Military Cutoff Disconnect Switch HMMWV Battery

[Coug]

I am not sure why you are asking but there is a 12V feed to the TCM that is hot all the time and a switched feed.

okay, that does answer my question.

 

[papakb]

If you want to kill all power to your truck for either security purposes or something else you need to break not only the ground line but the 12v tap also. Failing to break the 12v line leaves the "high side" battery connected and as stated some things may still power up. Breaking both leads will cut all power to the truck.

Other than the starter there's nothing else in these trucks that would draw more than 125 amps that I can think of. Even most heavy loads like winches aren't going to need that much power and even then it's not continuous.

 

[nikojo]

Ok here are the final pictures.

I installed a Noco dual plug for the Victron battery chargers. These chargers are really nice as they are completely waterproof as the electronics are potted in epoxy.

I have two of the chargers in the box plugged into the Noco plug and they are connected to each battery separately.


Kissling Dual Pole Single Throw (DPST) 500A continuous rating (1500A 240s; 2000A 90s; 2500A 10s

Link to switch Kissling switch link

Cable going from front battery (+) to bus.

Cable going from front battery (-) to switch.
Cable going from switch to rear battery (+).

Cable going from rear battery (-) to switch.
Cable going from switch to (-) shunt.

Works really well as it now completely eliminates even the false ground/reverse polarity that was present without disconnecting the interbattery cable. Lights and gauges no longer come on. Everything is dead.

Also interesting to note that if truck is running, disconnecting the batteries does not shut down the truck. Someone had asked about that earlier.

 

[nikojo]

Here is the pdf to the specs on the switch. This is identical to the military switch.

 

[Coug]

throwing the switch doesn't shut down the truck, but does it have any effect on the transmission control module? Do you get stuck in limp mode or does it still work properly?

 

[nikojo]

throwing the switch doesn't shut down the truck, but does it have any effect on the transmission control module? Do you get stuck in limp mode or does it still work properly?

It shuts down the TCM (aftermarket US Shift) which does throw it in limp mode.

I thought throwing the disconnect would shut off the fuel solenoid and thereby shut down the engine. But the generator must keep the solenoid alive.

 

[Coug]

It shuts down the TCM (aftermarket US Shift) which does throw it in limp mode.

I thought throwing the disconnect would shut off the fuel solenoid and thereby shut down the engine. But the generator must keep the solenoid alive.

Fortunately generators, unlike alternators, can run with no battery connected (or completely dead batteries) and not have issues. Alternators will burn up if you do that.

 

[Retiredwarhorses]

Am I missing something about how these trucks electrical system work?


It was my understanding that the 12V to the TCM was operated by a relay powered by the 24V system.

With the 24V system disconnected, wouldn't that also mean that the 12V system can't be operated either?

Or does the 12V circuit go to both the relay and the TCM directly at the same time?

The connection to the 14v tap off the regulator can and will also act as a ground when the ground is disconnected allowing the truck to be cranked over but on 12v only, I pointed this out years ago and stopped installing BCO’s on 200 amp equpiped trucks.
Ive duplicated the issue in front of many hmmwv owners and even other hmmwv shop owners while they were in my shop.
The OEM kit eliminates the problem.

 

[nikojo]

The connection to the 14v tap off the regulator can and will also act as a ground when the ground is disconnected allowing the truck to be cranked over but on 12v only, I pointed this out years ago and stopped installing BCO’s on 200 amp equpiped trucks.
Ive duplicated the issue in front of many hmmwv owners and even other hmmwv shop owners while they were in my shop.
The OEM kit eliminates the problem.

Steven I think that's true if you only disconnect the low battery ground. If you disconnect BOTH high and low battery ground it all goes dead.

I can say that was true for me when the battery interconnect was still connected, ie cable between high and low battery. As soon as I added that to the disconnect switch everything was dead.......gauges, lights, starter, everything.

You are a gagillion times more experienced then a me on this so I may not be understanding.

But by disconnecting BOTH grounds from BOTH batteries I don't see how there can be a circuit completed of any kind. Even if the electrons leave the positive poles (I know its the opposite in reality but just to follow easier think of it like this) they have no way to get back tot he battery if neither ground has any connection to the battery. I imagine it as completely removing the ground cables from both batteries. Have to think it's impossible at that point.

Steven you may have still had the interbattery cable hooked up in which case that's exactly what was happening with me, ie 12V to many systems, ie dim lights, slow gauges, slow starter. When I put the interbattery cable on disconnect everything went dead.

 

[Retiredwarhorses]

Steven I think that's true if you only disconnect the low battery ground. If you disconnect BOTH high and low battery ground it all goes dead.

I can say that was true for me when the battery interconnect was still connected, ie cable between high and low battery. As soon as I added that to the disconnect switch everything was dead.......gauges, lights, starter, everything.

You are a gagillion times more experienced then a me on this so I may not be understanding.

