installing a batt. disconnect switch

[Milcommoguy]

Are any here have an additional connections to the 12 Volt leg of the battery feeding say a radio or ???

Just asking, CAMO

 

[AtlantaSBR]

Are any here have an additional connections to the 12 Volt leg of the battery feeding say a radio or ???

Just asking, CAMO

I have absolutely nothing added to the truck that wasn’t on it when it came from Albany. Former B0625 compressed foam fire truck so maybe something there

 

[Coug]

I have mine on the positive cable, 24 volt side. Zero problems in over a year. I've done it in every military truck I have owned for 10 years.

I have a 4 speed truck with a couple additional 12V loads. Doing just a positive disconnect it won't kill those loads.
The other downside I see with this is if the cable gets damaged or something shorts out in the switch then you'll have the positive cable going to ground. Not a likely scenario under normal conditions, but having it on the ground side is just one less thing to worry about for me.

Up side is you can pick and choose individual circuits that you want to be able to power on with the primary positive cable disconnected, so you can still do things like stereo, internal lights, 12 or 24V accessories (or in my case I could use the lighting and stuff in my BEOD without worrying about anyone driving off with the truck while I'm asleep in the back)

 

[Coug]

Are any here have an additional connections to the 12 Volt leg of the battery feeding say a radio or ???

Just asking, CAMO

I have a 12V circuit going to my 7 pin RV trailer plug (30 amp fused), but that's the only thing there.

I do have my dash camera hardwired to the batteries, bypassing the battery disconnect completely, but it doesn't ground anywhere in the truck so a non-issue.

 

[BEASTMASTER]

y0u can also use a power disconnect switch from a catterpillar machine. you can even use the key switch ,if u want to take the key with u. of course anyone with a CAT key could start you're truck. but if someone wants you're truck they will take it.

 

[Mogman]

Let's try this again, these are a couple quick drawings I posted about 3 years ago , in this example we have a 12V radio, a 24v headlight and the two batteries, we are going to assume current flow from positive to negative to make it easier to understand, in the "normal" drawing you can see 12v flow to the radio and 24V flow to the headlight, the ground for each is shown between them, in the reverse drawing the current flows from the positive side of the high side battery through the headlight (headlight switch on but could be any 24V load) but because there is no ground reference (the low side negative is disconnected by a switch) the current ties to flow backwards through the 12V radio to the negative terminal of the high side battery reverse biasing the radio.

I have been refurbishing Motorola radios for over 20 years, many for volunteer fire departments using old military trucks and have seen many damaged by having the battery switch in the ground lead.

If a relay was installed as described in an earlier post was installed and switched by the 24V ign and all the 12V loads going through the contacts was used then a single ground side switch would work fine.

You could also install a diode in the positive lead of any 12V device to prevent reverse current flow but may devices would not like the additional voltage drop.

I assume the folks that designed the 200A system and the 4L80 controller have taken steps to prevent this kind of damage.

 

[sallystrothers]

I installed a hidden disconnect switch on the ground side mostly as a security device, but I did notice the batteris would still go dead after a while, even with the switch in the disconnect position. To fix it I was going to put it on the 24v side but since I also have a 24v winch on a separate line (optima batteries)I instead put it on the cable connecting the two batteries in series. It stopped the drain and appears to be working.

 

[Action]

I installed a hidden disconnect switch on the ground side mostly as a security device, but I did notice the batteris would still go dead after a while, even with the switch in the disconnect position. To fix it I was going to put it on the 24v side but since I also have a 24v winch on a separate line (optima batteries)I instead put it on the cable connecting the two batteries in series. It stopped the drain and appears to be working.

So what is left on that drains your batteries? Do you have a 24v to 12v converter installed?

 

[Coug]

I agree with Action. The only way the batteries should drain with a battery disconnect on the negative is if something else is hooked up into the system causing a drain.

 

[Bill Nutting]

Let's try this again, these are a couple quick drawings I posted about 3 years ago , in this example we have a 12V radio, a 24v headlight and the two batteries, we are going to assume current flow from positive to negative to make it easier to understand, in the "normal" drawing you can see 12v flow to the radio and 24V flow to the headlight, the ground for each is shown between them, in the reverse drawing the current flows from the positive side of the high side battery through the headlight (headlight switch on but could be any 24V load) but because there is no ground reference (the low side negative is disconnected by a switch) the current ties to flow backwards through the 12V radio to the negative terminal of the high side battery reverse biasing the radio.

I have been refurbishing Motorola radios for over 20 years, many for volunteer fire departments using old military trucks and have seen many damaged by having the battery switch in the ground lead.

If a relay was installed as described in an earlier post was installed and switched by the 24V ign and all the 12V loads going through the contacts was used then a single ground side switch would work fine.

You could also install a diode in the positive lead of any 12V device to prevent reverse current flow but may devices would not like the additional voltage drop.

I assume the folks that designed the 200A system and the 4L80 controller have taken steps to prevent this kind of damage.
View attachment 847159
View attachment 847160

This is another reason to use a 24 volt to 12 volt dc to dc converter and not “half tap” your 24 volt system. There are a lot of posts on the site about this topic. The short answer is, spend a few bucks on the dc to dc converter, install the battery cut off switch on the negative battery connection. In my humble opinion, this is the safest way to handle 24 and 12 volt devices and “kill” the entire truck when you want to know that nothing left on will drain your batteries and leave you unable to start the engine.

 

[osteo16]

So if I leave a 12v accessory on, it won’t draw down the batteries connected to the 24v converter ?

 

[Coug]

So if I leave a 12v accessory on, it won’t draw down the batteries connected to the 24v converter ?

it depends on how you wire it.

If you wire the converter straight to the battery, then yes, it can (if it isn't done with some type of relay).
If you wire it so that the negative side of the converter is on the DC shunt, (basically grounded to the chassis as opposed to the battery) then it will be disconnected also, and there will be no drain.