Installing a battery disconnect switch. Do I need to disconnect the starter?

[heymccall]

That’s unusual, at least in the ham radio and electrical world. You never switch the negative. In fact, the instructions provided by Deere service indicate that I should switch the positive.

Your situation might be different. I don’t rightly know.

All of my Deere TC54H, 544J, & 544K have a disconnect switch on the battery ground.
My Komatsu WA270-7 & WA270-8 have a disconnect on the battery ground.
Every one of my Caterpillar excavators has a disconnect on the battery ground, as do all of my Takeuchi excavators.

 

[Delmer]

I don't know why you wouldn't disconnect the ground in Ham radio. In AC wiring, you never disconnect the NEUTRAL, which is grounded, but that's entirely different.

In vehicles you always disconnect the ground first, because if you touch the ground to ground, there's no big spark. But if you accidentally touch the positive to ground then there is a big spark. Ground disconnect fails to ground, and your battery goes dead eventually, and you lose the benefit of the disconnect. Positive disconnect fails to ground and you have a fire.

 

[cuttin edge]

Any of our newer Cat stuff has a light beside the master switch that tells you when you can turn it off. Not sure how Volvo works, even after you kill the power, you can hear the DEF draining back to the tank. I think the trucks drain back with air. I think most stuff after a certain year comes with a master switch standard anyway. I assume any electronics in the cab still have power as you don't have to reset anything. Even the older loaders keep time and presets on the radio, and dash with the master off.

 

[1466IH]

That’s unusual, at least in the ham radio and electrical world. You never switch the negative. In fact, the instructions provided by Deere service indicate that I should switch the positive.

Your situation might be different. I don’t rightly know.

I would really like to see a copy of these instructions. I have worked on thousands of pieces of equipment and have never heard or seen a disconnect on the positive side of the system other than the master solenoids on a lot of 24VDC equipment but those are not a true disconnect. Not saying there isn't something out there but I have never seen it.

 

[John C.]

It's funny this comes up as I was in process of putting a video together on the subject. I have some photos of a couple of Komatsu battery disconnect switches. These are installed on nearly all Komatsu brand heavy equipment. They are the type that disconnect the batteries when the key is turned off.



Do you notice a difference? The one on the left side disconnects the batteries on the negative side.


The one on the right has insulators installed on the base of the switch and disconnects the batteries on the positive side.


What makes this more confusing is that Komatsu changed suppliers and the switches look completely different now. On top of all that, they have added a manually operated key switch that you can use to shut off the electrical system as soon as the green light that indicates the DEF is finished being pumped back into the tank goes out.

 

[Willie B]

If electrons are negatively charged, they come from the negative terminal of the battery. The "ground" cable conducts all the power in the machine.

Instructions to disconnect a battery always begin with the "ground" cable because you can't arc it out with the wrench that way.

I believe negative ground works as well as positive ground that was once common. All of the battery disconnects I've ever seen have ground cable switches.

 

[John C.]

Did you look at the photos above? One is a positive side disconnect.

 

[Tones]

Manual battery disconnect goes between (-) and frame. That kills everything from power.
Easy, peasy.

Exactly.

I have to disagree there fellers. If there is a wire shorting somewhere then the battery will still go flat. Fitting at switch to the (+) stops that happening.

 

[Willie B]

I have to disagree there fellers. If there is a wire shorting somewhere then the battery will still go flat. Fitting at switch to the (+) stops that happening.

Gee Ma, electrons only flow from a battery in a complete circuit. They move from the negative post usually these days to the frame of the machine. Interrupting either cable stops the flow of electrons. I don't believe it matters which you interrupt, but stopping near the battery connection to frame eliminates the risk of a short circuit from positive causing a problem. I have seen positive cables passing through sharp holes in sheet metal inches from their end. If the "ground" is disconnected no harm.

 

[heymccall]

I have to disagree there fellers. If there is a wire shorting somewhere then the battery will still go flat. Fitting at switch to the (+) stops that happening.

You wanna try that again?

 

[alaskaforby4]

Most all our equipment is Negative disconnect. We do have a 90 Pete with positive side switch. We use a few plow trucks for 2/3rds of the year and I usually just pull the neg (-) off. while they sit for summer. I've had a parasitic draw on one of the trucks draining battery 100% dead, happened 2 years in a row. I pulled the positive connection last season and it fired right up this year.

 

[cuttin edge]

I don't know why you wouldn't disconnect the ground in Ham radio. In AC wiring, you never disconnect the NEUTRAL, which is grounded, but that's entirely different.

In vehicles you always disconnect the ground first, because if you touch the ground to ground, there's no big spark. But if you accidentally touch the positive to ground then there is a big spark. Ground disconnect fails to ground, and your battery goes dead eventually, and you lose the benefit of the disconnect. Positive disconnect fails to ground and you have a fire.

I was always taught to remove the ground first on a car battery, and then the positive cable. For AC power it was your hot wire first, then your neutral, then ground last. Most master switches I have seen are to disconnect the ground. Perhaps in some electronic situations, maybe the manufacturer requires a positive disconnect, like the switches shown from Komatsu?

 

[edgephoto]

Install a disconnect where it is the most convenient for you to use it. You just need to open the circuit.

A battery that is dirty on top or between the terminals can cause it to go dead. Rare but it does happen. Just keep things clean.

 

[Swetz]

A battery that is dirty on top or between the terminals can cause it to go dead. Rare but it does happen. Just keep things clean.

Not as rare as you think, and a good point as well. I have seen plenty of batteries that you could read a voltage across the top of the battery. For sure, no matter how the cutoff is wired, it will not stop the battery from going dead if this condition exists!

 

[emmett518]

Btw, Deere specifies to leave power on for 10 minutes to let the Def system to do its thing. Turning power off early could freeze up the system.

 

[Willie B]

My father, like all fathers was older than me. He remembered rubber battery boxes, glass, and finally plastic. Stored batteries were NEVER allowed to sit on a gravel, or concrete floor. He looked for a cool dry place, cleaned the top of a battery. Batteries were removed from vehicles that wouldn't be used in winter, moved to a dry cellar & charged monthly.

 

[Willie B]

Ben Franklyn didn't at first know which direction electrons flow. He thought they flowed from a place of surplus "+" to a place of deficit "-". He later discovered electrons negatively charged do the traveling. They leave the negatively charged terminal of a battery, return to the positively charged terminal.

It makes little difference which cable you interrupt, but if you interrupt non grounded cable, do it very close to the battery.