Second Alternator for Charging House Batteries

[migriffin]

A few of the manufacturers are adding second alternators to the Mercedes Sprinter to charge the house batteries instead of needing a generator. The engine kicks on automatically if the batteries get below a certain point and it charges them relatively quickly. Seems like a great solution especially when you're camping in places that do not allow generators or you want to avoid the noise of the generator. I'm curious if it's possible to add this to the Airstream Interstates and if so, who could do it?

Here are some links for background:
Go Farther Off the Grid: Advanced RV Redesigns Battery System - Advanced-RV
Dual alternators, why or why not .... • Class B RV and Camper Van Discussion Forum

[Protagonist]

Originally Posted by migriffin

A few of the manufacturers are adding second alternators to the Mercedes Sprinter to charge the house batteries instead of needing a generator. The engine kicks on automatically if the batteries get below a certain point and it charges them relatively quickly. Seems like a great solution especially when you're camping in places that do not allow generators or you want to avoid the noise of the generator. I'm curious if it's possible to add this to the Airstream Interstates and if so, who could do it?

With the BIM, that automatically detects charging current and connects the house and chassis systems, can't you already charge the house batteries from the existing engine alternator? I don't know of anyone who does, but in theory it's possible. You would have to "high-idle" the engine to do it, but you'd have to do that with a second alternator as well.

As for who could do the install, in theory any authorized Sprinter upfitter could do it. Airstream (Jackson Center, not individual dealers) is an authorized upfitter, but you might want to check the Sprinter webpage to find someone more local to you.

[migriffin]

Hi Protag. Yes, you can do that, but my limited understanding is that it doesn't charge nearly as quickly as the second alternators that they are adding purely for charging the house batteries. If you've followed davydd's "Advancing Alvar" posts on the ClassBForum, he's reporting that he can charge his 800ah lithium batteries from about 30% charge in about 2 hours.

You're right about needing to be in high idle.

[HowieE]

Originally Posted by migriffin

Seems like a great solution especially when you're camping in places that do not allow generators or you want to avoid the noise of the generator. I'm curious if it's possible to add this to the Airstream Interstates and if so, who could do it?

If the campground will not allow a generator it will not allow you to run the engine to charge the coach batteries either.

There is a crossover point in the total battery amperage you have where a second alternator makes sense.

Any good generator/starter or good mechanic shop could do the mode, it is a simple bolt on change.

[m.hony]

With the right brackets and belts it can be done. It is common to have 2 alternators in tool sales trucks with an on board show room (Mac, Snap-On, S-K) and high power custom car audio. I imagine ambulances, bookmobiles, mobile shoe sales vehicles, mobile hearing test vehicles, and others have 2 alternators.

[Gnorts]

An alternator designed specifically for charging a deep cycle house battery bank is very different than the standard automotive alternator. It needs a special regulator that will provide the proper three-step charging routine (bulk, absorption, float) just like a three-step battery charger/converter. It also needs to be "hot rated" to withstand the type of duty required of it. This kind of setup is routine in cruising sailboats and powerboats, but pretty rare in the RV market. A m.hony mentions, it also is found in mobile applications where demand is high (ambulances, utility line trucks, etc.) and where large battery banks power inverters for running respirators, power tools, etc. It's a specialized and expensive setup, but certainly worth the effort if you're serious about self-sufficient boondocking, which is pretty much like "anchoring out" in a boat.

[Boxster1971]

Originally Posted by Protagonist

With the BIM, that automatically detects charging current and connects the house and chassis systems, can't you already charge the house batteries from the existing engine alternator? I don't know of anyone who does, but in theory it's possible. You would have to "high-idle" the engine to do it, but you'd have to do that with a second alternator as well.



As for who could do the install, in theory any authorized Sprinter upfitter could do it. Airstream (Jackson Center, not individual dealers) is an authorized upfitter, but you might want to check the Sprinter webpage to find someone more local to you.

I agree with Protag about the BIM - it is adequate for charging the stock Interstate house batteries. Now if you install a much larger battery pack having a second alternator with separate charge profile might make sense.


- - Mike
2013 Lounge EXT on 2012 Sprinter

[73shark]

Check out the Roadtrek E-trek. It uses a chassis driven generator.

[lewster]

If anyone is interested in adding a second alternator specifically for battery charging, look up Balmar.

