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Old 06-11-2019, 05:08 PM   #1
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2002 22' International
2019 25' Flying Cloud
Austin , Texas
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Posts: 237
Battery Disconnect Switch Function on New Airstreams

Things are different on our new FC 25FB. I was told that I need to leave the battery switch on all the time except when the unit is stored and not used. This is different than the practice on my old 2002 trailer.

In my old trailer, the 12v system got it's power whenever plugged into AC. So the battery switch only needed to be on when I wanted the battery to get charged, or when I needed to use the battery for 12v power if I was not plugged into AC power. (I did have to engage the switch when traveling to make sure the trailer brakes had the power they needed)

Now, it appears something else is going on. Even if I am plugged into AC current, the 12v system may not be getting powered. (I noticed my LED lights didn't work when I plugged in the trailer).

So, I guess I can get used to this system, but what is the point of the difference. Don't I need to worry about the batteries getting overcharged and eventually fail because they are connected to the charger 100% of the time?

I suppose I wonder if you folks think my system is wired correctly? Is there some modification (simple/cheap) that I could make to improve anything)? Is there anything I have to worry about with the current rule? "Just turn on the switch, leave it on, and don't worry about anything:.

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Old 06-11-2019, 05:24 PM   #2
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Park City , Utah
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What does your manual say? I know up until recently, you could put in "Store" while plugged in and the battery wouldn't charge but you'd still have 12V power to everything. I know they had changed it so that if you kept in 'store' it would still charge the batteries...but was unaware it would also cut power from the converter (if plugged in) to the the 12v system.

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Old 06-11-2019, 05:34 PM   #3
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2002 22' International
2019 25' Flying Cloud
Austin , Texas
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Posts: 237
Manual Quote:

"The battery disconnect switch is used to separate the batteries from the 12-volt distribution panel

When the trailer is plugged into an external AC power source the 12-volt distribution panel will receive power from the converter and the batteries will be charged through the converter charging system regardless of if the battery switch is in the ON/OFF position."

Isn't that a little confusing if you want to learn what is happening to the batteries?

Just went out to check. Trailer is plugged in to AC. Turned overhead lights on --- no lights. Turned battery sw to USE -- lights came on. Turned batter sw to STORE -- lights went off.
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Old 06-11-2019, 05:41 PM   #4
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2017 30' Classic
Carlisle , Pennsylvania
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Keep in mind that there now are *two* switches on some trailers. One is a true battery disconnect. The other is a use / store switch. Just as in the past, there seems to be a bit of randomness about the use / store switch. On a lot of trailers, the battery charges either in the use or the store setting. In some it charges only in the use position (which I believe is a wiring error ....).

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Old 06-11-2019, 06:51 PM   #5
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2018 23' Flying Cloud
Peru , Illinois
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FC Manual 5-8

It's very simple. Leave your switch ON all the time.

When your trailer is pluged into shore power, being towed and connected with the 7-way cord, being connected to a running generator, connected to solar panels or trailer batteries connected to a Battery Tender, the batteries are being charged regardless of the setting of the switch. Leave the switch ON.

The OFF position of the switch is intended for storage of the trailer or when power conservaion is desired.

Cindy & Randy
2018 AS Flying Cloud 23FB
2018 GMC Sierra Denali 4x4 6.2L
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Old 06-11-2019, 07:31 PM   #6
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2002 22' International
2019 25' Flying Cloud
Austin , Texas
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Posts: 237 maybe I need to recognize that the converters in modern Airstreams are smart enough to protect the batteries. I have read that they have variable charging modes. And, hopefully, the lower charging mode does not harm the batteries when the batteries are connected over a long term.

I have been accustomed, when staying at a site for several days, to disconnect the battery because I didn't need it. I got all my 12v power I needed from the converter. Current wiring does not allow me to do that. So let the battery run all the time.
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Old 06-12-2019, 06:07 PM   #7
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2006 34' Classic S/O
Fort Worth , Texas
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This is the same old dilemma that has haunted Airstream owners for years. The object is to isolate the battery bank from the trailer and/or residual current draws while in storage so your batteries will be ready to go when you are. The wizards at the NEC think there are safety items that must be powered, no mater what. Even if, you are not in the trailer and no one can hear any of the warnings. I personally feel that once you buy a trailer so wired you can do as you please to make it the most useful to you. The argument they have is if you have such a wired switch you may forget to turn it on before you travel. That same argument could be made for keeping the TT hooked up to the TV all the time so you want forget to hook up for a trip. If it were my trailer and I wanted it so wired, I would find a technician to do it if I couldn't. Company X, would not plumb my trailer propane system for internal and eternal low pressure quick connect with a shut off valve due to liability reasons. Guess who has that installed now. Everyday, some bureaucrat finds another way to protect us from ourselves. The irony of this is, in my case, with cochlear implants, I am stone deaf without them, and when I go to bed none of the warnings including tornado sirens benefit me. So there.
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Old 06-13-2019, 04:11 PM   #8
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2016 25' Flying Cloud
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I'm in the process of converting a WHY manual I wrote for a different trailer over to the 2016 FC because when travelling with family and guests, the same questions get asked over and over. Gives us a place to organize the daily tasks, knowledge base for our trailer and allow family & guests to help out doing what we want done without having to guess what comes next. Plus, we forget the details of things we've already figured out and wanted a place to put it all. Since it directly answers the OP question, figured I'd post it here.

