Strange fluctuating voltage readings

[azr]

Hey all. I'm helping someone out with their recently purchased 79' 1000E. Put in a new Stator from Steve, Reg/Rec from Duane and am having some odd readings. When I'm testing the charging volts at the battery the numbers will spiratically drop, ie; be sitting at 14.7 at 2500 or 5000 then hit 10V, back to 14.7, then 6 volts and back to 14.7, etc.... I've tested 2 multimeters with the same issue and made sure my meter connects were perfect, I even put in a known good Reg/Rec and have the same results. I was having an over charging issue until I figured out the org/white wire to the rear brake for the sense wire has low voltage, so for the moment I've connected the sense wire to the batter + until I find an org/white wire with close to 12V. Is this dropping voltage a problem?

[JTGS850GL]

Where are you measuring the charge voltage? If it's across the battery terminals then I'm having a hard time believing those readings unless the battery is totally discharged. How long does the voltage spike low?

[azr]

I'm measuring across the battery terminals. Battery is fully charged, 12.9-13.0V sitting. The voltage drop only stays for a split second, maybe half a second, likely less. Then right back to the 14.7. I haven't tried swapping battery's yet as the one in the bike is new from the PO.

[azr]

Ok, checked a bit more. The battery reading will not fluctuate until I start the bike. It does it when testing directly to the battery, and as well if testing the voltage at the org/white for the rear brake light, where I would normally connect the sense wire. I'm guessing I have a bad connection somewhere..........

[posplayr]

You can be sure that the battery voltage itself is not changing that much, without a fire. There is apparently some type of EMI coming from the bike causing the jumps. Wrap some tin foil around the leads and the meter with teh face away from the bike. Does it still jump?

It could be that the shunting of the stator is causing the EMI and it might be made worse by a potentially failing stator. I know for a fact that there are large spikes associated with the chopping on and off of the R/R. Shorting and non shorting a stator is bound to cause more. And if the stator is shorted and then insulation breaking down and shorting further then it could be the source of the higher EMI that is affecting the VOM.

Do the Revised Phase B stator tests to see if you can get a clue of insulation break down at 5000 RPM leg to ground.

[azr]

It's a brand new stator from Steve, he's got a guy that rewinds them. I'll do the tin foil thing and post back up, along with the revised phase b results.

[posplayr]

It's a brand new stator from Steve, he's got a guy that rewinds them. I'll do the tin foil thing and post back up, along with the revised phase b results.

The other form of EMI is the ignition especially if you have bad wires.

[JTGS850GL]

My guess is you're seeing the meter re-ranging during voltage spikes causing the reading to jump for that split second. The numbers you're seeing are not real measurements but rather short duration measurement errors. You may be getting high voltage spikes from a poor connection to the sense line causing the regulator to bump up the voltage or as posplayr said it may be a failing stator throwing a lot of spurs on the AC line.

[azr]

Ok, this is really starting to tick me off. Went out to do the tinfoil thing, now the bike will not charge at all???? tested the reading again from the stator, 1.4ohms on all 3 readings, infinite resistance on all three and three equal readings off approx 78. arrr.......

[bwringer]

Could be measurement error...

Before you start serious hair pulling, try a different meter. Or change the battery in your meter.

[posplayr]

Ok, this is really starting to tick me off. Went out to do the tinfoil thing, now the bike will not charge at all???? tested the reading again from the stator, 1.4ohms on all 3 readings, infinite resistance on all three and three equal readings off approx 78. arrr.......

It doesn't look like you did the leg to ground test (at 5K RPM) as described here.

A revised test is at this link; The actual test is on Page 6 of 9. We added the leg to ground AC voltage test as this helps isolate insulation breakdowns to ground using the relatively high 60-80 VAC stator voltage when it is open loop.

Link to Revised PHASE B of Stator Pages with discussion of testing methods:
http://www.keepandshare.com/doc/3977...4-pm-649k?da=y

[azr]

I've already tried a different meter with the same results. I just put in a different battery for the bike and the charging has returned??? The voltage dropping remains though. You know, some days I just want to kick them over. I'll try the tinfoil and revised phase B test. Interesting point about the ignition, the bike still has the points system on it and I had to put in a relay for the coils.

[JTGS850GL]

Still think you're just seeing switching transients at the meter. Just for a sanity check, where and how are each of the R/R wires connected. Pics would be very cool.

[posplayr]

I've already tried a different meter with the same results. I just put in a different battery for the bike and the charging has returned??? The voltage dropping remains though. You know, some days I just want to kick them over. I'll try the tinfoil and revised phase B test. Interesting point about the ignition, the bike still has the points system on it and I had to put in a relay for the coils.

Sorry for not clarifying earlier, If the tin foil has no impact then it is not Radiated emissions but conducted emission. The ignition would be the primary source of radiated emissions the charging system and especially a failing one would be a source of conducted emissions. That being said, switching 2- amps on an ignition coil obviously will generate some conducted emissions as well.

[posplayr]

Still think you're just seeing switching transients at the meter. Just for a sanity check, where and how are each of the R/R wires connected. Pics would be very cool.

Yes if trying to shield the leads twist them as in "twisted pair" and then wrap the foil. This is to rule out radiated EMI. Obviously conducted emissions will come right through to the test leads.