23fd Battery disconnect switch install

[tjwoods1]

I have been following the threads on this forum and others regarding the battery disconnect switch. It has greatly improved my knowledge- but has also raised some questions, most likely from my vast ignorance and my own misunderstanding. I have a 2018 19’ Flying Cloud with two 6v Golf Cart batteries wired in series. I am thinking of putting in a disconnect switch for when I store the trailer.
1) I understand that the “Store/Use” switch in the Airstream does not completely turn off everything. Besides the Propane/CO detector and the converter, what else would be a parasitic draw not turned off by that switch?
2) I was planning on putting a cut off switch on the negative to positive cable that connects the two 6v batteries. Would that NOT cut off the CO and converter draw? If not, than what would be the point of the cut off switch?
3) I presume the inverter switch that turns of the inverter, really DOES cut it off. Correct?

[steverino]

As the inverter is usually connected directly to the battery, no, the inverter switch will not completely cut off phantom draw of the inverter when it is shut down. That phantom current can be as much as 100 mA, as in the case of the WFCO 1000 watt inverter which is OEM equipment in late model Airstreams

[wulfraat]

I think I posted this earlier in this thread somewhere... but this diagram shows the most common approach to truly disconnecting the batteries from any/all loads using either a 2 position or 4 position mechanical switch (with the exception of the power jack, but that can easily be switched as well)

[FloydCoVa]

Wufraat, I followed your method last spring and this has been working perfect for me. Thanks for posting this info.

[gypsydad]

Originally Posted by tjwoods1

I have been following the threads on this forum and others regarding the battery disconnect switch. It has greatly improved my knowledge- but has also raised some questions, most likely from my vast ignorance and my own misunderstanding. I have a 2018 19’ Flying Cloud with two 6v Golf Cart batteries wired in series. I am thinking of putting in a disconnect switch for when I store the trailer.
1) I understand that the “Store/Use” switch in the Airstream does not completely turn off everything. Besides the Propane/CO detector and the converter, what else would be a parasitic draw not turned off by that switch?
2) I was planning on putting a cut off switch on the negative to positive cable that connects the two 6v batteries. Would that NOT cut off the CO and converter draw? If not, than what would be the point of the cut off switch?
3) I presume the inverter switch that turns of the inverter, really DOES cut it off. Correct?

The Store/Use switch on or off will still allow parasitic draw. A "cut off" switch will disconnect the batteries from the coach completely. And, yes, I have cut off switch with my 6V installed between my - on one battery to the + connection of the other. I throw this when in storage and my converter will still function inside if needed to run things, but no battery issues. A day or so before heading out, I throw the cut off switch "on" to top off the batteries from the converter...works fine.

[tjwoods1]

So let me make sure I am understanding this correctly - sorry if I am so dense:
As per my photo of my 6v series configuration -
1) To disconnect completely I would have to put a disconnect switch at either A+ or A- terminal. This disconnects the inverter/converter/propane detector draws.
2) Due to the web of wires on either of those terminals, I was hoping to put a disconnect switch at the B- terminal. If I did that, then the inverter/converter/propane detector draws would still be present? In that case, what is the point of a disconnect switch there? What exactly is being disconnected except breaking the connecting between the two batteries?

[gypsydad]

Originally Posted by tjwoods1

So let me make sure I am understanding this correctly - sorry if I am so dense:
As per my photo of my 6v series configuration -
1) To disconnect completely I would have to put a disconnect switch at either A+ or A- terminal. This disconnects the inverter/converter/propane detector draws.
2) Due to the web of wires on either of those terminals, I was hoping to put a disconnect switch at the B- terminal. If I did that, then the inverter/converter/propane detector draws would still be present? In that case, what is the point of a disconnect switch there? What exactly is being disconnected except breaking the connecting between the two batteries?

In a series connection with the 6V's, you connect the - (negative terminal) from one battery, to the + (positive terminal) of the other battery, right? That's just one wire connecting the two batteries, (- to +) completing the circuit for 12V. Your + & - wires are connected appropriately, to the other terminal of each battery; one is -; the other is +. In order for the circuit to be complete supplying the 12V to the trailer, that single wire needs to connect both batteries. Your picture above, has the single wire that I would use inline with the disconnect switch, at B-. When the circuit is "broken", no power will flow to the trailer.

Note in the picture of my batteries below; the single red wire in upper left connects the - (negative) terminal from upper battery to disconnect switch terminal, which is attached to the + (positive) terminal. All positive wires from the AS go to the red "other" positive terminal upper right (red wires); all negative wires from the AS go to the "other" negative terminal, lower right (black wires) If you click on the picture twice, it will enlarge to see better.

[rmkrum]

These batteries are wired as two 6-volt batteries in series to get the usual 12 volt supply. If you don’t have enough slack in the cables on A+ or the A- leads to run them to a switch and still get all the wires on it, your only real place to put a switch is between B- and the wire to the other battery. If the box lid is metal, and there is not enough clearance, one of the knife switch disconnects will not work. You could extend the B- connections to an external switch.

Since the batteries are in series, disconnecting the jumper between them at B- will still kill all the parasitic loads, but you might still have +12 volts on terminal A+ from the solar system or the converter.

That’s not an issue if the jumper is disconnected or switched, but does leave a “hot” positive lead in the box. Not a big issue as long as you keep it in mind when working inside the battery box.

Personally, I’d rewrite this to put an insulated positive bussbar somewhere inside the Airstream to put all those wires away from the battery environment (acid vapor, etc) inside the coach, and do the same thing with the wires on A- to another insulated ground bussbar inside the coach.

Then put a manual disconnect switch (like a blue sea systems marine-rated disconnect) on the outside of the battery box and a fuse right on the A+ post before the switch to protect the wiring. That’s how mine is rigged.

