Master cut off switch for 12 volt?

[Musicinabottle]

I have an older International truck with a DTA 360, that has 3 commercial batteries for starting, and some rather large cables interconnecting the batteries and running to the starter. I wanted to install a master kill switch and located one on ebay that is rated at 185 amps. Is that hefty enough or would I need something heftier? I'm just now replacing the batteries, and want to be sure nothing runs them down. Any input appreciated. Thank you!

 

[Bruce Amacker]

No, a 185 amp rated switch is not enough, your starter could pull several times that. I suggest against a master disconnect on that truck as the ones I've measured on fire trucks with similar engines have a voltage drop over 1v when cranking, and those HD switches may be $100-200+.

You may be overthinking it, as delivered from the factory your truck has nothing that would run the batteries down. If you only use it once in a great while keep a battery maintainer on it. Three (group 31) batteries was an option on that truck, 2 are more than enough to start it unless you're in subzero temps.

 

[brownbagg]

summitt racing

 

[Marctrees]

Possible help here - Marc

https://www.google.com/search?q=mar.....69i57j0l5.6689j1j1&sourceid=chrome&ie=UTF-8

 

[EOC_Jason]

This might also point you in the right direction... This is what a lot of people install on a M32A2 which is 24V though so amps are not as high as you probably need...

https://www.eriksmilitarysurplus.com/bamadisw83ms.html

 

[Musicinabottle]

No, a 185 amp rated switch is not enough, your starter could pull several times that. I suggest against a master disconnect on that truck as the ones I've measured on fire trucks with similar engines have a voltage drop over 1v when cranking, and those HD switches may be $100-200+.

You may be overthinking it, as delivered from the factory your truck has nothing that would run the batteries down. If you only use it once in a great while keep a battery maintainer on it. Three (group 31) batteries was an option on that truck, 2 are more than enough to start it unless you're in subzero temps.

It can get below zero here easily, but I'd never attempt to start it even when it is below freezing since it has no block heater..... yet!

This truck does have a stereo in it, and maybe the batteries were just bad, but when I first bought it, it started up just fine, then I left it set for a week, and had to jump start it, then run it for 40 minutes. Two weeks later I went out to start it again and the batteries were dead again. I'll check to see if it has any draw on the batteries with the key off, but I was thinking a cut off might be the answer, but I think a battery tender as you suggest, would be a good idea too. That's just a battery charger isn't it? I see this has a large brass lug on the front side of the battery box, and a positive cable hooked to it from the inside, so I assume that you'd hook to that and ground so that the battery compartment can be kept closed?

 

[Worsedog]

Your other option is to leave the heavy cables to the starter in place and put the cut-off switch between everything else in the truck and the batteries. This way the cut-off is not having to carry the starter load. When I operated the wreckers years ago, the home-built ones were wired this way.

 

[Musicinabottle]

Your other option is to leave the heavy cables to the starter in place and put the cut-off switch between everything else in the truck and the batteries. This way the cut-off is not having to carry the starter load. When I operated the wreckers years ago, the home-built ones were wired this way.

Excellent point. Hadn't thought about that, but thank you for mentioning it.

 

[tarmy]

I use marine cut off switches....have them on all the boats, tractor and trucks. Not only saves the battery...put it someplace that is hidden and it can deter thieves too...

 

[Musicinabottle]

I use marine cut off switches....have them on all the boats, tractor and trucks. Not only saves the battery...put it someplace that is hidden and it can deter thieves too...

Well, this is why I was contemplating these options after going and buying batteries at $130 a pop. I really want to protect them! I do like the marine grade cut off switches. I used to run a tug boat with a huge 4 cylinder Detroit and it had the cut off switch in the engine room what with all the water oil and grease down there.

 

[Richard Cranium]

I was going to say that I have seen lots of fire trucks with a/b/or off switches on them. They are either on battery a or battery b or all off.

 

[MarlynOC]

Marine store for diesel cutoff switch.

 

[unslow1]

I was going to say that I have seen lots of fire trucks with a/b/or off switches on them. They are either on battery a or battery b or all off.

Like this?

https://www.overtons.com/modperl/pr...MI9Nuih9-o2wIVErvsCh0q5QAkEAQYAyABEgLz0_D_BwE

 

[txvwnut]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

 

[unslow1]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

Huh?

 

[Bruce Amacker]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

Amperage is the same anywhere in a circuit. If there's 500 amps going through the positive cable, there's 500 amps going through the negative cable.

Your other option is to leave the heavy cables to the starter in place and put the cut-off switch between everything else in the truck and the batteries. This way the cut-off is not having to carry the starter load. When I operated the wreckers years ago, the home-built ones were wired this way.

This is tough in two ways- his truck is probably wired with a stack of (fusible link) eyelets on the starter positive stud that feed the dash and fusebox. That means to separate the low amperage circuits and starter leads would probably require some creative relocation of the low amperage circuit feeds. Plus, this would basically defeat the reason for installing a cutoff- if you have a parasitic draw it's probably going to be in the low amperage circuits, not the starter itself.

It can get below zero here easily, but I'd never attempt to start it even when it is below freezing since it has no block heater..... yet!

