Unhooking Battery Hooking up Battery

[Kirk]

Mark B

I agree with Mark and am wondering about the test you have in mind? Might you just be thinking of using them as the test?

 

[RedsToy]

Typical GC2's are about 65lbs. If they're new then they should already be charged. If you want to top them off just to be sure then fine. The "best" technique is using a multistage charger and letting it operate to completion. What "test" are you interested in doing?

Mark B.
Albuquerque, NM

Oh, I was just saying, test to see where the batteries are at charge wise. Nothing else. Sorry should of been more clear. Thanks tho!

 

[DutchmenSport]

I found this interesting regarding disconnecting the positive first and then the ground, especially for inverters.....

BUT, BUT, BUT??? If you have a cut off switch between the battery and the inverter and the switch is "off", does it really matter then which is disconnected first (provided you don't touch the positive first to anything grounded)?????

Since reading this thread, I realize the inverter cut-off switch is plumbed into the Positive side of the battery. I guess I never really payed attention to that before.

It's the red switch right in the middle of the photo:

https://imgur.com/gTvxa6p

 

[DonTom]

BUT (don'tcha love the "but"?) some inverter models specify to disconnect the positive first, contrary to standard automotive convention of negative first.

That falls under:

"There is an exception to every rule".

We can always find that exception if we try hard enough. And many here are trying hard.

But the OP asked about batteries, not inverters.

-Don- Auburn, CA

 

[Lou Schneider]

I found this interesting regarding disconnecting the positive first and then the ground, especially for inverters.....

BUT, BUT, BUT??? If you have a cut off switch between the battery and the inverter and the switch is "off", does it really matter then which is disconnected first (provided you don't touch the positive first to anything grounded)?????

Since reading this thread, I realize the inverter cut-off switch is plumbed into the Positive side of the battery. I guess I never really payed attention to that before.

It's the red switch right in the middle of the photo:

https://imgur.com/gTvxa6p

Opening the circuit ANYWHERE stops the current flow. The reason to disconnect the negative first is strictly so your wrench doesn't arc-weld itself into place and/or turn red hot if it accidentally gets between the battery pole and any part connected to the grounded chassis.

A disconnect switch has nothing to do with a shorted battery wrench.

 

[DutchmenSport]

...

A disconnect switch has nothing to do with a shorted battery wrench.

Absolutely agree. I have always disconnected the negative first on everything, ever since I was 13 years old working in my uncles gas station.

What I found interesting was, if the inverter has to be connected from the positive side of the battery first, the manufactures of my Montana wired it that way, as the cut off switch cuts off the positive side. So, if disconnecting the battery from my camper, I just need to make sure I flip the positive red wire going to that switch to disconnect the positive first. Once it's switched off, then it doesn't matter which side of the battery itself is disconnected, AS FAR AS THE INVERTER is concerned then.

But yes, it has always been the rule to disconnect negative fire. I had no clue disconnecting an inverter meant disconnecting the positive first. Well, that makes 100% logical sense then WHY the RV manufactures put the cut off switch to the inverter then, on the positive side? I didn't know until reading this thread. I guess a 66 year old retired old fart can learn something new!

 

[Mark_K5LXP]

The problem is there are too many unknowns as far as installation variables. "Most" of what you see is straightforward with equipment connected to a single battery positive bus and there's a single battery negative to chassis ground. In that case it doesn't matter which you'd disconnect first, "open" is "open". Now, here's the "but" - add in that some connected equipment may also source current instead of just sink it. Let's throw in a salesman switch/solenoid that has connections on both the switched and the battery side - what's hot and what's not, and when? Some battery monitors have sensors connected directly to individual batteries. How are they isolated? And for good measure include a chassis battery that is likely grounded somewhere other than the house battery ground point but likely might have a positive connection to the house batteries - sometimes. Solar controllers are usually directly connected to one or both sets of batteries. Just with the above scenario, what do you disconnect first? Depending on exactly how things are physically connected it's not just possible but likely there are "inadvertent" current paths through or across points you may not want or expect to have just by lifting one battery lead. So for this kind of situation the inverter manufacturer is covering their arse by disconnecting their stuff with it's positive supply lead first, then even if something is still energized (or from their perspective is damaged) it's not really their issue.

Mark B.
Albuquerque, NM

 

[billwild]

One helpful hint. Before disconnecting any cables, take a picture of all the connections from above the batteries so you can easily hook up later on. Helped me.

 

[KenTep]

The problem is there are too many unknowns as far as installation variables. "Most" of what you see is straightforward with equipment connected to a single battery positive bus and there's a single battery negative to chassis ground. In that case it doesn't matter which you'd disconnect first, "open" is "open". Now, here's the "but" - add in that some connected equipment may also source current instead of just sink it. Let's throw in a salesman switch/solenoid that has connections on both the switched and the battery side - what's hot and what's not, and when? Some battery monitors have sensors connected directly to individual batteries. How are they isolated? And for good measure include a chassis battery that is likely grounded somewhere other than the house battery ground point but likely might have a positive connection to the house batteries - sometimes. Solar controllers are usually directly connected to one or both sets of batteries. Just with the above scenario, what do you disconnect first? Depending on exactly how things are physically connected it's not just possible but likely there are "inadvertent" current paths through or across points you may not want or expect to have just by lifting one battery lead. So for this kind of situation the inverter manufacturer is covering their arse by disconnecting their stuff with it's positive supply lead first, then even if something is still energized (or from their perspective is damaged) it's not really their issue.

Mark B.
Albuquerque, NM

The installation manual for the Magnum ME-BMK (B_attery M_onitor K_it) includes the warning mentioned in a prior post:

"Ensure all battery negative circuits are always connected before connecting or disconnecting battery positive. This prevents any communication chips/lines from becoming the DC return path to the battery—causing permanent damage to all connected accessories."

There is a link to the manual here: Battery Monitor Kit | Magnum Dimensions

The wiring diagram on page 4 of the manual connects the ME-BMK's Sense Module directly to the battery bank (through a 2 amp fuse). Although it isn't 100% clear in the diagram, it appears that the Sense module's connection to the battery bank may remain if the battery cables are disconnected.

The ME-BMK is connected via a network cable to the Inverter and (if present), the AGS, and the Inverter Remote Control. Perhaps the Inverter through the network-cable to the ME-BMK to the negative-battery-terminal is the referred to return path.

 

[John From Detroit]

One helpful hint. Before disconnecting any cables, take a picture of all the connections from above the batteries so you can easily hook up later on. Helped me.

I will double down on that.. Also not for battery to battery jumpers bot for the main Positive wire and the main ground wire Paint, Nail polish or some other way of coloring them (If not already colored) RED for Positive. black for negative.. Testors spray is good. over spray onto the battery does not hurt as you simply match the colors.

 

[COCJ]

Regarding the issue of possible inverter damage by disconnecting the negative cable first, does that apply to the chassis battery, too? When changing the chassis battery, would it be a good idea to turn off the main power switch for the house system? I have a Mercedes Sprinter chassis and the positive cable connection has several cables connected to it.