Sprinter House Batt Charging

[Wyz3rd]

Hello Friends,

There is no doubt that this topic has been discussed to death, but I have very specific question that I hope can be answered on this forum. I have a Freedom Elite 24FE. It's a small motorhome built on a 3500 Sprinter chassis. The Sprinter is a 2019 model, but the Motorhome is 2021. I guess the Sprinter was sitting around for a couple of years waiting for me.

This much I do know, the house batteries will charge with either shore power connected, or the generator running, and with the 100W (dinky) solar panels that it came with.

What I cannot find out is, will the house batteries charge from the alternator when the vehicle is on the move? There were changes in the Sprinter after 2018, and I've seen various and conflicting posts about whether the HB charge from the alternator. I know there are BIMs available to allow both batteries to charge with generator/shore power...I think.

But my question remains - will the alternator charge feed the converter and house batteries?

Thanks to all of you fine folks for listening.

[Bob Denman]

Yes.
If you have your "Use/Store" switch set on "On": you will see the voltage climb.

[Wyz3rd]

Originally Posted by Bob Denman

Yes.
If you have your "Use/Store" switch set on "On": you will see the voltage climb.

I guess the obvious question is, would have to put a volt meter on the battery before starting the engine, then the reading should jump from ~13.1 to ~14.2 or something close, right? Would the solar controller also be feeding the battery and interfere with the reading?

Thanks!

[Bob Denman]

No. Just turn the switch on without starting the engine...
You'll get the "before & after" picture.

[EA37TS]

OK, dumb question here.

At one point in time it was mentioned that MB did not allow Thor to connect the house batteries into the chassis charging circuit. Was that incorrect information or did that change somewhere in time? Or is it possible I am imagining a discussion or thread on the forum that does not exist?

[Bob Denman]

They allow a "one-way" street to exist...
The alternator will charge the coach batteries; but shorepower and generator just hang the chassis battery out to dry.

[16ACE27]

Originally Posted by Wyz3rd

I guess the obvious question is, would have to put a volt meter on the battery before starting the engine, then the reading should jump from ~13.1 to ~14.2 or something close, right? Would the solar controller also be feeding the battery and interfere with the reading?

Thanks!

This is correct for a system with no solar charger. So either disconnect the solar charger and wait an hour before taking the BEFORE reading (I'm assuming all house loads are off), or do the test at night.

BTW, 13.1 VDC is float charge voltage, 12.6 - 12.7 VDC is a fully charged battery at rest. Just to be clear, you should not have the coach plugged into SP or the generator running when you do this test. Charging voltage from the engine may be as high as 14.9 VDC but normally doesn't exceed 14.5 VDC.

[Wyz3rd]

Originally Posted by EA37TS

OK, dumb question here.

At one point in time it was mentioned that MB did not allow Thor to connect the house batteries into the chassis charging circuit. Was that incorrect information or did that change somewhere in time? Or is it possible I am imagining a discussion or thread on the forum that does not exist?

This is not a dumb question. It helps my understanding of how MB works because I had also seen a post about that. Looks like Denman answered that the shore power and generator will only charge the house battery, which addresses my immediate concern of keeping the house battery charged up while on the move.

for the chassis battery, there is something called a Battery Isolation Manager which goes between the house and chassis to maintain both batteries when either battery is charging. Seems like a good product for an MB.

https://integrityrvparts.com/product...QaAr_6EALw_wcB

[Wyz3rd]

Originally Posted by 16ACE27

This is correct for a system with no solar charger. So either disconnect the solar charger and wait an hour before taking the BEFORE reading (I'm assuming all house loads are off), or do the test at night.

BTW, 13.1 VDC is float charge voltage, 12.6 - 12.7 VDC is a fully charged battery at rest. Just to be clear, you should not have the coach plugged into SP or the generator running when you do this test. Charging voltage from the engine may be as high as 14.9 VDC but normally doesn't exceed 14.5 VDC.

Awesome! Thanks for mentioning that. Not sure which wire comes from the solar controller but would imagine that it's the smaller gauge wire.

[paulwadley]

When parked in storage, I plug in a solar battery tender to the chassis battery to help keep a charge flowing to the chassis battery. The engine when running will charge both the chassis battery and send a charge to the house batteries. I did have my dealership install an emergency start switch that allows a charge to go from the house batteries to the chassis battery in the event my chassis battery goes dead. It was something I had in my previous class B Winnebago class B which was built on a 3500 MB Sprinter chassis. Thor did not have that option so my dealership ordered it from Winnebago for my Thor Siesta.

Paul

[Bob Denman]

I also use a solar battery charger on mine when it ain't moving.
(40 watts)

[sanjaun2]

My 2017/2018 MB sprinter based 24FS charges great off the Engine alternator. Once the engine battery reaches a certain voltage it trips a relay under the drivers seat and then charges the house bank. Absolute fact and wired that way when new. So, I think it depends on the model and year of the coach. Just like right and wrong answers found here. Anyone with a motorhome should buy a voltmeter and learn to use it. One of the most important tools to carry with you. Harbor freight sells a basic one under ten bucks and its light and compact.

[eodchik@yahoo.com]

We thought that our RV wasn’t wired to charge the house from the alternator because that is what Thor told us. When we pulled the driver’s seat we found the trombetta that sends charge to the house once the vehicle battery is charged. The problem was a wire that hadn’t been properly tightened. We now have installed a voltmeter to check and make sure house batteries are receiving a charge. If you install the meter make sure it has an on/off switch so you don’t have a parasitic drain. Also watch the videos before you pull the drivers seat. There is an expensive airbag wire you can easily damage

[Bob Denman]

Glad that it turned out to be so simple!

[M&M_MURPHYS]

I called Thor to find out about thus on our 2016 3500 MB chassis.

I wanted to know if the wiring needed to be upgraded because I added lithium batteries and some times the alternator wires are not large enough for that type of set up.

I was told by Thor that, for whatever reason, they do not wire the batteries to the alternator in the MB chassis. Thus driving the rv does not charge the batteries.

I have my lithium batteries installed and i assume the batteries are not being charged by the alternator. Just shore power and our solar panel

[Bob Denman]

Thor may very well have changed this in the past five years...
Check the voltage at your house batteries with the engine off...
... and then check it again; with the engine on...

[EA37TS]

MB does not allow Thor to connect the house batteries to alternator. Know issue for years.

[Bob Denman]

Tiffin does...

[JMF]

Originally Posted by EA37TS

MB does not allow Thor to connect the house batteries to alternator. Know issue for years.

They do, but it is a one way transfer. They use a Trombetta solenoid to isolate power. I think newer models use a BIM. The batteries are tied when alternator is running.

[JMF]

Originally Posted by M&M_MURPHYS

I called Thor to find out about thus on our 2016 3500 MB chassis.

I wanted to know if the wiring needed to be upgraded because I added lithium batteries and some times the alternator wires are not large enough for that type of set up.

I was told by Thor that, for whatever reason, they do not wire the batteries to the alternator in the MB chassis. Thus driving the rv does not charge the batteries.

Well you were told wrong. I just did this a few months ago on my 2019 Siesta. The most important thing when you upgrade to LiFePo batteries is to put a DC to DC charger in place of the Trombetta solenoid under your driver’s seat. Failure to do so can stress your alternator and possibly result in it’s failure. This is especially true if your house batteries are in a low state of charge. The added benefit of the DC to DC charger is that it will charge the batteries at the proper voltage to achieve full charge. The converter power supply and the solar controller will work as is, but will not fully charge the batteries unless you upgrade them.