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Old 01-22-2018, 11:30 AM   #1
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Install Battery Disconnect Switch

We have a 2018 FC 25 FB with 50 amp service. We are parked for the winter and are on shore power. My understanding is that the Parallax converter is not a 'smart' four stage unit and that it will slowly kill our batteries.

This happened to us with our 30 amp 2017 FC and I installed the multi-stage Progressive Dynamics unit to solve the problem. That was a relatively easy DIY but that's not true for our 50 amp FC.

Here's my plan to protect the batteries:

1. Install a battery disconnect switch on one of the batteries.
2. While on shore power for extended stays, flip the switch to disconnect the batteries from the converter and connect a smart battery tender to maintain proper voltage.
3. When we hitch up to move, flip the switch back to the connect position and remove the battery tender.

I've been reading related threads that recommend one of the positive terminals. See, for example, http://www.airforums.com/forums/f542...ll-168120.html

The electrical diagram shows that a 4 ga wire connects one of the batteries to the inverter and that a 6 ga wire connects the other battery to everything else, including the jack.

Should I install the disconnect switch on the positive terminal of the 6 ga battery? If so, will this protect the batteries from the 13.6 volts put out by the converter? While on shore power, will everything work normally?

Thoughts? Thanks, Dave
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Old 01-22-2018, 12:26 PM   #2
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Quote:
Originally Posted by dasams View Post
My understanding is that the Parallax converter is not a 'smart' four stage unit and that it will slowly kill our batteries.
Oopsie. Our 2018 FC came with a WF-9855 converter, not a Parallax...
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Old 01-23-2018, 12:02 AM   #3
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Install Battery Disconnect Switch

Hi Dave -

That was my diagram you are referencing. The stock batteries in your battery box are connected in parallel so they act as a single, larger capacity 12v battery. So you don’t disconnect one or the other, you disconnect both at the same time.

You need to remove both the invterter positive cable and house positive cable from the battery terminals and attach both to one side of the switch, then run a new cable from the other side of the switch to the positive batt terminal. You will need to install a ring terminal on the house 12v positive line because by default airstream stick an automotive clamp on it, and the switch requires a ring terminal connector.

While you are at it it’s a good idea to also upgrade the parallel cables that connect the batteries together to a heavier guage as a best practice. 1/0 guage is what I chose.

Look carefully again the attached wiring diagrams to include the embedded comments and also the attached photo. You can choose from a 2 pole or 3 pole switch - your choice.

Finally, I wouldn’t bother with a separate maintainer. Just leave your batteries connected for 36-48 hours while on shore power and they’ll get a full charge by your converter/charger. Then disconnect and leave them sit until you are ready to break camp. If you are camped at the same site for more than 2 or 3 weeks on shore power you can re-connect them 12 hours before departure to top them off if you really wanted to as they have a small self-discharge with no loads.

Batteries don’t need to be connected to the system for all your 12v items to work when on shore power, your converter will produce 12v to the system independent of the batteries being present / connected.
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Old 01-23-2018, 09:16 AM   #4
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This is great info. Thanks for putting it together.

On a related note, the wires on the bottom battery block access to the cells, ie, very difficult to check the water level. Wouldn't it make sense to rotate the battery 180 deg so that the wires would be out of the way? I tried to check my levels yesterday but couldn't remove one of the caps because it was blocked by a heavy gauge wire
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Old 01-23-2018, 10:29 AM   #5
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Quote:
Originally Posted by dasams View Post
Oopsie. Our 2018 FC came with a WF-9855 converter, not a Parallax...
Starting with the 2018 models Airstream changed to a multistage converter.
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Old 01-23-2018, 11:20 AM   #6
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I think if you install a disconnect switch, as shown in earlier thread or a knife switch like I did, you should be fine. I leave mine disconnected while still plugged into shore power, just as a safeguard. I still have power when I want to do something inside, or in our case, bad weather below freezing, so I run the internal heater at 40deg to make sure everything is kept from freezing. (In TX not so bad...if I was in colder climates, I would likely winterize, but we do use our trailer in winter months here.)

I have not used our AS for past 1.5 months, so I will connect the switch today and let my multi-stage charge and charge/tend the batteries a few days. I don't have the WFCO unit; I have installed the Boondocker 50amp unit and it works fine. I have not seen anything bad from AS users on the new WFCO multistage unit on the Forum yet. I know some folks say the WFCO units are not as good as the Parallel Dynamics or Boondocker, or some other models, but I am not an expert here. I would use it unless you have issues.
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Old 01-23-2018, 01:01 PM   #7
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Originally Posted by dasams View Post
This is great info. Thanks for putting it together.

On a related note, the wires on the bottom battery block access to the cells, ie, very difficult to check the water level. Wouldn't it make sense to rotate the battery 180 deg so that the wires would be out of the way? I tried to check my levels yesterday but couldn't remove one of the caps because it was blocked by a heavy gauge wire
I've seen nice pre-made cable assemblies in an assortment of sizes and lengths with ring terminals on Amazon. They also come in red and black.

Consider getting longer cables that route better between the batteries. I can see it's crowded in there...

