Charging system woes...what now?

Alright, so I too am having charging system issues on my 1982 Seca 750 w/7500 miles.
When I start the bike, It cranks good, with a good battery in it (obviously) and starts fine. But, the headlight is really, really dim until about 3000rpm. If I try to have both the little and big light on simultaneously, it struggles. With the bike running, @ over 2500rpm, all I get at the battery is 11.8VDC

Here's what I have checked so far:
Green+Brown coming off the alternator: 6Ω
3 White wire to each other: .9Ω
As a constant, I measured my meter leads at .25-.35Ω
Then I checked the V¹ & V² at the R/R plug while it was joined, as per the manual.
V² @ Black(-) & Brown(+) = 11.4-11.8VDC
V¹ @ Black(-) & Green (+) = 4.2-4.7VDC

I know I am seeing a fail here, but is it the R/R or the Alternator?
I checked brush length, and they are @ 10mil or so, but I went ahead and resurfaced them and the rotor face anyways. Also, I visually inspected all the molex plugs in the system and they seem to be in good shape.

Show me the way XJ gods!

 

If the lights get brighter around 3K, it says your alternator is putting out. Did you measure the voltage at 3K? It should read around 14 when the alternator is putting out. You measured 11.8 volts at the battery at low idle. That is way low for a lead acid battery. (It's dead at 10 volts). It sounds to me like you have a bad battery. I'd remove and test it to see if it will take and hold a charge.

 

The battery metered for VDC at all RPM's is ~ 11.8. I am not getting a rise or increase in readings if I change engine speed.

 

v2 is showing you what the battery voltage is.
Which part is a fail? My xj has a different alternator but I had to find this out the hard way!

The stator sounds ok but the field (6 ohms) is twice what my manual says (My manual is a 600!!!)

It also gives 10mm as the brush minimum.

Make sure neither field or stator have a circuit to ground (A couple of people have shorted the alternator wires where they come through the gromet recently)

I also have a xj550 Yamaha genuine manual and checking this it actually shows v1 abd v2 the opposite way round and I am not convinced the manual is right!!

BUT. One of the readings is the battery voltage - brown and black. This should not go over about 14,5v.

The other is showing the voltage dropped (And hence current) in the field windings.

According to the manual, at switch on the value black to green should be less than 1.8v. As the engine starts and the revs rise, less current flows through the field (Because the alternator output goes up). The manual says the voltage on the green wire will rise to 9 - 11v as the revs go up.

Hope this helps - rather than confuses!

 

According to The Book, V1 should be charge voltage. As it so eloquently puts it:
"Switch on the ignition and note the reading of V2. This should be less than 1.8VDC (mine is 11.4-11.8). Start the engine and check that V2 reading gradually increses to 9-11 volts as the engine speed rises. The V1 reading should rise to 14.2-14.8VDC when the engine is started and should stabilize at this level despite variations in engine speed."
Then it goes on to say that if the readings are outside these limits then it's time to buy a new R/R (which I guess i skimmed over before).
So I am going to assume that I need a new R/R unless someone else has some insight into it.

Thanks all.

 

did you test this

 

If the Green to black reading doesnt change, then (As long as there IS a circuit througn Brown to Green) then the regulator is faulty.

If you have the same voltage on the brown wire and the green wire then no current is flowing through the field coil. (And it is the regulator that controls this).

BE CAREFUL using Polocks diode testing guide as it was written for an analogue meter - and a digital meter with a diode test works the opposite way round!

 

shouldent he be able to measure a AC voltage between the 3 white wires ? 1/2, 2/3, 3/1 to prove the alternator output
i don't know what the voltage should be but they should be very close
they would have to be plugged in while you tested them

 

I tried measuring VAC across the various white wires on a whim, and the results were either 5VAC or 25VAC depending on the combo

 

Measure the Alternator Brush Lengths.

Clean the Alternator Rotor Brush Contact Orbits with a Large Rubber Eraser.

(Note: A great Tool for Cleaning the Alt Rotor Brush Orbits is an Old-Time Typing Eraser -- Pink & Gray -- The Gray Side contains Pumice Stone and helps remove dark spots from arcing)

The "Twin Meter" Test of the Voltage Regulator is tedious.
The exercise is time consuming.
A Charging System Check with a SHOP TEST Regulator (A known good one) ... will tell you the score in two minutes.

Examine the Quick Connect Terminals with a Magnifying Glass
Look for any sign of Melting on the Big Red Wire.

 

i just went out and tried the AC on the white wires and any combination got 10 to 15 volts AC depending on the rpm's

 

I didn't modulate RPM while checking for AC, but it sounds like the mechanical part of my charging system is up to snuff. I bought a couple R/R's off ebay so when they get here I'll know if I have chosen wisely.

....I bought a couple in case one shows up DOA, and if not I'll have an extra one. Just in case anyone was wondering

 

Well, I threw one of the new R/R's in and I still have 11.8VDC at the battery @ 2500-3000rpm. I'm hoping I had a DOA R/R, otherwise it looks like I might need the alternator coil?

 

Sorry to drag this thread up again, but I figured that rather than start a new thread, I'd piggyback on this one.

So I have now tried 3 R/R's including the original one. I have also installed a new (to me, but ohmed out good stator). All this and I am still having no worky with the charging system.

My field coil appears to ohm out good
My white wires (stator) seem to ohm good

I keep coming back to the V1/V2 test where v2 is supposed to start <1.8VDC @ switch on, then rise to 9-11VDC with the engine running. Mine starts at battery voltage with switch on.

What is going on here?

 

Dragging up an old thread of mine so with the solution to my problem.

When i would check resistance through the wire harness of my rotor, it checked good, but when I checked it on the rotor face, it was very low resistance (bad). I changed the brushes, rotor, and the whole wire harness because mine was sorta chopped up. The bike starts, runs, and charges as advertised now.