Technical Necessity of Master Battery disconnect Swithch

Just my opinion but it seems that this should be a necessity placed directly at the battery; both to prevent your car from being stolen and be able to disconnect the entire electrical system in case of a short in a moments notice. I see there are lot of switches on the market. My electrical knowledge is very limited. I see a lot of them are based on amperage draw.The higher the amperage capability the higher the cost. can you explain this to me, the best one to use,which will function the best ? Thx Gene

 

The nearly fool-proof ones are the type that attach to a battery post and use a knob to tighten against, or loosen an disconnect the battery cable. They have the highest amp rating in as much as the 'contacts' in the 'switch' type are much smaller than the contact area attainable with the Tighten The Knob variety. I have a 1947 Studebaker with the original , and very tattered, cotton covered wiring....it's a 100% necessity to disconnect EVERYTHING at the battery or the old girl could burn up in the middle of the day.

 

Subscribed.btt good topic, maybe some links from many threads b4, looking forward to replys.

 

One disadvantage of having a disconnect switch directly at the battery is you'll have to include the starter load. On a six volt car, this can be around 400 amps or more. A twelve volt car, figure at least 250 amps. These numbers will usually give you some 'headroom' in case of a hard-start, hot start issues, a dragging starter, or a low battery. Big inch motors or motors with high compression may need more. Another issue is any battery will outgas some corrosive 'stuff', so maintaining the switch contacts can be an issue. A remote switch not including the starter circuit won't have these issues, and you can reduce the required amp rating to 100 amps or less.

 

I use Cole Hersee part # 24200, it is a latching solenoid that mounts in the positive cable, between the battery and starter solenoid. It is tripped by a remote, hidden, button that serves as a ground. When you park the vehicle, press the button, and all power is shut off. Clean, simple and safe !

 

Here is picture.

 

Almost all heavy equipment has a battery disconnect switch that will handle over 400 amps but they are quite expensive. 2 of the less expensive switches could be installed in parallel. The bad thing about the key type disconnect switches is that they all use the same key and the key can be purchased separately.

 

Neither the switch that Marty showed nor one like what Engine Man mentioned are real spendy.
The Cole Herse 24200 that would be better for cutting off all but the feed to the starter it's self. It is rated at 110 amps so you wouldn't want to run a starter on a big engine through it.
The heavy equipment switch
https://www.amazon.com/Caterpillar-Equipment-Battery-Disconnect-Ignition/dp/B00AFOU2AE This one could be a discrete battery power shutoff that woudn't be real noticeable when turned off and the key

 

Having just experienced a hung starter I will be doing this immediately.

 

I've always used marine units. Work great.

 

On Caterpillar equipment the main disconnect works on the ground lead and not the power lead. No reason it can't be used on the power feed but shutting the ground off shuts everything off. That might be a better theft deterrent than shutting the power off in some cases.

 

Yes a Perko marine switch works great

 

Remember that the starter is a 'momentary' load, these solenoids have 2 different ratings: a continuous duty and momemtary. The continuous might be 100a and momentary several hundred.

 

(On Caterpillar equipment the main disconnect works on the ground lead and not the power lead. No reason it can't be used on the power feed but shutting the ground off shuts everything off. That might be a better theft deterrent than shutting the power off in some cases.)
In previous discussions of this it's been pointed out that if you have a faulty ground and your switch is wired this way, you can have voltage flowing even with the switch in the off position. I'm at this point in re-wiring my car right now and would like to hear more opinions/explanations about this. I had my switch wired this way and when I read the ground fault explanation I changed it to the power lead. It worked fine for several years like that but since I've changed everything else this time around I'm open to using the ground lead if it makes sense. Opinions?
Rich

 

I haven't seen a production car with a battery cutoff switch as original equipment. Maybe I'm missing something here....

 

If you're using it for anti-theft, either lead works. If you're using it to cut power in an emergency involving the wiring, put it on the positive side, as close to the battery as possible. If you have a wiring melt down, the wiring could self-ground, bypassing a ground side switch, and continuing the short circuit, where a positive side switch at the battery would disconnect power from the wiring.

