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Old 02-23-2017, 05:15 PM   #1
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2016 19' Flying Cloud
Portland , Oregon
Join Date: Feb 2017
Posts: 155
Dual Battery Setup with Automatic Charge Relays

While our Airstream is new to us, vacations with a trailer is not as we previously owned a CampInn teardrop. Many of the places we visit have full hookups but many do not and from these experiences I knew we would need to upgrade the electrical system. This is a long thread but I hope it gives others some ideas for their setup.

First upgrade was to 235 AH batteries installed in the stock battery box location: http://www.airforums.com/forums/f449...ud-163074.html

200 Watt of Solar: http://www.airforums.com/forums/f448...-a-163067.html

Upgrade of the converter: http://www.airforums.com/forums/f449...es-162905.html

My final project (for now) was to install a second battery bank. When we first got the trailer I noticed a substantial amount of room under the bed. I’m not talking about taking up the space of the valuable storage unit under the bed, but behind that next to the fender wells, water heater and stock inverter. My idea, install second set of batteries here.

The circuit diagram and long winded explanation.



In the diagram you can see the house and the secondary “AUX” battery bank, it’s the AUX bank which will install under the bed. One key point in my desired setup is that the two battery banks are not directly joined together. The house batteries power the trailer as normal and this second set will power the inverters.

In this setup if we choose to use the inverters, which are a luxury, we do not drain our important house battery. The switch seen has two inputs and two separate outputs. Off, On and emergency. Off, both inputs are disconnected from their outputs. On, input 1 is connected to output 1 and input 2 is connected to output 2. Emergency, connects #1 and #2 together.

While this setup ensures that the batteries are kept separate it also poses a challenge in respect to charging. If #1 and #2 are not connected then each battery would need its own charge connection. This problem is solved with an automatic charge relay, ACR for short. (BlueSea product) The ACR is a little device that senses charge voltage on either battery and when sensed creates a parallel connection sharing the charge between batteries. No charge sensed, no connection and the batteries are completely isolated.

In my case I disconnected the old stock inverter positive and feed that into the switch and then to the ACR. As I have solar charging (or converter when plugged in), when the ACR senses a charge voltage on the house battery cable it triggers and shares that charge to the second battery bank. However, this in itself poses a possible problem. There could be a scenario where I have solar charge current, the ACR has triggered and connected the house to aux batteries in parallel and you use the inverter. In this scenario the inverter will pull current from both the aux battery and house battery through the ACR connection. The ACR has a capability which I used to solve this problem too. It has an inhibit or isolate function which via a switch enables manual override, disconnecting the ACR. Of course you would have to remember to press the button but even in the worst case scenario it just means you create a drain on both batteries.

Finally, I wanted a setup that if we accidently drained the house batteries, light on, furnace etc, that we had a way to use the aux batteries in their place. In this scenario you would disconnect the house batteries (resettable fuse in my case) and turn the switch to emergency which would connect the aux battery to the house circuit via the cables which used to run to the inverter.

I’ll cover the 12 volt system and later discuss why I have two inverters and how they are both connected.

First, lets look under the bed, wow, look at all that space! This is what I saw just looking through the access panel.





Removing the wooden bed base confirms the amount of space



Silver box at bottom of picture is the stock installed 1000 watt inverter. At the top is the water heater.

First I remove the stock inverter wiring and fuse, cut a small chunk out of the panel support as this is where the second battery bank would sit.



This box was around the same size as one of the 6 Volt batteries I planned to install. So far so good, everything would easily fit.



Next a test fit of moving the stock inverter and a place for a second larger 2000 Watt inverter.



At this point you are scratching your head as to why I plan to keep the stock 1000 Watt inverter… Simple really, it was there, I didn’t want to waste it, I didn’t want a button on the wall of the airstream interior that didn’t do anything. Hindsight and all that, I should have just scraped it.

I wanted a larger 2000 Watt inverter as I have a guilty pleasure that I wanted to enable… my travel espresso machine. That and this inverter is better than the stock one. Hey in my setup you get to keep both. More on that later.
The switch was mounted at the end of the bed, it is sort of hidden low down and in a space between the end of the bed and the fridge in our Airstream. There is still enough room to get your hand in.



Here you can see the back of the switch with only the positive cable from the front batteries connected.



For the new cabling I purchased a mixture of 1/0 flexible welding cable for the 1000 Watt inverter and ACR runs. For the bigger 2000 Watt inverter I purchased 2/0 cable. I’ve done a couple of other projects with this cable and love working with it.



