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Topic: Duvac or not to Duvac? (Read 375 times) previous topic - next topic

Duvac or not to Duvac?

So what does everyone do when they've added a B2B battery charger to safely regulate what your LiFePO4 battery bank can demand from the alternator AND you have removed the isolator from the coach? 

I need to replace my alternator and ordered what was already in there (Leece Neville 2824LC).  I know there are folks who went with the Delco Remy 28SI.

Does it really matter?  If it does, then replacing the alternator is required when removing the isolator from the coach.

Just curious.  I've already received feedback from another forum member.  I am interested in what others have to say.
Dave & Diane
2001 U270 36' WTFE #5820
2016 Jeep Wrangler Hard Rock
Motorcade #18156

Re: Duvac or not to Duvac?

Reply #1 –
LN 2824LC alternator is externally excited and will work with a diode isolator.

Delco 28SI alternator is self-excited and will not work with a stock diode isolator but there are isolators with an excite terminal that a Delco will work with. See this post for more information.

Lithium Conversion - 2014 IH-45

Either alternator will work without a diode isolator when connected directly to the chassis battery. LN requires an excite wire, Delco has no excite terminal.

Either alternator has a "sense" terminal that will compensate for voltage drop due to a diode isolator (if present) or in the wiring to the battery.

DUVAC means DUal Voltage Alternator Control - this is the alternator voltage "sense" capability.

DUVAC doesn't refer to a specific brand of alternator or require the use of a diode isolator.

Any alternator with voltage "sense" capability is a "DUVAC" alternator.

So with all that said you will be fine using the LN alternator without the isolator. Connect the alternator sense wire to the chassis battery + terminal.

Additional notes:

Delco 28SI will function without the sense wire, but your system will perform much better with it.

LN 2824LC must have the sense wire connected otherwise the charge voltage will be uncontrolled and go all the way to the maximum and can damage your batteries.

Recommended upgrades for the LN 2824LC:
Delco 28SI 200 amp (brushes)
DelStar 100-16100 200 amp (brushless)
Delco 40SI 240 amp (brushless)
DelStar 100-17107 250 amp (brushless)
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Duvac or not to Duvac?

Reply #2 –
Quote from: Dave & Diane –
So what does everyone do when they've added a B2B battery charger to safely regulate what your LiFePO4 battery bank can demand from the alternator AND you have removed the isolator from the coach? 

Does it really matter?  If it does, then replacing the alternator is required when removing the isolator from the coach.

OK, disclaimer-- I have no first hand experience with B2B battery chargers.

But, I believe that the B2B battery charger functions as a battery isolator and successfully replaces it.

And, a DUVAC alternator will work with either.  Its battery sense terminal only needs to be connected to the chassis battery. 
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: Duvac or not to Duvac?

Reply #3 –
Thanks for the info! 
Dave & Diane
2001 U270 36' WTFE #5820
2016 Jeep Wrangler Hard Rock
Motorcade #18156
 

Re: Duvac or not to Duvac?

Reply #4 –
Replacing the alternator can also be ideal time to upgrade it. Part of that decision is really how you intend to charge a larger battery bank and also if you want to operate other loads from the battery bank, engine alternator. For example, some want to run one or 2 roof top ACs while driving. Using DC-DC converters just to control or reduce alternator loading is really a miss application and again, with the BMS in most batteries they can add duplicate and restrictive controls with limited benefit.

Foretravel is amongst a few manufacturers that are using the Duvac control method. There are some downsides but also some real benefits. The combination of the diode method, with voltage sensing on only the chassis batteries, and size, length of cables actually work to provide current to a large battery pack that will allow for voltage drop, based on battery charge acceptance which will also reduce current loading to the house battery bank. Basically, current limitation is already in place. Having experimented and taken measurements I see limited current draw change from my three, 210 A/H AGM to now three 300 A/H lithium's.  Even with the batteries pulled down to 20% SOC, upon just starting I see a high of ~160 amps going into the batteries. After about 15-20 minutes this drops to ~120. Voltage on the chassis side is near 14-14.2, (dash shows 13.8), and the house batter bank is around 13.6-13.8. After about 45 minutes the current is down to about 90 and the voltage is raising some. As the batteries approach full charge the current actually drops in stages as each battery BMS turns charging off. Voltage then will be equal for both chassis and house batteries. Note that I have a 270 amp alternator.

For my inverter charger, I have a 150 amp charge section. If I start the generator and let the charger go while the engine is running you can see that the inverter current gets added to the alternator output. I can peak over 200 amps going into the batteries. As the charger can go to 14.5 volts as the batteries charge it will overcome the alternator and there will be no current coming from it. Closing the boost relay the house battery bank and inverter charge can raise the voltage of the chassis batteries.

My plan was to replace the diode set with a voltage-controlled relay. But seeing how well this is working I am going to leave as is for now.
Dennis Haynes
Bohemia NY
2008 Nimbus 342 SE Carlyle
Build #6475
Motorcade #19148