Battery cutoff switch
- Thread starter 30-9
- Start date
tiger.1000
Well-known member
In the past much has been written about battery isolators.
I personally would attach to the POSTIVE terminal on a positive ground car. The majority of the green knob variety are manufactured for a negative earth car and thus the tapered hole for that terminal is considerably smaller than the positive terminal. What'smore, the green knob variety, although often advertised as brass are in fact brass plated pot-metal or some similar zinc based material. They DO offer a very high resistance when in use. If you have the facilities to make one from solid brass; do so....just retain the nylon insulator from the green knob version....bin the rest.
I created the tapered hole by boring a round hole first the diameter of the smallest part of the positive terminal (the top) and then easing out with a Snap On female terminal cleaner....cut the tensioning slot afterwards.
I personally would attach to the POSTIVE terminal on a positive ground car. The majority of the green knob variety are manufactured for a negative earth car and thus the tapered hole for that terminal is considerably smaller than the positive terminal. What'smore, the green knob variety, although often advertised as brass are in fact brass plated pot-metal or some similar zinc based material. They DO offer a very high resistance when in use. If you have the facilities to make one from solid brass; do so....just retain the nylon insulator from the green knob version....bin the rest.
I created the tapered hole by boring a round hole first the diameter of the smallest part of the positive terminal (the top) and then easing out with a Snap On female terminal cleaner....cut the tensioning slot afterwards.
Attachments
Since I think my last question will get lost in these threads - I'll ask again
What size wire is good to add for second wire to ground strap
0 or 00 is good for 6 volt. Smart move putting it in the ground cable. I don't understand what you mean by "second wire"?
Bill
MGG
Senior Member
What am I missing? The way I understand it, to put it in lay man's terms, nothing happens electrically unless the current can both exit one battery terminal and come back to the battery through the other terminal to complete the circuit. If so, what difference does it make in which terminal has the switch? I personally have mine on the positive side of my six volt positive ground system with no problems yet. Also, the current is not trying to get to the ground I stand on (earth) but back to the battery through the other terminal.
The only problem with your theory is the positive ground systems were utilized long before those cheap a-- green knob switches were even thought of.
As with home wiring, you should "switch" the hot side, in your case, the negative post.
If you take the ground cable off nothing is hot. You could strike a wrench on the hot post and no spark. Now if you leave the ground cable on and strike your wrench while attempting to take the hot cable off,Big sparks.
The only safe way to isolate the battery is disconnect the ground cable.
Most service manuals tell you to disconnect the ground before working on the car to prevent arcing and related problems. They don't tell you to disconnect the hot cable!
Bill
Let's not over think these simple tasks. Buy a heavy duty switch from Bob Shuman and install in on the negative post.
In this picture the hot post and one terminal on the back of the switch is still hot when the switch is turned off. If the switch was in the ground cable nothing would be hot when turned off.
Bill
oldford2
Well-known member
Bill, You are correct in your theory. All we are trying to do is to kill power to the system when the car is not in use to prevent a bad wire from draining the battery or worse yet cause a fire. Everyone knows to be careful when working near the hot terminal of the battery. If you could describe your system or post a picture of how you alleviate potential problems it would be helpful.
Thanks
John
JSeery
Member Emeritus
I have no idea what you are talking about here! I'm an electrical engineer and can't follow your point. I guess you are under the impression that the (+) post on the battery is the "hot" post? It is considered the hot on a negative ground car system, on a positive ground system the (-) post is the "hot" post. If you are worried about electron flow it's from the (-) post to the (+) post so the movement is from the negitive (as if it mattered).
39portlander
Well-known member
I think I've heard this before.
This poor guy 30-9, nice handle by the way must be pullin his hair out. Dangit, this thread has turned in to a "whats the best oil".
Everyone take a deeeep breath and let it out sloooowly.
JSeery
Member Emeritus
Total nonsense, but whatever. What in the world makes you think the (+) post the battery post makes it the hot post? The electrons flow from the neg to the pos. But it doesn't matter you can think of it as holes (slots for electrons) flowing from the pos to the neg
Nobody is worried about electron flow,It's very simple the ungrounded post whether + or - is the hot post.
The grounded post is not hot and is the proper place for the switch, When the switch is off/open the battery is not grounded so nothing is hot.
When the switch is off it is the same as removing the ground cable .
With the ground cable removed the system is not hot,Right?
Bill
Battery cut-off on my 39 and 77 got them from the Autozone, made in the U.S.A. Mine are on my positive as they are 12V, yes put it on your negative.
If you recall in most service books they ask you to "dis-connect" the negative side of the battery" before doing a repair. Same idea for your application with 6V.
This thread can quickly turn into a thread about "what is the best Oil" good luck
The books tell you disconnect the battery ground cable!
Bill