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Topic: Duo-Vac Vs 'regular' Leece alt?? (Read 651 times) previous topic - next topic

Duo-Vac Vs 'regular' Leece alt??

My alt quit....I had a spare 250 amp leece neville left over from CB days. I replaced the duo with the standard alt.
Works fine....I don't see any difference in my guages??

What should I be noticing or looking for?.....both the house and starting batteries are charging with the motor running!

Only difference is....one wire ain't hooked up at the alt...??

Someone enlighten me please.

This one sends power to the isolator and it sends it to the battery system(s)......

BTW...old habit.....I always run an extra #4 wire from my alt to my starting batteries....direct. More unmolested power straight to my batteries.
I even do this with cars and trucks.......

Peace...

Happy 4th.....God Bless our Troops!!

SemperFi............Ol'Ben

Re: Duo-Vac Vs 'regular' Leece alt??

Reply #1 –
Quote from: BenDare2 –


This one sends power to the isolator and it sends it to the battery system(s)......

BTW...old habit.....I always run an extra #4 wire from my alt to my starting batteries....direct. More unmolested power straight to my batteries.


SemperFi[/color]............Ol'Ben

Ben,

Bad idea to have both direct wire from alternator to one battery bank and that same bank wired through the diode-based isolator.  If the external sense wire is on the battery side of the isolator (as it should be), alternator voltage will be about .7 VDC higher than on the battery side of the diode-based isolator.  Depending on where the sense wire is connected, one bank or the other will have wrong charging voltage-- could be too high or too low, but will not be correct. 

You would need to removed the diode based isolator and use a mechanical switch OR solenoid-based isolator as the use of a diode-based isolator has a voltage drop across the isolator.

Brett
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: Duo-Vac Vs 'regular' Leece alt??

Reply #2 –
Quote from: BenDare2 –

Only difference is....one wire ain't hooked up at the alt...??

Someone enlighten me please.

Your Leece Neville alternator probably has a jumper between the field and the ign so that when the ignition key is on the field is excited by that voltage.

This will be about .6vdc lower than the "real" battery voltage and, depending upon how the regulator is set, could be over-working the alternator making it try to charge up a bank that is already charged up. Not so good for the batteries either. That "extra" wire that is not hooked up probably goes to the "field" (battery sense) connection on the regulator. I took that jumper off and connected a wire that indicated the "real" battery voltage (minus the voltage drop across the wire, of course).

In addition to the warning from Brett, that  #4 wire you have connected from the alternator output  to the batteries will "buck" the charging current from the generator/converter if you run the gennie when underway. Not sure what that will do to the AC charger/converter; maybe nothing.

I'm also not sure what it will do to the system when you hit the "boost" switch; perhaps try to route starting current through the alternator windings if everything is "just right" (or wrong). I would not be comfortable with that #4 wire. You should have no voltage at the output terminal of the alternator when the engine is not running. This is unlike a car or truck but then they don't have "house" systems.

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."
 

Re: Duo-Vac Vs 'regular' Leece alt??

Reply #3 –


 
These alternators can be confusing because there are so many models.  While many of them can be converted to Duvac, explanation below, it typically requires removing the diode trio (on alternator, not the isolator diodes) if present, removing regulator and disconnecting one wire from it, and then using the disconnected wire as your voltage sense wire.  It varies between alternators, you need the model number.  Using a standard, or improperly converted alternator can lead to parasitic drain, fried alternator, dead batteries because the alternator never turns on, fluctuating voltage. You might want to check the leece neville tech support forum  Forum Category | Prestolite News  Just sayin....

Chuck

The Duvac terminal is actually a remote voltage sense terminal.

If your motor home has a battery isolator then you will need this terminal in order for the alternator to function.

A battery isolator is blocking diodes that isolate the crank batteries from the house batteries. Since the battery isolator has blocking diodes no voltage is present to the alternator output terminal so additional measures are needed to excite the alternator.

The sense terminal (Duvac) serves two purposes, one it takes into account the voltage drop across the isolator and two it supplies field current to the alternator in order for it to turn on and excite.

The second terminal next to the Duvac terminal is the ignition terminal. This terminal basically turns on or off the alternator.  Voltage must be present on this terminal while the engine is running and removed when the engine is off.
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS