Chassis and house battery charging; boost button

I was just browsing the net for RV battery information and I ran into something that surprised me. In another forum somebody wrote:

"Two shortcomings LTV told me are due to Mercedes restrictions:

The chassis battery is not charged from shore power. Apparently, Mercedes forbids this connection. So there's no boost button as is common in most motor homes."

Is it really true that shore power doesn't charge the chassis battery in the MB? If that's true, do things like the car stereo/GPS/DVD unit run from the chassis battery or the house battery?

Also, I have a big black Battery Boost button on the dashboard, so 2012 MB's definitely have them <g>... BUT - I've never had one on an RV or van before, and I have no idea what it does? What's it for?

And finally - I may have asked this before, early on - when you turn the big round battery disconnect rotary switch to OFF, does it entirely disconnect the house battery, so that it won't trickle charge even if you're plugged into shore power when you store the RV? Or does the switch jus disconnect all the LOADS so the house battery can't be run down but still can charge?

Peter Tourin said:

Also, I have a big black Battery Boost button on the dashboard, so 2012 MB's definitely have them <g>... BUT - I've never had one on an RV or van before, and I have no idea what it does? What's it for?

Click to expand...

That button allows you to use the house batteries to start the engine if the chassis battery is dead.
LTV stopped putting that switch in as there were issues with a 70amp fuse blowing if the switch was held down too long. The fuse, I believe, is in line between the house batteries and the chassis battery circuit.
My 2012 has it as well but the newer models do not.
Sounds like if it is used sparingly it may work as described.

Thanks - that was my first guess, but I really had no idea and never needed to try it - after one whole 2-week trip <g>...

Well, back to some of the original questions:

How do house and chassis batteries get charged?

Driving: both charged from alternator? If so, what does it put out - trying to understand how fast it'll charge batteries.

Shore power: house battery charged from converter? Again - what does converter put out for charging? Does it do a decent job of voltage control for good charging?

Is it really true that shore power doesn't charge the chassis battery?

When you turn the battery disconnect rotary switch to OFF, does it entirely disconnect the house battery, so that it won't trickle charge even if you're plugged into shore power when you store the RV? Or does the switch just disconnect all the LOADS so the house battery can't be run down but still can charge?

Yo Peter!!! Here you go ...... http://www.leisurevans.com/owners/manuals/2013_Unity.pdf

Here's what I do..... take that PDF file and put it in your computer, iPad, what ever. In "Documents" make a folder... 2012 Unity. Save the PDF file to the folder... It's a handy reference when you are away from the van. I also use 'Dropbox' and put a copy of all my manuals in a vehicle specific folder in my Dropbox. Dropbox is cloud storage and available to me anywhere I have a computer and the internet.

I also find all the manuals and instructions for all the accessory equipment on line and do the same. If I can't find a manual/instruction on line, I scan a paper copy to PDF and put that in my computer and Dropbox. I also do the same for any technical bulletins, installation instructions, etc. Eventually, I have an electronic notebook/manual for the vehicle in two or three places....

Cheers!

You're more organized than I am! I carry all the manuals with me when I travel, but I haven't tried to build an online folder - not a bad idea, it'd sure be useful right now!

I just read through the manual you posted, and actually I've gone online to the LTV site and looked at it a few times. But it seems to be rather generically written, without much detail. That doesn't help me much - I remember things by understanding how they work - if there's a transfer switch in the Onan wiring or in the inverter, I want to know it's there and how it's hooked up - then I'll remember what it does. Not to get into a rant here - but that manual is one of the reasons I'm asking all these questions on the forum - it doesn't have complete information, it's not always clearly written, and it's sometimes not relevant to my unit.

* It doesn't show the thermostat that's in my unit and doesn't explain how it works. Neither does the printed manual that's in the RV. The thermostat manual talks about a FURN mode, but I don't have an AC/heat pump manual and couldn't find one online for my model, so there was no way to find out about the DIP switch problem until a forum member mentioned it.

* TV/entertainment equipment - the manual doesn't explain how they're powered. It kind of covers this in the inverter section, but it makes no mention of the inverter transfer switch. That model inverter has one, and I assume that if I plug in to shore power, the transfer switch disconnects the inverter - but I can't find that out from the manual. Also no mention of the fact that the only AC receptacle powered by the inverter is underneath the counter for the disappearing TV, so it can't easily be used for anything, since you can't reach it easily to plug things in.

* It does show a photo of the house batteries and explain battery locations - i missed that. It says that the 2 coach batteries are charged by the alternator or by shore power or the generator (but it doesn't say through the converter - I just assume that because it makes sense). It says the converter charges the coach batteries - so I assume that only the alternator charges the chassis battery. It says that the house 12v system runs on the house batteries when parked, but on the chassis battery when driving - that surprises me, I thought the house 12v system was always powered by the house batteries.

