Jump to content

Battery disconnect switch


Buick35

Recommended Posts

Here's how I did it in my '35 Lincoln. My battery is under the passenger side floorboard, so I used a switch recessed into the floor. Easy to reach but unobtrusive. Be sure to use the heavy-duty 200 amp version that costs $50, not the $16 eBay special built for 50 amps. 6V cars need the big cables and the big switch to pass the current. Here's a link to the entry:

 

 

  • Like 5
Link to comment
Share on other sites

Get a 6 volt high amp switch.....NOT the crappy Chinese stuff......needs to handle 700 amps surge. Summit racing has good ones, just put it on a V-16 Caddy.

Screenshot 2024-02-07 at 3.12.59 PM.png

  • Like 8
Link to comment
Share on other sites

22 minutes ago, Buick35 said:

Silly question but doesn't the ignition on/off switch act as a battery disconnect? I realize that the battery is still connected .

 

No. On pre war stuff, you can cook a cars harness especially if the cut out gets stuck closed........and also in the event of an electrical fire or electric fuel pump shut off. Many shipping companies want batteries disconnected.......easier with a switch than opening up a painted battery box and using tools. Same goes if you fly the car on an airplane........talk about headaches!

Edited by edinmass (see edit history)
  • Like 1
Link to comment
Share on other sites

18 hours ago, Buick35 said:

I'm thinking of mounting it under the car on the frame near the battery.

Make sure the switch is rated for a wet environment (e.g., IP-65 or better IP-67).  If unsure, i would mount it somewhere in the cab or engine compartment where it will be protected from water ingress.

  • Like 1
Link to comment
Share on other sites

Another option would be near the starter.   Most early cars have inline engines and the starter is within view.

A bracket on the frame or firewall near the starter (because that is were the positive cable is located) might be 

easier to install and use. 

Link to comment
Share on other sites

44 minutes ago, Barney Eaton said:

Another option would be near the starter.   Most early cars have inline engines and the starter is within view.

A bracket on the frame or firewall near the starter (because that is were the positive cable is located) might be 

easier to install and use. 

If I mounted it by the starter it would have to be connected to the positive cable where I thought negative was better ,safer.

  • Like 1
Link to comment
Share on other sites

You will use it more often if you mount it on the floor in the passenger compartment, rather than having to raise the hood twice each time (one to turn off, one to turn on).  IIRC, your Buick's battery compartment is under the front passenger's seat, so I'd mount it in the center.  Run one (preferably 00) cable from the negative (ground) battery terminal to one pole on the switch, and one from the other switch pole to a hole through the frame.  Be sure to test-orient the switch before finalizing its mounting so that you have unobstructed on-off range of movement.  There are rubber/plastic caps for the switch poles available, or just add protective "goose grease" (vaseline etc) of your choice to protect them from water.

  • Like 4
Link to comment
Share on other sites

 

Battery Disconnect Switch Top Post,Top Post Knife Blade Master Switch, 12V / 24V Battery Shut Off Switch, Heavy Duty Knife Blade Battery Cut Off Switch, for Auto Car RV Boat Truck(Negative,Vertical)

 

I'm cheap  Less than $10 on Amazon

 

Has worked great for years

 

Do not use the ones with the twist knob on them.  I have seen several older cars that would crank but not start because the voltage drop across the knob style cut offs was so great.  I didn't believe it at first until the guy removed it and it solved all his starting problems.  Reinstalled and they returned.

 

Ampper Top Post Battery Disconnect Switch, Battery Master Switch Isolator for Power Disconnect Cut Off

  • Like 3
  • Thanks 1
Link to comment
Share on other sites

On 2/8/2024 at 1:22 PM, Buick35 said:

Silly question but doesn't the ignition on/off switch act as a battery disconnect? I realize that the battery is still connected .

An electric clock will eventually kill the battery.   Although if you don't have a draw and you have a new harness then no reason to kill the battery....   Unless you have aluminum in your engine in which case the ground can be facilitating the galvanic corrosion so kill it anyways.

Link to comment
Share on other sites

39 minutes ago, Brian_Heil said:

 

Battery Disconnect Switch Top Post,Top Post Knife Blade Master Switch, 12V / 24V Battery Shut Off Switch, Heavy Duty Knife Blade Battery Cut Off Switch, for Auto Car RV Boat Truck(Negative,Vertical)

 

I'm cheap  Less than $10 on Amazon

 

Has worked great for years

 

Do not use the ones with the twist knob on them.  I have seen several older cars that would crank but not start because the voltage drop across the knob style cut offs was so great.  I didn't believe it at first until the guy removed it and it solved all his starting problems.  Reinstalled and they returned.

 

Ampper Top Post Battery Disconnect Switch, Battery Master Switch Isolator for Power Disconnect Cut Off

The twist knob ones like this green one are a menace and will eventually burn your house down.  Or if you are lucky, just keep your car from starting.

Link to comment
Share on other sites

2 hours ago, Brian_Heil said:

Do not use the ones with the twist knob on them.  I have seen several older cars that would crank but not start because the voltage drop across the knob style cut offs was so great.  I didn't believe it at first until the guy removed it and it solved all his starting problems.  Reinstalled and they returned.

