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Thread: Factory Battery Disconnect
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06-24-2022, 05:30 AM #11
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Here is a simplified drawing I made that shows the routing of the Converter/Charger Positive and Negative wiring in a typical RV trailer setup. Yours may vary to some degree, but this is the basic setup.
So, if you are on Shore Power.....or have a generator running, the converter/charger (C/C) will be producing 12VDC straight to the typical breaker panel in the RV.....which is ALSO where the 12VDC fuse and circuits originate for most stuff that is 12VDC. Please note....I am NOT showing any of the 120VAC breakers or circuits coming off of the breaker panel...AND I'm not showing any of the 12VDC circuits or fuses, just know that the power for all of that is in the Breaker/Fuse Panel.
So the 12VDC from the C/C goes straight to the 12VDC buss in the breaker/fuse panel and provide 12VDC when you are on shore power or genny, as I stated above. Another l2VDC Positive line comes from the 12V Pos. buss in that panel and goes to the OEM Battery switch, and then from the Battery switch to a set of breakers. One side of that line of breakers (usually the auto reset type of breaker) has a copper buss that goes from breaker to breaker to breaker and so on.....so that the incoming 12V pos cable can feed all of them. Those individual breaker go out to various places, and I'll just leave it at that. One of the breakers though, feeds over to the Battery Pos. terminal, as you can see in my drawing. If you have shore power on, or the generator is running, and and the C/C is operating.....you are feeding charging voltage to the battery, AS LONG AS THE BATTERY SWITCH IS CLOSED. If you are unplugged from shore power and the generator is NOT running....the battery is feeding power to the trailer....AS LONG AS THE BATTERY SWITCH IS CLOSED
So, given a visual of this setup, it's pretty easy to see that anything that is fed to the items that are marked "To Various Devices" could be a "phantom" drain on the battery, as the 12VDC is continuous from the battery POS terminal, through the bottom breaker in my pic, through the copper buss to all the breakers there, and out to the "phantom load". That is the reason that simply turning off the OEM battery switch does NOT eliminate all the Phantom loads and will drain your battery in days/weeks if you aren't hooked up to shore power when storing the RV.....OR....if you haven't disconnected a battery lead...OR...you haven't installed a true battery disconnect to break the circuit from the battery lead out towards the rest of the stuff.
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06-24-2022, 05:42 AM #12
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That statement is ALMOST true, but not quite. With LFP battery setups, there is a BMS located somewhere in the system. In order for the BMS to work, it will have sensing leads connected directly to all four of the positive battery posts.....one lead for each of the four cells in the battery. You are not going to see them in a Plug and Play battery like Battle Born and others, as the BMS and it's circuitry is inside the battery case....but they are there. And with those being directly connected to the Pos. battery terminals, there will be some amount of "phantom" draw from the battery. The amount of draw will vary per battery manufacturer and the type of BMS that they use, but it is still there.....think milli-amps, not amps. But over time, those milli-amp draws will slowly take the battery down a bit....plus the very slight self discharge of the battery itself....which is a pretty small amount in LFP batteries.....think of maybe 1% to 2% per month. That self discharge cannot be stopped....battery disconnect or not, it doesn't matter, it just happens.
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Excessive Payload is a Wonderful Thing
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06-24-2022, 09:08 PM #13
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06-30-2022, 08:48 AM #14
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Just as you said in your second point, disconnecting the ground (-) side of the battery helps from a safety standpoint. This can be helpful to understand also one should always, when installing or removing your car/truck battery that you should disconnect the negative wire first and when installing a battery connect the negative wire last.
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07-03-2022, 06:09 PM #15
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On my trailer there was a drain when using the factory disconnect. Some say it comes from the Carbon Monoxide detector and maybe some other things. I installed a disconnect to the negative terminal and now have no drain. Electricity flows from positive to negative so there is no chance of anything in the trailer getting current even if grounded either intentionally or accidentally.
Last edited by GaryS1964; 07-03-2022 at 06:12 PM.
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07-03-2022, 06:26 PM #16
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In my opinion, the battery disconnect switch is not named correctly, as they wire them from the factory. The pos. lead coming from the battery goes to a row of auto reset breakers in my trailer and the battery disconnect switch is "downstream" of that and only kills the 12VDC that would normally go to the 12VDC fuse panel, which is normally located in the 120VAC breaker panel. That is shown on the drawing that I made in a post above.
A TRUE battery disconnect switch would be in the pos. line between the pos. battery post....and that row of auto reset breakers. Beware though, if a true battery disconnect is installed, it will kill the power to EVERYTHING that is operated on 12VDC....including the Carbon Monoxide detector, the radio/DVD player and the emergency breakaway circuit for the brakes on the trailer. That simply means that you should NEVER TOW THE TRAILER with a true battery disconnect in the OFF position....if you have installed one.Last edited by xrated; 07-03-2022 at 06:32 PM.
2016 F350 CrewCab Dually
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2023 Suzuki GSX-S1000 GT+
Excessive Payload is a Wonderful Thing
"If it ain't fast....It ain't Fun"
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07-04-2022, 03:05 AM #17
This is my 4th RV, and the first one to have a battery disconnect.... GD does state in the manual that one needs to disconnect the battery cables for storage. I installled the battery gardian with the disconnect feature enabled. It does disconnect everrything. I am not concerned about forgetting to turn it on, as I need to do that in order to hitch up.
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07-04-2022, 11:25 AM #18
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It is my understanding that the battery disconnect is between the negative ground of the battery or batteries & the ground. That is the way I installed mine. I added a battery disconnect right after my negative post on the batteries & there is no parasitic drain. I’m interested to find out which way others have installed their battery disconnects.
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07-06-2022, 03:35 PM #19
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I hadn’t thought about the breakaway. That’s a great point, but as hunting dog pointed out on another post below, I have to power up to hitch up, so I’d have to intentionally disconnect the 12v power after hitching up. I might have done that for some reason, not have it thought about this, so thanks for bringing it up. I won’t now.
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07-06-2022, 03:51 PM #20
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I'm in the same boat with the 6 point hydraulic leveling.....nothing is going anywhere that battery switch turned on. I was envisioning maybe someone hooking up the day before travel...or even a couple of days before travel and turning the battery switch back off to try and help conserve battery power, then forgetting to turn it back on before jumping in the truck and taking off.
In my case, I leave the new battery disconnect that I installed, off sometimes if the trailer is going to sit for a while. I'm usually plugged into my 50A shore power at the house and I don't want the charger/converter sending charging power to the LiFePo battery and it sitting at 100% SOC, which is not great for them to be at when not in use. I put a warning sticker on both my switch for operating the slides as well as the leveling/landing gear controller warning me to make sure the battery disconnect was ON. If you try to run the hydraulic system from just the converter, you'll likely smoke it because of the amount of current that the motor pulls, vs. the amount of current the converter can produce. Hydraulic motor is in the 70 amps range, my converter is a new unit made to take care of LFP batteries and it's output is 43 amps max. Don't want to let the smoke out!2016 F350 CrewCab Dually
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2023 Suzuki GSX-S1000 GT+
Excessive Payload is a Wonderful Thing
"If it ain't fast....It ain't Fun"
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