Voltage meter spikes intermittently.

[77Z]

I'm from the test and measurement business, that stuff is cool.  Want it?

[77Z]

So, summing up what I've learned here: My 03/77 used an external mechanical contact type VR originally and somewhere along the line it was replaced with a solid state unit (Unipoint). So, it's still external and un-converted and my alternator has no internal VR. I'll be installing the new VR from S30Driver and crossing my fingers that the spiking volt meter issue is resolved.

This is despite some configuration sites that seem to show Nissan changed to internal at 03/77. Maybe mine was right on the cusp of the change.

[SteveJ]

1 minute ago, 77Z said:

So, summing up what I've learned here: My 03/77 used an external mechanical contact type VR originally and somewhere along the line it was replaced with a solid state unit (Unipoint). So, it's still external and un-converted and my alternator has no internal VR. I'll be installing the new VR from S30Driver and crossing my fingers that the spiking volt meter issue is resolved.

This is despite some configuration sites that seem to show Nissan changed to internal at 03/77. Maybe mine was right on the cusp of the change.

From the parts manuals, I only see the alternator changing in 3/77 to the externally regulated 60A. Our friends north of the border were getting that alternator even earlier.

[77Z]

Got the VR from S30Driver and installed it.  It is significantly (3x) taller than the one I removed (which we determined isn't original).  But, there is clearance (see photo).  And, awfully glad I got the one with the Datsun label on it proudly displayed  🙂

Unfortunately, now I've got a charge light.  The volt meter is 13 volts and is just battery power since it should be reading near 16 if charging.  So, logically, would the VR disallow charging to the battery if its the wrong VR? I reinstalled the old VR and the alternator is charging and there's no charge light. 

Ideas?

[Dave WM]

fyi should nver be near 16v, 14v max. the Mechanical VR are very easy to trouble shoot, break out the FSM and study the circuit. its pretty simple, two relays, one duty cycles the alt field coil with battery voltage to maintain output, the other relay operates the charge light and prevent current flow thru the alt windings when the car is not running. 

IF the mechanical VR is at fault, its generally going to be relay contacts corroded or an open or shorted coil.

 

Edited February 18, 2022 by Dave WM

[77Z]

I don't have a mechanical VR.  See photos early in the thread for the Uni-point solid state VR.

[Dave WM]

I was  not talking about the SS VR but the one you just installed.

the FYI 16v was just that FYI not about the mechanical one you are trying to get working. 

 

Edited February 18, 2022 by Dave WM

[Zed Head]

Actually the mechanical VR's can charge up in to the 15 volt range.  It's shown in the FSM.  Might be that the external solid state VR's do also.

I have memories of different wiring schemes for VR's over the years. Did you compare the wires at the plugs between the two VR's?  Not clear that the one you got is correct for your year.

 

77Z, your post is a little confusing because you didn't say exactly which one gave 16 and which one gave 13.  Sounds like you're saying that old one, that spiked, shows 16 on the meter, and the new one with the charge light on shows 13.  

1 hour ago, 77Z said:

The volt meter is 13 volts and is just battery power since it should be reading near 16 if charging.  So, logically, would the VR disallow charging to the battery if its the wrong VR? I reinstalled the old VR and the alternator is charging and there's no charge light. 

 

[Zed Head]

Actually, it looks like just the plug changed, but the wires and orientation are the same.

You might reconnect it and give it a few sharp raps with a plastic screw driver handle.  It is mechanical and it's been sitting a long time.  Or take the cover off (should be easier than the Unipoint) and check the points for corrosion.

1974

1977

[Dave WM]

ok 15v but it should not go that high for long. Ideally I like to see 14v max.

Edited February 18, 2022 by Dave WM

[Zed Head]

I think that he might be using the gauge in the dash, which is not very accurate.

[S30Driver]

You can tell its the correct regulator for the 77 280 by the round plug with the recessed male pins.   The 240 is a rectangular connector and the 260 is a different round connector with external pins.

Possibly a change was made to the harness wiring pins when the solid state regulator was installed.

   240 connector          260 connector