This cable lug installer is cheap and easy to use just hit it with a hammer. I’ve installed over 100 lugs with this one.



Below you can see the start of the 12v wiring. #1 input is from the house battery which in turn is connected to the solar charger and converter charger. The #1 output goes only to the ACR. The #2 input will in the end be connected to the second battery bank, 2/0 cable. You can see a couple of connections on output #2, one goes to the ACR, one goes to the 1000 Watt inverter via a 100amp fuse and one to the 2000 Watt inverter via a 200amp fuse.



Now onto the inverters; I really don’t need two inverters but ho hum, I have two now. The output of each inverter is connected to the inputs of an automatic transfer switch. This switch seamlessly switches between 110v inputs.



The automatic transfer switch’s output is connected to the trailers inverter sockets. The 2000 Watt inverter has priority. Regardless of the state of the 1000 watt inverter, if you turn on the 2000 Watt inverter the automatic transfer switch will connect it to the trailer inverter sockets. Hey at least this way we can continue to use the stock inverter switch, which is more conveniently placed.



Maybe in the future I’ll disconnect the stock 1000 Watt inverter and route in a shore power line into the automatic transfer switch instead. I would switch the input so shore power would have the priority. If you look closely in the picture you can see I used plug and sockets to make the connections so it’s easy to disconnect and reconnect.

I installed the inverter remote power switch in the storage cupboard under the bed.



At the top of the above you can also see the small battery voltage meter. While I installed a AH meter on the house battery I didn’t bother for the aux set.

Now onto the second battery bank. There is a lot to see in these pictures. Note the negative connection post, this joins the negative from the house battery to the aux battery and inverters. You can see the ACR unit partly installed, it has 50 amp fuses on it’s connections and a negative fused connection which is required for it to function. The isolator connection is not installed here but it connects to the middle spade on the ACR. You run 12v to this middle connection to disable the ACR relay.



The batteries are securely attached to the trailer floor via a strap and you can see the fused bus bar I built connecting the two 6v batteries in series. If you didn’t read my other thread, this fuse is a failsafe and acts as a battery disconnect if needed.



This completed the secondary battery install.



Above you can see a photo of all the components in place. Below from a different angle.



The disappointing thing, but the thing my wife likes, is that all you see once the bed frame is back on is this view of the battery and disconnect fuse from the access panel.



The only visible part of the install is the switch and inverter panel, and both of those are out of sight.

I did replicate the 12 volt connections in the rear storage area as well.



This has two uses, first is the black battery box is a portable backup battery, 22 AH. If we screw up and kill both house and aux banks, this can also power the trailer in an emergency. The aux battery switch would be turned to off and this switch to emergency with the house battery fuse in disconnect position.

The second use is that the cables unplug from the battery backup box and can be plugged into our portable solar panel with integrated charger. The idea behind this is that we can use the portable solar as either a solar charge boost or if the trailer is undercover. The cables for the portable solar are long enough to reach about 20 feet from the trailer. Of course the back storage door has to be open when you are connected here. You don’t want to leave your portable solar while you are away anyway.

You don’t see it in this picture but I connected a homemade extension code to the second output of the 2000 Watt inverter and the other end of that is also in the storage area. You can unroll it and have a 110v connection out the back of the storage unit. No idea what I would use this for but that didn’t stop me installing it just in case.

I hope you have enjoyed this thread. Feel free to ask me questions. I didn’t see others creating dual battery banks with ACR’s so I thought it would be helpful ideas for others.
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Old 02-23-2017, 08:38 PM   #2
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Smile

"I wanted a larger 2000 Watt inverter as I have a guilty pleasure that I wanted to enable… my travel espresso machine. "

Did you do this job to make coffee or did the coffee make you do it?

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Old 02-23-2017, 09:44 PM   #3
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Mmmmm coffee
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Old 02-24-2017, 03:26 AM   #4
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"The switch seen has two inputs and two separate outputs. Off, On and emergency. Off, both inputs are disconnected from their outputs. On, input 1 is connected to output 1 and input 2 is connected to output 2. Emergency, connects #1 and #2 together.

While this setup ensures that the batteries are kept separate it also poses a challenge in respect to charging. If #1 and #2 are not connected then each battery would need its own charge connection. "

Mr. Coffee,
Could you please clarify your switch by indicating inputs and outputs and #1, and #2, emergency positions, and all that? You have done a lot of great work but the drawing has my pea brain in a twist. That is a two pole single throw switch?