Batteries gradually lose charge through chemical processes whether they are in use or not. They further get depleted by the “vampire” or “phantom” drains that come from electrical equipment that appear to be turned off but are really drawing small amounts of current. The inverter, radio and subwoofer come to mind. When the trailer is in regular use and the batteries are getting recharged, this isn’t readily apparent. It’s when the trailer goes into extended storage that we need a way to disconnect the battery from the minor draws while keeping the LP Leak Detector operating for safety.

Airstream wired some 12-VDC equipment (LED Lights, water pump, USB ports, etc) to the Converter/Charger Panel but not everything. Some devices are powered directly from the battery either at the battery post or from the positive buss. This means there are 3 places you need to look to determine where something is getting power from. The STORE/USE switch only disconnects the Converter/Charger Panel from the battery leaving all the direct connections intact. By looking at the table below of what isn’t controlled by the switch, you can deduce what it does control.

The Intellitec BXD Battery Disconnect relay is located under the bed along the front wall and is connected by low voltage wires to a remote USE/STORE panel by the main door on the other end of the trailer. It is technically a “latching electromechanical switch”, or relay, which requires at least 10.5 V-DC current to operate. This means that in order to turn it from USE (ON) to STORE (OFF), there needs to be enough charge in the battery to operate the switch. One common cause of confusion is interpreting the RED light to mean that the latching relay is in the USE position. The red light illuminates whenever there is 12-VDC available to the latching relay so it is possible to have the switch in the STORE mode and have the RED light illuminate because the trailer is plugged into shore power and the converter is making 12-VDC available to the relay.

When debugging the Battery Disconnect Switch system, you need to keep in mind that failure could be from:
1) Insufficient (less than 10.5) volts DC are available.
2) Either one or both 7.5 AMP ATC fuses have blown
3) The relay is defective
4) The RED light doesn’t indicate that the switch is in USE position.

In the STORE position, the following are still connected directly to the battery:
1) Hitch Jack *B
2) Inverter *B
3) Propane Detector *+
4) Breakaway Electric Brake *+
5) 7-WAY Connector *+
6) Victron Solar Controller *B
7) Zamp Solar Plug-in Port *B
8) Victron Battery Monitor *B

*B item is wired directly to the battery
*+ item is wired to the unswitched positive buss bar in trailer
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Old 06-13-2019, 05:22 PM   #9
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2014 25' FB Flying Cloud
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4th AS in 12 years...battery questions always come up. The newer converters are supposed to be "better" then the single stage models that were used up until 2018l. That being said, I am not sure how much better?? We have replaced our converter with a true 4 stage model and we leave our trailer plugged in when in storage, but we also installed a mechanical disconnect switch at the battery. I never mess with the on/off switch inside the is "never" really off and as someone here mentioned...the power is always draining either way. When we travel, it's always connected and no issues.

Get a good set of batteries and a disconnect switch. Maintain your batteries per manufacturer recommendation if wet cell type, and you should be fine.

Side note: If your batteries seem they are loosing charge too quickly, have them checked by Interstate...assuming you have Interstate..They are pretty good about replacment if needed.
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2017 F250 King Ranch, 4X4, Blue-Ox WDH
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Old 06-14-2019, 07:49 PM   #10
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2019 25' Flying Cloud
Austin , Texas
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Thanks AirstreamCSH for the explanation.
But you said
" The red light illuminates whenever there is 12-VDC available to the latching relay so it is possible to have the switch in the STORE mode and have the RED light illuminate because the trailer is plugged into shore power and the converter is making 12-VDC available to the relay. "

On my new trailer, when I put the switch in the STORE mode the light goes out. It has even more meaning because then there is NO 12v to my systems, EVEN THOUGH I am plugged in to AC power. I plug in the trailer and there are NO lights unless I remember the battery switch.

I really liked my old ways: Plug the trailer in and everything works as needed. Once plugged in, the only function of the the Battery Disconnect Switch is to charge the battery or not charge the battery -- user decision.

How does your trailer work?

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