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Old 09-14-2020, 03:38 PM   #1
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2021 16' Caravel
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The purpose of the master 12v switch Like Blue Sea?

Hi,
What's the purpose of the big red Blue Sea($40-$50) switch people add to their 12v system? Particularly when people adding them right next to the battery, inside the battery compartment like under the dinette seating or bed.
My 16' AS doesn't seem to have a kill switch for the 12v system, there is one "Use", "Storage" switch above light switches by the door, and it's relay based. I can think of 2 things here-
1. Relay based use/storage switch requires power to function, which means it will add to the parasitic draw, and in case of an emergency, it might not work.
2. Adding a master switch that turns off everything(actually probably doesn't, as BMS inside a LiPoFe battery enclosure cannot be turned off that way) probably has safety implications - propane, monoxide detectors, breakaway brake are still connected in "Storage" mode.

If my understanding is correct, then there are 2 options I have -

1. install the inline master switch, right out of battery terminal, make it quickly accessible in case of 12v system malfunction, and accept the risk that if I forget to turn it back on before sleep in or travel with it, I am risking my own or someone else's life.

2. Do not install the inline master switch, but use a breaker with reset button, save the cost ($40) and the space. This also make me less likely to use it accidentally or unnecessarily. The tradeoff here is that it will take me 5 more second to open the dinette seating to turn it off from the breaker, which could make a difference.

I am inlined to option 2. But I am not sure if I am missing anything.

Thanks in advance!

-Hovr
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Old 09-14-2020, 07:29 PM   #2
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The purpose of the master 12v switch Like Blue Sea?

Then thereís my Department of Overkill Engineering solution:

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BlueSea Systems 250 amp switch kills all power from the positive side of the batteries. Safety cover to slow down pranksters. There is an 80 amp MRBF fuse bolted directly onto the positive battery post to protect the wiring downstream. Absolutely kills all power when used.
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Old 09-14-2020, 08:21 PM   #3
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A master switch installed correctly will kill power to everything you want it to. I have a four position switch so I can have 1) inverter only 2) trailer only 3) both 4) all off.

The only thing I donít turn off is the electric jack. You really need one of these to store your AS if you leave the batteries in due to parasitic loads.
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Old 09-14-2020, 09:12 PM   #4
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The purpose of the master 12v switch Like Blue Sea?

I failed to mention that there are actually two MRBF fuses bolted to the battery positive terminal on my rig. One supplies power to the tongue jack and powered WD jacks. The other feeds the master switch. BlueSea Systems makes a nice double MRBF holder that has a red rubber safety cover that bolts directly to the battery post.

If you do this, be sure to stock a few spare MRBF replacement parts in the right rating. They tend to be slow to ship out and are not something you easily find on the road.

I tend to use BlueSea Systems products because they are waterproof, marine grade, and heavy duty compared to the usual RV supplier bits and pieces. My dad was a professional sailor all his life, and taught me the value of good tools and parts when you are out there far from support. My Navy experience drove the lesson home. Donít go cheap on stuff vital for your personal comfort or possible continued survival...

Iím also planning to replace the weird use/store relay with a BlueSea Systems one. It has the advantage of having a positive on/off indicator and can be manually operated if need be. Yup, still more overkill, but thatís how I roll.

A master disconnect is vital in case of an electrical short or electrical fire. One of those many things you donít need until you REALLY need it.

( Like 4WD, iron rations, bottled water, radio communications hardware, and survival gear plus a comprehensive first aid kit. My buddy, Justin Case, demands a certain level of preparation. )
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Old 09-14-2020, 10:48 PM   #5
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Quote:
Originally Posted by billrector View Post
The only thing I donít turn off is the electric jack. You really need one of these to store your AS if you leave the batteries in due to parasitic loads.
Sorry if it's obvious (I am very new to AS/RV), why can't you use the power jack to level/store your AS, then walk into your trailer cabine, turn off the master switch, walk out and lock the door?, This way no one can mess with your jack.

Thanks!
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Old 09-14-2020, 11:43 PM   #6
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The purpose of the master 12v switch Like Blue Sea?

Personally, Iíd rather not be able to accidentally lose or forget to turn on power to the tongue jack, my power WD jacks, and my breakaway switch. These three items are vital to getting the Airstream under way in a hurry in an emergency departure or a bail-out scenario here in California lately. The last fire, fortunately put out overnight and only 75 acres, was less than a mile north from my house. If I need to bail, the last thing I need to do is mess with a jack that isnít powered.

I can see the utility of having the master power switch inside the Airstream cut off all outside powered circuits in a storage situation, but believe me, itís real hard to move an Airstream when the tires on both sides are chained together and the lug nuts are also booted.

