Test for the alternator

Ok, here is another question for you. I was riding on a 30 mile jog to home at about 11:30 pm last week. I turned on the brights, but the bugs were thick. So I turned on the bottom headlight. Great lighting. I then tried the brights too. BAD MOVE! I blew the fuse and was running about 65mph with a curve ahead in a rural area with no lights or farmhouses ahead. After slowing down and gearing down, I followed the curve and came to a church about 2 miles ahead. I had spare fuses, so I changed it and was back in business. Then on Thursday, the bike did not want to start and I ran down the battery. I put my main battery charger on it and I think it was bad. I was going to a funeral Friday night and the bike just died. I walked a few miles (don't wear cowboy boots when riding, my feet still hurt) and got a jump and limped home. When I used my trickle charger, it charged the battery right up. My son showed me in a magazine that if you have a bad cell in your battery, your motorcycle can miss out. I am not sure if the battery is bad or if it is the alternator.

Any ideas on how to tell???

___________________
82 XJ750J Maxim

 

A simple method to tell if your alternator is working:

Start the bike, let it idle really low and see how bright your hedlight is. When you rev it, the light should get brighter. If not, you may have an alternator or regulator problem.

Another simple test.

Start the bike, disconnect the battery. With no battery and a bad alternator, it will die instantly.

Hope this helps.
Chris

 

Get multimeter and test the battery voltage with the battery connected to the bike. Should be somewhere around 12.3 volts. Start the bike and check voltage again with bike running. Should now read somewhere around 13.5 to 14.5. This means your charging circuit is working.
If you still get 12.3 and the power is dropping then most likely the brush in the alternator cover needs replacing.

 

I tested the battery with my multimeter. It was showing 11.7 volts. I tested it running and it was between 13.8 and 15.2 volts. This morning, it will not start, and the battery is low again. So maybe I do need a new battery?

 

Yep new battery. I usually take mine to Auto Zone and have it load tested just to be sure. The 15.2 volts maybe a little high. I am weak on most electrical stuff so I hope someone else let us know if that is a point of concern.

 

I checked the XJCD and anything over 14.8 is indicative of a faulty R/R.
(regulator/rectifier). What this means is that the charging system is being allowed by the R/R to over charge and therefore burn up your battery. So far I haven't found a way to send you the page from the XJCD. I will keep trying.

 

Brushes ... You really need to check the BRUSHES ... right away. If they are "Short - out of specs" ... don't run the engine until you replace them. Brushes not making good contact will arc and scortch the alternator rotor.

Brushes are the #-1 cause for the all the symptoms you described. If there's evidence of the arcing ... "Bluing or dark spots" ... you can resurface the copper slip rings with "Glass Paper" ... lightly refinishing the surface following the rings in a circular motion.

 

Ok I will check on both items there tonight. When I went to start it yesterday, it would not start. So I bought a new battery. It fired right up today, but I kept the old battery. I will open it up and look at the brushes.

 

Ok so I put in the new battery. It ready 12.8 volts. When I started it, my multimeter read 14.5 volts. So I rode my usual Sunday 60 mile ride. When I got there, no problem starting again. I made a few stops in town, then I rode home (30 miles one way) Sunday night, I tried to start her and low battery (10.8 volts).

So I do have a charging problem ( and 2 batteries now) How do I replace the brushes? Any idea where I can buy new ones? I am about 45 miles from a Yamaha dealer.

Any and all ideas are appreciated.

 

Chris, your disconnecting the alternator suggestion unfortunately could fry the rectifier diodes. Under no circumstances should that step be taken. Older technology alternators on cars can handle it but bikes have very sensitive (gotta laugh at that one) components.
BlackHammer, your alternator is getting there with the 14.5 volts, but your loss of battery voltage after some fairly lengthy trips is puzzling. My humble advice is to obtain a copy of the Haynes or factory manual and hit the troubleshooting matrix, it would help you more than my guessing. I'm rummaging through my Haynes now and the voltage at 2000 RPM or better should be 14.5 (+/- 0.3)VDC. The book lists the following points:
Battery sulphation (you have already replaced it so this is moot, small note, make sure you put the new battery on a trickle charger, 1 to 2 amps max, for about 6 to 8 hours before placing it into service, it will extend it's life expectancy)
Battery leads corroded, clean and cover with petroleum jelly or terminal preservative.
Load excessive, got accessories? Too many of these and the alternator will not be able to keep up.
Regulator/rectifier failure, hope this isn't your problem, they are pricey.
Alternator generating coils open-circuit or shorted (I doubt this given your voltage output)
Charging circuit shorting or open circuit, my take on this is that you wouldn't have the correct voltage at the battery if this was the case so I'd ignore this one too.
Best I can sling at you without laying hands on the beast. Best of luck and keep posting details as you find them, we'll crack this gremlin.

