Charging house batteries while driving

[Heckler56]

Originally Posted by Photoshooter

Boy, I have an Interstate 24 GT coming in 2 months and I wish I understand any of these replies. It has solar and lithium batteries. Apparently, my brain is not wired to understand electricity at all. Simply over my head. I read these to try and get educated but it doesn’t seem to work. Would someone wanna bottom line these conversations for a complete idiot to understand?

Thank you.

Mythbuster said it. You are ahead of the curve to start now before you get in the vehicle and begin experiencing all the systems. My education was by fire and trying to interpret what these discussions were/are saying had my head spinning.

To answer your question here is my novice and simple attempt. There are a couple of battery types out there you will hear about: flooded (add water), AGM (these come standard) and lithium. These different battery types come with different charging and usage characteristics. Since you have the lithium upgrade I will only speak about those.

Lithium batteries provide a relatively stable current during use down to a baseline bottom of the battery, like 10% of its capacity, as established in the batteries bms (battery management system- software). Flooded or AGM you never want to run down below 50% capacity or it can damage the batteries and there is no BMS that stops the draining. Lithium can allow large amounts of amperage to charge it. Hence the discussions here on how much can your alternator deliver but also service the engine, ac, and other vehicle needs while charging the lithium batteries. Think of it like a 6 way extension cord. If you plug too much in it will blow. Some have solved this through a second alternator and for me I have a charger (Sterling brand) (think of it like a cell phone charger) that essentially runs off of the alternator. These Sterling chargers are also called dc to dc.

For you having the lithium set up you are ahead of the curve most of us deal with in either adding more AGMs or switching over to lithium to get to battery banks large enough to use these the way we want them. Someone else here will likely mention how Airstream built your lithium system so you will understand where it gets it’s charging and at what level of charge. Someone else here will also correct my use of terms, current amperage, etc but hopefully this gives you a better understanding.

[Photoshooter]

Originally Posted by Heckler56

Mythbuster said it. You are ahead of the curve to start now before you get in the vehicle and begin experiencing all the systems. My education was by fire and trying to interpret what these discussions were/are saying had my head spinning.

To answer your question here is my novice and simple attempt. There are a couple of battery types out there you will hear about: flooded (add water), AGM (these come standard) and lithium. These different battery types come with different charging and usage characteristics. Since you have the lithium upgrade I will only speak about those.

Lithium batteries provide a relatively stable current during use down to a baseline bottom of the battery, like 10% of its capacity, as established in the batteries bms (battery management system- software). Flooded or AGM you never want to run down below 50% capacity or it can damage the batteries and there is no BMS that stops the draining. Lithium can allow large amounts of amperage to charge it. Hence the discussions here on how much can your alternator deliver but also service the engine, ac, and other vehicle needs while charging the lithium batteries. Think of it like a 6 way extension cord. If you plug too much in it will blow. Some have solved this through a second alternator and for me I have a charger (Sterling brand) (think of it like a cell phone charger) that essentially runs off of the alternator. These Sterling chargers are also called dc to dc.

For you having the lithium set up you are ahead of the curve most of us deal with in either adding more AGMs or switching over to lithium to get to battery banks large enough to use these the way we want them. Someone else here will likely mention how Airstream built your lithium system so you will understand where it gets it’s charging and at what level of charge. Someone else here will also correct my use of terms, current amperage, etc but hopefully this gives you a better understanding.

Thank you.

[Hawk-ination]

To anyone reading through this feed, please remember that we have people posting that have trailer setups with tow vehicles. They give advice on adding or changing your alternator, but that is not necessarily applicable to our Mercedes-Benz Sprinter vans. It’s also a little bit of a difference between the systems our vans integrate vs. the setups they have.

I personally feel like that should be discussed in a different thread all together because it confuses the issue.
If I were great at debating, I’d go at it about the Victron video in having fixed and warranties alternators for years, but I’m not in the mood, and also think that discussion is meant for a different feed, as I said.

Two points of confusion. There’s those of us who are upgrading our system to lithium. In a different group, there will now be owners who are buying their Interstates with lithium new, or new to them.

Also to add to the confusion, the difference in the length of time it takes to charge a lithium battery. It will take longer because it’s like a big suitcase. They take longer to pack over a small suitcase, because they hold more. Lithium is just the same. They take longer to charge, because they hold more capacity to do so. I’ve read they take a charge faster than AGM and lead-acid batteries though, so it’s a percentage difference.

If you are getting a lithium setup from the factory, you might end up wanting to enhance your charging capabilities in the future, but know they should come fully functioning without needing to upgrade or change anything from the factory. Someone will probably come on and dispute that, as I read something about the Bim not being correct from some of what I’d assume were the first installs. I’m sure Airstream has corrected that.

For the rest of us with Interstates who are upgrading, unless you start to understand how electricity, charging, alternators, batteries, etc. works in depth, you just change your old Bim out to a Li-Bim, or add a DC-DC isolator. Any more in depth discussion falls under the enhancing the system. They are entirely different things.

