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Topic: DelcoRemy 28SI alternator (Read 2845 times) previous topic - next topic

DelcoRemy 28SI alternator

In October Cabin Diesel determined that the alternator we had was dying, so it was replaced with a DelcoRemy 28SI unit. Since day one this alternator doesn't kick in until I get the engine up to about 1700 rpm for a minute or so. Then it works great. Twice, now, it has failed to come on. In both cases it was after a fuel stop a short distance from the campground. Today I decided to see what I could see.

All connections are tight. I didn't start the engine, or even turn the key on, but I couldn't find 12 volts on any of the terminals. I thought I would. Perhaps I didn't have a good ground connection, or perhaps the key needs to be on.

Tonight I pulled up the information on the alternator, and I wonder if it is wired correctly. The old alternator had the expected two larger terminals for the + and - cables, and a "box" with two terminals with two smaller wires (sense wire). The new one has the two expected larger terminals for the + and - cables, and three additional terminals. Those terminals are remote sense, indicator/ignition, and optional relay. I have wires to the remote sense and relay terminals.

1. Is the wiring correct?
2. Should I see 12 volts on any of those terminals with the key off?

Monday's drive is all of 66 miles or so, so even if the alternator isn't working I should be able to easily make it there with the generator running.

Re: DelcoRemy 28SI alternator

Reply #1 –
I think your remote sense may have an ignition driven relay in the circuit, maybe a fuse.  So if the ignition is on, the sense wire from the start battery connected to the S post should show 12 v.
The big ground wire goes to ground (usually the engine block). The big red wire goes from the B+ post the the cemter post on the isolator.

I don't think anything needs to be connected to the relay post or the ignition post. 
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: DelcoRemy 28SI alternator

Reply #2 –
We had an intermittent problem with the little relay that powered the exciter wire on the LN alternator.  I got a Wilson identical to the LN at NAPA and it's working perfectly after solving the relay issue

Rick & Rhonda
2003 U320 4220  Build #6199
Was
91 36' GV 300 Caterpillar, 92 40' U280 300 Cummins, 97 36' U295 300 Cummins, 2002
U320 450 Cummins
(Guess we're hooked)

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Re: DelcoRemy 28SI alternator

Reply #3 –
The Delco alternators (24SI, 28SI, 40SI, 55SI) are not a drop in replacement for use with a RV diode based battery isolator.  The standard diode battery isolator must also be replaced with one with an exciter post, and the coach ignition excite wire will connect to that. See attached Delco bulletin for use with a diode battery isolator.

Roger is correct, on a Delco alternator nothing should be connected to the R relay post or I ignition post, only the sense wire should be connected to the S sense post. On a Delco alternator the I post is not the excite post, it is used for a dash indicator lamp. See attached Delco 28SI install instructions.

With engine off, and key off, the S sense post should measure 12 volts, the B+ post should measure 0 volts. With the correct isolator, with engine off, and key on, the B+ post should measure 12 volts.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: DelcoRemy 28SI alternator

Reply #4 –
Thanks, Peter. I'll try to check the sense wire voltage again and make sure that I have a GOOD ground connection. Yes, the isolator has been replaced with a modern one.

Re: DelcoRemy 28SI alternator

Reply #5 –
Replaced my isolater with a combiner,

Boost switch is now a three way toggle.

Top is manually connected.  Mid is auto. Lower is disconnect.

Magnetic engagement.

"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: DelcoRemy 28SI alternator

Reply #6 –
Bob,

What combiner did you go with?