 

Robert: I have the Yamaha Sevices manual. It lacks in the troubleshooting area for electrical. I remember a website that was dedicated to the XJ's electrical but I can't find it.
Addressing the Hayne's issues"
" The book lists the following points:
Battery sulphation --NA
Battery leads corroded, --I cleaned them
Load excessive, got accessories? --No accessories
Regulator/rectifier failure, ---- This is a possibility---

I will search out the RR. I have a Motorcycle junkyard at the other end ot the county that I may call and see if he has any.

 

Don't just shotgun it, test it out. There is a fine check out in the Haynes (sound like a broken record, sorry) and I would hate for you to pop in a replacement only to find that something else is wrong and fry your new part. Here is the link I have, think it might help. Good luck. http://www.geocities.com/MotorCity/Speedway/7795/

 

Another possibility could be eccessive electrical drain on your battery as your charging voltage appears good. There's an easy way to check:

Connect a multimeter in-line at the battery to measure a key-off current draw, it should be less than 1A. If it's greater, remove your fuses one at a time untill the you see a big change in your reading, the last fuse that you pulled will help you identify the circuit causing the drain, and you can troubleshoot from there.

HTH,
-Matt, CO

 

Brushes ... You really need to check the BRUSHES ... right away. If they are "Short - out of specs" ... don't run the engine until you replace them. Brushes not making good contact will arc and scortch the alternator rotor.

Brushes are the #-1 cause for the all the symptoms you described. If there's evidence of the arcing ... "Bluing or dark spots" ... you can resurface the copper slip rings with "Glass Paper" ... lightly refinishing the surface following the rings in a circular motion.

 

Rick

I have been scouring the forum for how to check these brushes and where they are located. Can you help me?

 

Rather simple. According to the wonderful Haynes manual laying here, your brush lengths should be no less than 10mm but no longer than 17mm (doubtful they are this long at this point in time). Now for the how to. Page 216, section 4, Figure 6.1 shows the assembly. I would assume (yes, I know what that means, I'm rather used to it) that the brush carrier is immediately under the alternator cover, located on the left side of the bike, just behind the cylinder block and under the carbs. Three cap head bolts as I recall. Pull them out and pull the cover. Then simply unscrew the brush carrier and your in there. Any questions?

 

Left side of bike ... as if you were sitting on bike.
Round cover to left of starter motor.
3-Fasteners.
Withdraw cover.
Brushes mounted to inside of cover.

Length: New = 17mm (0.67in)

Service limit = 10mm (0.39in)

Individual brushes have "Scribe" marking on them. (like tire wear bars)
If inspection reveals brush to be worn to (or close to) wear limit - replace.

Inspect rings on face of alternator for evidence of brushes at wear limit.
Bluing, burning -- pitting from arcing ... etc.
Clean-up rings with Glass Paper - (electric supply shop)

Burned or severely pitted slip rings will do damage to your electrical system -- (regulator; particularly)

 

Sounds simple enough. I will give it a shot tonight. I have just remembered that I blew a fuse 2 weeks ago with all of the headlights and brights on. I read that a fuse problem can cause similar problems to what I am seeing, so tonight will also be the conversion to spade type fuses.

 

Rick, your write-up is so much easier to follow than my own. I'm going to try to emulate your style, with your blessing I hope. Nicely done. Don't think I could replace you, but I would love to be as clear.

 

Thank you very much for the kind words. Imitation is absolutely the most sincere form of flattery!

I try to write it better than they do in the manuals. Sometimes, it has to get a touch wordy ... the manual is written for those who have wrenched a little bit.

For those who are diving-in to a project for the first time; it helps to be comprehensive without confusion.

I'm happy to know the information that I am passing along is doing some good!