Battery Disconnect Quick Question

[osteo16]

How are you guys installing master battery disconnect switch? I’m under the impression that breaking the ground side is maybe the way to go, but should I be taking it off the end of the second battery or between batteries ?? Confused.... Here’s a picture of what I’m using..


Pollak keyed disconnect. 2/0 wire... 180amp continuous/1000amp surge... Thanks again, and pictures are worth a thousand words... so if you have one, please post it..

Ocho Out

 

[simp5782]

Take the ground away and there is no 24v or 12v

 

[osteo16]

So, just wire it in line.. ground off battery to switch, other side switch back to battery..figured it was easy... but easy always gets me in trouble...

 

[MilitarySurplusBrent]

I like that switch! Where did you get it? I might want to get 2 of them for my M1123's instead of the keyed one that replaces that start/stop switch.

 

[Milcommoguy]

Are you running any 12 volt gear off the 12 volt battery?

This currently is a sneaky question, CAMO

 

[osteo16]

Are you running any 12 volt gear off the 12 volt battery?

This currently is a sneaky question, CAMO

Currently original setup.. looking to do 24v to 12v converter to blue sea fuse block to run radio and misc... would this effect my placement ?? And why per se ?

sorry... I know your gonna ask more info..

1988 M998, 60amp generator.. all stock except LED headlights.. will add 24/12v converter and small fuseblock..

 

[kendelrio]

My .....

I connected mine between the positive of the battery and starter.

All you need is a ground from any wire and the system is still hot. Take away the positive, and it can't accidentally be hot.

 

[INFChief]

By isolating the ground side the battery potential is still available in the system.

Remove the ground on your car battery then go to your starter and check voltage from the positive battery lead to ground.

Check it with a “wrench” and you’ll see sparks.

Isolate the positive cable with the disconnect.

 

[Milcommoguy]

Currently original setup.. looking to do 24v to 12v converter to blue sea fuse block to run radio and misc... would this effect my placement ?? And why per se ?

sorry... I know your gonna ask more info..

1988 M998, 60amp generator.. all stock except LED headlights.. will add 24/12v converter and small fuseblock..

I try to get one's thinker going. AND note everyone has their own way to skin the cat.

Pencil and paper time. Draw out the two batteries. show the front +24 volts going to the truck, the - & + strapping the two together. Add the placement of the switch on the - ground rear battery. GOOD. Move to the front of the class. No copying!

Yes, we / most can do this in our head. You got your back battery and it's ground post is connected to the shunt and down to the real ground stud which is on the starter frame bolted to the engine. SO far so good and for simplicity sake GROUND, breaking that back battery ground with the disconnect breaks the ground and all is good. This set up removes both batteries from providing 24 volts to your rig. (providing NO wonky 12 volt tap to run your 12 volt stuff) Security or safety switch all GOOD.

Where it get sideways is those making connections to the 12 Volt connection to run 12 volt equipment. If you OPEN the ground with the disconnect switch, the ground potentially now moves up to the front battery thru your 12 volt equipment. Draw that connection

With the switch OPEN in the disconnected security / safety position AND any attempt to pull a load on the 24 volts leg...say try and start, turn on the lights... the front + 12 volt battery will be the source (can't be 24 volts, the back was disconnected, right), so front -12 volt battery becomes the return or ground thru your 12 volt equipment. This configuration will likely damage the 12 volt equipment. This is the sneak - current not anticipated or a false ground return. Good chance the equipment becomes the "fusible link" and poof.

You could do the disconnect on the positive + 24 volts lead. Again a bad idea should you leave the 12 volt gear on. Now a dead rear battery requiring charging the dead one and then balancing the two. BIG pain in the butt. 60 Amp dudes, raise your hand if your arm pressing - swapping batteries to keep the 12 volts stuff working. Trying to run a QUALITY, reliable 12 volt feed using the 60 Amp system above is problematic.

I too have the 60 amp alternator set up. (and lots of radios) Your choice to use a 24 to 12 volt converter is the way to go (proper capacity/rating). Even better, one that is a battery equalizer. This way at least the two batteries are seeing a balanced charging / discharging condition.

Use best wiring practice and fusing.

Sure, BEST would be the 200 Amp alternator with the 14 volt regulator connection to batteries. To switch up could be the cats meow and big $$$.

I went with the Eaton Sure Power 100 Amp equalizer with excellent results and IMO the best answer to 60 Amp operators. Almost plug and play.

New in the box cheap. Go with what you got, CAMO

 

[Mullaney]

I try to get one's thinker going. AND note everyone has their own way to skin the cat.

Pencil and paper time. Draw out the two batteries. show the front +24 volts going to the truck, the - & + strapping the two together the placement of the switch on the - ground rear battery. GOOD. Move to the front of the class. No copying!

