Erratic charging voltage

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elefantrider

elefantrider

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With a multimeter on the battery posts and engine at idle, it is rapid fluctuating from 11v to 17v.

Is that due to a bad regulator or bad zeener or bad ground?

The bike, a '71 Commando, is all stock but the frame has been powdercoated.
 
Digital multimeter ? , if so then its more likely the multimeter is being interfered with by EMF from the HT side and your real voltage is fine. You need an analogue multimeter or a better quality digital one.
 
Ok but it works fine on my other Norton. Steady 13.5v voltage on that one.
On this one, after a long ride, the battery still wants to take a charge.

Will try another meter.
 
Had similar issue last fall , it was broken wire within the Sparkx stator , spent most of a day mining the stator wire , re-soldering and filling with epoxy .... next day while digging around found a used original rotor and stator in box on shelf clearly marked .... my fix has worked fine so far ... defined my issue with a clamp on type multi-meter and found juice in just one of two leads from stator ....
 
If your electrics are standard, at idle you should be getting no charge from the alternator (you use more power than you put in at idle)

A fully charged Lead Acid battery should be around 12.6 volts
At idle, I would expect to see 12 volts or just under.

If you are seeing peaks of 17 volts, it would suggest your zener diode isn’t working.

Before you throw it away, take it off, give it a good clean, and make sure the wiring to it is good.
Don’t forget it’s connection to your positive battery terminal is via the thread it’s screwed in by - make sure there is no corrosion around the threads - using copper grease as thread lube or better still a contact lube that will not act as an insulator but will still prevent corrosion is good.

When you reassemble, use your multimeter to make sure there is no resistance between you z-plate and the battery positive terminal.
 
If it was just erratic readings, could be a variety of causes. What made my initial inclination to blame the meter is that I can't see how you could have 17VDC at idle, regardless of what's wrong with other components. IOW, I don't think there's enough alternator output at idle to get the charging voltage to 17VDC. Also, the lowest voltage you would expect to see on the meter would be that of the battery itself. So any fluctuations would be between the existing battery voltage - let's say it's 12.4, up to whatever the charging system is producing. What is the battery voltage with the engine off?
 
A properly charged battery should smooth out voltage fluctuations below the batt charge level. Sporadic spikes over about 14.5-15v could be emf interference on the meter or possibly abad zener. Are you running resistor/suppressor plugs or caps? What happens when held at 2, 3, and 4k rpm? If you can see high volts steady, suspect zener. Can you swap it from other bike as a test?
 
Yes , I left out that my zeners are both lost in mail after being sent to a fellow member on here .. using a Podtronic R/R now , had a black box R/R (can’t remember brand) installed when my trouble started .... battery slowly died during rides until I was left coasting down hill to home .... battery was on tender so always had juice to start and Ride but as days wore on rides got shorter until almost stranded ....
 
Battery is at 13.3V, fully charged.

The cheap meter was not playing nice with this bike.
This bike has a lot of interference whereas my other bike does not.

Maybe it is time to bite the bullet and finally step up to a Fluke 88????
 
Alas, had the same meter and it did not pass the 3 meter drop test. Probably in a box with the rest of my “might need this one day” stuff.
 
I think the clamp on meter I borrowed to check stator leads was an older little used analogue Simpson brand .... it worked great compared to the $20 Canadian Tire MM I had been trying to use ....
 
Curious - I found a VTVM to be completely reliable for measuring oscillator voltage, etc where there was RF present. DMMs wouldn't work at all and would even cause an oscillator to quit working sometimes. Oh well...doesn't really pertain either way to Nortons - I just made the VTVM comment to be humorous - A Fluke 88 is what I use for everything, including modern tube gear. VTVM for working on old tube gear.
 
I like tube audio also and the old Simpson meter is pretty cool but I still want a Fluke.
They are rather pricey new, especially with all the accessories. I'll probably wait to find a good used one.
 
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