Motorcycle Repair: Charging System, yamaha virago, regulator rectifier

Question
QUESTION: I have a 1986 Yamaha Virago and the battery doesn't hold a charge very well.  We just replaced the Stator and the Rectifier checked out ok, the battery is new.  The voltage coming off the Stator with the bike running at 2000rpm is 20v and the voltage at the headlight is 9.7v.  The battery cables are tight, clean and look fine.

Hope you can help

Thanks, Karen.

ANSWER: Karen,
 All I can share with you is a few things that I would try...I dont profess to be an expert on the metric bikes....

 1. Start with checking the voltage at the battery with your motorcycle off...should be 12.6 for a fully charged battery...
 2.  What is the voltage at the battery (not the headlite)with the bike running?  It should be in the low 13's at 2000 rpm.
 3.  If the voltage is within spec at the battery, then there must be a voltage "draw" somewhere else on the bike...if the voltage is not what it should be at the battery , then you will have to go back the the regulator/rectifier and recheck , as well as checking the wire connections between the reg/rec and also reg/rec to battery....If your stator is producing properly and the rec is working as it should , and the wire connections are proper, the battery should have 12.5 to 13.5 volts,engine running.
 4 If the battery is receiving proper voltage and it is still not holding a charge properly, then you will have to do a draw test with a dvom(digital volt ohm meter).  Disconnect the positive lead of the battery..set your dvom to 10 amp(not all meters have this so please check).  Hook one lead to the cable(pos) and one lead to the battery post(pos). YOur meter should give you an amperage draw(if one is present).  If you have a draw, then you have a short somewhere in your wiring system.

Some final thoughts......Trace your problem from the stator outward(rectifier, then battery, then the rest of the bike,  the fact that your head lite only has 9.7 volts can be a separate problem .

 I hope this helps

Deron


---------- FOLLOW-UP ----------

QUESTION: Hi. This is Karen's husband Scott. Do you know if the electrical pocket testers used are RMS, peak, or peak to peak? It makes a difference and what reading you expect on the output of the stator. Correct me if i'm wrong. I remember from school if you read 21 volts AC RMS then you divide by .707 for a peak measurement which would be 29.7vac and then double that for peak to peak which would be 59.4vac.

Please advise.

Scott

ANSWER: Scott,
 I must admit that you have stumped me on that one..I do not know what the calculations are....You would have to call the dealer for the specs...he should be happy to give them to you , given  you just bought a new stator from him.  Im sorry that I dont have a better answer for you.  What is your voltage at the battery? (bike running)

---------- FOLLOW-UP ----------

QUESTION: OK. 1st of all I really appreciate your efforts !
I had 12.52vdc on the battery before starting. As the bike runs that voltage slowly goes down, which tells me that the charging system is not keeping up with all the lights. I then installed a current meter in series with the fused line of the bike just off of the battery. Not in the starter circuit of course. I turned on the key and get 6.99A of current flow. This seems normal after adding up the wattage of all the bulbs that are on. With the headlight fuse out I get a charge to the battery.
So this brings me back to the stator output again. With the stator unplugged and checking at the 3 wires I only get 21 vac @ 3,000 RPM's
Have you ever heard of the magnets getting week on the rotor I think it is called? The spinning thing that the magnets are mounted on? I put an allen wrench near it and it pulls the wrench to it rather strong.


Answer
Scott,  
 You have good battery voltage as a starting point...

 I do not have the specs for the stator output...if the dealer will not give them to you , you may be forced to purchase a service manual for specs and test procedure..

 I have not seen a rotor go bad on a metric bike.

You still may have  a rec/reg problem...if it is malfunctioning, it will not allow more voltage to the battery under a load.
 
 Karen mentioned that you replaced the stator...new or used?

 The draw that you mention is not excessive by any stretch.

 Some dealers will sell you copies of pages out their service manuals for a small fee, this may save you from purchasing the whole thing...its worth a try....I think that this is our next step...

Good luck
Deron