Info on 300 amp Alt surge

[Donald Watson]

Ralph,

I have a friend with a '97 BMC coach, Cummins and Leece-Neville alternator.
He's been having a problem with either no alternator output or a strong
pulsing output, with peaks upward of 16 volts, as if the alternator was
getting cylcling 12 volts to the field. He does not have a schematic and
until recently could not tell me where the diode isolator and an associated
solenoid were. When I checked out the coach, I found over 12 volts on a
solenoid actuated by the ignition switch that supplied a relay bank positive
bus via a short 10 ga. wire, but strangely enough, only 10 volts on the
positive alternator output terminal. Not having a schematic, I was confused
thinking that I should either have 12.6 volts or nothing providing a diode
isolator was installed inline. I cleaned the alternator output terminal and
nearby junction with no improvement. He replaced the original internal
regulator without luck, then had the alternator rebuilt and bench tested
with him observing the test. The alternator is back in the bus. The output
surges up and down which is a similar symptom to this post.

This factory mod is having a relay switch the sense wire instead of relying
on another path, right? Just what exactly was the original symptom? I
suspected a sense wire problem, but couldn't confirm it because the
alternator was faulty. I told him not to run the engine with the two wire
sense/ignition cable attached to the alternator until he could diagnose the
problem. I told him the problem was further forward. This post reflects a
similar problem.

What was the exact cause of the problem that necessitated this relay mod?

Thanks in advance.

Donn
76' FC33
South Kingstown, RI


From: WanderlodgeForum@yahoogroups.com
[mailto:WanderlodgeForum@yahoogroups.com] On Behalf Of Ralph L. Fullenwider
Sent: Monday, April 28, 2008 10:10 AM
To: WanderlodgeForum@yahoogroups.com
Subject: [WanderlodgeForum] Info on 300 amp Alt surge

Good morning everyone:

I have up loaded a pdf file that is BB's answer to a surging problem on 200
and up LX and LXI's with the 300 amp alternators and external adjustable
voltage regulators.

The '95 up Series 60 looks to be the same but I am not sure if they have
this problem.

The file recently came to me from Ron and Ruth J who full time in a 2002
LXI with Rusty a springer spaniel furry people.

Safe travels,

Ralph and Charolette Fullenwider
84FC35 "Ruff Diamond"
Duncan, Oklahoma