T1N Safe Alternator charging of AGM house batteries

[Baruch]

I have a 2005 Interstate and am upgrading my Converter/Charger to an AGM friendly 3 phase Converter/charger.
I want to also prevent the alternator from damaging the AGM batteries by the alternator charging that cannot be turned off.
I am considering installing a on/off switch in the circuit so I can turn it on when my batteries are low and I'm driving and then turn it off when they're getting full.
Or upgrade the 12v factory switch to one that somehow is safer for my house batteries.
I cannot find a wiring diagram for the alternator to house battery circuit and haven't yet visualized the current switch which I think is under the drivers seat.
Help please

 

[autostaretx]

An "AGM friendly" charger should be able to be left on all the time ... when it senses that the AGM is fully charged, it should drop to "float" charging (proper voltage, very little current) which is designed to just operate as a "battery maintainer".

--dick

 

[Baruch]

Thanks Dick
What I'm trying to improve is the alternator to isolator solenoid to chassis battery & house battery system so that the house batteries don't get too high a voltage when they are full and I'm driving.

 

[ECU]

Thanks Dick
What I'm trying to improve is the alternator to isolator solenoid to chassis battery & house battery system so that the house batteries don't get too high a voltage when they are full and I'm driving.

That isn't a concern. If you Had LiFePo4 batteries, there would be a battery management system. But AGMs are not a concern.

 

[Baruch]

Thanks much ECU.
The schematic I presume it what's under the drivers seat?
Where is the isolator battery switch solenoid?
My concern is that my house AGM battery is sensitive to ongoing high voltage "float" charge that the aternator / solenoid doesn't dial down the way a smart charger would.

 

[autostaretx]

ECU's schematic is from an NCV3 or VS30 (T1Ns don't have F55/3 and F55/4, nor a "BCM" controlling them.)
His layout diagram does apply to the T1N

Yes, in the T1N the isolation relay is one of those on the relay rail under the US driver's seat.
(there was a thread a few days ago with a photo of it)

--dick

 

[autostaretx]

An AGM actually can handle a higher float voltage than a normal flooded lead acid.

On my 2005 T1N, the alternator puts out 14.2 volts immediately after starting, but about ten minutes later drops to 13.6 to 13.8 (depending upon load) for the rest of the drive.

Any Sprinter that comes with an MB-installed auxiliary AGM battery *also* gets an AGM battery in the starter position.
The alternator appears to stay the same. (AGM versus flooded)

In the T1N, it's the Instrument Cluster that controls the alternator's output. It's the source of the signal being sent down the thin wire to the alternator.
In Ye Olden Days that was known as the DF (dynamo field) signal ... it powered the coils generating the magnetic field that the dynamo/generator/alternator spins its rotor through. (in an alternator, the moving part is the "field" and the surrounding coils receive the induced voltage/current).

--dick

 

[Baruch]

Thanks!
My AGM house batteries specs say to float at 13.3.
To take extra good care of them, I'm thinking to interrupt the trigger wire for the solenoid with a switch with the believe that if the switch is open (off) the alternator will charge the chassis battery only and if I close the switch (on) it will charge the house batteries once the chassis battery is charged.
With that setup I can turn on the switch when I need the van to charge the house batteries and closing it when they get to 14.0 v / 90%.
Does that make sense to you all even if you don't agree with the need to protect the battery?

By the way, Happy New Year!

Baruch

 

[autostaretx]

I sincerely doubt that they'll ever get to 14.0v (except during the first 10 minutes since start-up)

A voltmeter is your friend:



--dick

 

[Baruch]

Yeah, I wasn't sure about the 14.0. Idea is just to not have the alternator charge them at 13.8 volts or so after they're about 90% charged and prefer a 13.3 or so float voltage.
I have one of those cool little 12v socket voltmeters for the vehilcle battery.
For my house batteries I have a Victron Smart Shunt to track the voltage on my phone along with my Victron Solar Charger and 375w panel.
Is my possible switch understanding consistent with your's regarding the trigger wire from the instrument panel?
And might you have a link to the photo of the isolation relay you mentioned? I searched and couldn't find it.

thanks again

 

[SSTraveler]

Consider replacing your isolator solenoid with a DC-DC charger, that way you're house AGM batteries will be charged with a proper AGM battery charging algorithm. Here are 2 videos I've done showing 2 different brands of DC-DC charger installation. I use an ignition controlled isolator relay to isolate the chassis battery from the house battery system when the ignition is off. This is important if you want to charge the chassis battery. I also recommend adding a chassis battery charger, so when your house batteries are being charged from shore/generator power or solar your AGM chassis battery is maintained. I use a Xantrex ECHO-Charger in the videos, but the House2Start is an excellent choice, simpler to install, and less expensive. I have videos on my channel showing its installation if you need it. Click on the video title when watching to open my description which contains the links to everything.

 

[autostaretx]

Yeah, I wasn't sure about the 14.0. Idea is just to not have the alternator charge them at 13.8 volts or so after they're about 90% charged and prefer a 13.3 or so float voltage.
I have one of those cool little 12v socket voltmeters for the vehilcle battery.
For my house batteries I have a Victron Smart Shunt to track the voltage on my phone along with my Victron Solar Charger and 375w panel.
Is my possible switch understanding consistent with your's regarding the trigger wire from the instrument panel?
And might you have a link to the photo of the isolation relay you mentioned? I searched and couldn't find it.

thanks again

Here's the specific posting with the photo: (photo cropped and repeated below this note's text)

Wiring stock MB Aux battery relay

Hello, I am looking for some help hooking up a stock Mercedes auxiliary battery relay to charge an AGM house battery in my '04 Sprinter. I will be triggering the relay from the EK1 terminal under the driver's seat. However, the relay itself has no markings on plug/pins for the trigger and...

sprinter-source.com

The NCV3 and VS30 mounted a *different* relay at the "center rear" of the driver's seat pedestal (near the parking brake hinge)
(those models have the terminal bolts oriented differently)
I have no idea specifically *where* MB put this (pictured) relay in the T1N (under the driver's seat: yes)
Based upon the mounting "bracket" shown in the photo, it could be screwed on to the pedestal's walls.



The "trigger wire" from the instrument panel undoubtedly also powers a smaller relay that then powers the D+ post on the EK1 terminal strip (which, in a T1N, is mounted on the center wall of the seat pedestal)
The EK1 strip:



D+ relay trigger (not isolation relay): First, how the coil is powered:


Now the contacts on that relay feeding the EK1 strip itself:




--dick

 

[SSTraveler]

I found the Mercedes relay under the driver's seat in this 2006 T1N LTV Free Spirit.