Alternator Brushes - so school me?

I've seen many times here that alternator brushes are a serious problem on our XJ's, and reportedly seem to be voodoo in fixing things that normally charging system stuff wouldn't have anything to do with. Can somebody explain this one for me?

I am asking seriously and not trying to be an a$$. If there is something else going on here on these bikes I want to know.

I have been a tech since before the XJ's were around and in my experience the charging system (generally speaking) maintains the voltage in the battery and that's it. The battery itself is where the the rest of the bike (car, truck, airplane etc) gets it's power to run the electrical circuits and that feed is 12 volts. If you have 12 volts at the battery then the thing will run, until the voltage drops below whatever the ignition (FI, computor etc) requires to do their job.

A healthy charging system will create a charge of somewhere around 14.7 volts to keep the battery "float" at 12 volts. The cells of the battery alone dictate how many volts the battery will output.

Is there something on the XJ's that "sees" the higher charging system voltage in order to run right? What is up here?

Once again, I'm asking seriously. Why is it that alternator brushes seem to miraculously cure many of these weird little problems on these bikes?

 

The Alternator is constantly providing 14.2 ~ 14.5 Volts to the system when rpm's exceed roughly 18-Hundred rev's.

The Battery is the sole power source ... needing to supply a constant 12V to make the bike run and power everything while the engine's running.

Unless the Alternator is in a healthy state. The battery will quickly fall below 12V and problems manifest.

Everything needing 12V begin to fade.
Headlight
Turn Signals not blinking
Eventually ... Coils and performance

Until you coast to a stop.
Try to Start the bike on weak battery.

The Alternator wants to keep the bike in the game.
It tries ... but, the Brushes are too short for solid contact.

They arc and burn the face of the rotor.
The bikes dead.

Instead of needing 25-Bucks worth of two 17mm long, Carbon Brushes ...
You need $450.00 worth of a new Alternator Rotor.

All you really need to do is peek at the little magic-fingers to see if they are up to handling the load.
Looking at them and measuring how long they are ... is free!

 

Are the alternator brushes on XJs a standard size? I was in the Sears Hardware today and saw some brushes for tractors and other lawn equipment. They were really cheap. Would any of these fit?

 

domroc:

Ask yourself this question.

Would the Yamaha Engineers be allowed to design the Alternator Brushes, that Yamaha sells, in little plastic bags, with a YAMAHA Sticker on the bag ... that you could cheaply find in a Lawn and Garden Equipment Store???

"Wheel of Fortune"

N_....F_CK_NG....W_Y

Wanna buy a vowel?

 

I'd like to buy an "E".



ROTFLMAO!!

 

Likewise!!

Rick you need to change your job description from "technical writer" to
Comedy Writer!

What a kick!

Dan

 

Okay, so I notice that since I have purchased my bike (I've put close to 500 miles on it since then), my turn signals are slow or get stuck when I am at a light and have my brake applied, however, they have always been this way. Is my alternator going bad?

 

My Seca 550 was doing exactly the same thing when I bought it. I replaced the alternator brushes and that solved the problem.

 

Kishkumen

If you have a voltometer, connect it to the battery. Read the voltage when the bike is off. Should be 12.5 v or more.

Start the bike. At idle the voltage should be ~14v. If that is not the case the battery is not receiving a full charge. If the battery is not receiving a full charge when you start using power (brakes, lights, indicators, horn etc) the voltage will drop and the performance of electically dependant devices will degrade - slow signals, stuck signal, low or no horn, dim lights, engine missing, etc.

So - start by checking the voltage. Then as a precaution - check the brushes size - if they are past the wear limit ? IIRC 13mm? then replace them anyhow as part of your regular maintance. (Sort of like how you replace brake pads before the pads wear out and score the rotors).

 

The Voltage actually doesn't (shouldn't) exceed 12.5V ~ 13V until 1,750 rpm.

Then, as the rev's increase above 1,800 ~ 2,000 the Volatge will head for
14+V with 14.2 -to- 14.5V being within specs.

