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BOBCONEYBEER 07-12-2015 09:48 PM

2014 Interstate battery draining
I plug my interstate to external power and charge batteries completely. With everything in motorhome turned off the batteries discharge. What is the problem

Al and Missy 07-12-2015 09:54 PM

How long does it take for them to discharge? Are you using the store switch?

Protagonist 07-12-2015 10:25 PM


Originally Posted by BOBCONEYBER (Post 1651048)
I plug my interstate to external power and charge batteries completely. With everything in motorhome turned off the batteries discharge. What is the problem

First, welcome to the AirForums! And welcome to the wonderful and sometimes frustrating world of Airstream Interstate owners!

The phenomenon you're experiencing is known as "phantom drains," or "phantom draws." Basically, when you shut down the 12vDC power on the house systems, you're not actually shutting off everything. Some systems remain powered all the time.

The actual items that remain powered vary slightly from one model year to the next, but some items remain constant from one year to the next.

First, you have to shut down the 120vAC side as well as the 12vDC side. Make sure all of your breakers are turned off. The inverter/charger is NOT turned off by the 12vDC disconnect, so any items that draw 120vAC power from the inverter are still powered until you turn off the breakers. For example, the televisions still draw a small amount of power even when turned off, otherwise you couldn't turn them on with a remote control. In addition, the inverter/charger is itself a user of battery power, because it has to run its own cooling fan, and has to monitor the electrical system to determine whether it's supposed to be in inverter mode or charger mode.

The refrigerator operates on 120vAC as long as there is a source of AC power— including the inverter. You have to turn it off separately using the dial inside the fridge, or else turn off the fridge's breaker.

Also, even with all of the breakers turned off, there are still some items that draw power, such as the Battery Isolation Module (BIM). The purpose of the BIM is to connect the house and chassis batteries so they all charge together, but disconnect them when no charging current is available, so that the house and chassis systems drain separately. The only way it can do its job is to always be powered, even when everything else is switched off.

Also, the solar charge controller draws power from the house batteries, not from the solar panel. If there's not enough sunlight for the solar panel to work, the charge controller is a parasitic draw.

If you park in the sun, your rooftop solar panel should— on average— keep up with the parasitic draws and keep your batteries topped off. But if you're not parked in the sun and not plugged into shore power, the solar panel won't work, and the house batteries will gradually drain.

Remember too that just plugging in the shore power cable isn't enough to charge the batteries. The inverter/charger also has to be turned on, so that it can go into charge mode. Plugging in while the inverter/charger is turned off does NOT charge the batteries!

The 2014 models have a Magnum inverter/charger, which is a very good system except for one omission— Airstream does not install the temperature sensor. With the temperature sensor installed, the inverter/charger will compensate for battery temperature to avoid over-charging or under-charging the house batteries, and so the van can be left plugged into shore power 24/7 without worrying about the batteries, and parasitic draws become a non-issue except when boondocking.

Don't forget you have an on-board propane-fueled generator that should be exercised at least once a month to keep it properly lubricated. If you can't hook up to shore power and can't park where there is consistent sunlight to keep the solar panel working, you should operate the generator for about an hour every couple of weeks to keep the house batteries charged and keep the generator in good working order.

And finally, don't forget that if it's working properly, the BIM allows the house batteries to charge off the engine alternator. If your house batteries start getting low, driving your van somewhere should be enough to recharge the house batteries, too. You don't have to take it camping; when I still worked for a living, I used to drive my Interstate to work a couple of days a month, for that very reason. And because I couldn't bear to let it sit unused for more than two weeks at a time.

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