But by disconnecting BOTH grounds from BOTH batteries I don't see how there can be a circuit completed of any kind. Even if the electrons leave the positive poles (I know its the opposite in reality but just to follow easier think of it like this) they have no way to get back tot he battery if neither ground has any connection to the battery. I imagine it as completely removing the ground cables from both batteries. Have to think it's impossible at that point.

Steven you may have still had the interbattery cable hooked up in which case that's exactly what was happening with me, ie 12V to many systems, ie dim lights, slow gauges, slow starter. When I put the interbattery cable on disconnect everything went dead.

Correct, but without going into the differences of BCO on pos or negative, AM General kills the rear battery ground and the 14v positive feed, it ultimately does the same the same thing just a different approach

 

[nikojo]

Correct, but without going into the differences of BCO on pos or negative, AM General kills the rear battery ground and the 14v positive feed, it ultimately does the same the same thing just a different approach

Got it. That makes sense.

I can attest leaving the inter battery OR 14V feed connected is bad idea for BCO.

 

[Crapgame]

If anybody replicated the AM General 57K6230 Battery Cutoff Switch Kit, we worked withGreg at Dataplates.net to make the 3 instruction plates for the battery box exterior. The yellow on black battery wiring diagram plate that comes with the kit is the regular plate you see on most HMMWV that you can find for under $10. Contact me for details if you want to order a set.

 

[SmartDrug]

The advantage to using a ground side switch for the 24V is if any of the cable or connections accidentally finds ground it will not start a huge fireworks display.
If you use a dual switch, one on the ground side of the low side battery and one disconnecting the 12V connection between the batteries there will be no current flow anywhere, basically doing the same job as using the 24V (high current) switch between the batteries or on the positive side of the high side battery, makes no difference only breaking the low side battery ground is as I said safer.

I’m in the process of setting up a dual disconnect for my M1123 and was planning to copy your setup.

Is this what you’re running?

Switch 1 cuts the 12v (low side/rear) ground connection

Switch 2 cuts the positive connection between the two batteries

Electrical is not my strong suit, I’ve spent a couple hours trying to decipher all this.

Secondary question- why do we need such high momentary amperage ratings? Would a 500/1000a switch be enough to disconnect a truck with no accessories beyond TCM/gauges/lights/basic running gear?

 

[Mogman]

Switch 1 the BIG switch cuts the ground side of the low side battery (24V) the smaller switch that most folks think is good enough for the main switch is used to disconnect the connection to the middle of the batteries (12V) turn off the small switch first and turn on the small switch last.

 

[Mogman]

The small switch cuts the smaller 12V connection to the middle of the batteries not the heavy connection between the batteries.

 

[SmartDrug]

So I figure this was easier than trying to describe it.

Big switch is labeled in red.

Little switch is one of those colors?

I haven’t traced those wires, but yellow is labeled 290, 291, 537.

I was planning on running the 2500a Hella (metal) and a 1000a Hella (red plastic), is that enough switch for this role?

Battery Switches | Hella Marine

A complete range of battery switches to suit a variety of applications and power loads

www.hellamarine.com

100 Amp Battery Master Switch - Accessories, Battery Switches - Hella Marine

Heavy duty switch for high loads.Key can be removed in the OFF position, current interrupted. Positive or negative cable can be switched as required. Note: Not suitable for areas exposed to water or moisture.

www.hellamarine.com

 

[Mogman]

The yellow and blue would go through the small switch, and the big switch on the red, no switch on the green
Those switches will work fine.
2500A for 10 seconds should do the job , same switch I use, I use a Cole Hersey like this one for the small but that Hella will be fine.

 

[SmartDrug]

Thank you, sir!

 

[Mogman]

So I figure this was easier than trying to describe it.

Big switch is labeled in red.

Little switch is one of those colors?

I haven’t traced those wires, but yellow is labeled 290, 291, 537.

I was planning on running the 2500a Hella (metal) and a 1000a Hella (red plastic), is that enough switch for this role?

Battery Switches | Hella Marine

A complete range of battery switches to suit a variety of applications and power loads

www.hellamarine.com

100 Amp Battery Master Switch - Accessories, Battery Switches - Hella Marine

Heavy duty switch for high loads.Key can be removed in the OFF position, current interrupted. Positive or negative cable can be switched as required. Note: Not suitable for areas exposed to water or moisture.

www.hellamarine.com

View attachment 905842

That may not be the right one, This one is the one I use, it is rated for 250A continious service

Hella Main Switch, battery - Turn knob control - Number of connect 6EK008458-011 | eBay

Cross-references : AMAZONE NG084 | FORD V1C4414526A | HITACHI CONSTRUCTION YA0000584500 | KRONE 200817450 | TEREX 20028109 | VDL 30016214 | AMAZONE NG084 | HELLA 008458011 | HELLA 6EK 008 458-011. Number of connectors: 2.

www.ebay.com

 

[Mogman]

I don't see how if both can handle 2500a/10s why there would be a difference.
There are many examples of a company creating a new part number to fill say a gov. contract, if the gov says they want a 100A switch they will not buy a 250A switch.
The M1101 and the M1102 trailers are prime examples, they are exactly the same but for the data plate.