At 2,250 (or so) the Constant Voltage should hold steady within specs.

Anything above or below specs needs to be investigated.

 

and therein lies the problem with my CBR. At idle with the fan and the lights she drains the battery. In traffic I can't keep enough revs to keep the battery fully charged... I need about 3000 rpm to make the 14v.

 

Add a switch to the High Beam wiring.

Such that ... when the switch is Open and the High Beam is selected ... the Headlight will be OFF.

During the day ... in stop-go ... Open the switch and select High Beam and Kill the Headlight!!!

 

Good idea Rick, but it wouldn't fly here in Minnesota. Motorcycles have to have daytime running headlights by law.

 

No ... no ...

When your stopped ... you Switch to High Beam ... canceling the Headlight.

As soon as you're in motion ... flip to Low Beam ... and you're compliant!

 

New here, have an XJ750RH Seca.

I've known about the 8K alternator brush maintainance, but kept putting it off for years and years since tha battery was charging fine. Recently out of guilt(the bike has over 20K miles), I ordered a new set of brushes and pulled the cover. Big surprise, the old ones were barely half worn. I put the new ones in anyway, but while searching the net, I ran across some posts about Goldwings having variable field alternators with electronic regulators. From what I understood, in these the regulator varies the field current, which reduces the output to only what's needed, resulting in much longer brush life. Apparently one other manufacturer did this, but was sued by Honda and stopped. Do some of the U.S. market XJ's have these in order to deal with always on headlights?

 

Welcome to the site al_xh750r, from what I understand all the XJ's have this type of alternator.

A quote taken from...... http://www.geocities.com/MotorCity/Speedway/7795/

"This bike uses Hitachi's three phase regulated alternator. What this means is, instead of rotating a permanent magnet around or inside stator coils, generating a voltage, the regulated alternator uses what is essentially a variable rotating electromagnet. This "electromagnet" rotor is fed a current which is adjusted to keep the output of the alternator between 14.2 and 14.8 volts (with no load)."

 

Thanks for the info. That would explain why my brushes lasted so long. In re-reading old usenet posts, it almost sounds like Yamaha had problems on the older XS series bikes and possibly carried over the maintenance spec to the XJs?

 

Here I am, bringing another old thread back from the grave (reduce, reuse, recycle!).

Yesterday, I pulled my brushes. Both were at or less than 10mm in total length, but still have several mm before the limit line. One is shorter than the other.

I know about the measuring brushes thing. I know the factory brushes have a wear limit line on them. That being established:

Is the limit line 11mm from the end of the brush when it's new?

If so, the brushes should be usable until the end of the brush reaches the line...?

If not, why have a limit line in the first place?


These questions are academic, as I'm sending Chacal some more money for a new set of brushes; as I like to say, Paranoia Pays. But, it couldn't hurt to ask, right?

 

The Limit Line is the minimum length the Brush needs to be ... to be under sufficient pressure from its Spring to MAINTAIN Contact withh the Alternator Rotor and NOT just be skimming the surface too lightly and causing an Arc to form between the Brush and the Rotor.

When the Brush is too lightly seated; there is an opportunity for an Air Gap to occur. When that happens, the Rotor Arcs to the Brush and the spot of the arc can begin to make the Brush chatter away form Full Contact making the problem worse.

The Rotor becomes scored or burned in places and the Brush; at Low RPM"s can havve the spot of the ark weld the Brush to the Rotor and Break it right off.

Having enough Spring Load on the Brush prevents the Arcing and insures that the Alternator will put-out full strength current during operation.

Burned Rotors are expensive hard to replace.
The Brushes are cheap in comparison and not too hard to renew!

 

So, going by what you said, the brushes are probably still useable. Screw it -- I'm swapping them anyway. I'll post some pics of my brushes later tonight.


EDIT: I tried attaching the pics, but it seems the site software is all full up and won't let anybody attach any more. I'll stick them in the gallery.

As an added note, I think I misread the tape when I was remeasuring the brushes; I thought the overall length was ~10mm, when it's actually closer to 15.