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Topic: Alternator problem (Read 531 times) previous topic - next topic

Alternator problem

started having problems with my isolator or alternator  I have over 16 volts going to the coach auxiliaries batteries and under 12 volts going to the coach starting batteries if I use the the Boost  switch I have 14.2 at both sets I have a good ground on alternator  and isolator 12 volts at ignition side of alternator voltage at the alternator output over 15 volts plus.    looks to me like it's the isolator  ,this started yesterday.  this morning I I started it up it was charging perfectly on both set ran it for an hour shut it down started it back up and the problem was back and is still there any suggestion it has a 4 stud isolator one  wire goes to the back of alternator a small 12 gauge wire  and the other 3 wire about 4 gauge main wire output on alternator and other two goes to each battery set  there is one thing I find odd on the ignition wire that what I'm calling it I didn't Reese trace it out.  it is live  all the time key on or off .
  I also had it plugged in to shore power I can see that Would interfering with the battery if coach was running for over an hr or so would the alternator and the inverter working at the same time be hard on the isolator
Rick & Hilda looking forward to full- timing one day for now couple of months at a time
1999 U270 3602
Built number  5530.  Feb 1999            Motorcade  number 18438
8.3 Cummins Allison six speed with brake  retarder
Purchased Nov 28 2019

Re: Alternator problem

Reply #1 –
Rick,  this looks like the isolator is on its way out. Time for a new diode based isolator like you have or a zero voltage drop isolator or an automatic combiner or voltage sensitive relay.

The first two charge both the house and start batteries while driving.  The second two also do that and while charging from the inverter/charger or solar will do both depending on voltages.

Best done sooner than later. 
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Alternator problem

Reply #2 –
The wire that is hot all the time should be the sense wire. The ignition wire is only hot with the key on.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Alternator problem

Reply #3 –
Quote from: red tractor –
The wire that is hot all the time should be the sense wire. The ignition wire is only hot with the key on.
Will recheck tomorrow
Rick & Hilda looking forward to full- timing one day for now couple of months at a time
1999 U270 3602
Built number  5530.  Feb 1999            Motorcade  number 18438
8.3 Cummins Allison six speed with brake  retarder
Purchased Nov 28 2019

Re: Alternator problem

Reply #4 –
Quote from: Roger & Susan in Home2 –
Rick,  this looks like the isolator is on its way out. Time for a new diode based isolator like you have or a zero voltage drop isolator or an automatic combiner or voltage sensitive relay.

The first two charge both the house and start batteries while driving.  The second two also do that and while charging from the inverter/charger or solar will do both depending on voltages.

Best done sooner than later.
Will do some research on the last two
Rick & Hilda looking forward to full- timing one day for now couple of months at a time
1999 U270 3602
Built number  5530.  Feb 1999            Motorcade  number 18438
8.3 Cummins Allison six speed with brake  retarder
Purchased Nov 28 2019

Re: Alternator problem

Reply #5 –
Read an article one time, don't remember where, that said the isolator was good for 16 to 20 years under normal use. Don't know exactly what that means.... Sounds like it may be time for a replacement.
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Lynn & Marilyn Sickel
Tollville, AR
1997  U320  40'
2021 Chevrolet Silverado pickup
Motorcader  17257