[uncle_bob]

Hi

If you dig into the Sprinter upfitter manuals on the Mercedes site, they actually get into this a bit. Up to about the end of last year they had a limit of 40A on the alternator. Without any changes to the alternator or other (obvious) chassis changes, that morphed into 80A earlier this year. Did something actually change or was 80A ok all along? Who knows ....

The term they use for this load is something like "maximum power to non-chassis loads. Current in excess of this limit may damage the chassis electrical components". That's probably not word for word, but it's close.

Link to the "front door" of the portal:

https://www.upfitterportal.com/en-us/

You click on "technical resources" and give them your email info. You then can download an absolutely mind numbing amount of info on the Sprinter chassis.

Bob

[Boxster1971]

Originally Posted by uncle_bob

Hi

If you dig into the Sprinter upfitter manuals on the Mercedes site, they actually get into this a bit. Up to about the end of last year they had a limit of 40A on the alternator. Without any changes to the alternator or other (obvious) chassis changes, that morphed into 80A earlier this year. Did something actually change or was 80A ok all along? Who knows ....

The term they use for this load is something like "maximum power to non-chassis loads. Current in excess of this limit may damage the chassis electrical components". That's probably not word for word, but it's close. . . .

The 40A limit was apparently dropped with the new 907 (VS30) Sprinter in 2018-2019. I have copy of first 907 Body and Equipment Guidelines (BEG) dated 12/2019. Both versions have restriction that does not allow connecting large house batteries to the chassis without a current limiter.

Here is quote from the Note on page 245 and 246 from the new 4/2021 BEG:
"Aftermarket battery with capacities > 100 Ah must
not be connected directly to the vehicle electrical
system, as damage to the basic vehicle may occur.
Please select a suitable generator to ensure a
positive overall charge balance"

The same Note is in the 12/2019 version of BEG.

I wonder if the current Interstates have current limiter as required by Mercedes.

[uncle_bob]

Originally Posted by Boxster1971

The 40A limit was apparently dropped with the new 907 (VS30) Sprinter in 2018-2019. I have copy of first 907 Body and Equipment Guidelines (BEG) dated 12/2019. Both versions have restriction that does not allow connecting large house batteries to the chassis without a current limiter.

Here is quote from the Note on page 245 and 246 from the new 4/2021 BEG:
"Aftermarket battery with capacities > 100 Ah must
not be connected directly to the vehicle electrical
system, as damage to the basic vehicle may occur.
Please select a suitable generator to ensure a
positive overall charge balance"

The same Note is in the 12/2019 version of BEG.

I wonder if the current Interstates have current limiter as required by Mercedes.

Hi

At least the 2021 GT's as described in the owners manual do. They have a Victron DC/DC converter. It limits the current to 50A (or less, it can be programmed ....)

Bob

[Boxster1971]

Originally Posted by uncle_bob

Hi

At least the 2021 GT's as described in the owners manual do. They have a Victron DC/DC converter. It limits the current to 50A (or less, it can be programmed ....)

Bob

Good to know. My 2013 Interstate just has a device that connects the batteries without current limits. I'm sure it never met the Mercedes engineering requirements of 40A limit when it was built.

[uncle_bob]

Originally Posted by Boxster1971

Good to know. My 2013 Interstate just has a device that connects the batteries without current limits. I'm sure it never met the Mercedes engineering requirements of 40A limit when it was built.

Hi

I don't know for sure just how far back the 40A / 80A notes go. I did not do a deep dive into the history. I was mainly trying to work out what will be what when (if) my GT gets here in the fall.

Bob

[Yak-55]

Originally Posted by uncle_bob

Hi

At least the 2021 GT's as described in the owners manual do. They have a Victron DC/DC converter. It limits the current to 50A (or less, it can be programmed ....)

Bob

Bob (or others),
Do you have a link for the Victron DC/DC converter manual (as installed in the 2021 GT) ? I’m curious how it’s set up for the Battleborn lithium batteries.

Thanks,
Peter

[Boxster1971]

Originally Posted by Boxster1971

Yes - the Airstream OEM battery isolator is useless if you have any solar. In daylight solar raises the house battery voltage and the isolator thinks they are charged because it only monitors voltage. I added a manual switch to mine so I can force a battery connection if needed. Works great and only involved changing the battery boost switch by the drivers LH knee to allow constant connection rather than the momentary switch installed by Airstream. Also added a current meter so I can monitor the energy flow to and from the batteries.

I received a PM question on this post so I'm adding some details about how I modified the battery isolator on my 2013 Interstate.

Attached is a diagram of the wiring changes I made. Also photo of current meter I installed to monitor the current flow when the boost switch is on.

[uncle_bob]

Originally Posted by Yak-55

Bob (or others),
Do you have a link for the Victron DC/DC converter manual (as installed in the 2021 GT) ? I’m curious how it’s set up for the Battleborn lithium batteries.

Thanks,
Peter

Hi

From other posts, the claim is that it's a Victron TS800:

https://www.victronenergy.com/dc-dc-...verter-25a-50a

Do they use the 50A version or the 25A? If it's the 50A do they program it for a lower current limit? No idea yet ....

It would be nice to see some screen dumps from the programming software. It's a pretty good bet that some percentage of what's on the road doesn't quite have the right settings programmed into it.....

Bob