Battery disconnect - 6v series

[sivartb000]

I have 2 6v batteries in series. I know its ideal to disconnect the negative (though I don't fully understand why to be honest). Am I ok to disconnect the cable the connects the batteries together? See image of what I mean. I borrowed the image from online, and drew the red line, indicating the switch.

 

[ronster]

Would work fine.Unorthodox,but would do the job.

 

[Isaac-1]

The danger here is if the loose end of that cable or the wrench you are using touches the metal from of the RV you will get a BIG spark.  It is FAR safer to disconnect the negative end cable first.

 

[grashley]

As I understand, if you disconnect the NEG first, and your wrench hits any surrounding metal, aka ground, nothing happens.  With this disconnected, if your wrench hits ground while disconnecting the POS, no sparks because the circuit is already broken with the NEG disconnected.

With your proposal to disconnect the "middle wire", it will open the circuit.  However, if the disconnected wire flops around and hits a ground, you have issues.  In one case, POS cable to ground, it is a direct short across the battery.  In the other case, NEG cable to ground, you now energize the camper with 6 volt power.

Inexpensive disconnects are available such as this.  All cables remain connected, but the circuit is easily broken, or disconnected.  This will work on any battery terminal.

https://smile.amazon.com/Battery-Terminal-Disconnect-Switch-Vehicle/dp/B0788PY53V/ref=sr_1_11_sspa?crid=RIBCXV1GF1H6&keywords=battery+disconnect&qid=1580009115&sprefix=battery+dis%2Caps%2C161&sr=8-11-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVEVISEtNVDJTUUlRJmVuY3J5cHRlZElkPUEwMzkwNzg2MlNIWkpMUFNaMVRWTSZlbmNyeXB0ZWRBZElkPUEwOTk4NDM4MTRKVjIzSTlHWE5XMiZ3aWRnZXROYW1lPXNwX210ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

 

[John From Detroit]

If the reason is to simply disconnect (not removing batteries) it matters not if the switch is in the positive. negative or jumper on 6V pairs.

If you are removing the batteries start with the most negative cable.  You have to disconnect it anyway and that way if your wrench slips and hits the metal frame you don't get burned....literally. .by the hot wrench.

 

[Gary RV_Wizard]

Would work fine.Unorthodox,but would do the job.

Sorry, but I have to disagree. That merely converts it to a 6v system. Others have explained in more detail. 

 

[steveblonde]

i disconnect my batteries everytime i take my trailer back to storage as sometimes it will be 3-4 weeks or more before i use it again. i have 2 -6volts.
i simply make sure the power disconnect to the trailer is turned off and i undo the  wing nut on one of the posts - pos or neg depending on my mood lol i always leave the connecting wire between the 2 batteries hooked up - ive never had any issues and generally when i go back to the trailer i hook them up again and just go

 

[sivartb000]

Thanks everyone for the replies. I wrote the initial post on my phone, which is difficult, and so I kept it short and didn't give a full explanation. I pulled out my laptop, so let me elaborate a little more. I am installing an actual switch, so I can quickly disconnect the batteries. My main question was just to make sure that disconnecting that one cable with a switch truly broke the circuit.

I definitely know why you want to disconnect the negative first when removing battery, and at least during the initial install, I'd have to have at least one connection that is dangerous and not ideal.

My main purpose was just to make sure that breaking the link at that point would adequately disconnect the batteries from load, as I had read installing a switch on the positive side still allows a load, which makes no sense to me (hence why I stated I didn't understand why you have to switch the neutral always), that was also in regards to a single battery, so I wasn't sure how that affected a 6v series like I have.

The reason for me switching the "jumper" (not sure if that's accurate terminology) instead of the neutral is simply because of how my battery compartment is set up, I would have to modify my battery compartment to make it work. However - I've decided I'm just going to do that modification anyways, and have it all set up correctly. As it is, I always have to disconnect one live wire to take one of the batteries out, and then disconnect the neutral with the battery halfway out of the compartment. Its an older 5th wheel, and less than ideal set up, so I'll just take the time and set it up correctly.

 

[sivartb000]

Sorry, but I have to disagree. That merely converts it to a 6v system. Others have explained in more detail.

I dont understand what you mean by this, as the circuit should be broken - can you point me to the thread, or give a hint on what to search for?

 

[Gary RV_Wizard]

You still have a 6v battery connected to the positive and another connected to chassis ground. Interrupting the jumper between the two breaks the normal use circuit but doesn't prevent accidental "circuits" (see other relies about that). 

Theoretically power can flow from the 6v positive of one battery to the 6v negative of another, separate battery.  Generally it doesn't, but it can happen if conditions are right.  You have live 6v power (voltage) connected, plus a solid return path to the second 6v battery which is still connected to the chassis ground lug.  The best way to guarantee no such event can occur is to disconnect the ground (negative side) entirely.

Vehicle 12v systems typically use the entire chassis and house metal structure as a ground side path back to the battery. That's convenient for wiring but fraught with the possibility of a short to ground anywhere in the system.

