated?

[OldSchool_IsCool]

Hey Kaw,

Lot of things going on here!! A true short would pop your fuse instantly, so I don't think that there is a wire worn thru or pinched and grounding out. 

Popping a bulb?? hmmmm that sounds like a serious OVER-VOLT which could only come from your charging system.  Are the failed bulbs the correct type for your bike?

Have you noticed the need to fill your battery to top off the acid a lot?  Do you have a volt meter?  If so, what are the voltage readings at the battery when the bike is off, at idle and when reved above 4k?

[kawazacky]

Hrrrrm. The taillight bulb is the only bulb to go, though. But if you are correct and it's a charging system problem, this'd lead me to suspect a rectifier unit. BUT anyways, the electrolyte levels seem OK, and no, I haven't had opportunity to put my voltmeter on it. Unfortunately, when fumbling around with my battery charger in the dark last night, I put the battery on 10 amps, not trickle charge, so after 10 hours of that, it's probably toast now anyway. . .

[kawazacky]

OK! Here is what I have noticed so far. And for any who are wondering, my bike is a 78 CB550 with a CB650 engine in it. The wiring harness is original, but the rectifier unit may be off the CB650, I'm not sure. I never did the switchover, I bought it that way, and it worked fine for years. UNTIL LAST WEEK!

I was driving along the highway and noticed the bike wouln't rev. It seemed like I was running on empty, so I pulled over and gassed up. There was gas in the tank already, though, and when I went to start it, the bike wouldnt turn over, even though the engine was still hot. So I bumpstarted it and rode it about 95 kms home (important) after turning off most of my electrical options (taillights, etc). All the way home, the bike wouldn't rev very high (and don't ask specific rev ranges, I have a 550 tach on a 650 engine so it's all screwed up) but I was still able to cruise about 80 km/h.

I put the battery on a trickle charger for about 9 hours, put it in the bike, let it sit for a couple hours, tried to start it, and it wouldn't even budge. Strange! It should have had enough charge to at least tickle the engine over, but no luck. Is the battery draining while in the bike, and was the two hours spent sitting enough to deplete it? Read on . . .

I fully charged the battery again, and have since been riding back and forth to work (recharging while at home overnight on a trickle charger). But even though I'm only travelling about 20 minutes to work, the battery dies every night on the way home. I'm even turning all my electrical accessories off on the way in! How did I manage to get home from my long road trip, if now I can't even make it to town?

Furthermore, the taillight (which I would always suspect would be the LAST item to turn off) is always the first light in the bike to shut down. I've been pulled over by the cops twice this week because of it.

Once I get out on the highway, the bike won't rev high enough to get past about 80 kph on the way home. This is after a half hour of riding! My XS650 would go for hours on a freshly charged battery, even if the charging system was kaput. What's up?

Furthermore, my 7 amp accessory ? fuse blew last night (it's the first fuse in the box on the left hand size, not sure what it does, I'm guessing its for accessories) and I had an 8 amp fuse in it. My taillight bulb works intermittently,and I suspect it burned out at one point (there were pieces of filament in the bottom of the bulb, but maybe that was just from vibration). Could my rectifier be shot, overcharging my battery, and burning bulbs? If so, wouldn't my battery be really low on electrolyte? There seems to be lots of fluid in it now . . . .

I realize this is a long and convoluted post, but if anyone has seen this sort of thing before, please let me know.

Thanks!

[Tower]

In order of likelihood:

Go with your gut - reset the regulator to factory specs.

Also possible is a loose wire that will spike voltage when reconnecting-disconnecting - these voltage spikes can burn bulbs and fuses.  Similar to a loose line is a rusted connector.  It may be constantly trickling power to ground, and likely drawing more amperage than the fuse can carry.

Also possible but lesslikely, if a short is across lines rather than to ground, then the tail light line may be getting a constant overvoltage and burning the bulb.

[TwoTired]

Given the post history of cb650 charging issues on this forum, I would go straight to the alternator rotor and measure its resistance.
If less than 5-7 ohms, you've found your first problem that causes extra battery drain.  If you do have a 650 regulator, it's probably now toast, too.  As the alternator rotor's too low resistance drew too much power through it.
The third problem is getting over the shock of replacement component costs.

Or, you could be lucky and just need new slip ring brushes and a deglaze of the slip rings themselves.

Anyway, you are going to need a multimeter to take voltage and resistance readings to sort this out properly.

Or, just keep replacing components until it works again. $$$$

Be aware, deep discharging of your battery will severely shorten its life.  If not already damaged, the routine of constantly running it down will soon kill it altogether.

Cheers,

[kawazacky]

Errrr, I popped off the stator cover and didn't see anything charred, but that doesn't mean much I suppose. The rotor has already been replaced once by the PO, with one from a CB750 (they are the same). I have access to an entire charging system for about $150, so I might just replace the whole thing. That doesn't mean it'll fix the problem, though  - if it's a short, I don't feel like flushing that much cash down the drain.