Fortunately my series-connected Golf Cart batteries are end-to-end in the battery box and the cables don't interfere much. I also have a battery watering system that does not need cap removal to add water...have a look at them.

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Old 01-23-2018, 01:14 PM   #8
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Quote:
Originally Posted by dasams View Post
We have a 2018 FC 25 FB with 50 amp service.
Here's my plan to protect the batteries:

1. Install a battery disconnect switch on one of the batteries.
2. While on shore power for extended stays, flip the switch to disconnect the batteries from the converter and connect a smart battery tender to maintain proper voltage.
3. When we hitch up to move, flip the switch back to the connect position and remove the battery tender.

The electrical diagram shows that a 4 ga wire connects one of the batteries to the inverter and that a 6 ga wire connects the other battery to everything else, including the jack.

Should I install the disconnect switch on the positive terminal of the 6 ga battery? If so, will this protect the batteries from the 13.6 volts put out by the converter? While on shore power, will everything work normally?

Thoughts? Thanks, Dave
Okay let's take these one at a time.
Quote:
1. Install a battery disconnect switch on one of the batteries.
You'll find that your converter has a positive on one battery and the negative on the other. Same with the inverter, just using the positive from the other battery. You'll need to interrupt the flow with a switch, and I don't think what you propose will work.

Quote:
2. While on shore power for extended stays, flip the switch to disconnect the batteries from the converter and connect a smart battery tender to maintain proper voltage.
Okay.
Quote:
3. When we hitch up to move, flip the switch back to the connect position and remove the battery tender.
You're battery tender has the same kind of connector that's used in the Zamp connector. Check polarity, but you may be able to just plug into the zamp.

Quote:
The electrical diagram shows that a 4 ga wire connects one of the batteries to the inverter and that a 6 ga wire connects the other battery to everything else, including the jack.
The batteries are in parallel, so both batteries are connected to each device. It's just that the red inverter cable is on one battery, while the red converter cable is on the other.
This is done to equalize the load on the batteries. I'm above my pay grade here, but I think the idea is to have the electrons flow through BOTH batteries, rather than be sucked out of one and replaced by the other.

The jack is a separate wire (black with a yellow ring crimp)
and that's the positive of the jack. The negative is through the frame to a terminal block and the black battery cables.

In theory, your 2018 has a three stage charger, so you may be able to leave it plugged in.

My "work in progress" will replace the too short battery jumpers which are 6 AWG with 2 AWG and make them about
14" long, creating a "S" curve that allows getting to the filler caps.
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Old 01-23-2018, 01:31 PM   #9
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Originally Posted by Mollysdad View Post
Okay let's take these one at a time.
You'll find that your converter has a positive on one battery and the negative on the other. Same with the inverter, just using the positive from the other battery. You'll need to interrupt the flow with a switch, and I don't think what you propose will work.

Okay.
You're battery tender has the same kind of connector that's used in the Zamp connector. Check polarity, but you may be able to just plug into the zamp.

The batteries are in parallel, so both batteries are connected to each device. It's just that the red inverter cable is on one battery, while the red converter cable is on the other.
This is done to equalize the load on the batteries. I'm above my pay grade here, but I think the idea is to have the electrons flow through BOTH batteries, rather than be sucked out of one and replaced by the other.

The jack is a separate wire (black with a yellow ring crimp)
and that's the positive of the jack. The negative is through the frame to a terminal block and the black battery cables.

In theory, your 2018 has a three stage charger, so you may be able to leave it plugged in.

My "work in progress" will replace the too short battery jumpers which are 6 AWG with 2 AWG and make them about
14" long, creating a "S" curve that allows getting to the filler caps.
" think the idea is to have the electrons flow through BOTH batteries, rather than be sucked out of one and replaced by the other."

When all the leads are connected and the switch is "on", load will be equal, with minor resistance perhaps due to cable length, size. In other words, when all connected, each battery will be working as "one" unit. The hookup of one load cable to one battery terminal and one to the other battery and terminal suggests there may be a load sharing, but not really much difference when all connected. Now, here come the experts likely to split hairs...
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Old 01-23-2018, 01:44 PM   #10
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No expert as an old navy mechanic, but disconnects on the negative posts are better, worse, or same?. And btw, electrons obviously flow from positive to negative, right?
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Old 01-23-2018, 02:22 PM   #11
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No expert as an old navy mechanic, but disconnects on the negative posts are better, worse, or same?. And btw, electrons obviously flow from positive to negative, right?
No, electrons flow from negative to positive. However, it makes no real difference which lead you use. You're interrupting the flow.
The difference is that an exposed switch on the positive terminal might cause a giant spark if you accidentally touch something to it, like a wrench to the frame.

The beauty of using the negative cable on the Airstream is they are longer than the positive and therefore you have more options in mounting the switch. Airstream places the batteries with the negative forward, so the cables entering the battery box have longer leads on the negative by 4-5 inches.
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Old 01-23-2018, 03:06 PM   #12
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My aftermarket (bigger, taller) battery box is all plastic..less hazard for shorts...although its still possible. Always best practice to disconnect negative lead(s) first anytime we're working on them...

It holds a couple of (ridiculously heavy) GC-2 Golf Cart batteries in series.
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