• Welcome to the new SAOCA website. Already a member? Simply click Log In/Sign Up up and to the right and use your same username and password from the old site. If you've forgotten your password, please send an email to membership@sunbeamalpine.org for assistance.

    If you're new here, click Log In/Sign Up and enter your information. We'll approve your account as quickly as possible, typically in about 24 hours. If it takes longer, you were probably caught in our spam/scam filter.

    Enjoy.

Battery size

rixter

Gold Level Sponsor
Hi,

Couple things. Every instructions I've ever seen for attaching these battery cutoff devices has been to attach them to the negative terminal. The size of the clamp matches a NEG post which is smaller. Further, these devices usually have green wheels.. a common color used for NEG terminals as opposed to red for POS. Instructions for removing cables from batteries always suggest disconnecting the NEG cable first. That is not to say that there isn't a lot of negative information floating around out there (pun intended), but is sure seems very common practice. More opinions welcome.

In my photo, I have a group 47 battery (not the correct battery). The green cutoff device is connected to the NEG post on this battery, not the POS post. I think you are concerned that my POS post would be arcing to the side of the battery box, but that is not the case. This could be another good reason for having the cutoff device connected to the NEG post.

Rick
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
I would put the battery shutoff switch you got there on the positive terminal, not the ground. Killing power by opening a ground path is generally not the best practice.
Jerry: can you expand on this, please? I put my switch on the ground about 11 years ago, based on advice others had posted here at the time. I need to do some wiring work sometime in the near future, and would certainly consider changing that, if it is worth the effort.
 

DanR

Diamond Level Sponsor
I may be off in the head but it seems that Jerry is correct in any logical manner I can come up with. I have always made the cut off on the (+)….. you can still "short out" by creating a (-) contact elsewhere as I understand it. I am dumb on DC circuits, so I did it my Dad's way:)

I think "Killing power by opening a ground path" is the key to what jerry stated
 
Last edited:

Alpine 1789

SAOCA President
Diamond Level Sponsor
I just did a little forum searching and found this thread from 2007: http://forum.sunbeamalpine.org/index.php?threads/locating-a-battery-cut-off-switch.5606/#post-31739. There were other strong recommendations from the time to switch the ground terminal and it made sense to me, so that is what I did. However, I recognize that Jerry is far more educated on this topic than those who commented at the time (forget 11 years ago - make that 13!), which is why I am bringing it back up.

Jack: sorry for hijacking your thread. I think your original question was answered, so I'll leave it, unless someone wants me to move this to a new discussion for posterity.
 

Warren

Bronze Level Sponsor
No kidding one time a wrong size battery was fitted to a car of mine . When the hood closed an it was like an atc welder burned a hole in the hood....
How does that battery hold down work without causing a similar problem.
 

65beam

Donation Time
I think you'll find a battery kill switch has to be on the positive cable to eliminate feed back to the ignition circuit if equipped with an alternator. Would this apply if the car uses a generator?
 

rixter

Gold Level Sponsor
In our discussions on this topic, we are interchanging the terms "kill switch" and "cut off switch". I have seen information on the use of switches to "kill" the engine and in such cases concern of the issues of the alternator continuing to supply voltage to the system for a bit as being an issue. Race car kill switches can have provisions to address this. But as a basic cut off switch... that is to say a means to disconnect the battery on a car that is not running, how is it any different than manually pulling off the NEG (ground) cable? Cases for the latter being when the car is to be parked for a length of time, when you are working on the electrical system or perhaps even for security reasons.

Rick
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
Mine is a cut-off switch that I use for safety when the car is sitting and for security when parked. I have a thermal fuse across the terminals of the switch--an NOS Lucas one that I bought a long time ago (like this: https://www.ebay.com/itm/Classic-Mi...1&hash=item3ab5efd312:g:MgcAAOSwYHxWPW7M)--to protect the radio circuit and keep the clock running, although there is another problem with the clock circuit that I need to spend some time tracking down. Turning the key without throwing the switch 'blows' the fuse and kills the power to the radio, which means I have to reset the stations, but that isn't a big deal as there are only a couple of worthwhile stations out here.
 

Gary T

Gold Level Sponsor
Dan R you are correct about the close proximity of the wire to the battery box, but that wire is the ground wire if you follow it around the battery to the lug on the side of the battery box. I also agree that the shutoff switch should be on the power side of the battery and not the ground side.
 

65beam

Donation Time
Taking into consideration how easy it is to access the battery of an Alpine you'll find I disconnect one post whenever the car is going to be parked for any length of time. This includes shows where the doors will be open quite a lot and the trunk is open thru out the show. I have interior courtesy lights on all of my cars with a couple having trunk lights.
 

loose_electron

Donation Time
Jerry: can you expand on this, please? I put my switch on the ground about 11 years ago, based on advice others had posted here at the time. I need to do some wiring work sometime in the near future, and would certainly consider changing that, if it is worth the effort.

Sorry for the slow response here, I have been making face masks for people the last couple days for the whole CV19 mess. Please stay in everyone, please wash your hands and stay safe. OK...

Why is it not a good idea to break open electrical paths in the ground side of the system?