The fuses look like resistors, but they are more like circuit breakers right ?

These forums need an electrical drawing mode.

RC
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Old 02-24-2017, 08:32 AM   #5
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Admittedly that's a sloppy circuit diagram, and yes my fuses look like resistors. Here is an equally sloppy diagram which is supposed to add a bit of clarity to the switch and ACR magic


Click image for larger version

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(Posting from my phone so I hope this works)

Notice both the switch in emergency position and the ACR active will essentially parallel the battery connections.

For the switch, Off, everything is disconnected, including the ACR in my configuration.

In the On position, the connections between input #1 and separately input #2 and it's associated output are closed.

In the Emergency switch position, think of the switch also closing a connection between outputs #1 and #2.

Clearer?
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Old 02-24-2017, 08:10 PM   #6
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Urg, just measured the standby power of the airstream stock 1000w vs. the Xantrex proWatt 2000 I installed.

Airstream 1.8 amps
Xantrex 0.5 amps

As in, that's the draw with nothing plugged in.

On the bright side, it'll be easy to swap out. I might put a little thought into how to get a shore line in at the same time
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Old 03-09-2017, 04:22 PM   #7
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Removed the Airstream 1000 watt and replaced with a Xantrex proWatt 1000. Standby power is about 0.2 amps. Much better.

Fun project
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Old 04-07-2017, 06:52 PM   #8
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Dual Battery Setup with Automatic Charge Relays

Loving the dual battery setup. Gives us peace of mind while we watch a movie (or 2) on the TV powered by the inverter on the aux batteries while dry camping. Zero drain on the house batteries reserved for lighting, fridge, furnace etc

Oh, and while at first my wife made fun of me doing all this to power an espresso maker, she sure does enjoy her coffee in the morning.
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Old 04-07-2017, 10:11 PM   #9
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Cool project. You fit a ton in a small space. Curious as to why you put another 1000W inverter in? Why replace it? Do you actually use it?
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Old 04-07-2017, 11:17 PM   #10
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Originally Posted by Troutboy View Post
Cool project. You fit a ton in a small space. Curious as to why you put another 1000W inverter in? Why replace it? Do you actually use it?

Long story, mostly I didn't have to, but I did want to play with automatic transfer switches. My wife says I have too much time on my hands (which I really don't but engineering and building things is what I do as my relaxing hobby)

Now I've wired the 1000 into the stock switch position we use that one more than the 2000. However I could have easily just wired the 2000 to that switch too.

The 1000 has slightly less no load draw. 1000 trips with my espresso maker.

If I did it all over I'd do a single inverter with passthrough. As it happens I've hooked up a passthrough from shore power to this setup too. Very easy.

When we tear dropped my nick name was More Power. Can't fathom why [emoji12]
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Old 04-14-2017, 07:26 PM   #11
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Updated picture of the aux battery bank, inverters and automatic transfer switches

Click image for larger version

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Old 05-01-2017, 10:57 AM   #12
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Quote:
Originally Posted by Snowy View Post
Urg, just measured the standby power of the airstream stock 1000w vs. the Xantrex proWatt 2000 I installed.

Airstream 1.8 amps
Xantrex 0.5 amps

As in, that's the draw with nothing plugged in.

On the bright side, it'll be easy to swap out. I might put a little thought into how to get a shore line in at the same time

Thats a huge difference!
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Old 05-01-2017, 06:30 PM   #13
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Snowy, do you have a part number for that switch?
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Old 05-01-2017, 11:16 PM   #14
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Originally Posted by mythbuster88 View Post
Snowy, do you have a part number for that switch?


Are you talking about the Blue sea Automatic Charge Relay or the Switch?

They both came in the blue sea add-a-battery kit

Blue Sea Systems Add-A-Battery Kit https://www.amazon.com/dp/B000RZNP5K..._ArbczbWEFV8HB

Here is the switch, dual circuit

Blue Sea Systems e-Series Dual Circuit Plus Battery Switch https://www.amazon.com/dp/B000MMH1SK..._uxbczbV7Z37XT

Cheers
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Old 05-02-2017, 02:48 PM   #15
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Thanks S,

In my trailer under a cushion there is an area about 2' x 2' x 1.5' . And just lying on the floor is my cheapo factory inverter. Not screwed into anything and limited in movement only by the 6 (?) gauge +/- 12 volt cables.

So I was thinking, perfect place for a battery bank! I could do the Snowy thing and use a fancy ACR for charging and have some extra 12V mojo for those special Nespresso moments!
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