* The 2 mentions of the battery disconnect switch are very confusing. On 1-50 it says that it switches between 12v power and shore power. That wording makes absolutely no sense to me, as the switch has no 120vac function at all - all I want to know is what happens when you turn the switch, and this doesn't tell me. ON 1-80 the maintenance section says that the switch disconnects both chassis and house batteries. Again, that's not clear to me - I'll bet I can turn that switch off and the engine will start.

End of rant - you know what I'm getting at, and the manuals in my previous units were pretty much the same. I just wish they'd provide a simple operators manual and a more detailed manual that covered some of this stuff in detail. These are pretty complex machines, especially electrically. We have forum members with a lot of technical expertise and a lot of miles travelled in various RV's, but it's still hard to get these things sorted out for sure.

Peter Tourin said:

Well, back to some of the original questions:

How do house and chassis batteries get charged?

Driving: both charged from alternator? If so, what does it put out - trying to understand how fast it'll charge batteries.

Shore power: house battery charged from converter? Again - what does converter put out for charging? Does it do a decent job of voltage control for good charging?

Is it really true that shore power doesn't charge the chassis battery?

When you turn the battery disconnect rotary switch to OFF, does it entirely disconnect the house battery, so that it won't trickle charge even if you're plugged into shore power when you store the RV? Or does the switch just disconnect all the LOADS so the house battery can't be run down but still can charge?

Click to expand...

Hi Peter,
I have a 2010 Winnebago View which is on a 2008 Sprinter chassis and the electrical systems are probably very similar to your Unity.

Your Chassis battery(s) are charged by the alternator at ~14.2 volts. Easy to check when the engine is running take your trusty Digital MultiMeter (you do have one...) and set it for DC volts and verify the voltage when the engine is running...you should see the above mentioned number. Now with the engine running check your house batteries as well...they should be receiving a similar charge as well...right around 14.0 to 14.2 volts.

Your house batteries are charged through your converter/charger as well. So when you plug into shore power or run your onboard generator (if you have one) and I believe when you have your house batteries turned on or not disconnected (like my Winnebago View) the conv/charger will most likely put out ~13.6 volts to charge the house batteries...again easy to verify with that trusty DMM you have. So you see the alternator will charge your batteries quicker than your onboard conv/charger....unless you have a more sophisticated 3 stage charger that can put out similar charge voltage of 14.2+
Hope that helps.
Best,
Jim

IslandGuy said:

Your Chassis battery(s) are charged by the alternator at ~14.2 volts. Easy to check when the engine is running take your trusty Digital MultiMeter (you do have one...) and set it for DC volts and verify the voltage when the engine is running...you should see the above mentioned number. Now with the engine running check your house batteries as well...they should be receiving a similar charge as well...right around 14.0 to 14.2 volts.

Click to expand...

To expand on that: the alternator has an "amperes" specification (perhaps 200 amps?)
That current is what determines the rate of charge (if the batteries and vehicle loads want more, the voltage would drop).
When the engine is running (and vehicle "up to speed", so the alternator is spinning at a reasonable rate), the isolator relay pulls in and ties everything together: alternator, starting battery, all "run the Sprinter" loads (headlights, etc), the house batteries and thereby all "house" loads (fridge, reading lights).

That's why the manual says that the house loads are "on the starting battery" when running.
In truth, they're on the Alternator (which is putting out a higher voltage than the batteries, thus it's the source of the electrons running around and doing work).

When you kill the engine, the isolation relay "drops out" and separates vehicle systems from the "house" systems.

--dick

Look into Trik-L-Start to keep the engine battery float-charged whenever the house batteries have more juice, and when on external power. I learned about this device back when I had a PleasureWay (see old post http://www.sprinter-source.com/forum/showthread.php?t=1150&highlight=Trik-l-start with pdf files of install). Now that we have an LTV Serenity, I have also installed a Trik-L-Start.

This is my 4th attempt to thank you guys for all the comments - PC keeps dropping the internet and I keep losing my typing...

Dick, your description is just what I'd expect, and is a lot clear than what's in any of the LTV operators manuals. I ended up downloading the 2013 and 2011 manuals - they're different, and each one describes some of the things in my unit. The 2011 manual has a very good description of isolator function - it's not in the 2013 manual at all. Seems that as voltage drops, the isolator opens and protects the chassis battery, but it does it at a different voltage when the engine is running and when it's not. Then it closes and connects the batteries again when it sees 13.3 volts or more - it'll do this either when the alternator pulls the voltage up or when the converter pulls it up.

Jim - my Pleasure-Way has a converter that just charges the house battery at a single voltage, but they sell a $25 plug-in module that provides 3-stage charging. I bought the module, and also added a small digital read-out in my control panel area - I attached a somewhat lousy photo of the area, with voltmeter and also a Kill-a-Watt plugged in. It was really cool to have that little voltmeter - I could start the RV and watch the house voltage kick way up in the 14's, then taper down a bit as we drove. Then we'd park and shut down the engine, and the voltage would drop - and keep dropping as we used the house batteries. When we either connected to shore power or started the generator, we'd see the voltage kick up to 14.4 for awhile, then down to 13.6 when we were almost fully charged, then finally down to 13.2 - very neat to see it all in action.