 

A ground side switch will disconnect negative side of power from ground, which will be just as effective at disconnecting power from the wiring. Either way works.

 

New cars have other anti theft mechanisms, and are unlikely to have dodgy wiring. But dodgy wiring can be replaced, which is much safer than a disconnect.

 

I try to build my cars with good wiring, I can't remember ever having needed a disconnect switch in the past 35+ years that I've been doing this stuff. I suppose there's always the first time...

 

The $10 plastic cut off switches are worthless! I have a $30 cut off switch from So-Cal with a metal key. It appears to be very similar to the marine switches at West Marine. I use the battery disconnects on a car that sits for months at a time. All of my battery disconnects are installed on the negative side of the battery.

 

I used one of the green knobbed things for years. The off gases would cause the contact plate
To not make good contact at the most inopertune times. I used it for cutting off power when parked. I got a remote and mounted it using a solenode with a button. Works great.

 

I had a nut come loose and wedge between the + cable lug on the starter and the case....fire and burned up the wires back to the battery. It was under the seat and car was tight in the garage so I had to roll it outside to access first before I could remove the seat base, get cutters and cut the wire.Would have been a lot easier to turn off an accessible switch .

I got lucky as it could have cooked the whole house.and garage.

There is a cut off switch now and any future cars will have one of those and a mega fuse at the battery large enough to handle the load

 

The only thing that you are missing is paranoia.

if you are using switch as a theft deterrent the best one and the cheapest came from Ford of the '90s. They had a chip that you could remove and it killed every major electrical component for the car.

If you are using a switch because your wiring may burn your car down it is like putting a band aide on a cancer, fix the damned wiring. if you want one for safety reasons, like your car is really fast and you may climb the rail and become incapacitated companies like Moroso make them that are NHRA legal. They are not as simple to wire in as one would expect, for example many won't kill the motor if you are running an alternator.

I can imagine it being a good deal in some cases. I had an OT car short an AMP meter and there was no putting it out until the cable was pulled. If your battery is under the back set that could be a real problem. I fixed the problem, it was my mistake that caused the problem in the first place.

On a side note GM used to run a fusible link tat would kill the power in the event of a major electrical problem. They can still be purchased pretty cheap and are a good idea.

 

Really appreciate all your responses but still not sure now if I want a switch or not. As one of you touched on ; the contacts on a switch are going to be smaller than the post on the battery and with the heavy load will any switch be sufficiant or down the road be a problem ?? Gene

 

As a point of reference...NHRA requires a battery disconnect switch (which is required to act as a kill switch also), on any vehicle that has had the battery relocated from the original position. Or any car that runs 9.99 or quicker ET.

I guess they learned a long time ago, that hot rodders aren't so good at doing wiring safely!

 

The Moroso I got has been in several cars, some with lots of electronics, it is a heavier switch than most stock ignition switches. if it layed down on the road it would be as simple as a 3/8" bolt and nut and some electrical tape to cure. They normally fail open not closed designed that way.


It will probably use it in my A not because it is going to be soooooo faaaast. It will probably only be an 11 second car on a good day. But my battery will be basically not accessible (under a bulkhead where the back seat should be)so it will be handy if I want to kill the power.

 

not required for your race car?

x2
Master Battery Disconnect on/off Kill Switch, 2-post by Moroso # 74101 at summitracing.com is a good example of a heavy duty style switch - good for when needing to disconnect a remote battery with limited access, wire short emergency , storage for long periods of time, etc

 

Moroso, Taylor, mr gasket, most of the big names have the same style cut off switch which are all heavy duty. Have had one in my camaro for ever. Have it wired into the main ground from the starter. Simple and effective hence why every race car had one. Put it in an easily accessed area when u get in the car where it can't be seen and it's a great anti theft. Really not a big deal. http://www.jegs.com/images/photos/700/710/710-74101.jpg

 

nope, battery is up front where it belongs, and the two nine second runs I made with it don't count (and I've done a few things to slow it down, so it won't go that fast again)