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SilverRhino
01-30-2011, 08:02 PM
I plan on installing a battery disconnect switch on our BC this spring when I bring it out of storage. My first inclination was to put the switch on the negative leg of the circuit. As I was considering this it came to mind that somewhere I had read and/or heard that the switch in this type of circuit should be on the positive side.

Does it make a difference?? Is it safer one way over the other?

Don't really want to do anything that would jeopardize the inverter or other electronics.

Invizatu
01-30-2011, 08:26 PM
I have always been told and done.... Disconnect on the positive.

boatdoc
01-30-2011, 08:29 PM
I always put the switch on the B+ side in my rigs and in all boats.

DougS
01-30-2011, 08:36 PM
My battery disconnect is on the positive side and it came from the factory that way.

wyleyrabbit
01-30-2011, 09:23 PM
I installed ours on the positive side. I believe it's much safer this way. It would be easy for something to ground out to the frame, I suppose, and that would complete the circuit even if the negative terminal to the battery was off.

caissiel
01-30-2011, 11:40 PM
I always disconnect the ground because I have always had great success doing it that way.
The collector cars I store over the winter has the ground side of the battery disconnect over winter.
Its the only way the batteries will have full power the next spring when I start the vehicles.
The batteries hold their charge better with the ground disconnected. Don't know why but it works.

When you boost a car with jumpers or booster cables the ground is what is the most dangerous connection.
The batteries will blow up with ground problem as well.

branson4020
01-31-2011, 01:37 AM
Here (http://manuals.heartlandowners.org/Electrical/DC_Buss_Bar/Heartland/Buss_Bar_for_LM-BH-BC.pdf) is the Heartland engineering drawing showing how they wire the disconect switch from the factory. The important things to note is that when the switch is off, the truck can still charge the battery and, most importantly, the breakaway switch will still work.

hoefler
01-31-2011, 08:20 AM
It really doesn't matter. If you look at any service manual for anything with batteries, it will always tell you to disconnect the negative cable.

gmc
01-31-2011, 09:35 AM
I to have my switch on the ground side. this is what most mechanics have told me

wyleyrabbit
01-31-2011, 10:53 AM
Everything I've seen in RV or Marine applications seem to have the disconnect on the positive side. Is there something different about marine or RV applications and/or wiring vs. automotive?

I had a look at the wiring diagram that Bob posted, and the factory uses the positive side as well. I'd love to understand why.

TedS
01-31-2011, 12:16 PM
If you are removing a wire from the battery, remove the negative first. That way if the wrench hits the frame you don't short the battery as you could if you were removing the positive first.

Switches are generally in the positive side. Both in my boat and 5th wheel. But then in the boat it was used to connect one, both, or no battery.

caissiel
01-31-2011, 12:43 PM
When parked for a long time on shore power I usually disconnect 2 of the 3 batteries and cycle them including the truck that I seldom drive. The batteries all have a ground isolater that I bought at Wally World and I have a battery power extension that I sometimes plug the truck in to keep the batteries fully charged if I don't use the truck for extended time.

My friend has an SOB unit with a positif Battery isolator and blew up one of his batteries while switching it on. So far we have not been able the find the problem other then the power converter also blew at the same time. Very expensive occasion that we cannot explain.

SilverRhino
01-31-2011, 07:56 PM
Everything I've seen in RV or Marine applications seem to have the disconnect on the positive side. Is there something different about marine or RV applications and/or wiring vs. automotive?

I had a look at the wiring diagram that Bob posted, and the factory uses the positive side as well. I'd love to understand why.

I have read all the responses and I guess I'm still confused. Like wylerabbit, I too don't understand why RVs and boats seem to always use the positive side. I have always disconnected the negative terminal on autos or equipement that needed to be stored for any length of time.

It seems to me that someone mentioned on this forum something about arcing when throwing the switch that could harm appliances etc.

So at this point I'm still not sure what is the correct method and why it's the correct method.

Buford445
01-31-2011, 08:08 PM
You should unhook the positive on Auto's also

TedS
01-31-2011, 10:06 PM
With regard to arching, connecting or disconnecting either terminal in an otherwise continuous circuit will draw a spark.

I will guess that with our common dc circuits being negative ground systems, disconnecting the positive terminal keeps the ground side negative. Disconnecting the negative terminal makes the ground side positive. I don't have an answer for the followup 'So what?'. Accessories/devices are wired to the positive side and then connected to a convenient ground. I suppose the disconnect switch could be considered a device and gets wired into the positive side. I prefer having both a positive and a negative busbars for connections instead of depending on the chassis for ground path.

porthole
02-04-2011, 03:03 PM
Battery disconnects go on the positive side as close to the battery as possible.
With some switches you find may have a "field disconnect" That is for use in a automotive style charging system. The basic switch is the same and can be used.

Higher quality switches will have a make before break connection. This will keep your circuit live while you switch between 1-2 or both. Meaning that if battery #1 is connected and you switch to battery #2, #1 will not be disconnected until the connection is made with #2

If just disconnecting the battery for maintenance or repairs etc, the negative comes off first. Prevents you from causing a direct short with a wrench while removing the positive. Negative is last on for same reason.