The LTV data sheet for my MB says that I have a Parallax 7355 converter - that unit just charges at 13.8v. They do sell an upgrade that provides tiered charging and temperature compensation - rather nice, but it's not a $25 plug-in, it's a replacement module for $260. Ouch - but from what I'm reading about battery charging, maintenance and longevity, it's probably money well spent.

Al - I just went and looked at your Trik-L-Start thread - very interesting thread, lots of discussions of things I'm looking into now. I'm getting interested in battery charging voltages for getting the different types of batteries up to full charge - I've been reading lots of interesting things on that topic, with a fair amount of different opinions. Gotta say I wish someone would give me one of those Trimetric monitors for my birthday <g>...

A separate charge source is not needed for the chassis battery as shown by Advanced RV. When the house batteries are being charged by shore power, and when they are up to a preset high level, the computer automatically connects the house and chassis batteries when and if the chassis battery falls below a preset voltage. When the chassis battery is back up the computer breaks the connection.

Something i forgot to mention in my first post: what's also very handy for chasing "who's charging and how much?" is a clamp-on DC ammeter.
Like this $60 (frequently on sale for less) unit from Sears: http://www.sears.com/shc/s/p_10153_12605_03482369000P



It's also great for checking out glow plug draw and other Sprinter mysteries...

--dick

Here's what the 2011 manual says about the isolator and charging both house and chassis batteries - it's a good detailed description:

"The Bi-Directional Isolator Relay Delay constantly senses the voltage on the coach and chassis batteries. If either voltage is above
13.3 volts, which indicates the batteries are being charged, the control closes the isolator relay. This parallels the batteries, charging
them both.

If the ignition is OFF and the voltage falls below 12.8 volts for approximately five seconds, the relay will open to prevent
the coach loads from discharging the chassis battery. When the voltage goes back above 13.3 volts, the relay will close again.

If the ignition is ON and the voltage falls below 12.0 volts for approximately five seconds, the relay will open to prevent the
coach loads from overloading the alternator and discharging the chassis battery. When the voltage on the chassis goes
back above 13.3 volts, the relay will close again. Allowing the batteries to stay connected together to a lower voltage helps
charge a heavily discharged coach more quickly with the varying output of the alternator.

A lockout lead is provided to prevent conflicts if both the converter/genset and the alternator are trying to charge the batteries
at the same time."

So when you're travelling you charge both batteries (alternator); when you're on shore power or generator you also charge both batteries. When the battery bank drops below a certain voltage the isolator opens and protects the chassis battery.

Al, what's the Trik-L-Charge for? I'm assuming it's for when you store the RV between trips, but I'm still not sure why you'd install one on a Unity. If you're not plugged in there's no issue - no batteries are getting charged. If you're plugged in and you leave your house battery switch turned on, then I assume the isolator will still connect the house and chassis batteries as the converter charges them. It won't be the greatest charge if it only puts out a steady 13.8 volts, but it'll keep both batteries from going down. So I don't understand yet where the gain is.

So when i am plugged into shore power and storing the rig for winter i do not need a trickle charger for the house batteries as i understand or not, but what about the engine battery this still could use a trickle or float charge?

I'm the newbie here, so you guys chime in. But as I read it, if you're storing the rig for winter and you're plugged in, the isolator will connect both chassis and house batteries, and the converter will then be charging them both. That assumes that you haven't disconnected any of the batteries or turned the battery disconnect switch off (as they suggest in the storage checklist).

Peter Tourin said:

I'm the newbie here, so you guys chime in. But as I read it, if you're storing the rig for winter and you're plugged in, the isolator will connect both chassis and house batteries, and the converter will then be charging them both. That assumes that you haven't disconnected any of the batteries or turned the battery disconnect switch off (as they suggest in the storage checklist).

Click to expand...

Reads like that will work but you know with your DMM you can verify that...right?

Maybe YOU can - but not ME - I'm in Vermont and the MB is stored in Maryland till the end of March <lol>... I soooo wish I'd brought it all the way home and stored it in the snow here by the house - then I could be playing with it instead of doing all this long-distance education stuff <s>...

autostaretx said:

Something i forgot to mention in my first post: what's also very handy for chasing "who's charging and how much?" is a clamp-on DC ammeter.
Like this $60 (frequently on sale for less) unit from Sears: http://www.sears.com/shc/s/p_10153_12605_03482369000P

View attachment 57363

It's also great for checking out glow plug draw and other Sprinter mysteries...

--dick

Click to expand...

Clamp on meters are really the "cats meow"....
I have a Fluke i410 I use with my Fluke 87V and it is great for all things DC. Have used it to trouble shoot car batteries, charging and starting systems in a host of autos...great stuff!!

+1 IslandGuy - I bought an Extech MA435T - I was down for 4 days last week unwinterizing the MB and troubleshooting damage that was probably from lightning, and I used it constantly. Very cool tool!