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Old 04-12-2014, 10:13 AM   #15
2014 Interstate Ext. Coach
Poconos of Pa , Pennsylvania
Join Date: Sep 2013
Posts: 239
I just looked over the 12volt Main Schematic for my 2014/13 Ext body, Rear Lounge Airstream WITH solar. These are the various connections that COULD draw/use electrical power from the RV batteries. All other 12 volt electrical items are on the other side of the Main Battery Disconnect (the switch on the door frame). If the Master Battery Switch is off, those other items have no ability to access 12 volts from the RV batteries. I do not know the possible wattage draw on these items. I keep it plugged in when I'm not using it.

1. Inverter receives 12v constantly from RV batteries.
2. BIM (also called Battery Separator)
3. Dash radio is always powered to keep its memory.
4. Solar controller-it probably has some draw as it has an electrical circuit.
5. Tank heaters--only if turned on of course.
6. Rear lounge motor--only if in use to lower/raise the lounge.
7. By-pass engine start push button for Mercedes--only if pushed of course.
8. Master battery disconnect switch--if off then no draw on what is hooked to the main power distribution box.

Per Magnum specs....inverter usually draws 5 watts and NO LOAD 19 watts typical

The BIM-battery separator will charge the Mercedes start battery IF the voltages of the RV batteries are sufficient (don't know the settings) AND the MB engine battery voltages are BELOW a set-point voltage (don't know the settings).

The Carbon Monoxide (C) and Propane (LP) detectors along with the LP tank shut-off valve and the 12v side of the refrigerator do not receive ANY 12volts with the Master Switch OFF. NOTE: the CO detector does have a 9volt battery internally and it reminds you to turn off the 12v Master before opening and changing the 9v battery.

The motorized side step, the step alarm, the power awning (if equipped) and the backup camera all are supplied 12volts from the Mercedes engine starting battery.

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Old 04-12-2014, 12:51 PM   #16
2014 Interstate Ext. Coach
Poconos of Pa , Pennsylvania
Join Date: Sep 2013
Posts: 239
Proper charging for Lifeline AGM Batteries and probably most other AGM batteries is BEST achieved with shore/generator power and a 3-stage charging profile type charger/inverter. I will not quote everything but here is the link and you want to go to section 5.4 which is page 19.

But in a nutshell, you CAN charge your AGM batteries by driving and running the engine of your Mercedes Sprinter, but it must be at a faster RPM than an idle. What I have been told by Jim Parrett at Airstream and also a tech at Magnum, yes, many people think that they can just run the engine for a short period of time to "charge their batteries." BUT this is not the proper or best way to charge your batteries. No one has a good definition of "short" nor do they tell you at what RPM to operate. But we all know that driving your Airstream for several hours a day while traveling will bring your batteries up to proper voltage. BUT what you don't realize is that it is more than bringing up the voltage. It has to do with first BULK charging and then with ABSORPTION charging and then FLOAT charging which all take place with different voltages and amperages. This basically is not done the best when you are using an engine alternator type charging system. The voltages vary when you are driving as the alternator is feeding into the Mercedes engine battery AND the RV batteries. And there is no temperature calculations being taken into the voltage and time variables. That is one reason I added the Magnum temp sensor to our Lifeline battery system. Airstream still does not believe in adding the temp sensor to the batteries.

So the best way to maintain your batteries, keep them plugged into shore power. I've owned 3 Class A motorhomes in the past 20+ years, always garaged when not in use, always plugged in and I never had any flooded cell/AGM batteries fail or run short on life-useage, and the last Class A was 15 years old with 6-8D AGM Lifelines (replaced 2 times in 15 years). And if you do not have access to a 30amp circuit, you can do it with a 15/20amp outdoor outlet. All you have to do is remember to NOT use any appliances that draw high currents: air conditioner, water heater, coffee maker, microwave to name a few. Also reset your Power Control System from 30 down to 20 and this will help just in case you do plug in or turn on high wattage appliances. The amount of amperage/wattage needed to operate the charger portion of your inverter is not that high and the batteries will be able to be properly maintained. Even if you can only "borrow" an outlet from your neighbor in your condo or parking are, its only going to need power for your inverter for maybe 7-8 hours to properly charge your AGM batteries.

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Old 04-12-2014, 01:33 PM   #17
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toskeysam's Avatar
2013 Interstate Coach
Townsend , Tennessee
Join Date: Nov 2013
Posts: 376
Great discussion you, I also added the temperature sensor. It did improve the charging profile somewhat. Especially in those cold winter nights. I am having the guys replace the ME-MR controller with the ME-RC controller and add the battery monitor as well. Also, after log discussions with our tech, they are going to pull the batteries for bench testing. I was able to get a longer lasting (in storage) charge, but it would never stay above 85% for more than 10 minutes (with everything off). The postings from you and many others out there have helped me locate and control a lot of the drains. Mucho thanks.....

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