Battery Disconnect Switch - Fiberglass RV


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Old 07-04-2006, 11:04 PM   #1
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I have found a great marine-style key-like battery disconnect switch that I plan to install on the main battery cable. This will ensure no over-charging occurs during long periods on shore power, and facilitate easy electrical work.

Do I install it on the negative (ground) cable or the positive (hot) cable?

Thanks in advance...

Victor
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Old 07-04-2006, 11:12 PM   #2
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Hot. Just like any other switch.
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Old 07-04-2006, 11:53 PM   #3
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Check with your converter manf to ensure the system will function properly without a battery attached to it -- Some converter designs require the battery to be attached.

Presuming it's OK to disconnect the battery, if you don't want to mess with a switch, most RV wiring has a 30Amp fuse right at the battery (on the positive or hot wire, of course); you can just open the fuse holder...
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Old 07-05-2006, 05:29 AM   #4
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Will you tell us where you found the switch, part number, manufacturer, etc.?
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Old 07-05-2006, 06:57 AM   #5
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Will you tell us where you found the switch, part number, manufacturer, etc.?
Here's five to chose from available from JC Whitney:
JC Whitney Battery Disconnect Switch
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Old 07-05-2006, 09:00 AM   #6
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Will you tell us where you found the switch, part number, manufacturer, etc.?
I found it at a local auto supplier here in Spruce Grove. It did not have a label left, but it looked just like this one.

http://www.partsformodelafords.com/store/m...77&CFTOKEN=3265

The only difference is that mine has an all-weather boot for the switch and the key.

Victor
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Old 07-05-2006, 09:06 AM   #7
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Check with your converter manf to ensure the system will function properly without a battery attached to it -- Some converter designs require the battery to be attached.

Presuming it's OK to disconnect the battery, if you don't want to mess with a switch, most RV wiring has a 30Amp fuse right at the battery (on the positive or hot wire, of course); you can just open the fuse holder...
I contacted the converter manufacturer (Progressive Dynamics) some time ago, and it was his technician's suggestion to install a switch to use when connected to shore power for long periods.

I do indeed have a 30 amp fuse at the battery, but it is just between the battery and the converter. A number of circuits are wired directly to the battery with their own in-line fuses.

So the concensus is the switch should be install on the positive (hot) cable. That actually makes it easier for me.

Thanks everyone!

Victor
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Old 07-05-2006, 09:18 AM   #8
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You need to check this out because connecting to the negative is the terminal to connect to.
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Old 07-05-2006, 09:38 AM   #9
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This battery disconnect switch from the Eastwood company says you can put it on either negative or positive...now I'm really confused

Eastwood Battery Shutoff Switch w/Instructions
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Old 07-05-2006, 09:41 AM   #10
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I do indeed have a 30 amp fuse at the battery, but it is just between the battery and the converter. A number of circuits are wired directly to the battery with their own in-line fuses.



Thanks everyone!

Victor

If you put the switch right at the battery, it doesn't matter which side.

If you have several wires going to the positive side of the battery that run stuff you want to be able to run while on shore power and battery disconnected, put the switch in the negative side.
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Old 07-05-2006, 10:47 AM   #11
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This may help clear the confusion. Here is a simple wiring schematic of my trailer.

Click image for larger version

Name:	Trailer_Wiring_Sketch.jpg
Views:	122
Size:	155.5 KB
ID:	3813

I have 6 gauge cables going from the battery to the two terminal blocks. Everything is now connected to those terminal blocks. The future installation of a solar package purchased at Costco is also shown for completeness. It will be wired directly to the battery, since it comes with a battery controller.

The two options for installation of the disconnect are indicated by the green circles with numbers. Location 1 is on the positive (hot) cable. Location 2 is on the negative (ground) cable. I initially leaned to location 2, because any accidental shorting to ground would only potentially compromise the switch.

Any comments?


Victor
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Old 07-05-2006, 11:30 AM   #12
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This may help clear the confusion. Here is a simple wiring schematic of my trailer.

Attachment 3813

I have 6 gauge cables going from the battery to the two terminal blocks. Everything is now connected to those terminal blocks. The future installation of a solar package purchased at Costco is also shown for completeness. It will be wired directly to the battery, since it comes with a battery controller.

The two options for installation of the disconnect are indicated by the green circles with numbers. Location 1 is on the positive (hot) cable. Location 2 is on the negative (ground) cable. I initially leaned to location 2, because any accidental shorting to ground would only potentially compromise the switch.

