Alternator Problem

[traveler999]

I have a 1999 Windsor that has been sitting for 18 months. I was getting it ready to travel and when I cranked it up I had no RPM on the Tach. I went in the back and the alternator output was 1.8 volts. I have started it up during the storage period, about every 2 weeks, and I don't recall seeing this problem, but I couldn't say I specifically looked at it. I just got a Scan Gauge, that I'm still learning how to use, and it shows the proper RPM. Is there any hope or do I need a new alternator?

[BFlinn181]

Where did you read the voltage of the alternator? It could just be a bad wire connection. I'd remove, clean, and reconnect all wires to the alternator and battery cables, including grounds. Then check alternator voltage again.

[Papa_Jim]

It could be that the alternator brushes are stuck or glazed from the 18 months of sitting. An electrical repair shop would tell you pretty quick. I'd favor having that alternator serviced over replacing it with another.

Jim

[twinboat]

Before you start looking for 12 volts on the BIG + wire on the alternator, you need to find what type of isolator system you have

Many of your vintage MHs used a diode based isolator to split the charge between the house batteries and chassis batteries, while the engine is running.

Having that style isolator, will give you a zero reading on the alternator output wire.

There is a small wires connected to the alternator that should give you battery voltage with engine off. If it matches the actual battery voltage at the battery you probably should get the alt. checked.

If the alt. is bad, be very carefull that the replacement is a Dulvac alternator. It is a better idea to get your rebuilt.

If you don't use a diode based isolator and instead use a solenoid setup, you should have 12 volts at the alternator + terminal.

[DtBt]

Not so twinboat,
His Windsor came from the factory with a DUVAC/isolator system. If the alternator, DUVAC sense connection and isolator are working correctly then the BIG+ terminal on the alternator will be at nominally 14.4V. The purpose of the DUVAC ( aka remote sense) is to compensate for the drop across the isolation diodes. The regulator tries to maintain 14.1V at the DUVAC terminal which is usually tied to the Chassis battery positive terminal. It will raise the voltage on the alternator output to around 14.4V depending on the actual forward voltage of the isolation diodes. These voltages are for fully charged chassis and house batteries,
The fact that the tach has shut down indicates the alternator is not functioning. That does not mean for sure the alternator needs rebuilding but is a good bet once you verify the wiring (loose or poor connections or rodent damage) and the isolation diode. Good luck.

[twinboat]

Originally Posted by DtBt

Not so twinboat,
His Windsor came from the factory with a DUVAC/isolator system. If the alternator, DUVAC sense connection and isolator are working correctly then the BIG+ terminal on the alternator will be at nominally 14.4V. The purpose of the DUVAC ( aka remote sense) is to compensate for the drop across the isolation diodes. The regulator tries to maintain 14.1V at the DUVAC terminal which is usually tied to the Chassis battery positive terminal. It will raise the voltage on the alternator output to around 14.4V depending on the actual forward voltage of the isolation diodes. These voltages are for fully charged chassis and house batteries,
The fact that the tach has shut down indicates the alternator is not functioning. That does not mean for sure the alternator needs rebuilding but is a good bet once you verify the wiring (loose or poor connections or rodent damage) and the isolation diode. Good luck.

Agree it should show 14.4 volts running.

I should have been clearer that checking the alternator + terminal with engine off, with an isolator system will read 0 volts.

Many people will test "engine off" and "engine on" voltage, and report no voltage at either time.

That starts the confusing response's by many on here, not familiar with diode isolator systems.

[pphake]

Originally Posted by traveler999

I have a 1999 Windsor that has been sitting for 18 months. I was getting it ready to travel and when I cranked it up I had no RPM on the Tach. I went in the back and the alternator output was 1.8 volts. I have started it up during the storage period, about every 2 weeks, and I don't recall seeing this problem, but I couldn't say I specifically looked at it. I just got a Scan Gauge, that I'm still learning how to use, and it shows the proper RPM. Is there any hope or do I need a new alternator?

1999 Windsor hello!
As others have posted over the years, I too replaced the alternator in my 1999 Windsor with the very common Delco 28si (160 amps). It cost just over $200 at a local truck shop, new. The job also required replacement of the old isolator which I sourced on Amazon for about $75. This new modification has worked perfectly so far (14.3V output) for over 3,000 miles and about 100 starts and stops.

My view is that the old Leece-Neville is much too heavy, too tired, too dirty and corroded (examine your alternator cooling vents) to trust any longer and also is a hassle to diagnose and rebuild.

To replace it I bought 1. a new, lighter Delco 28si, 2. a new isolator (as required by a Delco Application Engineering Bulletin of 2008), 3. a 20 ft. length of 10 AWG wire and 4. an automotive fuse.

The new isolator (NOCO IGD200HP) 200 Amp BatteryIsolator is a near drop-in replacement for the old Cole Hersee (200 Amps) except that it has four terminals rather than three.

Preparation: Add one new wire. The new, smaller “excite” terminal on the isolator receives current from the wire that was previously connected to the “I” terminal of the old L-N alternator. So run a new 10 AWG wire (in a tied, corrugated sheath, protected from abrasion) from the isolator area of the RV to the alternator area. I also placed a 10A fuse in this line near the isolator. Join this excite wire to the wire that fed the old L-N “I” terminal and most of the job is done. The “I” terminal on the 28si must not be used for any purpose.
I apologize for a lot of repetition below but I combined several draft descriptions.

