The connection between a bad rotor and the fuse blowing? B circuit type.

[weekendrider]

I have experienced a lack of charging due to a bad rotor before (5 or 6 x's). But never had this happen before.
Switching the key on the fuse ('77 single fuse system) would blow.
Checking the coupling at the regulator I found continuity on all 3 wires (blk/grn/brwn).
Unplugging the coupling for the stator/rotor and only the grd on the regulator had continuity.
Checking the slip rings on the rotor showed high (16-18) ohms.
Checking the slip rings to clam shell no continuity.
So the test (and replacement) showed the rotor to be bad.
How or what "test" would one do to find out why the fuse was blowing?
The rotor(only the rotor all else the same) has been replaced and we are back to charging (12.9 v idling and 14.1 v @ 3K rpm).

Side note the glass fuse in a physical size to fit OEM is NLA?
Tried several auto parts stores but couldn't find one the right length to fit the plastic case.
So while I said nothing else changed, I did plumb a 20 a blade fuse into the system to replace the glass tube fuse.

 

[mrtwowheel]

Do the test on the unplugged stator.

Scott

 

[fredintoon]

Hi WER,
Your blown fuse problem may have had an accidental fix.
There's another thing that may have changed with all the wire-wiggling that happened during the checking, fuse & rotor swapping.
A hot wire that had been grounding out may have gotten moved so it's worn spot wasn't grounded any more.

 

[weekendrider]

Scott I am not sure what test you are referring to.
With the stator unplugged I did check for continuity from the spade fittings to the case of the stator. No continuity except the grd.

 

[Paul Sutton]

With a short you can replace the fuse with a 12V bulb and start unplugging things to see in which area the short is - unless of course the short is no longer active.

 

[mrtwowheel]

Scott I am not sure what test you are referring to.
With the stator unplugged I did check for continuity from the spade fittings to the case of the stator. No continuity except the grd.

With the connection block to the alternator unplugged, the manuals tell how to check the stator for shorts by probing the wires to the alternator. All of the three white wires should have a resistance to any other one of the white wires of .8 - 1.0 ohms. Also, none of the white wires should have a connection to ground. These shorts can be intermittent.

Shorts at the rotor to ground can also be intermittent.

 

[gggGary]

I would check for cut insulation on wires at the grommets in the headlight shell. That's a popular short circuit area. 16-18 ohms on the slip rings is pretty unusual.............

 

[peanut]

Scott I am not sure what test you are referring to.
.

I
Switching the key on the fuse ('77 single fuse system) would blow.
.

I took Scott to mean test to see if the fuse still blows when you switch the ignition on with the stator disconnected from the rectifier/regulator.... its a good suggestion and the one I immediately thought of too.

 

[weekendrider]

Unplugging the stator rotor coupling showed loss of continuity at the harness side of the regulator coupling and no blowing of the fuse. You also loose the neutral light (what I was using for a power indicator) and it took a moment or three for me to snap to the "push the starter button" to check for power solution. I did and it did. That led me to checking the stator and rotor.

Yes gggGary the first time I have experienced this. All other bad rotors have checked a very low resistance.

This particular rotor had been dropped at some point breaking the Bakelite (?) In two places which I repaired with JB weld. At the time I repaired it the insulation on the windings was cooked black but the slip ring test checked OK so I guess I was lucky to get a years service from it. Now I wonder if it was the cause of the two VR 115 regulators going bad?

 

[Paul Sutton]

I have wondered if there are also cheap Chinese regulators as there are cheap Chinese PMA systems. A search of Ebay UK shows the price of the same A-Type regulator ranging from £7 for Chinese to £16 for Italian and £24 for those stamped "Made in Germany". Perhaps this explains the VR115 issues????