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Voltage regulator setting for new alternator

We have 3 group 31 agm start batteries. Having a new alternator installed. How high should the voltage regulator be?

Would the setting be when measured at the batteries at high idle?

If it matters, the house batteries are gel cells, want to be sure they are not overcharged.

Thanks
Mike & Molly Patronick
2001 U320 40'
2011 Forester

Re: Voltage regulator setting for new alternator

Reply #1 –
Here is how I understand this end of the electrical system. If you have the Leece-Neville alternator and the original diode based isolator then with the engine at high idle (cruise control on, press Resume) I believe the voltage should read about 13.8 volts at the start batteries.  Measure at the opposite corners of the three batteries where the main cables are connected.

Some alternators are smarter than others.  The diode based isolators lose up to one volt across the diodes. Other isolators have near zero voltage drop.

If your new alternator needs a sense wire make sure it has 12 volts all the time.
(Thanks for the help, Chuck and Brett)

Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Voltage regulator setting for new alternator

Reply #2 –
Mike,

A bit of a complex question,  Because OE, the alternator B+ is connected to a DIODE-BASED ISOLATOR (as is a sense wire).

So, as long as they know that you are talking about voltage on the FAR SIDE of the isolator (where the sense wire is connected), you can have it adjusted.

Not sure there is one single answer, as fine tuning voltage depends on temperature, depth of discharge (i.e. do you want bulk mode charging or float mode) as well as how long you drive. 

If you are really concerned about charge voltage, there ARE some very good smart regulators, most developed for marine applications (we have one on the sailboat).

You can also modify how alternator output is handled.  A simple marine on-off switch can be used either in place of the diode based isolator, or in the charge line for the house battery bank.  If driving all day, very easy to take the house bank out of the charge circuit.

Irrespective of what route you take, remember, the alternator HAS TO charge the chassis battery while driving (both to protect the alternator diodes and to keep voltage up for the many systems that use 12 VDC while driving).
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: Voltage regulator setting for new alternator

Reply #3 –
Quote from: Chuck & Jeannie –
The "sense" wire, if required, should have 12 volt on it all the time.
The "excite" wire, if required, should have 12 volt on it when the ignition is on.

Correct
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: Voltage regulator setting for new alternator

Reply #4 –
Easy to change the voltage in seconds with a screwdriver on a lot of our alternators with built in regulators. Here is a site for troubleshooting and voltage adjustment Prestolite and Leece-Neville: Prestolite - Leece Neville

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Voltage regulator setting for new alternator

Reply #5 –
We do not know what alternator the OP has or what kind of isolator. 
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Voltage regulator setting for new alternator

Reply #6 –

We do not know what alternator the OP has or what kind of isolator.
[/quote]

The alternator is a Leece Neville #2824LC, 14v, 160 amp.

The isolator is a Cole Hersee #48160 200 amp.

Both of these were from FOT parts earlier this year, specifically for this coach year and model.

In 2014 MOT replaced the start batteries with the current AGM's. Keith Risch adjusted the voltage regulator to achieve a particular voltage at the start batteries. My memory says he set it for 13.8v but I've learned not to trust my memory past 5 minutes.

Thanks



Mike & Molly Patronick
2001 U320 40'
2011 Forester

Re: Voltage regulator setting for new alternator

Reply #7 –
13.8 is a good "compromise" voltage. Lower than ideal for fast charge and a bit higher than ideal for "float rate".
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: Voltage regulator setting for new alternator

Reply #8 –
Same alternator rebuilt correctly. Set for 13.6 volts.

Charges at 13.5 at the dash plug in gauges.

Works well as I tested this a few days ago running the convection oven(850 watts?) at 150 degrees  and the chest refer in the bays and domestic ice maker for two hours drive time

Tach Gauge flickered a bit and voltage was around 13.1 or so so I assume I was using all the 160 amps available.

Good sw2812 it seems.

Not using an Isolator anymore my buddy installed a blue sea ml-acr automatic charging relay with a three position switch where the boost switch was previously
"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: Voltage regulator setting for new alternator

Reply #9 –
The VMSpc shows my voltage at 14.6 driving down the road.  Is that an issue, or OK based on where the reading to VMSpc is taken?

(2003 U320)

Dan - Full timing since 2009
2003 U320 40' Tag 2 slide

Re: Voltage regulator setting for new alternator

Reply #10 –
Quote from: AC7880 –
The VMSpc shows my voltage at 14.6 driving down the road.  Is that an issue, or OK based on where the reading to VMSpc is taken?

(2003 U320)



Use a digital voltmeter to verify voltage at the chassis battery.  14.6 VDC is TOO HIGH if that is really what it is.
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: Voltage regulator setting for new alternator

Reply #11 –
Quote from: AC7880 –
The VMSpc shows my voltage at 14.6 driving down the road.  Is that an issue, or OK based on where the reading to VMSpc is taken?


IIRC that alternator was set to 14.1 VDC when installed by FOT in 2014 (check the paperwork).  Our VMSpc usually ran 13.6-14.1 VDC.  Wonder if there's a loose connection on something like the sense wire.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Voltage regulator setting for new alternator

Reply #12 –
Will go for 13.6v. Avoiding overcharge to house gels is more important to me than fast charge for the start batteries.

Thanks to all.
Mike & Molly Patronick
2001 U320 40'
2011 Forester

Re: Voltage regulator setting for new alternator

Reply #13 –
Early morning starts may see higher voltages for a short time but the voltage should drop to the 13+ volts after a short time. Our solar controller manufacturer said we could leave the array on while driving but it raised the voltage over 14V so I shut it off while driving. Use a digital voltmeter at dash and batteries to check to see if they agree.

Here is a quote from an excellent AGM charging article:
"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive"

Complete article at: Absorbent Glass Mat (AGM) Battery Information - Battery University

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Voltage regulator setting for new alternator

Reply #14 –
Quote from: AC7880 –
The VMSpc shows my voltage at 14.6 driving down the road.  Is that an issue, or OK based on where the reading to VMSpc is taken?

(2003 U320)



Update on my post above.  Immediately after Cummins ISM cold start, with no boost switch use, my VMSpc is bouncing between 14.6 and 14.7 volts.  Measured start batteries at the terminals with digital volt meter one minute later, and it's 14.15 volts on the mark.  The monitor that shows tank levels at the dash showed 14.1 volts at the same time.

So the VMSpc is showing erroneous voltage (as compared to start batteries).  While under the coach, I checked and there is no sense wire on the positive terminals at the start batteries.  Checked back of the Leece Neville alternator, I have normal positive and negative large cables, 2 smaller wires from 2 other terminals that go into wrapped main harness along the valve cover on the ISM. No visible wires out of place or disconnected near alternator nor start batteries.

I did not get model number of the leece neville alternator while in there, but it seems this one does not use a sense wire like my previous motorhome did (at least not directly to the positive terminals of the start batteries).

NOTE:  I did not check to see if it looks like the 2 wires (or one of two) mentioned above go to the battery isolator under the bed.  That is a distinct possibility.
Dan - Full timing since 2009
2003 U320 40' Tag 2 slide

Re: Voltage regulator setting for new alternator

Reply #15 –
Quite likely the sense wire is on the chassis battery lug of the isolator.  But "electrically" any connection on the chassis battery side of the isolator is just fine.

And, your 14.1 is not a problem. MUCH better than 14.7!
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: Voltage regulator setting for new alternator

Reply #16 –
Dan, VMSpc simply displays the voltage reported by the engine ECM (computer).  Have you seen any errors reported in the logs?  Before I replaced my alternator I got frequent low voltage faults at injectors.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN