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Topic: Alternator  (Read 1018 times) previous topic - next topic

Re: Alternator

Reply #25 –
Quote from: Moby –
1)  How do I tell if I have an isolator?
3)  My bad, meant "sense".
4)  Does it help to mention that my alternator has two charging lines coming out of it?
1)  You need to look around your coach - see if you see something like the photos below.  The isolator might be red in color, with 3 or 4 battery cable posts.  It will have large diameter battery cables attached to the posts.  It could be mounted in the engine compartment, or in one of your storage bays, or under the lift-up mattress platform at foot of bed, or ?

3)  In that case, yes, find the START battery (post) on the isolator, run a line from that to the SENSE terminal, and should be good.

4)  What would help is a photo of the back side of alternator showing all of the terminals.  OR, if you can see the ID plate on the alternator, tell us the model number.  We can look up the factory specs and then we'll know what you are working with.

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator

Reply #26 –
Quote from: Moby –
Ok.
 1)  How do I tell if I have an isolator?
 3)  My bad, meant "sense".
      Sorry.

 Does it help to mention that my alternator has two charging lines coming out of it?
Hi Moby!
Foretravel's original equipment is a diode isolator.  This is a big heat-sink with three battery terminals and a screw for a wire.  It's somewhere between the alternator and the batteries.

IF you have a Leece Neville DUVAC alternator and you have two heavy studs with 12+ on them with the engine running then you don't need an isolator -- the alternator does that for you.

A good voltmeter is your friend.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Alternator

Reply #27 –
Quote from: Moby –
Ok.
 1)  How do I tell if I have an isolator?
 3)  My bad, meant "sense".
      Sorry.

 Does it help to mention that my alternator has two charging lines coming out of it?

Your coach did come with a diode-based battery isolator.  Likely on front wall of engine compartment.  Just follow the large-gauge red wire from the alternator B+ terminal to it.

And to have the alternator properly functioning, you need both excite (only hot with ignition on) AND the sense wire connected. The sense wire is connected to any place "downstream" of the diode-based battery isolator and the chassis battery positive terminal.  The lug going to the chassis battery on the diode-based battery isolator is an easy location to connect the sense wire.
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: Alternator

Reply #28 –
Quote from: Moby –
Sorry for all the questions, I've never been good with vehicle electrical systems.
No need to be sorry - we all have varying degrees of knowledge/skill - that's why this Forum is so valuable.  We pool our knowledge and assist each other in areas where we may be a little "weak".

One potential "problem", when dealing with older coaches like yours and mine, is that prior owners may have made undocumented modifications to the original factory design.  That is why I resist the urge to make flat statements about what equipment another member will find on his/her coach.  I like to get positive evidence (photos or model numbers) of what exactly constitutes the existing setup before attempting to diagnose a problem or answer a technical question.

Example:  We can't tell you how to repair or restore the correct wiring to your alternator until we know exactly what alternator is mounted on your engine.  It might be the OEM factory installed Leece Neville, or it could be a good quality replacement alternator that is "the same as" a genuine Leece Neville, or it could be a rip-off generic rebuilt alternator sourced from a off-shore no-name provider.  In any case, it may or may not have the same wiring connection terminals as a genuine Leece Neville model.  Same thing applies to the isolator that you may or may not find on your coach.  Perhaps a prior owner removed the isolator and substituted another device, like a VSR, or perhaps they removed it and wired the alternator direct to the start battery.  Until we find out from you what equipment you currently have to work with, we can't really give you useful advice.

End of sermon.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Alternator

Reply #29 –
And even if the alternator was replaced by a "professional" shop they may have not known what to do with the sense wire. Mine had been cut and tucked back into the harness. Spent four days going crazy while going to a B2B charger and dealing with a sense wire bridged to the excite wire.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.

Re: Alternator

Reply #30 –
Got you all.
 The alternator WAS replaced, and the receipt is in the documents bag under the bed.

I distinctly remember it being a Leece on the reciept.
Model when I get it.

Time to go tracing big, fat, red wires.
In restless dreams I walked alone.
Narrow streets of cobblestone.


'93 U225
Build 4337
'14 CRV Toad