In the grand scheme of things it is not a big issue. The original design of the electrical system has a lot of things in it now recognized as not well thought out, or not safe, evidenced by a lot of fire extinguishers being carried and a lot of electrical fires. I rewired mine with a Pete wiring harness which many other here have used. I also add a 350A fuse on the positive side of the battery, so if the cable from battery to Starter relay, chafes through anywhere to the car frame, that fuse pops. I also have a 40A (60A???) fuse where the battery power goes from the starter relay to the dashboard ignition switch. That protects the heavy cables that are the power that goes through the ignition switch if any of those cables get shorted out. Shorts in those wires causes a fuse to pop at 40A and not melt the wires going all the way to 350A. After that, everything is fused through the fuse box.

Those two fuses are a smart addition to any car with old or new wiring setups.

However, I digress...

Best practices for any electrical system is to keep all of the grounds tied together. Everything is measured and defined electrically with respect to chassis ground. That way it is easily understood that all the things that are tied to ground remain tied to ground. In more complicated systems (Boats and aircraft come to mind) there can be multiple power sources (batteries, chargers, generators, etc) and all this systems are designed using a common ground strategy. (Boats are a complicated beast, but that's another story) All the switches are put on the positive side of the system, and all the parts share a common unbroken ground. That's my take on it.
 

loose_electron

Donation Time
I may be off in the head but it seems that Jerry is correct in any logical manner I can come up with. I have always made the cut off on the (+)….. you can still "short out" by creating a (-) contact elsewhere as I understand it. I am dumb on DC circuits, so I did it my Dad's way:)

I think "Killing power by opening a ground path" is the key to what jerry stated
Yeah, that is what I am not a fan of. Do people do it? For sure. It is the best way? Not to me.
 

rixter

Gold Level Sponsor
Jerry,

Thank you for your service. Let us hope this mess is over soon.

After installing my new group 24 battery yesterday and realizing it is bigger than the incorrect one that was in there previously, I opted to do away with a cut off/disconnect device. Things were getting too crowded in the box for it and I realized I didn't use it enough to implement it anymore.

Rick
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
Thanks, Jerry. That all makes sense. I have to do some electrical fine tuning this spring and will change the cut-off switch at that time.
 

Tom H

Platinum Level Sponsor
It's very simple. DOES NOT MATTER, except from a "consistency" standpoint. That is we all get used to having ground everywhere. While doing any troubleshooting we assume that the battery is connected to ground. I think that is what Jerry is getting at. However it does not really have any effect on the operation of the car. If you install a battery and only connect one terminal, there is no test, step, switch, impulse, or anything you can do anywhere on the vehicle, wires, cables, etc., that would get you ANY indication as to which cable is not connected. In fact you could not even tell if either cable is attached. You could even weigh the car on a precision scale and that could tell you if there is a battery in there, but could not tell if it was even connected at either end. You could smell the car, you could taste the battery cable. You could touch your tongue to one of the fuses. And you still could not tell. You'd have to lift the battery cover and look.

In spite of that, I do often see instructions for servicing a vehicle and they almost always tell you to remove the neg battery connection. I'm guessing that is because the ground connection is simpler with fewer cables and wires connected.

Tom
 

loose_electron

Donation Time
For whatever it's worth the NHRA rules have the battery kill switch in the positive side of the battery. As for tasting the battery cable Tom H? Probably not a good idea, a little too much lead for my liking.
 

Tom H

Platinum Level Sponsor
Jerry I think you understood that idea was "tongue in cheek" . Just trying to emphasize that there is NO way to tell which cable is not connected. I agree that consistency is useful, and that's probably why the NHRA rules are there. so that anyone working on or rescuing a car will know exactly what's what. I also would almost surely put my switch on the positive side for those reasons. But I want our members to understand that there is no physics or electrical reasons - at least none that I know of.
 

Warren

Bronze Level Sponsor
Mr. Spock could say there is a .0057999999 percent chance that a car could become crumpled for the neg terminal to become reattached to permit contact. The key is not turning into a Pinto and Richard Grimshaw

*fictional number derived in bored land larger chance is presumed. I'd go with the NHRA rule.
 

65beam

Donation Time
Mr. Spock could say there is a .0057999999 percent chance that a car could become crumpled for the neg terminal to become reattached to permit contact. The key is not turning into a Pinto and Richard Grimshaw

*fictional number derived in bored land larger chance is presumed. I'd go with the NHRA rule.
These cars all had a Lucas electrical system and most still do so everything works sometimes.
 

Warren

Bronze Level Sponsor
Oh I get it George Lucas not Gene Roddenberry designed the electrical system :) I always get Star Trek and Star wars cornfused :)
Obviously a boot mounted battery is more likely to be tossed about the back of the car along with lots of gas from the cross over tubes or the un fused brake light switch. Let's not make this another inertia switch thread gents...

I remember selling a car and pointing out the cracked J hook holding the battery down, and saying this car is being sold because I do not want to fix everything... should have said BYO smoke or wait it'll come loose when you are having fun..... But to be fair the battery is held somewhat by the false floor that was in the car. The one time I auto crossed that car it got additional lashing on the battery as well as the doors held shut with the passenger seat belt and a short piece of rope...
As sailors say rrrrr matey no one wants a loose cannon on the deck.... or battery below
 
Top