 

[grashley]

As I stated, if you disconnect the POS jumper connection, that cable is now connected to the NEG of the first battery, which is still connected to the camper POS.  If this cable touches or rests on a metal frame member or similar ground, you have a complete 6V circuit feeding the camper.

Obviously, if you use a switch, no wires are loose so this does not happen.

 

[John From Detroit]

Sorry, but I have to disagree. That merely converts it to a 6v system. Others have explained in more detail.

Gary let me draw 3 line drawings

Frame---Switch---{6v}{6v}-- 12 to loads if switch closed  (Swith in negative lead)

Frame---{6v}{6v}---Switch--- 12 volt to loads if switch closed (Switch in positive lead)

Frame --{6V}--Switch--{6v}--- 12 volt to loads if switch open (Switch in jumper)

Frame --{6v} open switch {6v} --- How is current going to flow. ZERO volts to loads.

 

[Gary RV_Wizard]

There is still a voltage differential between the positive of one battery and the negative of another.  And electrons can move across any differential, even though in this case they cannot return all the way to the source battery.  Generally speaking, little or no current will flow, but some is still possible.  Batteries with no cables at all still "self discharge", right?    And a little current will flow if you connect a wire from the positive battery terminal to the earth under the battery, even though there is no direct connection to the negative terminal. 

So yes, the primary circuit is broken and current flow is essentially zero. Lights don't light and circuit boards don't work. But there are still some electrons loose in the system so it's always better to eliminate as much of the electrical potential as possible. 

 

[catblaster]

    I have one other reason that has not been mentioned. IF you use the type of battery disconnect similar to a Perko switch which has its terminals mounted on the backside of its housing there is a possibility of the terminal shorting against anything metal that it is mounted to. The terminals are very close to the back surface and no insulation is provided, when the plastic housing deteriorates the terminals could touch. With them installed on the negative side it will not matter.  The other cheaper ones the are sold at horrible freight and northern have a similar problem especially when they get hot and begin to melt their plastic mount.

 

[John From Detroit]

There is still a voltage differential between the positive of one battery and the negative of another.  And electrons can move across any differential, even though in this case they cannot return all the way to the source battery.  Generally speaking, little or no current will flow, but some is still possible.  Batteries with no cables at all still "self discharge", right?    And a little current will flow if you connect a wire from the positive battery terminal to the earth under the battery, even though there is no direct connection to the negative terminal. 

So yes, the primary circuit is broken and current flow is essentially zero. Lights don't light and circuit boards don't work. But there are still some electrons loose in the system so it's always better to eliminate as much of the electrical potential as possible.

Gary in that case it still matters not where you put the switch. but the current flowing past the OPEN switch is so low you do not have anything that can measure it. Neither do I. Neither does the physics lab at my college.. Jet Propulsion Labs.. Perhaps. but frankly I doubt it.

An open circuit is... an open circuit. no matter where the open is.

 

[ChasA]

Concerning self-discharge. You can reduce it by keeping the tops of your wet-cell batteries clean. If you don't believe this, try this when your battery top are dirty:  put a volt meter on a battery, negative probe on ground, positive on the plastic battery top. You'll read minuscule voltage as you move the positive probe around. Note, your meter should be set on its lowest scale.  Now clean the battery top and repeat the test.

 

[House Husband]

You still have a 6v battery connected to the positive and another connected to chassis ground. Interrupting the jumper between the two breaks the normal use circuit but doesn't prevent accidental "circuits" (see other relies about that). 

Theoretically power can flow from the 6v positive of one battery to the 6v negative of another, separate battery.  Generally it doesn't, but it can happen if conditions are right.  You have live 6v power (voltage) connected, plus a solid return path to the second 6v battery which is still connected to the chassis ground lug.  The best way to guarantee no such event can occur is to disconnect the ground (negative side) entirely.

Vehicle 12v systems typically use the entire chassis and house metal structure as a ground side path back to the battery. That's convenient for wiring but fraught with the possibility of a short to ground anywhere in the system.

I have what he's drinking.

 

[Lou Schneider]

Current leakage isn't a problem between the pins of a 120 VAC plug or even a 240 VAC plug if you're in Europe, even if the area is slightly damp or less than perfectly clean.  Why would it be a measurable problem between the poles of an open switch a similar distance apart at 1/10th fo 1/20th the voltage?

 

[Ernie n Tara]

This discussion is getting misdirected. The reason for disconnecting the negative first is to avoid arcing if a wrench inadvertently hits ground while removing positive first. Removing the center connection prevents such an occurance for the positive side battery while leaving the potential for arcing by the ground side battery both while breaking the connection and subsequently.

Ernie

 

[Gary RV_Wizard]

Thanks, Ernie.  I surely didn't mean to drift off into a discussion of electrical physics, ground potentials, etc.  He just needs to put the disconnect where it belongs for maximum advantage and he has already done that. Let's move on.