 

This gets posted all the time, and I doubt most of those reading take it seriously enough. Years ago I tried to modify one of these to sit in a nonstandard way in a car that lacked clearance. I broke 3 of them trying and gave up. I would urge anyone who is considering using one of these to unscrew the green knob, take all the parts out and just have a good look around. Taking them apart reveals all their secrets. Here are a few: They are not brass, they are zinc (pot metal more or less) castings with some gold colored coating to make them look like brass. They are heavy because they are zinc. If they made them from aluminum, they couldn't fool you. Try to machine on it, or touch it with a file and the truth comes right out. The actual current is carried through two areas that have a very small cross section. That's where I was breaking them. No matter. There isn't enough metal there to work well on a 12 volt car, never mind 6. Zinc melts at a temperature just above leaded electronic solder. It wouldn't take much to melt this at the thin spots, and you can bet it is going to get hot from starter current. There's more wrong but it was a long time ago and I don't recall. The closer you look though, the worse it gets.

 

  • Thanks 1
Link to comment
Share on other sites

 

The green twist knob jobs are begging for a fire......they overheat and melt under normal 12v usage. Seen it a dozen times. Great way to make a claim on your insurance. 

Link to comment
Share on other sites

20 hours ago, David Zitzmann said:

And the knife ones too. I saw a 68 caddy smoking from one of those it got so hot. I only use the heavy duty ones like others have mentioned. 

A '68 Caddy would have a 472 cu in and 10.25:1 compression.  My '23 Buick is ~half of both of those and two cylinders less.  My knife switch has never gotten hot.  Maybe by Buick starts quicker too?

Edited by Brian_Heil (see edit history)
Link to comment
Share on other sites

I don't think you want any sort of switch on a high compression 472. Those cars draw what seems like too much current even when nothing is wrong. I had one, and battery cables made of large welding cable are what finally made it crank with authority, even in cold weather.

Link to comment
Share on other sites

It isn't the size of the engine. It is the current draw from the starter. If everything is brady new with proper gauge wire and clean I don't see there being a problem, but over time with dirty, lose, connections that causes resistance which equals heat and unhappy car owner.  Just my opinion:-)

  • Like 2
Link to comment
Share on other sites

On 2/9/2024 at 8:14 AM, Grimy said:

You will use it more often if you mount it on the floor in the passenger compartment, rather than having to raise the hood twice each time (one to turn off, one to turn on).  IIRC, your Buick's battery compartment is under the front passenger's seat, so I'd mount it in the center.  Run one (preferably 00) cable from the negative (ground) battery terminal to one pole on the switch, and one from the other switch pole to a hole through the frame.  Be sure to test-orient the switch before finalizing its mounting so that you have unobstructed on-off range of movement.  There are rubber/plastic caps for the switch poles available, or just add protective "goose grease" (vaseline etc) of your choice to protect them from water.

I agree with Grimy, I am in the process of moving the heavy duty disconnect switches to inside the cab under the seat or to the vertical seat riser. I have my 15 Buick, 28 Buick and 36 GMC all set up that way. I have the switch offset towards the passenger door.  I mark were it goes by setting in the drivers seat and then reach down with your right hand and mark the spot. On each of those vehicles the battery is near by under the floor boards and does not require a lot of routing to get it hooked up.  Perfect time to check and make sure you have the heaviest copper battery wire both positive and negative. I can’t wait to do my Packards as the super 8 has the disconnect on the left side under the hood and the twelve has it on the right side under the hood, both cars have side mounts. Typically I will jump in the car and turn on the key, with no results, jump out of the car and carefully open the hood trying not to scratch or chip the paint on the hood or the sidemounts, after successfully accomplishing that it’s then I realize that I opened the wrong side again……….. repeat………….

The Packards do not have a seat riser so I will have to mount the switch through the floor board, I will find a spot far enough under the seat that it can’t be seen, but not so far back that I can’t get to it.  By the way these heavier switches are also waterproof , I became familiar with them on some of our Caterpillar tracklayers, originally made by Cole-hersey, you can’t believe the environment they survived in 

IMG_0221.jpeg

  • Like 4
Link to comment
Share on other sites

Placement is important.........I have seen several cars dead on the side of the road when a foot or pocketbook killed the power going down the road and things start to cook.........so put them in spots where they won't accidentally get bumped into the off position. 

  • Like 4
Link to comment
Share on other sites

16 hours ago, David Zitzmann said:

It isn't the size of the engine. It is the current draw from the starter. If everything is brady new with proper gauge wire and clean I don't see there being a problem, but over time with dirty, lose, connections that causes resistance which equals heat and unhappy car owner.  Just my opinion:-)

I respectfully disagree. 

 

Number of cylinders, compression ratio and the displacement of that ratio are directly proportional to current draw of the starter.

 

Pull the rope on a lawn mower and then hand crank a high compression Cadillac V8 (if you could).  

  • Like 2
Link to comment
Share on other sites

47 minutes ago, edinmass said:

Placement is important.........I have seen several cars dead on the side of the road when a foot or pocketbook killed the power going down the road and things start to cook.........so put them in spots where they won't accidentally get bumped into the off position. 

