The Stovebolt Site Forums The Shop Area The Electrical Bay battery disconnect switch

I recently obtained a keyed battery disconnect switch. Wanted to use it for anti-theft/anti-fire device. I've got a '51 3100 6volt. I was thinking about running it off of the negative ground web cable and have the keyed portion stick up through the floorboard under the seat. The sequence would be: Battery to cable to switch to bracket to chasis.
It's rated for 1000 watts at 12 volts.
Any comments, critiques, compliments or condiments?

Be sure the switch has sufficient current capacity so it doesn't insert too much series resistance in the starting circuit. With the starter motor turning the engine, there should be less than 1/10 volt drop across the switch contacts. Be sure to use BIG cables with clean, tight connections to wire it into the circuit. Soldered connections on all the terminals are the best way to go.
Jerry

Edit: a 1,000 watt capacity is too small. It's not uncommon for a 6 volt starter to draw 300 amps at a cranking voltage of 4.5 volts or so, which calculates to be 1,300 watts at 100% efficiency, something that's never going to happen. Find a disconnect switch with heavier contacts/less resistance.
Jerry

Thanks, Jerry, for the info. This, I shall do.

Okay. I bought a heavier duty battery cut-off switch. Well, it didn't come with any ratings like the last one did, but it looks more heavy duty. Anyway, I hooked up a new negative webbed ground lead, and made sure all the connections were clean and tight. Started up the Blue Funk, turned on the lights, and ran the wiper motor. Everything was fine. Nothing got hot. Battery guage read normal. Is there anything else I should check?

I put mine on the POS cable. My NEG is a braided strap. My logic was if you put it on the NEG side then anything metal falling across the battery posts will create a circuit. On the POS side it can't. My 2 cents.
Another neat rumour about cut-off switches is that you have to polarize your regulator each time you disconnect the battery. The electrical shop in town insists it be done but others say not. I have had it in for 2 years and never polarized my regulator.

Thanks for your reply, olblu49. Your 2 cents is always welcomed here. It's the same thing as a nickel's worth of free advice, which is a the same as cash.

What type of switch do you have? Where did you put it?

Originally, I was going to put my switch on the positive side, too. I've had so many thoughts run through my head since then, I'm not really sure what the determining factor was in putting it on the negative side.

I dealt with the issue of grounding out by cutting a plastic mat to fit over my battery.

I recall reading some discussions in past forums regarding repolarizing or some such, and coming to the conclusion it wasn't really a big deal. I think your empirical perspective proves that.

That's one thing difficult about being an old dog learning new tricks: Repetitiously being exposed to this new information enough times that it is solidified within my memory and available for instantaneous recall.

Oh well. Time will tell.

Oh yeah- I was going to comment on the negative strap- I bought a new one from my FLAPS that has bolt holes on both ends. Worked out really well, seeings the switch is at the clamp. Okay. I think I'm finished now. Thanks.

I think olblue49 is correct. If you killed the negative all one would have to do is hold a screw driver from the neg terminal to the frame and start the engine. Seems to me that you would kill the positive between the battery and the starter. It still could be jumped across but take more time and time is not good for thieves. Just make certain the kill switch can handle the draw of the starter. I don't think there is any polarization of regulators that needs to be done. It's like removing your battery and replacing it. Nothing is necessary. It works.

Shorting across battery terminals makes a closed circuit for the battery and shorts it. There is no way fuses anywhere else can do anything. I think putting a disconnect in the ground is the wrong thing to do because
1. Defeated all fusing and switching in opposite polarity. In effect this is similar to cutting the neutral in house wiring - kind of poor comparison I know.
2. Easy to bypass and steal vehicle. If in the "hot" may be harder to bypass for theft.

Dan Bentler

Thanks for the other perspectives, guys. I'm not too concerned with the Blue Funk being stolen. (Oh, god. I hope I don't have to eat those words.) But, it is a little bit of a deterent. Primarily, I wanted to be able to easily disconnect the electrical system from its source of power for working on it, charging, and the like. I figure I'm taking a low resistance (abstractly speaking) course in my endeavors to learn. My solution fit the bill, for now. Perhaps later, when I'm more knowledgeable, I'll take a different course. You guys are seasoned and "I'm a little lost lamb whose lost in the woods." This is a beginning in dealing with warding off the Big Bad Wolf of Total Ignorance. Okay. Enough metaphors. I gotta get real. I've got a dentist appointment.

Seeya.

I never have thought that a "good" thief would be detered much by an obvious battery disconnect. I think a better choice is to install a hidden toggle switch which will interrupt the current to the coil. Most thieves don't have the time to trace that down to find out why the thing won't start.

If going the coil interrupt route, what kind of switch rating would one need?

yeah, a car thief isn't likely to be carrying a piece of wire with an alligator clip on both ends

disconnects like this are put on the pos terminal - take the knob off to deter theft ... the key concept is deter, nothing will prevent theft, it's not uncommon for desireable vehicles to be stolen by folks with rollback trucks, so even wheel locks are not certain

Bill

I hear ya, Tim K. Sounds like an easy, yet formidable way to deter thieves. A buddy once said, "I don't want something that will keep an honest man out. I want something that will keep a dishonest man out!"

Personally, I'd go for a shaped charge of C-4 with a 1-minute delay fuse under the driver's seat, aimed at the thief's testicles. Just be VERY sure to disable the trigger system when you drive it yourself!
Jerry

Yeah, Jerry, THAT would deter a theif (and any potential offspring he may father), but isn't something like that kinda, oh I don't know... dangerous?

Only if ya forget to turn it off!

Jerry

Yeah, I hate it when that (a self-administered orchiectomy) happens!

Thanks for the discussion and viewpoints, guys.

Did ya hear about the Alabama vasectomy? Drink a beer, light a cherry bomb, drop it in the beer can, and count to 10. Of course Bubba counts "1-2-3-4-5-", runs out of fingers to count on, puts the beer can between his legs, and counts "6-7-8-BOOM"! Works every time!
Jerry

Now, Jerry, I think we're getting off the subject a bit here. After all, this isn't the Greasy Spoon.

One of the reasons I went for the battery cutoff switch at the battery was because, I believe you said on a previous post, the fewer connections a 6 volt has, the better likelihood of more energy being transferred. And 6 volts need all the help they can get.

Is my recall adequate? Am I repeating myself?

"I get so confused!" - Vinnie Barbarino

You're right on keeping connections down to a minimum. 6-volt systems can have a voltage drop of 1/10 volt per connection, so adding a cutoff switch adds at least one more connection to the circuit, two if the switch isn't incorporated into the battery post terminal. Total voltage drop shouldn't be over 1 volt, adding all the connector losses and voltage drop in the cables. BIG cables are a must, to carry all the current possible and get it to where it needs to be- - - - -actually running the starter!
Jerry

Jerry-

Thanks for the reinforcement. I think I also remember reading something like that in an article in Tech Tips written by some smart guy. It was about 6 volt systems. Are you familiar with it? It's a little too "techy" for my tastebuds. I think you might enjoy it, however.

Oh yeah- you tell good jokes too. A little violent, but funny.