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Old 07-04-2014, 04:06 PM   #1
4day's Avatar
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Location: south lake tahoe, ca
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Alternator question on 2001 Alpine

Got back from a long trip recently, started hearing a sound like crickets from engine compartment. Isolated sound coming from the alternator. took off the serpentine belt and turned pulley by hand and found slight resistance when turning. started engine and crickets gone. Alternator charges fine, so figured bearing starting to go bad. question I have is when I took alternator off, I found the red positive cable connected to the post marked negative. On the Alternator there is a sticker marked " modified for use with duvac system, negative ground only. see tech. service letter no. 45. I have ordered a new one from local NAPA store. Unsure what duvac system is and if this is why red cable hooked to neg terminal?

This coach is new to me, but we just put 3200 miles on it and no issues. charging was good, want to replace alternator but don't want to connect wrong. Looks like this alternator is original equipment for coach. Napa is going to ask about alternator , to make sure we get the same one that is modified for Duvac system. I was hoping someone can fill me in on what is going on with this hook-up. thanks Bob
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Old 07-04-2014, 08:04 PM   #2
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I believe the Duvac system uses an external regulator instead of the built-in one on normal alternators. I don't know if your coach is unique but I haven't heard of anyone else having this system. Here is a link to a description of how one is modified Prestolite - Leece Neville

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Old 07-04-2014, 08:10 PM   #3
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Location: south lake tahoe, ca
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After taking a closer look, and lining the alternator up in it's bracket again the positive was on the right post. kinda feel like a dumb a--. still would like to know about the duvac system, and if a new one ordered will come with the modification. thanks again Bob
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Old 07-05-2014, 07:06 AM   #4
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You can do a "search" on this forum but I think most Alpines [my 03] have a "duvac" alternator--perhaps later models did not. Anyway, I use to think the duvac system was a black box hidden somewhere on the coach that sensed 12v current and did something to the alternator based on some set parameters--apparently not. From what I can learn, the duvac is simply a dedicated line to one or both battery banks that the duvac equipped alternator uses to manage battery charging. Not sure how it does what it [perhaps governs alternator output based on battery charge level] but you re-connect the wires as you found them and everything works......
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Old 07-05-2014, 07:49 AM   #5
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The duvac system I believe allows the alternator to be used with an external diode based battery isolator. The diode isolator blocks battery current flowing into the alternator. Normal alternators need battery current to excite the field winding to start the alternator generating power. The duvac enables the alternator to start without battery current. I replaced my Leece-Neville ducac alternator with a Delco 28si alternator (see http://www.irv2.com/forums/f104/how-to-replace-stock-alternator-with-delco-28si-195836.html ) and the delco unit would not self start. I solved the problem by installing a new battery isolator with an “alternator excite” function. Total cost was still less than a new OEM Leece-Neville and now I have a standard alternator. You can also switch to a relay based isolator to solve the problem.
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