Battery Discharge

[Dennis Crawford]

All,

I have a 2005 Monterey with the Xantrex whole coach system.  I also have a BIRD module and a Big Boy switch.  I think I have been mistaken over the years thinking the BIRD and Big Boy would keep my chassis batteries charged from the house batteries.  Then as the house batteries lost voltage, the auto gen start would  activate and house batteries would charge again.  I am thinking this is not the case, but don't know for sure.  The coach is in storage now without shore power.  My chassis batteries have a pretty heavy drain of about 2 Amps per hour.  It does not take long for the chassis batteries to discharge at that rate.  The biggest drain comes from the dash radio of all things, even if it is off.  Does anyone have any ideas on how to correct problem.  Can I move the Xantrex sensing module from the house batteries to the chassis batteries and use auto gen start when they drop?

Thanks

Dennis

[LEAH DRAPER]

Don't you have a switch(s) to turn off the chassis and the house batteries to prevent that kind of parasitic  drain?

Most coaches do.

[Gil_Johnson]

Leah, I bet your inverter and engine's ECM are powered with the 2 master switches off.

[Edward Buker]

Dennis,

As a start I would add a manual switch to the radio power feed that was causing the main current draw. You would lose some stored radio info while in storage but that would give you a longer discharge cycle. That may be enough.

I do not see a technical problem with moving the sense lead just for storage as far as the system sensing and starting. You would need to understand how the house battery bank actually does the charging of the chassis batteries. If they get paralled with high charge current capacity then that would work. If there is something like a 10 amp echo charger involved then you would be running the genset a long time delivering a slow chassis battery charge which would be grossly inefficient.

I'm not a huge fan of this idea but rather than having dead batteries all the time which shortens thier life you could run a jumper from the 12V of the house battery side to the 12V chassis battery side at the batteries (be sure it is a 12V connection point on the house side and not a 6V point) and enable the gen auto start. The drain would significantly delay the generator usage by having all your battery capacity in parallel. When dealing with the current available at the batteries you should use the same gauge wire as the current cabling uses with standard lug ends. It would also be possible to incorperate a high quality battery switch in that line for convenience and only have it on while in storage.

Before I did anything at the battery end as far as tieing them all in parallel I would see if there was an alternative with the Big Boy like maybe a timed start of the genset for 1hr every 4 days as long as the charge rate to the chassis batteries would be significant during that cycle. I think that was the intent of the Big Boy circuit but I do not have one and I'm not sure of that.

Later Ed

[Brad Burgess]

Hi Dennis

I had the same issue with a BIRD and Big Boy combiner.  I did a lengthy post on Monacoers about this.  When your coach is not connected to shore power and you run the generator to charge the house batteries, the BIRD will NOT allow the Big Boy to combine the chassis batteries with the house batteries.  The BIRD is set up so that if there is a signal to the generator lead on the BIRD it will absolutely prevent the Big Boy from combining - according to Intellitec, this is to prevent a conflict when both the inverter (from the generator) and the main engine alternator are providing charge current.  My solution was to disconnect the generator lead from the BIRD while the coach is in storage.  Worked perfectly and the BIRD now allows the Big Boy to combine when the house batteries are being charged from the inverter via the generator.  No need to relocate auto genstart sensors or install extra switches etc. Just be sure to reattach the generator lead to the BIRD before going on a trip.

If you have more questions please feel free to call me at 480-502-2651 - this was a difficult problem to diagnose but a simple one to solve.

Brad Burgess
06 Monterey

[Keith Oliver]

Denis:

i had the same issues when I first got this coach (March 2011).  I found the parasitic drain on the coach batteries too much, mostly the ECM, but also the clock in the radio woulds stay on.
I put a $35 knife switch on the battery terminal (neg side) and that solved the problem.

[Gil_Johnson]

Leah, I bet your inverter and engine's ECM are powered with the 2 master switches off.

[Bill Sprague]

......  My solution was to disconnect the generator lead from the BIRD while the coach is in storage....

Would it also work if a small automatic battery charger (like a Battery Minder) was plugged into an inverter powered socket.  The inverter and charger would draw down the house batteries while charging the chasis batteries.  That would cause the genset to cycle as necessary to keep the house batteries up.  

[Gil_Johnson]

It boggles my mind why the RV industry makes this so complicated.  In the marine industry, power systems are far more complex.   I've owned a boat with 4 battery systems.  If I designing the DC power system or having to replace the BigBoy, Bird, or whatever strange named component I have, I would consider this product for combining my battery banks:

http://bluesea.com/category/78/79/productline/388  

This self contained product automatically combines the banks for charging, disconnects to prevent one bank from taking both banks to low of a charge state, and provides manual paralleling for emergency starting of the engine.  It's current capability far exceeds what any coach would need, and it's meant to be in the harsh marine environment.

Gil

[Bill Sprague]

At the last rally, we were treated to have, as a guest, a guy named Bill, who runs Monaco for Navistar.  He related that he discovered there were no engineers in the Monaco system, and that they were designed and built by, what he called, "tribal knowledge".  

[Gil_Johnson]

Tell me you're kidding...I'm rolling on the floor with laughter...

At the last rally we were treated to have as a guest a guy named Bill you runs Monaco for Navistar.  He related that he discovered there were no engineers in the Monaco system and that they were designed and built by what he called "tribal knowledge".  

[Brad Burgess]

Hi Bill

Sounds like your idea would work if the battery charger will work on inverted electricity.  My desire was to not have to add any new equipment - simply unplug and plug as needed.

Brad Burgess

[Bill Sprague]

I'm not.  There were 80 or more BAC members in the room to confirm it.  

He said his background included a decade or so at Ford building trucks.  He explained his working environment was filled with engineering work and was surprised to see the lack of it in the entire MH assembly industry.  Of course there is engineering inside engines, transmissions and even refrigerators.  But, when you think about it, motorhomes like ours are an assembly of those "off the shelf" components.  Bill went on to say that part of the Navistar strategy will be to come to market (when demand sufficiently returns) with well engineered products.  It seems that Navistar has engineers!

[Gil_Johnson]

The integration and installation of those engineered products requires some engineering savvy.  Hmmm, should that be a 2/0 or #2 cable to the inverter....What's a Charge Air Cooler....what's a conduit run or why would anyone need a cable raceway...

Now I'm scared!  Time to do some more inspecting.  This does explain the dumb things I've found and corrected.

Gil

[Gil_Johnson]

Bill, your recommendation, although possible is counterintuitive.  The other Idea of just disconnecting (via a simple switch) the generator sense would make more sense to meet unique storage goals.  Your recommendation would create a lot more load on the house bank as you would have to keep the inverter on, accept the inefficiencies of the inverter process, and then the same in reverse for the charger having to produce DC charge voltage/current.

Gil

Would it also work if a small automatic battery charger (like a Battery Minder) was plugged into an inverter powered socket.  The inverter and charger would draw down the house batteries while charging the chasis batteries.  That would cause the genset to cycle as necessary to keep the house batteries up.