I used an 80 amp fuse on the battery A+ post and the red wire goes from there to the Blue Sea Systems manual disconnect switch directly. As always, use proper sized wire and switches for the current ALL the stuff connected to the batteries may draw. I’m wired with 4 gauge wire, which is overkill, but is marine rated and really flexible for the size. It handles my loads easily.

I also have a Trimetic battery monitor that has a shunt that connects to the battery A- lead and then connects to my ground bussbar inside the coach. That way I can accurately measure battery State Of Charge (SOC) and there is a lot less wire in the battery box.

I have a front bedroom and my positive and negative bussbars and use/store relay plus all wiring is all mounted on the front interior wall in one area under the bed. Hard to work on but neat and tidy, protected from damage with a plexiglass cover plate I added.

Another thing I added is a battery watering system for my golf cart battery set up like yours. Makes it very easy to add water to the batteries and avoids pulling all the caps of and spilling water everywhere. I think it came from Amazon or Camping World, of maybe Etrailer. I forget.

Your battery box looks nice and tidy and clean, by the way...shows good maintenance practices!

[gypsydad]

Originally Posted by rmkrum

These batteries are wired as two 6-volt batteries in series to get the usual 12 volt supply. If you don’t have enough slack in the cables on A+ or the A- leads to run them to a switch and still get all the wires on it, your only real place to put a switch is between B- and the wire to the other battery. If the box lid is metal, and there is not enough clearance, one of the knife switch disconnects will not work. You could extend the B- connections to an external switch.

Since the batteries are in series, disconnecting the jumper between them at B- will still kill all the parasitic loads, but you might still have +12 volts on terminal A+ from the solar system or the converter.

That’s not an issue if the jumper is disconnected or switched, but does leave a “hot” positive lead in the box. Not a big issue as long as you keep it in mind when working inside the battery box.

Personally, I’d rewrite this to put an insulated positive bussbar somewhere inside the Airstream to put all those wires away from the battery environment (acid vapor, etc) inside the coach, and do the same thing with the wires on A- to another insulated ground bussbar inside the coach.

Then put a manual disconnect switch (like a blue sea systems marine-rated disconnect) on the outside of the battery box and a fuse right on the A+ post before the switch to protect the wiring. That’s how mine is rigged.

I used an 80 amp fuse on the battery A+ post and the red wire goes from there to the Blue Sea Systems manual disconnect switch directly. As always, use proper sized wire and switches for the current ALL the stuff connected to the batteries may draw. I’m wired with 4 gauge wire, which is overkill, but is marine rated and really flexible for the size. It handles my loads easily.

I also have a Trimetic battery monitor that has a shunt that connects to the battery A- lead and then connects to my ground bussbar inside the coach. That way I can accurately measure battery State Of Charge (SOC) and there is a lot less wire in the battery box.

I have a front bedroom and my positive and negative bussbars and use/store relay plus all wiring is all mounted on the front interior wall in one area under the bed. Hard to work on but neat and tidy, protected from damage with a plexiglass cover plate I added.

Another thing I added is a battery watering system for my golf cart battery set up like yours. Makes it very easy to add water to the batteries and avoids pulling all the caps of and spilling water everywhere. I think it came from Amazon or Camping World, of maybe Etrailer. I forget.

Your battery box looks nice and tidy and clean, by the way...shows good maintenance practices!

The newer AS's have a deeper battery box; plenty of room in my 2017 model for the 6V's and the horizontal cut off switch shown in my post.

[tjwoods1]

Thanks to everyone - it has been incredibly helpful... but one more thing. The cut off switch I am considering has an Amp Rating of 150A continuous and 225 intermittent. I’ve seen some of the switches some use are rated at 200 -300A. Is that a concern? It seems that usage is at most 100 amps off the battery ... and chances are I’m not using the full 225A continuously, otherwise the battery would not last very long.

[rmkrum]

Better to have a little margin over the rated current that you plan to draw and fuse for. A heavy duty switch, within reason, will last longer.

The 150 amp one you are considering, if you do not have an inverter or plan to add one, is probably fine.

If you do want an inverter eventually, go for the 300 amp switch if you have room for it. My setup is using a 150 amp switch and 80 amp fuse for now. It’s all I have room for. If I do put in an inverter I have to upsize the wiring anyway, or add a separate circuit and stuff to power an inverter.

[tjwoods1]

My 2018 19’ Bambi came with an inverter and I presume Airstream has used the appropriate wiring. Another user from another post had posted his Amp Hour Usage. It was an extensive list but one of the readings he had noted had the furnace blower running with refrigerator, inverter, television, cell phone charging, and living room lights full bright using 14.8A. That seems well below the 150A draw of the switch.

[rmkrum]

What does the inverter draw at full load? Or, for a rough guess what’s it watt rating?

[tjwoods1]

Mine is a 1,000 watt inverter - which is 8.33 amps? To be honest, I have yet to use the inverter.

[wulfraat]

1,000 watts / 12.8v = 78.1 amps.

[rmkrum]

Minor decimal point error. Works out to 83.33 amps at 12 volts assuming 100% efficiency. Reality probably closer to 100-125 amps or more at full load assuming around 75% efficiency.

Based on that, the 150 amp switch could carry it, but I’d like some more margin. I’d go to the heavier duty switch. It would live longer and heat up less.

[tjwoods1]

Racking my brains for my inverter usage (for those times I am boondocking) and all I can come up with usage of the TV and the computer. Neither of which would be used at the same time. Given those circumstances I would presume the 150 amp continuous switch would be plenty.

[tjwoods1]

In other words, I would probably never run the inverter at full load.

[rmkrum]

Yup. If you are mostly under full load a 150 amp switch should be fine. An occasional full load will be just fine as well.