They have a huge presence in the marine industry.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center
Lifeline Batteries**Magnum Inverters
541-490-6357

[Gnorts]

Good referral, Lew. When I was installing high-demand charging systems in boats, I used Balmar products a lot.

Welcome to Balmar

[bennu36]

I am sure this has come up before in one of the many threads about batteries, but can any one tel me for certain (Portag) In a 2012 with the stock triplite charger (and yes I know there are those that would have me replace that first) does it charges the start battery as well has the house batteries?

[Protagonist]

Originally Posted by bennu36

I am sure this has come up before in one of the many threads about batteries, but can any one tel me for certain (Portag) In a 2012 with the stock triplite charger (and yes I know there are those that would have me replace that first) does it charges the start battery as well has the house batteries?

That is less about the type of charger than it is about the BIM. When the BIM detects that one bank of batteries is charging and the other isn't, it's supposed to connect both battery banks together so they can both charge. Regardless of which is charging or the source of the charge; engine alternator, generator, or shore power. Solar panel doesn't really provide enough charging power to make the BIM do its trick, though, so don't count on solar to keep the chassis battery charged.

When the BIM detects that one battery bank is discharging and the other isn't, it's supposed to disconnect the two banks so they don't both discharge together.

I don't recall the exact thresholds where the BIM connects or disconnects the battery banks, though.

[bennu36]

Like many I have spent the last two years (how long we have had it) looking at that spot in the over head and thinking something should go there. So I am going to put a ham radio up there. I am currently studying for my exam and hope to pass before the end of summer. Any way these radios are some what complex and to use most of the functions would take more attention that someone driving should spare. However it states in the installation instructions operation of the radio with out the engin running can deplete the battery in short order. So I was hoping that being plugged in to shore power or running the generator would keep the start battery from being depleted.

[73shark]

As Protag said, the generator, shore power, or the engine alternator will keep both the chassis batteries and the house batteries charged.

[bennu36]

Great thanks now I just have to past that test.

[Protagonist]

Originally Posted by bennu36

Any way these radios are some what complex and to use most of the functions would take more attention that someone driving should spare.

Then it should definitely be installed on the passenger side in the tray over the sun visor. Along with a 1DIN CB radio in the center where that blank is now if you like; if you pop that center panel off there is a 12v power pre-wire behind it, though admittedly it's a very fine-gauge wire.

[xrvr]

On the older Interstate one could buy a high idle system which allowed for extended idling and better battery charging. Is this already on the newer Sprinter? Newer diesels don't like to be idled for long periods of time at low rpms. Jim

[russ240]

Originally Posted by migriffin

davydd's "Advancing Alvar" posts on the ClassBForum, he's reporting that he can charge his 800ah lithium batteries from about 30% charge in about 2 hours.

I'd like to read about that but could not find it with a search? migriffin, any help locating? Thanks!

[migriffin]

Originally Posted by russ240

I'd like to read about that but could not find it with a search? migriffin, any help locating? Thanks!

You can find the thread here: Advancing Alvar - Class B Forums. It's a daunting 72 pages of posts, but a really fun read and got me really excited about some of the more innovative things that are happening in the space.

[Davydd]

I have the second alternator on my Advanced RV. It is a bit more sophisticated than just adding one. However, in prep for one you must order two options on a Sprinter. The first is an auxiliary alternator bracket for the alternator and that is a $409 option from Mercedes Benz. The second is the High Idle Fixed Package that is a $602 MB option. That is just the start and I have no idea if this can be done in a retrofit. That might be a point in this discussion in doing so for an Interstate.

Your engine alternator does charge your auxiliary batteries but not in an efficient manner. It and the computer module was never designed to do so and its primary function is to satisfy the chassis battery first.

My second alternator can charge my batteries at well over 240 amps and I think about twice the rate plugged into shore power will do. There is a 4.0 AWG copper wire from the alternator to the battery bank to do so. That is a humongous 1/2"+ diameter wire. I have an 800ah lithium ion battery bank that can take all the current you can slam at it and can restore a full charge to my batteries from an overnight stay where we draw down our batteries anywhere from about 120ah to as high as 300ah by driving generally about one hour at highway speeds. We have a total electric B, by the way, with no propane.

Roadtrek is installing second alternators they call an under hood generator but I don't know much about it and its capabilities. With all the cost involved I don't know if it would make sense for an AGM battery bank of two batteries.