See my instructions to my mechanic below:
How to wire the Delco 28SI paired with a new 4-terminal isolator: ( Delco has I, S, and R terminals in addition to B+ and Ground)
I terminal Delco 28si not used
Terminal “I” is not used on the new 28si + isolator system as stated in Delco Bulletin 2008 which reads: “The excitation of any other terminal besides B+ on the 28SI may result in damage.” Instead, the excite voltage is delivered by a new wire from the ignition “run” or “I” circuit to the excite terminal (smaller 4th terminal) of the isolator. This delivers the excite voltage to B+ (through an internal isolator diode) from the ignition “run” wire. (The diode prevents voltage feedback to ignition relays which would otherwise block engine shutdown). Because of the isolator, B+ of the alternator is functionally disconnected (in one direction) from the battery but needs 12 volts to excite the field. This is the function of the new “I” or excite circuit. Place a 10A circuit breaker into this new “I” circuit. Join the old I wire to the new, white, isolator excite wire that is connected to the isolator excite terminal.
S Delco 28si
Remote Sense “S” or Duvac terminal on the alternator monitors the chassis battery voltage via the red, 20A fused sense wire which is attached to the chassis battery (+) terminal. (This is already fused). The isolator, which keeps the two battery banks separated, causes a diode-related voltage drop at the batteries. The Sense wire informs the alternator’s regulator of this voltage drop and raises the output voltage of the alternator to precisely correct for the drop. Attach red S wire to S terminal on 28si.
R Delco 28si
The R relay terminal provides current for both the tachometer and for the ALT FAIL circuit (“Alt charge” lamp) via 6V relay in rear electrical bay. R provides pulsating DC current at ½ system voltage. Attach R wire to R terminal.
In some RV’s, after alternator modification, the engine will not shut down using the ignition key because of feedback from this “I” terminal (reverse current flows from I to the ignition relays). These modifications do not use the recommended 4-terminal isolators. Consequently, you must place a diode in this circuit to allow flow only towards the alternator and to prevent such feedback current from the alternator “I” stud, which otherwise keeps the ignition system alive. This connection is not allowed for the 28si. The 4th terminal of the new isolator accomplishes the goal of exciting B+.

NOTES:
For Delco 28si the “I” terminal is not used at all, instead B+ is excited by the Ign “run” wire at the isolator, via an isolator diode that prevents feedback. There is a conductive path from “excite” terminal of the new isolator to the isolator’s central post that is connected to B+. This provides the initial field current to excite the alternator.
Extras:
Dual Voltage Alternator Control (DUVAC)
The Duvac (or remote SENSE) system was designed so that a battery isolator can be used in combination with an alternator. The isolator allows the alternator to maintain two separate battery banks at a set voltage and for the two banks to remain isolated from each other.
But the isolator creates two new problems that are solved using different alternator models:
Problem 1. The isolator’s resistance reduces the voltage from the alternator arriving at the batteries. This is corrected by the DUVAC remote “SENSE” terminal wire (S) which allows the Alt to measure (and to correct) the reduced output voltage arriving at the battery. This thick, 20A fused red wire directly connects the battery(+) to the Alt terminal called DUVAC or SENSE (S).
Problem 2. The isolator prevents current flow from the batteries to the B+ post of the alternator. This B+ voltage normally allows the Alt to self-excite. For L-N this function is replaced by providing excitation voltage to the Alt (I) terminal by a wire from the ignition “run” system. (Excitation of the “I” terminal is required for L-N alternators but is NOT PERMITTED for Delco 28si when used with an isolator; see Delco Engineering Bulletin 2008). I is therefore left disconnected.
Thus in a Duvac system, the keyed ignition “run” system (instead of the B+) provides the alternator with excitation voltage to begin charging, by providing current from the ignition “run” system directly to the “I” terminal of L/N alternators.
By contrast, DELCO 28si alternators, when used with isolators, require voltage ONLY at the B+ terminal to self-excite. DELCO states: “The excitation of any other terminal besides B+ may result in damage”. Thus, Delco requires a special isolator (4-stud, not the usual 3-stud) to provide the voltage to B+.

[twinboat]

You could also but a 28si with the Delvac installed.

http://www.qualitypowerauto.com/item...lternators.htm

[DtBt]

You can also convert a LN2800JC to a DUVAC by performing the modification outlined in https://www.mediafire.com/?hadg27h18lnyia5

[traveler999]

I was pretty sure it was the alternater, so I pulled it out and looked at it on the bench. I pulled one brush out and it looked okay, when I tried to pull the second brush it is frozen in the holder. That means the spring can't put any pressure on it to make contact with the slip ring. It's the weekend, so I can't take it to a shop until Monday. If I get brave enough I might tear it apart and find out why the brush is frozen.

[traveler999]

I got the brush loose and put every thing back together, but it still didn't work. Will see if the alternator shop can fix it.

[traveler999]

Well I took the alternator in to the shop and they had a direct replacement (rebuilt) so I took the easy way out and got the rebuilt. Every thing works now. If any body in the Florida, St Pete area and needs Starter or Alternator service, I would recommend, Will's Starter/Alternator at 4695 49th St. N.