Unhooking Battery Hooking up Battery

[RedsToy]

I saw a post somewhere here that stated there is a very specific way of unhooking the cables from the battery. Specifically Negative first when Unhooking then Postive. And reverse this when hooking up. The post or comment made also stated that you have to do it this way. as on motorhomes if you don't you will have problems. Can anybody validate this? Thanks

 

[DonTom]

I say a post somewhere here that stated there is a very specific way of unhooking the cables from the battery. Specifically Negative first when Unhooking then Postive. And reverse this when hooking up. The post or comment made also stated that you have to do it this way. as on motorhomes if you don't you will have problems. Can anybody validate this? Thanks

It is ONLY for safety reasons. Since most vehicles are a negative ground to the frame, you remove the negative side first because it cannot short to ground as it is already grounded. After it is removed, if you short the positive to the frame, nothing happens because there is no return path.

In a positive grounded vehicle (very rare these days) the positive should then be removed first for the same reason.

If one is very extra careful, it makes no difference which you remove first. But it is a very good habit to remove the frame grounded side first regardless if it's a negative or positive ground.

-Don- Auburn, CA

 

[Mark_K5LXP]

BUT (don'tcha love the "but"?) some inverter models specify to disconnect the positive first, contrary to standard automotive convention of negative first. From what I understand this is to prevent an undesired current path through the equipment ground, I'm guessing maybe through the chassis battery (it can't be the house battery, there should only be one grounded terminal there). So which terminal you disconnect first can depend on what equipment is installed and what their recommended procedure is. I wish I could tell you the make and model of the inverters (I didn't pay attention, I don't have one) but probably the best way to go would be to identify the equipment in your RV and verify their specific connection procedures. At that point I'd make a permanent label of which to disconnect first for service in the battery compartment.

Mark B.
Albuquerque, NM

 

[Kirk]

Can anybody validate this? Thanks

It is ONLY for safety reasons.

It is mostly for safety reasons. But you can damage other things in your modern electronics controlled vehicles if you cause even a small arc with a tool and that will not happen if you always remove the negative cable first and put it on last. If you trace that cable you will see that it goes to the chassis frame.

In a positive grounded vehicle (very rare these days) the positive should then be removed first for the same reason.

I can't remember the last time that I saw any motor vehicle that had a positive ground. The last US auto manufacturer changed to negative ground in 1955. From an electronics point of view, virtually all modern semiconductors operate with a positive supply and negative 'ground'. Attempting to fit these systems in a positive ground vehicle would be almost impossible.

 

[Mark_K5LXP]

Not that hard really, you just have to isolate the equipment chassis or power them with a DC-DC converter. Back in my previous life it wasn't uncommon in the 2-way radio business to install radios in positive ground heavy equipment - dump trucks, cement mixers, bulldozers, garbage trucks. Not sure how much if any of that kind of equipment is still positive ground, it's just asking for trouble to have something like that in a fleet of vehicles.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

LOL! Ask a simple question and get far too much information as folks jump in to warn about obscure conditions.

Yes, disconnect the ground (negative terminal) first. And remove shore power [or turn off genset] so there is no power feeding into the battery.

 

[Rene T]

Disconnecting the ground first is the safest way but if you are super careful, you can get away with doing the positive first. I do it all the time but I know what will happen if I screw up and make contact with ground. Just know what you’re doing.

 

[Mark_K5LXP]

Not really "obscure", this wasn't hard to find. From the Magnum Energy installation instructions:

CAUTION: When connecting battery power to the inverter all battery negative connections must be connected prior to the battery positive connections. When removing battery power from the inverter, the battery positive should be removed before any battery negative connections are disconnected. This prevents any communication/chips/lines from becoming the DC return path to the battery -- causing permanent damage to all connected accessories.

Reading this literally though it's specific to the inverter connection and not the battery terminals themselves. I think a large part of the issue here is that under the right conditions the inverter can also source current, so opening up the negative path could result in things being powered or in a way you may not want them to. I would consider disconnection of an inverter positive lead a "hazard" as well unless there was some means to open the circuit first, so I think positive or negative battery lead first requires a review of the installation. IMO the predominant issue here is more about system connections outside of the battery or inverter and this is just their way of minimizing collateral damage that they might get blamed for (hence the CAUTION in the manual).

Mark B.
Albuquerque, NM

 

[Lou Schneider]

Disconnecting the ground first is the safest way but if you are super careful, do the positive first. I do it all the time but I know what will happen if I screw up and make contact with ground. Just know what you’re doing.

Sorry Rene, but there is absolutely no reason to disconnect the hot terminal first. When you disconnect either terminal the circuit is broken and you've removed the battery voltage from the rest of the RV.

