Rectifier or alternator ?

lazyeye6

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you can only exclude the things that test bad~!!!!!

open the primary and see if the rotor is well centered when you roll the bike over. If the stator plates are rainbow colored that's a sign of overheating from rubbing between the rotor and the stator. SO,... you could be testing and be finding good voltage due to the battery being new, but your Rotor/stator may have over heated due to rubbing and be shorting out intermittently. That would explain the meter going back and forth

This was the situation of my bike when I bought it. The previous owner was charging it, going for rides, and having to truck it back home when the battery ran low. Eventually he wanted to get rid of it because he didn't want to work on the bike or learn, so I got it from him for $500. The rotor plates had that rainbow coloration from overheating due to rubbing from the rotor.

In the case of my bike, a '70 model, I have an ammeter wired into the harness, so I can clearly see if my stator is charging the battery when I'm riding....
But wait! There's more! An ammeter will only tell you how much the output of the alternator is. It cannot tell you how much the battery is being
charged in volts. There is a regulator in-between which transmutes (is that a word?) amps to volts at the battery. Charging at the battery must
be measured at the battery.
 
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We've all talked about this many times. An ammeter in particular shows direction of current flow. A person who has an ammeter on their bike and knows a little about it, can intuitively deduce whether their rotor/stator is charging by just revving up the RPM's and watching the needle move as the RPM's change. (or not move if it's not working)

As other people will point out, If a they have a voltmeter on their bike, they see that same sort of voltage change when they revv up their bike and may have the same intuitive sense whether their rotor/stator is working or not from looking at the change on their guage. Personally, I don't know how noticeable a voltmeter's movement is because I don't have one.

Positive current flow means your rotor/stator is working to some degree...
 

olympus

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Depends on the meter - a Fluke or HP DMM won't go bonkers, whereas a Harbor Freight cheapie might.

Are you sure your meter leads are across the battery, or are you measuring from a ground point to one battery terminal?
8-15 V (if it's real) is the range you'll see from the charging system with the battery disconnected. 8V at idle, 15 at rpm.
Fluke digital meters are what trade people use.... they don't go bonker. Cheap ones in Christmas crackers and from marker stalls aren't that good
 

gtiller

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@Kjell if you want to test your regulator/rectifier there is a guide here: https://granttiller.com/testing-your-motorcycle-rectifier

It will only take you a few minutes to do, and will give you peace of mind that it working.

I had dismissed it as being an issue, as you say in your first post that you are seeing 15 volts.
That is over your battery rest voltage, which says to me that your alternator stator is working, the rectifier part of your reg/rec is converting the AC output in to DC and the rectifier part of your reg/rec is clipping the voltage to around 15 volts (which is about normal for one of these)


Do you have the red warning light and the silver can assimilator on the bike?
The 3AW assimilator, when it fails (not if, but when - they are a well known weak point) can sometimes affect the AC output from your alternator stator.
If you have it on the bike, try temporarily disconnecting it, and see if that helps.
B2F7CE4D-558B-493C-8F42-5E616F419793.jpeg
 

Kjell

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@Kjell if you want to test your regulator/rectifier there is a guide here: https://granttiller.com/testing-your-motorcycle-rectifier

It will only take you a few minutes to do, and will give you peace of mind that it working.

I had dismissed it as being an issue, as you say in your first post that you are seeing 15 volts.
That is over your battery rest voltage, which says to me that your alternator stator is working, the rectifier part of your reg/rec is converting the AC output in to DC and the rectifier part of your reg/rec is clipping the voltage to around 15 volts (which is about normal for one of these)


Do you have the red warning light and the silver can assimilator on the bike?
The 3AW assimilator, when it fails (not if, but when - they are a well known weak point) can sometimes affect the AC output from your alternator stator.
If you have it on the bike, try temporarily disconnecting it, and see if that helps.
View attachment 17940
Gtiller.

No assimilator light I am afraid. I havent openened up the headlamp yet to check the cause of that. Having read all the bad stories about that particular system I bought a CWL system from improvingclassicmotorcycle that seemed very nice and easy to incorporate into the system. I have also bought a Boyer Powerbox but both these items were part of my plans for the winter.
For now I was hoping to use the bike as it stands until the winter storms arrive
 

gtiller

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If the light is not lit when your ignition is on, check to see if the 3AW is connected, it maybe causing an issue.
These things are nothing more sophisticated than the bimetallic strip that turns on and off your central heating - they are unreliable and don’t do well with the vibrations.

Your purchase of the CWL is good - I have fitted this on the MK3 and it works a treat.

If you follow my guide to testing your reg/rec this is done off the bike anyway, so you won’t be getting any interference with your meter.
 
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One of the cheap analogue multimeters might help with the problem in hand.

It seems unlikely that a fluctuation between 8 and 15 volts is really what is being put out by the reg/rec. That would be an unusual fault.
 
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Re DMMS: I went through DMMS like a hot knife through butter. It seems that they worked OK for a while and then just gave up, specifically when I needed them. I finally said "Screw it" and bought a Fluke 179 some years back. Frankly, I think I saved money buying the Fluke since I haven't had to buy another DMM since! :)

Or maybe saying that helps me justify spending nearly $300! :)
 
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Craig

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Had very similar symptoms last fall , followed gtiller’s advice and discovered a broken wire/lead within the stator , fun time mining into that stuff and fixing break , so far so good , but have lost a measure of confidence , eventually will install a new one ....
 

maylar

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Seems like sourcing an analog mulitimeter is harder than I thought. Since the only area I can fathom having to use it is the circuitry from the alternator to the battery I will go ahead and invest in a bench meter
Find one of these, used. Much much more versitile.
You have eBay over there?

Simpson 260 VOM
 

maylar

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Craig

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Guess I was lucky , a ride buddy had a clamp on analogue meter ( Simpson) and he was very familiar with it’s use , we were able to find source of trouble very quickly , in fact first wire from stator he clamped around while bike was running was pretty much toast , we then went through the entire charging circuit as described by Gtiller , ended up fitting new R/R as well for peace of mind , the faulty stator was branded Wassell and was not very old ....
 

Craig

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I had previously tried my k-mart digital mm and just got flashing non-sensible numbers , checked here , followed advice , found issue , spent most of day digging into stator and repairing broken wire and re-epoxying it , works so far ....
 

Kjell

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Ordered a Draper as per Kommando's recommendation. Should be here within a week or so. Very curious to find out where the problem is......
 

maylar

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And when we are talking about "any part of the charging system". The charging system is pretty much a rotor and a stator supplying AC and a rectifier/regulator doing the rest.
This is true. And the typical failures are the stator wires either at the stator itself or at the connections to the rectifier/regulator, or the R/R being defective or not connected to the battery. It's actually quite simple to troubleshoot.

Do yourself a favor while you're waiting for your meter and open the primary to take a look at the stator wires. They often break where they exit the epoxy stator. Then follow those wires to where they connect to your regulator. Depending on the location of the r/r there's often extension wires and associated connectors leading from the alternator.
 

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