You need to tell everybody about the car that barely turned over because they ran the disconnect cable an extra 6 feet to make it accessible and creating all kinds of resistance in the process.   I believe that car might have had 12 volt cable on it too?

  • Like 2
  • Haha 1
Link to comment
Share on other sites

1 hour ago, alsancle said:

You need to tell everybody about the car that barely turned over because they ran the disconnect cable an extra 6 feet to make it accessible and creating all kinds of resistance in the process.   I believe that car might have had 12 volt cable on it too?

A.J & Ed , on my recently acquired Packard I found the most complicated solution to a simple problem, I call it a gift from a previous owner. When I did my repurchase inspection the car started normal for a twelve. Starter turn slower than what we are use to in the modern world, but it seemed strong and steady and of course with twelve cylinders there’s always seems to be one ready to fire. The previous owner then showed me the “proper way to start it” in the trunk was a beautiful hand made wooden box with a 12 volt battery that was connected to a “ford” type solenoid directly to the starter, then there was a hidden switch under the dash that was a momentary push bottom that you energized to the starter, I can only imagine what would happen if that solenoid would get stuck.  So all that was stripped out of the car. So we needed a extra 18” of battery cable to locate my disconnect switch as we pulled off the old fat cable we spotted what caused a previous owner to go to this crazy unsafe solution, the cable looked big but the thickness was the rubber insulation, the copper inside was no bigger than a cable you would buy at a discount auto parts. I will take a picture of the evidence and post later in the week.

  • Like 2
  • Thanks 2
Link to comment
Share on other sites

I just got finished installing the battery switch on my Buick.I located near the battery on the frame rail under the car, not too bad to get to. I got the heavy cable and terminals at NAPA. For the battery terminal end I bought one that uses a solder pellet that drops into the terminal and gets heated with a torch. I learned something new, works good.

  • Like 4
Link to comment
Share on other sites

21 hours ago, Buick35 said:

For the battery terminal end I bought one that uses a solder pellet that drops into the terminal and gets heated with a torch. I learned something new, works good.

Just wondering if using a torch how does one avoid igniting the hydrogen battery gas?  I had two battery gas explosions that allow me to say it is not a pleasant experience.

Link to comment
Share on other sites

31 minutes ago, 28Buick said:

Just wondering if using a torch how does one avoid igniting the hydrogen battery gas?  I had two battery gas explosions that allow me to say it is not a pleasant experience.

Build it on the bench, not on the battery.

  • Like 3
Link to comment
Share on other sites

This is the one I use. 300 amp. I mount them on the inner fender wall and use #00 cable. Only adds about 2 feet of cable, but my batteries are under hood.

 

Menards

https://www.menards.com/main/electrical/light-switches-dimmers-outlets/light-switches/gardner-bender-reg-battery-shutoff-switch/gsw-bt/p-1642874300255863-c-6324.htm?exp=false

Link to comment
Share on other sites

On 2/9/2024 at 9:43 AM, Buick35 said:

If I mounted it by the starter it would have to be connected to the positive cable where I thought negative was better ,safer.

A very common MISCONCEPTION! Since 90%+ of cars on the road are 12 volt negative ground, everyone (racers, etc. that have to have a disconnect) says it goes in the negative battery lead. But, that is because they have a Negative Ground Vehicle!

 

The disconnect switch always goes in the grounded lead of the battery. So on a positive ground car, it goes in the positive battery lead.

 

As to those green plastic shut offs, I couldn't even put them in my Lead recycling box, and I have no Zinc recycling box....😮  

 

  • Like 1
Link to comment
Share on other sites

22 hours ago, alsancle said:

 

Is that on the ground?

Yes of course on negative ground, you can see the uninsulated ground mesh cable attached to it. Plenty of space for it under the right floorboard on my '28. Easy lift of the floor panel from the drivers seat. Nice that the switch is solid brass rated at 750 Amps momentary. 

Edited by 28Buick (see edit history)
Link to comment
Share on other sites

28 minutes ago, 28Buick said:

Yes of course on negative ground, you can see the uninsulated ground mesh cable attached to it. Plenty of space for it under the right floorboard on my '28. Easy lift of the floor panel from the drivers seat. Nice that the switch is solid brass rated at 750 Amps momentary. 

I'm not sure how I feel about that switch, but at least its not the screw kind that gives you the 50/50 shot of burning your car to the ground.

 

I have only seen cut off switches installed on the power cable, not the ground cable.   That makes sense to me as a wire shorting to ground in the harness could cause a fire if the cutout is installed on the ground cable.

Link to comment
Share on other sites

2 hours ago, alsancle said:

I'm not sure how I feel about that switch, but at least its not the screw kind that gives you the 50/50 shot of burning your car to the ground.

 

I have only seen cut off switches installed on the power cable, not the ground cable.   That makes sense to me as a wire shorting to ground in the harness could cause a fire if the cutout is installed on the ground cable.

If the path to the battery is interrupted, a (theoretical) infinite resistance is in the circuit and no current will flow.

  • Thanks 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...