400A and Over-run pulley

[kromby]

I have a 400A dual voltage alternator that has been operating as expected for a couple years. Voltage always comes up directly and is consistent. Voltage regulator is new(er), N3318 stamped 2018. It came with a solid pulley so it squeals like a pig every shift and stop and steering/breaking pressure drops, no surprise there.

I just swapped in an overrun pulley with (with appropriate belt length) and its nice and quiet. At first it was confirmed bat voltage good but not charging at idle (both 24&12V) but would come right to life with an expected delay after giving it a few hundred RPM. After a drive bringing everything up to temp it charges at idle.... sometimes, batteries are good AGM 6mo old. Clutch pulley is new and does not appear to be slipping.

My question: Is a 400A alternator w/ N3318 regulator (appears to be the newest for the 400A) with overrun clutch an acceptable combination? I see in the Neihoff manual that it comes into regulaton when it detects the proper shaft speed but it does not mention what that speed is or if the larger overrun pulley is too big. Anyone with experience on this combo or some background knowledge? Regulator stator driver weak etc? I just love the 400A so much.

 

[Retiredwarhorses]

Of course it’s an acceptable combination, there is the possibility that the over run pulley is defective, can you spin the pulley in both directions
while engine is off? It should only spin free in one direction.
also, what was the part number of the new belt?

 

[kromby]

Of course it’s an acceptable combination, there is the possibility that the over run pulley is defective, can you spin the pulley in both directions
while engine is off? It should only spin free in one direction.
also, what was the part number of the new belt?

Thanks for the info, good to know its an approved combo and to check elsewhere. Thanks for the suggestions:

-The new belt is a 112.4" 01-488-5606 it takes up a bit more of the tensioner than the old belt did with the old pulley. No squealing on the belt.
-If I lean on a wrench on the pulley adapter which is connected to the alt shaft it free spins one way and locks up until the belt slips on the crank the other so it looks like its in good shape. Its new and what I can tell an actual pulley and not a clone, pn's and stickers present. Adapter and nut is from reputable vendor as well.

I put some paint marks on the nut+pulley and took a high speed phone video under forward rotation, looks locked there too.

So as its an approved combo it looks like the voltage regulator might have some issues at idle. Maybe weak field coil current (will have to check if its even trying). It never comes into regulation at idle after an overnight start (~25V to the alternator) however it will regulate at idle after a short drive and the bat voltage is 27-28v. So probably not a factory low RPM cut out. Regulation/charging during driving is still just fine today.

I checked the diodes, field coil and stator coils per the manual, no problems there. Unplugged, cleaned and checked the circular regulator and phase connectors, contacts and wires all clean and in good shape, no change after re-assembly.

Im assuming folks with the 400A with overrun pulley see solid charging at idle and I am not observing normal behavior with it not charging sometimes?

 

[Retiredwarhorses]

There is no “low voltage“ cut off, just Over voltage cut off, the reg has a soft start feature, meaning you wont see full charging voltage for up to a minute, if you have 24v at IGN terminal at ALL times while engine running and suddenly no output of 28.5VDC? its either the regulator or the actual Gen failing…ive replaced many 400amp gens for lack of output and the regulator worked fine when swapped into another truck.

 

[Mogman]

Is it possible someone tried to adjust the idle using the tach error and now it is idling too slow? I have had many alternators (non military) over the years that would not "kick in" at idle that worked just fine other than that so as long as it starts charging when the engine RPM is raised I would not worry too much about it.
Your tach should be at about 750 RPM at idle now