Remove The Negative Cable First,
Re-connect The Negative Cable Last:
Why? Because the wrench or socket is touching the live part of the electrical connector. There is a good chance that the wrench or socket handle will accidentally touch something. The entire car is connected to the negative terminal.
If your wrench is on the positive terminal and it accidentally touches anything metal, you will short circuit the battery. The voltage isn't harmful, but the sudden unexpected sparks will startle the ***** out of you, and could even burn you. There is so much current (amperage) available that your wrench literally becomes an arc welder.
If you disconnect the negative cable first, and reconnect it last, then the car is not electrically connected to the negative battery terminal. After that you can disconnect the positive battery terminal with minimal risk, because if your wrench touches any metal parts of the car there is no complete circuit, and nothing happens. The only risk comes from touching the other (i.e. negative) battery terminal.
While connecting or disconnecting the negative cable, you don't need to worry about the wrench touching metal parts of the car, because everything is at the same electrical potential. You only need to keep the wrench from touching the positive battery terminal. That's easy.



When you boost a car with jumpers or booster cables the ground is what is the most dangerous connection.

The batteries will blow up with ground problem as well.

Either connection can be dangerous. It is best to not connect to a batteries post when jumping if possible.
The ground lead should not be attached to the battery.

Jump start:
positive to dead battery positive post
positive to booster positive post
Negative to booster negative post

Last connection and the one that can cause your problems;
negative to an unpainted frame or bolt (dead battery). This keeps any potential sparks away from the battery.
Some vehicle (trucks) may have separate posts just for this.

After jump - reverse the process.

Batteries "blowing up" are rare.
I have seen at least a half dozen blow the top off in my career. Including a 36 volt forklift battery.
I have seen 2 blow up in the face of the mechanic - not a pretty sight.

BTW - batteries going dead because they are left on a concrete floor is an old wives tale.

Duramax1
02-04-2011, 08:16 PM
Your instructions about the sequence of connecting positive and negative battery cables when jumping a dead battery are the same as those instructions which come with every set of jumper cables sold by automotive parts retailers.

wyleyrabbit
02-04-2011, 08:40 PM
All great information.

So? What's the consensus? On an RV, should the battery disconnect be on the positive side (as Heartland and other mfgrs do)? Or should it be on the other side?

porthole
02-04-2011, 09:31 PM
So? What's the consensus? On an RV, should the battery disconnect be on the positive side (as Heartland and other mfgrs do)? Or should it be on the other side?


Battery disconnects go on the positive side as close to the battery as possible.



Your instructions about the sequence of connecting positive and negative battery cables when jumping a dead battery are the same as those instructions which come with every set of jumper cables sold by automotive parts retailers.

Never bought cables from a retailer and never read any of those instructions.

Who reads instructions anyway?

GOTTOYS
02-04-2011, 10:28 PM
Once one side is disconnected whether it's the Pos. or Neg. side...the battery is out of the equation. Really won't make any difference electrically. I like what Porthole has to say and totally agree...Don

SilverRhino
02-05-2011, 09:47 PM
Thanks for all the great posts!

After reading them and checking other sources....My disconnect will go on the Positive terminal side.

Willym
02-10-2011, 10:53 PM
Once one side is disconnected whether it's the Pos. or Neg. side...the battery is out of the equation. Really won't make any difference electrically. I like what Porthole has to say and totally agree...Don

Agree. The sequence for physical disconnection of battery cables is important from a safety perspective, but the location of a disconnect switch with respect to polarity doesn't matter. Put it where it's easiest to install/operate, but make sure that the vehicle charging connection and emergency brake switch cable are not isolated.

branson4020
02-11-2011, 12:03 PM
Once one side is disconnected whether it's the Pos. or Neg. side...the battery is out of the equation. Really won't make any difference electrically. I like what Porthole has to say and totally agree...Don

Agree. The sequence for physical disconnection of battery cables is important from a safety perspective, but the location of a disconnect switch with respect to polarity doesn't matter. Put it where it's easiest to install/operate, but make sure that the vehicle charging connection and emergency brake switch cable are not isolated.

Don't see how you can put it on the negative side without disabling the breakaway switch.

wyleyrabbit
02-11-2011, 04:56 PM
One suggestion is to use heavy gauge cables to the battery disconnect switch, and make sure to not have it any more than a couple of feet away from the batteries. Be careful when installing this and don't even for a split second let any wires touch the frame, or you're likely to blow the fuses in your converter (don't ask me how I know this).

Our disconnect is a very heavy-duty marine grade switch, on the positive side. It covers the entire + from the battery to the trailer. I don't really think that's a concern as there is no way we could hook up to the truck without flipping the switch, as our front jacks wouldn't work with it off. The switch heavily clicks into the on position, and I don't believe any amount of bumping around during travel could change its position.

Before we installed the switch, our batteries were slowly draining while the unit was in storage, because some things were still drawing power (propane alarm, etc). Now, we always have a fully charged battery when we pick up from storage. :-)

Chris

SilverRhino
02-11-2011, 05:03 PM
[QUOTE=wyleyrabbit;163593]Before we installed the switch, our batteries were slowly draining while the unit was in storage, because some things were still drawing power (propane alarm, etc). Now, we always have a fully charged battery when we pick up from storage. :-)

Chris....This is why I am installing the switch. During the majority of the year, our BC is only in storage for short periods of time between trips. I just wanted an easier way to disconnect the battery to prevent power loss between trips.

For the winter months and long term storage the battery comes out and goes in the garage and is hooked up to the Battery Minder.

Randy

wyleyrabbit
02-11-2011, 05:15 PM
I always leave our batteries in our trailer, even when in storage. I suppose our solar panels are kind of like an on-board battery minder. Btw, I have ours wired so the panels are always connected to the batteries. :-)

wyleyrabbit
02-11-2011, 05:23 PM
The switch I used is by Blue Sea, and I got it from West Marine. Link here (http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=17528&catalogId=10001&langId=-1&storeId=11151&storeNum=10109&subdeptNum=10548&classNum=10597). It's a 350 Amp switch which is complete overkill, but I like overkill. :-)