Yes, we / most can do this in our head. You got your back battery and it's ground post is connected to the shunt and down to the real ground stud which is on the starter frame bolted to the engine. SO far so good and for simplicity sake GROUND, breaking that back battery ground with the disconnect breaks the ground and all is good. This set up removes both batteries from providing 24 volts to your rig. (providing NO wonky 12 volt tap to run your 12 volt stuff) Security or safety switch all GOOD.

Where it get sideways is those making connections to the 12 Volt connection to run 12 volt equipment. If you OPEN the ground with the disconnect switch, the ground potentially now moves up to the front battery thru your 12 volt equipment. Draw that connection

With the switch OPEN in the disconnected security / safety position AND any attempt to pull a load on the 24 volts leg...say try and start, turn on the lights... the front + 12 volt battery will be the source (can't be 24 volts, the back was disconnected, right), so front -12 volt battery becomes the return or ground thru your 12 volt equipment. This configuration will likely damage the 12 volt equipment. This is the sneak - current not anticipated or a false ground return. Good chance the equipment becomes the "fusible link" and poof.

You could do the disconnect on the positive + 24 volts lead. Again a bad idea should you leave the 12 volt gear on. Now a dead rear battery requiring charging the dead and then balancing the two. BIG pain in the butt. 60 Amp dudes, raise your hand if your arm pressing - swapping batteries to keep the 12 volts stuff working. Trying to run a QUALITY, reliable 12 volt feed using the 60 Amp system above is problematic.

I too have the 60 amp alternator set up. (and lots of radios) Your choice to use a 24 to 12 volt converter is the way to go (proper capacity/rating). Even better, one that is a battery equalizer. This way at least the two batteries are seeing a balanced charging / discharging condition.

Sure, BEST would be the 200 Amp alternator with the 14 volt regulator connection to batteries. To switch up could be the cats meow and big $$$.

I went with the Eaton Sure Power 100 Amp equalizer with excellent results and IMO the best answer to 60 Amp operators. Almost plug and play.

New in the box cheap. Go with what you got, CAMO

.
Dang Milcommoguy ,

That writeup is about the best explanation of WHY you need an equalizer.
AND is has the best way to attach the disconnect switch I have seen.

Best part is that it seems like you even had fun writing it up too.

 

[Coug]

By isolating the ground side the battery potential is still available in the system.

Remove the ground on your car battery then go to your starter and check voltage from the positive battery lead to ground.

Check it with a “wrench” and you’ll see sparks.

Isolate the positive cable with the disconnect.

that does not make sense to me.
If EITHER of the battery cables are disconnected from the battery, and you are checking from the terminal that is still connected to ANYWHERE in the vehicle that is NOT the opposite battery terminal there should be ZERO voltage. Zip, Zilch, Nada.

It doesn't matter if you disconnect the negative or the positive, once the connection is broken, there will be no way for the current to go anywhere.

The ONLY way I could see there being sparks is if there is a large enough capacitor somewhere in the system that you are shorting to ground somehow. Otherwise, it's not a complete circuit, and no power can possibly flow.


The reason WHY the ground cable is the first one disconnected and the last one connected in modern, negative ground systems, is because if you are loosening the clamp for the cable that runs from negative to ground, and accidentally touch the chassis with the wrench, it won't do anything. If you are loosening the positive terminal clamp and touch the chassis, you'll throw sparks, and possibly arc weld the wrench to the vehicle and burn your hand.

 

[kendelrio]

...you'll throw sparks, and possibly arc weld the wrench to the vehicle and burn your hand.

true story...

 

[osteo16]

Came across this... Now my mind is blown..... Equalizer really screws it all up.. Now I need 2 disconnects..

https://www.waytekwire.com/datasheet/extend%20battery%20life.pdf

 

[INFChief]

that does not make sense to me.
If EITHER of the battery cables are disconnected from the battery, and you are checking from the terminal that is still connected to ANYWHERE in the vehicle that is NOT the opposite battery terminal there should be ZERO voltage. Zip, Zilch, Nada.

It doesn't matter if you disconnect the negative or the positive, once the connection is broken, there will be no way for the current to go anywhere.

The ONLY way I could see there being sparks is if there is a large enough capacitor somewhere in the system that you are shorting to ground somehow. Otherwise, it's not a complete circuit, and no power can possibly flow.


The reason WHY the ground cable is the first one disconnected and the last one connected in modern, negative ground systems, is because if you are loosening the clamp for the cable that runs from negative to ground, and accidentally touch the chassis with the wrench, it won't do anything. If you are loosening the positive terminal clamp and touch the chassis, you'll throw sparks, and possibly arc weld the wrench to the vehicle and burn your hand.

Are you saying that with the negative cable disconnected that you will not get a battery voltage reading by placing the read voltmeter probe on a positive battery post and the black lead to a clean section of the vehicle frame?