Besides, my Airstream is stored in a locked and guarded long term storage area where the watchman is a darn good shot, has a clear field of fire, and has promised not to hit my Airstream if he has to defend it...thatís why it is parked in the space it is in!

He likes Airstreams!
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Old 09-15-2020, 11:58 AM   #7
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A switch that completely disconnects the battery bank from the trailer is primarily used to eliminate what is referred to as a parasitic load. If you look at the schematic for the Airstream, not all 12 Volt loads are disconnected by the "Use" / "Storage" switch inside the Airstream. Small devices such as the gas detector alarm is one such load that is not removed from the battery bank.

By removing all loads from the battery, you are able to ensure that the battery voltage will drop as slowly as possible while in storage (be it for a day, week, or months). With the battery disconnect open, the only factor that should affect the battery voltage dropping will be its own internal self-discharge rate. The self-discharge rate is lower in colder weather but is never zero.
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Old 09-15-2020, 07:46 PM   #8
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I like hovr's idea �� isolating the jack circuit, that would certainly help slow a thief . In my opinion, any parasitic loads should be turned off when in store setting, that might require some rewiring The breakaway system should be a direct connection to the battery. I don’t know but if airstream uses a nonparasitic relay. That would be a “latching relay” which does not use any current after it latches.
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Old 09-15-2020, 08:12 PM   #9
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Quote:
Originally Posted by hovr View Post
Sorry if it's obvious (I am very new to AS/RV), why can't you use the power jack to level/store your AS, then walk into your trailer cabine, turn off the master switch, walk out and lock the door?, This way no one can mess with your jack.

Thanks!
Many trailer storage yards and RV centers require the jack to be functional without any hindrance so it is generally independently direct wired to the battery posts so it is ready to function. Except for those with wireless remotes they have no parasitic draw.

The brake away switch and gas detector bypass the load center and are connected to the battery bus bars. The brake away switch has no draw.

The inverter is connected separately to the battery and has a parasitic draw of about 0.02 amps for the remote device.

Also of note the Use/Store relay is momentary throw in both directions and does not have any draw except when being thrown.
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Old 09-15-2020, 08:15 PM   #10
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The standard use/store relay is in fact a magnetically latching relay.

Where the fun comes in is that the indicator LED only tells you there is power on the 12 volt circuits. It does not tell the true state of the relay. It also lights up if the convertor is powered by the AC input to the Airstream.

Iím moving to a BlueSea Systems relay that has a positive indicator at the price of a little power for the indicator LED. No more confusing indicator. The BlueSea relay also has a manual control handle.
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Old 09-23-2020, 10:56 AM   #11
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Only way to totally eliminate the parasitic loads.
Here's my offering.


Quote:
Originally Posted by hovr View Post
Sorry if it's obvious (I am very new to AS/RV), why can't you use the power jack to level/store your AS, then walk into your trailer cabine, turn off the master switch, walk out and lock the door?, This way no one can mess with your jack.Thanks!
The factory setup has the jack wired directly to the battery.
When I installed my switch, I learned the negative cables were longer and if I used then with the switch, I wouldn't need to splice any wire. So I did. But that means the jack, even though direct to the battery, won't work because the ground is open. Since my switch is outside, it doesn't provide security, but that a good idea.
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Old 09-23-2020, 01:52 PM   #12
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Originally comes from the boating world i believe.
Allows you to turn off your rig when not around?

On my boat, i turn everything off when I leave.
The only 2 circuits that remain on are the bilge pump and the solar panel.
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Old 09-24-2020, 08:59 AM   #13
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Hi Shipmate. Glad to read that you recognize the value of good stuff. Help a newbie, please. What are iron rations? I was on an old submarine that (in the 70's) still had dehydrated food in cans from the 50's. We kept them for scaring the visitors who came to eat onboard. Do you use much canned food when traveling? Thanks,
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Old 09-24-2020, 11:19 AM   #14
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The purpose of the master 12v switch Like Blue Sea?

Iíve learned, sometimes the hard way, that cheap stuff ends up having to be bought twice. Quality hardware lasts a lot longer.

Nowadays ďiron rationsĒ would be stuff like MREs or the like. In the old days it would be stuff in cans like the old ďCĒ or ďKĒ rations. Some of that stuff was actually tasty.

We carry a few MRE packets just in case, plus long lasting water and the like. Each vehicle has some sort of 72 hour kit and even the dogs have a kit we carry for them. Since weather and fire can cut us off or generally screw up travel in Southern California we take a few precautions.

We donít generally use canned food when traveling. It weighs a lot and tends to be bulky. Wife also does not like canned stuff in general.

Most of our emergency long term food is dehydrated and sealed in plastic buckets. We keep some of that at home, along with a well-stocked pantry. We used to live very far out in the desert, and grocery shopping was a major trip into a bigger town every 4-6 weeks. Some food storage habits stay with you.
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