This truck does have a stereo in it, and maybe the batteries were just bad, but when I first bought it, it started up just fine, then I left it set for a week, and had to jump start it, then run it for 40 minutes. Two weeks later I went out to start it again and the batteries were dead again. I'll check to see if it has any draw on the batteries with the key off, but I was thinking a cut off might be the answer, but I think a battery tender as you suggest, would be a good idea too. That's just a battery charger isn't it? I see this has a large brass lug on the front side of the battery box, and a positive cable hooked to it from the inside, so I assume that you'd hook to that and ground so that the battery compartment can be kept closed?

A battery tender is slightly different than a charger so make sure you get a tender. Yes, hook it to the jumper lug. Your stereo is unlikely to be the source of the draw (if you have a draw!) if it's wired correctly. FWIW, IH specs 50mA (.05A) as maximum parasitic draw on their trucks.

PS I've written several books on IH engines including the DT series, and a book on automotive electrical systems.

Good Luck!

 

[Worsedog]

This is tough in two ways- his truck is probably wired with a stack of (fusible link) eyelets on the starter positive stud that feed the dash and fusebox. That means to separate the low amperage circuits and starter leads would probably require some creative relocation of the low amperage circuit feeds. Plus, this would basically defeat the reason for installing a cutoff- if you have a parasitic draw it's probably going to be in the low amperage circuits, not the starter itself.

The best way is not always the easiest.

How does moving all circuits except the starter to the cut-off defeat the purpose of the cut-off?

 

[The Cobbler]

disconnects are wired on the ground side , not the pos side

 

[mark#3]

I put a catapillar off/on switch in series with the battery ground cable on my vietnam vintage jeeps

 

[Worsedog]

disconnects are wired on the ground side , not the pos side

Often, but not always. Like most things it's application dependent. We have an ambulance that our SWAT team uses as an equipment truck and the disconnect is on the hot side. All of the power runs through it except the starter load and the keyless entry. If the cut off were on the ground side you could wire around it for the keyless, but now you have provided a drain path from the pos side.

If you have nothing that requires full time power, and your disconnect can handle the full load then the ground side is the place for it. If not then obviously there are multiple ways to skin the proverbial cat.

 

[ishiboo]

Battery switches are typically rated for continuous amperage, and rush. So a 185amp switch is normally capable of 185 amps continuous, and ~600+ or whatever amps starting. Only way to find out is to look at the specs though.

All the boats and equipment I have ever owned has had the battery switch(es) on the positive side.

 

[Mooky]

Several types, simple on-off and three position...

http://m.littelfuse.com/industries/...see/switches/battery-disconnect-switches.aspx

 

[flan]

The truck I drive at work has 6 group 31’s and has a blue sea systems single circuit 3000 master switch on it.

 

[LS6 Tommy]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

disconnects are wired on the ground side , not the pos side

Never break the ground! If the engine is running, it will continue to run off the alternator even if the battery switch is open. Also if you only disconnect the negative and kill the battery when you experience an accessory switch short where you cannot turn something off, you will not be able to disconnect the battery to de-engergize the accessory and it continues to run. You would fail tech inspection at any race (other than NASCAR, they do things completely differently with a relay) if you wired the kill switch that way.

Tommy

 

[Daves69]

Your starter will not drain the batteries and won;t need to be switched. Locate the cable that powers the cab and chassis, place your switch there.

 

[firebirdparts]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

Nope.

 

[kabinenroller]

If you go with a battery disconnect it goes in the ground side not the positive, there’s less draw and heat through the ground circuit when cranking.

YES!! With out a ground to complete the circuit there is no chance of the battery discharging by a parasitic drain or a dead short in the harness.
I always install a master disconnect between the battery and the main grounding point.

 

[AA/FC]

All the garbage companies around here put main disconnects on their garbage trucks. Several over the road companies based out of here also put main disconnects on their road tractors. Almost all of them are the Flaming River "Big Switch". In fact, if you walk into the local Peterbilt dealership parts department and ask for a main disconnect switch they will hand you the one made by Flaming River. Its the only brand of disconnect switch they stock.

250 amp continuous, 2500 amp for 5 seconds.

http://www.flamingriver.com/index.php/products/c0015/s0003/FR1003

 

[LS6 Tommy]

YES!! With out a ground to complete the circuit there is no chance of the battery discharging by a parasitic drain or a dead short in the harness.
I always install a master disconnect between the battery and the main grounding point.

If there is no positive, there is no chance of parasitic loss either, and far less chance of safety issues. Again, NEVER switch the ground. Auto electric 101, people. See my above post...

Tommy

 

[Ole Slewfoot]

Your starter will not drain the batteries and won;t need to be switched. Locate the cable that powers the cab and chassis, place your switch there.

I've seen it happen, but the starter getting hot with the engine off is pretty much a dead giveaway.

 

[Falcon67]

disconnects are wired on the ground side , not the pos side

Use a 4 pole and cut the ignition power, make sure the alternator is hooked directly to the battery.

Never break the ground! If the engine is running, it will continue to run off the alternator even if the battery switch is open.

Only if there is a return path to the battery. This is how I wire the door cars, meets xHRA "letter of the law".

In the dragster, I use a 75A relay in the ignition power circuit to drop the alternator out when I shut down the car.

 

[Falcon67]

The 4 pole part - Moroso Battery Disconnect Switche 74108

https://www.summitracing.com/parts/mor-74108/overview/