Battery Disconnect Switch - Page 2 - Fiberglass RV

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Old 07-05-2006, 01:48 PM   #15
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Name: Brian
Trailer: Boler (B1700RGH) 1979
Posts: 5,000
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.

1979 Boler B1700RGH, pulled by 2004 Toyota Sienna LE 2WD
Information is good. Lack of information is not so good, but misinformation is much worse. Check facts, and apply common sense liberally.
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Old 07-05-2006, 06:41 PM   #16
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Trailer: 17 ft Casita Spirit Deluxe
Posts: 257
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? 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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Name: Byron
Trailer: 2006 Scamp 13' towed with a 2005 Dodge Dakota 4.7l Magnum W/full tow package (over kill)
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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.

Here's normal operation of any battery operated device. Trailer, Auto, flashlight.

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.

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.
Byron & Anne enjoying the everyday Saturday thing.
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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.


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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