 

[Coug]

Are you saying that with the negative cable disconnected that you will not get a battery voltage reading by placing the read voltmeter probe on a positive battery post and the black lead to a clean section of the vehicle frame?

That is exactly what I am saying.
With the meter reading for voltage, you are checking to see what the difference in voltage between the locations where you are placing each of the leads.
With the negative battery cable disconnected, there should be no possible way for there to be any type of voltage differential between the battery positive and the frame.

there HAS to be some type of physical connection between where the probes are, and the battery itself. If there isn't, then there is nothing to measure.



I will admit that you may get some type of reading (but not 24V) between the positive terminal and chassis in the 200 amp or other dual voltage systems, as the 12V stuff shares a common ground with the 24V stuff, and even with the negative cable disconnected there are wires going between the positive terminal of the second battery (which is the same as the negative of the first battery), but the only thing drawing off of that is the transmission control module, which should be turned on/off by a relay, meaning with no 24V power the entire 12V circuit should be disconnected.

 

[Milcommoguy]

Came across this... Now my mind is blown..... Equalizer really screws it all up.. Now I need 2 disconnects..

https://www.waytekwire.com/datasheet/extend%20battery%20life.pdf

Nice research and find OSTEO16 A++++ for doing the homework.

This is a GD paper for understanding the in's and out's of smart battery management. Users of 60 Amp alternators will benefit from a balanced and equalized battery stack. Very important to battery life in this series battery system. And finally, the ability to pull reliability 12 / 14 volts high current loads. (I wouldn't go as far as a 12 Volt winch IMO)

Being a BIG radio guy this is exactly the route I took. Sure, I could have swapped in the 200 Amp set up,... but the converter / equalizer was the cheaper option. (new in the box $125 Ebay find, in store 500 + buck )

In testing it is good to know that the regulation and charging is spot on, even at idle both batteries 14.2 Volts and when pulling 60 amp loads off the 12 Volt buss... Not even a hick-up. Mine is rated at 100 Amps. If you think about it... It is like having both batteries in parallel feeding the 12 volt buss.

As far as 24 Volt requirements in a hobby "plain Jane M998" they are minimal... some lights or led's, couple of solenoids, heater, wiper motor. Glow and start are intermittent and right back to charging / topping off both batteries.

Going on 6 years. Same Cheap-O batteries, $117 each, starts right nOw first time, lots-O-radios, no wOOries.

It does require a little planing...what doesn't. The end result... a working solution for those running 60 Amp alternators. (YES it's can handle it)

NO MORE funky work around's flipping batteries every few months, dead one's, shorter life, etc.

The magic of the device, CAMO

That was a "quick question" > https://www.eaton.com/RU/Eaton/Prod...qualizers/24Vto12VBatteryEqualizers/index.htm

 

[Hammer]

I will admit that you may get some type of reading (but not 24V) between the positive terminal and chassis in the 200 amp or other dual voltage systems, as the 12V stuff shares a common ground with the 24V stuff, and even with the negative cable disconnected there are wires going between the positive terminal of the second battery (which is the same as the negative of the first battery), but the only thing drawing off of that is the transmission control module, which should be turned on/off by a relay, meaning with no 24V power the entire 12V circuit should be disconnected.

Coug,
Here is the 'potential' issue. Only when you have something hooked up via the positive off the first battery for a 12v load.
You disconnect the main negative lead.
It could create a positive ground scenario where the 12v lead pulls from the second battery if you try and run a 12v load. Dumb loads will not have a problem running a positive ground. But anything/everything else WILL have problems.
Having said that, not sure if the TCM would be triggered at all to even try and draw power.
But if you have other 12v loads, and try and turn them on while the main negative lead is disconnected, you have the potential for a positive ground scenario.

I know I am not explaining this right. I need more sleep... But the system still sees and has access to the second battery, just reverse polarization. And that tends to let the magic smoke out.

 

[Hammer]

This concerns me directly, as I have the dual voltage setup, and WILL be running 12v loads, and have the TCM to consider as well.
Disconnecting both the main positive and main negative would seem to be the only safe method.

 

[Action]

I’m not an electrician, but I did stay at a Holiday Inn Express once.
what if the disconnect is put on the link between the batteries? That would cut Neg from front battery and Pos from rear battery. Any 12v accessory hooked to rear battery and turned on, may still get 12v. I also dont know about any electrical components that may link the 2 batteries.

 

[Hammer]

I’m not an electrician, but I did stay at a Holiday Inn Express once.
what if the disconnect is put on the link between the batteries? That would cut Neg from front battery and Pos from rear battery. Any 12v accessory hooked to rear battery and turned on, may still get 12v. I also dont know about any electrical components that may link the 2 batteries.

It works for a few things, but littlerally will let you kill the first battery that is running 12v loads. It won't let any 24v loads happen, as that battery will have no ground. So it is safe in the sense of not killing electronics, but doesn't disconnect the 12v battery.