Any comments?
Victor

Either side will work just fine.
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Old 07-05-2006, 11:50 AM   #13
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The reason that it is recommended to connect to the negative terminal is because the neg terminal goes to the vehicle frame. Once it is disconnected from the frame there is no way it can short out if something were to contact the + side. This follows the rules of connecting / disconnecting batteries. This is recommended how to connect one of these switches in antique cars. Here is what JC Whitney has to say about it.

http://www.jcwhitney.com/autoparts/Product...=battery+switch



BATTERY DISCONNECT SWITCHES

JC Whitney Price: $7.99 - $17.99

Be the first to review this product
o Easy to install on negative battery post
o Battery is disconnected by unscrewing the knob a few turns and reconnected by tightening the knob
o Knob can be removed completely to deter theft
Compact size fits most battery compartments. 12-volt rating: 500 amps surge, 125 amps continuous. Great for cars, boats, RVs or any vehicle used occasionally or stored for long periods of time. Limited one-year warranty.
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Old 07-05-2006, 12:33 PM   #14
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The reason that it is recommended to connect to the negative terminal is because the neg terminal goes to the vehicle frame. Once it is disconnected from the frame there is no way it can short out if something were to contact the + side. This follows the rules of connecting / disconnecting batteries. This is recommended how to connect one of these switches in antique cars. Here is what JC Whitney has to say about it.

http://www.jcwhitney.com/autoparts/Product...=battery+switch



BATTERY DISCONNECT SWITCHES

JC Whitney Price: $7.99 - $17.99

Be the first to review this product
o Easy to install on negative battery post
o Battery is disconnected by unscrewing the knob a few turns and reconnected by tightening the knob
o Knob can be removed completely to deter theft
Compact size fits most battery compartments. 12-volt rating: 500 amps surge, 125 amps continuous. Great for cars, boats, RVs or any vehicle used occasionally or stored for long periods of time. Limited one-year warranty.




If I disconnect a battery at the battery it's out of the electrical system, period.... Any battery in anything. It doesn't matter which side of the battery is disconnected it's still no longer in the system. There is NOT anyplace in the system that it can draw current when one side of the source (battery) is disconnected.


The above recommendation only makes sense when the switch has a fuse to keep the automobile computer running. Then any current draw, such as the starter, will blow the fuse and then everything is out of the system.
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Old 07-05-2006, 01:48 PM   #15
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Victor, that disconnect switch looks just like the Hella which I used in my race car 15 years ago, and which I have seen in various Edmonton-area auto parts stores since then. Since Hella is an electrical equipment manufacturer (best known for driving lights), they might be the original maker. It is a solid and clever design which mounts easily in a panel. It was rated for (as I recall) 400 amps, to handle starter current. The plastic "key" handle did snap eventually, making it annoying to use now, but I believe that was due to use in cold (-20 C) weather.

In the race car I followed the standard practice of disconnecting the positive cable, which made sense to me. I'm not disputing anyone else's logic - that's just how it was done. It may be helpful to note that in a race car the object is to remove power from ignition and other circuits, while in other applications of battery disconnection the object is to prevent accidental shock in contact with hot-side components.
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Old 07-05-2006, 06:41 PM   #16
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Why would a person need to disconnect the positive battery cable if they are using a battery disconnect switch?


The negative terminal is disconnected first because it is electrically connected to the metal parts of the vehicle. This being the case, if you should touch a metal part of the vehicle with the end of the wrench while on the negative battery terminal nothing will happen.

If you have something with a positive ground you should naturally disconnect the positive terminal first.
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Old 07-05-2006, 10:29 PM   #17
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I`m just curious where is the ground connection coming off the negative terminal block connected to?......is that just a frame ground or is there a another negative connection some place? Benny
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Old 07-05-2006, 10:32 PM   #18
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Any of you that are trying to say it should be one side or the other please draw me an electric schematic and explaining how it matters.

Here's three little sketchs to explain why it don't make any difference.


[ATTACH][/ATTACH]
Here's normal operation of any battery operated device. Trailer, Auto, flashlight.


[ATTACH][/ATTACH]
Here's the switch open in the negative side. Notice that No electrons can flow. It takes a complete loop for electrons to flow, the loop is broken.


[ATTACH][/ATTACH]
Now the switch is in the positive side and no electrons can flow.


So what's the difference between the positive side switch and the negative side switch? Reminder, the switch is at that battery, no connection from the battery to anything.
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Old 07-06-2006, 04:33 AM   #19
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So what's the difference between the positive side switch and the negative side switch?
I don't think there is a practical difference - though personally I would never put the switch on the grounded side, as it just doesn't seem right!

But then we're talking about electricity and, as a mechanical engineer, it's all pretty unnatural stuff - indeed I am standing on a rubber sheet to write this message, just in case.....

I wonder if the strong opinions have come from hooking up the battery in a metal vehicle. For this there are good reasons for connecting the positive (or ungrounded) side first and the negative (or grounded) side second - the reason being that when holding the second cable, you cannot get a dead short if you touch it to the bodywork of the vehicle - which you could if you connected the ground first. However this doesn't have any relevance to where a switch should be fitted.

Andrew

PS Brian, those plastic keys are easily purchased on their own over here - all track marshals tend to have one in their pocket.
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