1979 KZ400 Charging issue, help!

I’ll try and keep this simple.

1979 Kz400 not charging.
I have been conducting tests as per my workshop manual and these are my results;

-Resistance between two stator output wires= .3 ohms (ok)
-voltage output from stator wires (with voltage reg disconnected) at 4000rpm 70 ish volts ac (good)
-I have two new regulator rectifiers that both seem to pass the diode test
-I have run my own wires from stator to RR to eliminate sketchy wiring
- with the RR plugged in and the DC output disconnected from the battery I measure around 14.3V when the engine is running BUT plugging the RR in seems to load up the engine and drop RPM(????)

When I connect the RR DC output to the battery the voltage drops back to 12.4v ish and the ac output of the stator drops to 10v AC and does not increase with RPM.

There’s also around 17V Ac to ground from the stator output wires. (Is this a sign that it’s faulty?)

So, is my stator faulty? Is there anything I’m missing?

Regards from New Zealand.
Jordan

The AC voltage measurement on the stator wires while connected to the reg/rec is not a meaningful indicator. It is no longer a sinewave and thus the average AC voltmeter will not correctly estimate the RMS voltages. The unconnected measurement works because an unloaded stator output is mostly a sinewave.

The loading down RPMs a little bit is a sign that the stator is doing work. This would be expected, but a large RPM drop is not normal.

Let it run a bit with the lights off and see if the battery voltage slowly climbs up to 14v or so.

Thanks for the reply.

The load that the stator causes on the engine seems too much to me. There shouldn’t be much load at all considering the battery is new.

I’ll try unplugging the headlight to reduce load and run it again. From what I’ve read the fact I have ac voltage to ground from the stator at all means there’s an issue but it’s just weird because all the other tests are good. Resistance between the stator windings and ground is OL so that passes but maybe under load the insulation breaks down.......?
Will report back

79kz400nz wrote: ...From what I’ve read the fact I have ac voltage to ground from the stator at all means there’s an issue ... but maybe under load the insulation breaks down.......?

Once the stator is connected to the reg/rec and the reg/rec is connected to the battery and rest of the bike, there is then a completed circuit between the stator and the bike including ground. The voltmeter is just measuring the AC component of the pulsing DC voltage. It is then estimating the RMS value of the AC component. But since the AC component is not a sinewave, the estimation is way off.

Without careful study using a o-scope, or using one voltmeter compare an identical bike under exact identical battery and load conditions, measuring the stator leads is meaningless unless they are completely unconnected. Different brands of voltmeters may use different methods of estimating RMS voltage so you must use identical or the same meter for apples-to-apples comparison.

Here are some notes on alternator and charging signals:
s3.amazonaws.com/gpzweb/GPZAltntrWaves/AlternatorWaveforms.html

Here are some notes on AC voltmeters:
s3.amazonaws.com/gpzweb/ACvoltmeter.pdf

79kz400nz wrote: Thanks for the reply.

The load that the stator causes on the engine seems too much to me. There shouldn’t be much load at all considering the battery is new.

I’ll try unplugging the headlight to reduce load and run it again. From what I’ve read the fact I have ac voltage to ground from the stator at all means there’s an issue but it’s just weird because all the other tests are good. Resistance between the stator windings and ground is OL so that passes but maybe under load the insulation breaks down.......?
Will report back

The stator is under load when it is connected to the regulator. If the bike doesn't need the power, the regulator burns away the excess. So whether the battery is charged or not, the stator is under a significant load.

Whoever is saying the insulation is breaking down is probably confusing it with ignition coils. When the stator is loaded, the immediate voltage on the stator drops. Vibration or heat might affect insulation efficacy but load will reduce the voltage affecting breakdown between opposing legs of the stator where the highest voltage differential is found.