 

[uchu]

Isn't that the same logic that goes when jumpstarting a car?

1. Red cable to positive terminal in discharged battery.
2.Red cable to positive terminal in charged battery.
3. Black cable to negative terminal in charged battery.
4. Black cable to ground (exposed metal) in vehicle with discharged battery.

 

[Lou Schneider]

Isn't that the same logic that goes when jumpstarting a car?

1. Red cable to positive terminal in discharged battery.
2.Red cable to positive terminal in charged battery.
3. Black cable to negative terminal in charged battery.
4. Black cable to ground (exposed metal) in vehicle with discharged battery.

Yes, the logic is there's no possibility of current flow until the final connection is made.

 

[RedsToy]

Negative first as was always my thought. I was brought up with a mechanic father. I was just asking if there was something diff with motor homes as somebody had posted something somewhere that just didn't make sense to me. Thanks for all the input. Have a great day. Let's bow our heads and pray that Ukraine can survive without any more death and destruction. Peace to all.

 

[RedsToy]

LOL! Ask a simple question and get far too much information as folks jump in to warn about obscure conditions.

Yes, disconnect the ground (negative terminal) first. And remove shore power [or turn off genset] so there is no power feeding into the battery.

So, so true! It makes me smile how that happens.

 

[DonTom]

It is mostly for safety reasons. But you can damage other things in your modern electronics controlled vehicles if you cause even a small arc with a tool and that will not happen if you always remove the negative cable first and put it on last. I

100% for safety. Which includes "safety" to the equipment.

As for vehicle positive grounds, I have seen many while I was working. Fire engines, fire trucks, etc. But I didn't know the age of these vehicles.

But I know of no cars, motorcycles or RVs that use a positive ground. But I do know some EVs, such as my Zero motorcycles do NOT use a ground at all. Not even on the 12 volt lights after the DC2DCC. Uses a "floating ground", which means a common wire. Cannot use the frame for a negative wire on a voltmeter to anything. So I use the headlamp low side to check voltages.

I think EVs with a metal frame make sure there is no possible return path to ground in case metal tools need to be needed to pry somebody out after an accident. Not really needed on a motorcycle where such cannot apply. Perhaps is a law and they didn't make an exception for motorcycles, but I really don't know.

-Don- Auburn, CA

 

[uchu]

Let's bow our heads and pray that Ukraine can survive without any more death and destruction

Amen to that . There are several organisations where you can donate and help the Ukrainian people.

 

[Rene T]

Sorry Rene, but there is absolutely no reason to disconnect the hot terminal first. When you disconnect either terminal the circuit is broken and you've removed the battery voltage from the rest of the RV.

I did say that removing the ground first is the safest way and that if you’re super careful you can get away with removing the positive first. I emphased that because I think the majority of the people here may disconnect once every ten years or longer and they will forget but if they are super careful lit will work.

 

[Henry J Fate]

I loosen the cables up and pull them off simultaneously to avoid threads like this.

I is a electrecal genious

 

[Old_Crow]

100% for safety. Which includes "safety" to the equipment.

As for vehicle positive grounds, I have seen many while I was working. Fire engines, fire trucks, etc. But I didn't know the age of these vehicles.

But I know of no cars, motorcycles or RVs that use a positive ground. But I do know some EVs, such as my Zero motorcycles do NOT use a ground at all. Not even on the 12 volt lights after the DC2DCC. Uses a "floating ground", which means a common wire. Cannot use the frame for a negative wire on a voltmeter to anything. So I use the headlamp low side to check voltages.

I think EVs with a metal frame make sure there is no possible return path to ground in case metal tools need to be needed to pry somebody out after an accident. Not really needed on a motorcycle where such cannot apply. Perhaps is a law and they didn't make an exception for motorcycles, but I really don't know.

-Don- Auburn, CA

Lets see. 38 Packard, 46 Chevy, and on the motorcycle side, my wife's old 57 Triumph chopper was positive ground when we first got it.

When we did the Packard, we sent the original electric dash clock out for an overhaul. They re-wound it for negative ground. The clock was supposed to ground though the mounting bracket and contact with the dash. It was extremely entertaining re-engineering the mounting system so the case was insulated from the metal dash. Always fun taking a grinder to fresh custom paint.

 

[RedsToy]

Well, anyways. I just bought two Golf Cart batteries. Man those suckers are heavy. I would bet over 70 pounds each. That adds alot of extra weight to the rig. But, I can't wait to get them installed and working. Should I put each one on a charger for a couple of hours before installing them? And is there a better technique to charge these batteries? Should I start on low charge then test the batteries? Or is there a better way?
Thanks

 

[Mark_K5LXP]

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