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: DelcoRemy 28SI alternator

Reply #7 –
Just replaced my Leece Neville 160 Amp alternator with DelcoRemy 200 AMP 28SI.  Added a Cole Hersee 250 Amp battery isolator
which didn't have 4th terminal IGN connection. (only 3 studs). The sense terminal should always show voltage as previously stated.  The
Ignition wire should be hot only when the key is on.  Voltage at pos terminal only when engine is running.  Pos runs to center post of isolator, which will be hot when engine is running.  This info is for 4 wire alternator and the Cole Hersee 250 Amp isolator No. 48080.
The relay terminal on the 28SI is optional and not needed.  This is my understanding but I am certainly not the sharpest tool in the electrical box.  I'll finish the rest of the story on a new topic because the 10KW Powertech

Re: DelcoRemy 28SI alternator

Reply #8 –
Quote from: Art & Polly –
Just replaced my Leece Neville 160 Amp alternator with DelcoRemy 200 AMP 28SI.  Added a Cole Hersee 250 Amp battery isolator
which didn't have 4th terminal IGN connection. (only 3 studs). The sense terminal should always show voltage as previously stated.  The
Ignition wire should be hot only when the key is on.  Voltage at pos terminal only when engine is running.
Art,
The Delcos require 12V on the B+ stud at start up to power up the ASIC chip microprocessor that controls the voltage regulator. So, your statement that the B+ will only have voltage when engine is running is not quite correct. With the correct isolator with ignition stud, with key on and engine off, the isolator will apply 12V to the center stud (connected to the alternator B+) which will start up the ASIC chip. This may explain why David's alternator didn't provide power until 1700 RPM, or sometimes not at all.

Can you possibly exchange your new isolator for one with the ignition post? Without the correct isolator with ignition post your new Delco won't work properly.

Here is the 240 amp isolator I used that I would recommend, with the Delco ignition post.

Sure Power 240 amp isolator with ignition post
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: DelcoRemy 28SI alternator

Reply #9 –
If all he needs is an "ignition hot" wire, there are plenty of them in the engine room that can be tapped.  Back of remote start switch comes to mind.  We are not talking about many amps, so power draw should not be an issue.  Yes, install an in-line fuse at the source since the wire will need to run near a lot of "moving parts".
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: DelcoRemy 28SI alternator

Reply #10 –
Looks like I chose a poor ground spot to check the voltage on the wire. I used the actual ground wire on the alternator and had proper voltage. We'll see what happens Monday on the long 65-mile trip.

I "love" intermittent electrical problems.

Re: DelcoRemy 28SI alternator

Reply #11 –
Yesterday I ran a fast idle (~1700 rmp) for a minute to see if the alternator would come on. It didn't, so I left the boost switch on and headed out. Since it was raining I wanted the headlights on. About a mile down the road the alternator came on, so I turned the boost switch off. Guess I need to be more patient.

Re: DelcoRemy 28SI alternator

Reply #12 –
I have been chewing on this for a while, I followed Peters link and that was for a CS delco I have a 28SI with a 48080 cole hersee isolator.  Me thinks the model numbers are way too similar.  Also to complicate the issue even more I looked at a downloaded cole hersee catalogue see attached and that states 48080 is a 42 amp with attached wires mine has no such wires. The plate on the isolator says 250 amp rating.  Would sure like to speak to Cole Hersee rep Can't find contact #.  Email has not been answered.  Thanks for all the input and help.

Re: DelcoRemy 28SI alternator

Reply #13 –
Sorry couldn't understand discrepancy in numbers.  The box number for the isolator did not match the plate on the isolator.  I have a
a 48160, 200 Amp isolator again sorry for the confusion. 

Re: DelcoRemy 28SI alternator

Reply #14 –
Quote from: kb0zke –
I "love" intermittent electrical problems.
Ah yes, the joy of masochism....... 8)
Tim Dianics
Pam Sapienza
Vader PupZilla Labrador Canine Beast (AKA Pup)
Columbia, MO
1996 U320 4000
2021 Jeep Gladiator, Diesel

Re: DelcoRemy 28SI alternator

Reply #15 –
My normal comment my guru system friend worked into my head is that no new coach comes with a isolator.  All have a combiner.  One mistake kills a expensive set of engine batteries.  I killed 2 sets before the combiner install.  But I guess I was stubborn like maybe a few here?

As a sort of prepper in shaky town the failure of the engine batteries was not an option. 

God bless if killing a set of starting batteries is not a safety issue for you
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4