Battery disconnect questions

[DJL1967]

I bought a new but used battery disconnect switch that came without instructions. Is it better to utilize the ground wire for the disconnect? I have included a couple pics of the switch and also where I would like to put it. By placing it under the propane tank cover it will protect it from the elements, be easily accessible as well as be close to the battery. Any thoughts.
Thanks, Don

[bankr63]

Personally, I would put the switch in a weatherproof box attached to the side of the battery case. If you plan on leaving the terminals exposed like you show in your pictures, there is a chance that you could complete the circuit from the floating neutral to ground (say changing your tank) when the switch is in disconnect mode, and that can spark. Or, for that matter unless it is an explosion proof (sealed) switch, a spark at the switch while engaging inside an enclosed space (under the tank cover) with a leaking propane cylinder could be a risk.

IMO, exposed terminals don't belong in a covered/enclosed space with a propane tank. Call me overly cautious. An appropriate outdoor electrical box is a few bucks at Home Despot.

[Sundancer330]

You can place the switch on either side (pos or neg) and get the same results.

[Doug]

Most applications on a TT call for the switch to control the ground wire.
If you search threads, you will see this result.

D.

[Doug]

Most applications on a TT call for the switch to control the ground wire.
If you search threads, you will see this result.

D.

[DJL1967]

Originally Posted by bankr63

Personally, I would put the switch in a weatherproof box attached to the side of the battery case. If you plan on leaving the terminals exposed like you show in your pictures, there is a chance that you could complete the circuit from the floating neutral to ground (say changing your tank) when the switch is in disconnect mode, and that can spark. Or, for that matter unless it is an explosion proof (sealed) switch, a spark at the switch while engaging inside an enclosed space (under the tank cover) with a leaking propane cylinder could be a risk.

IMO, exposed terminals don't belong in a covered/enclosed space with a propane tank. Call me overly cautious. An appropriate outdoor electrical box is a few bucks at Home Despot.

An outdoor electrical box is a great idea. Thanks I will look into this as an option.

[DJL1967]

Originally Posted by Doug

Most applications on a TT call for the switch to control the ground wire.
If you search threads, you will see this result.

D.

Thanks for the reply. I did do a search before I posted and found varied preferences. Just wanted a few more opinions.

[Mustang65]

Here is how easy you can add your own battery cut off switch.

Parts List:
- Purchase a 4"x4" PVC Electrical Box (Home Depot/Lowes)
- Purchase a 4"x4" PVC Blank Electrical Box cover
- Purchase a 6" or 12" (BLACK) battery cable
- Purchase a Battery Disconnect Switch (You already have one.. like mine)

- Drill holes for switch (in blank cover plate) and 2 in the bottom of the 4x4 box for cables
- Mount the switch in the blank cover plate
- Mount the 4"x4" electrical box to the frame

1. Pull the 30 amp main fuse on the (+) POSITIVE battery cable.
2. Disconnect the existing ground cable from the frame bolt (other end is connected to the negative battery terminal)
3. Sand the frame around the bolt hole to insure a good connection
4. Connect the short (BLACK) cable you purchased to the ground bolt and tighten back to the frame.
6. Push the frame ground cable (other end) through one of the holes in the bottom of the 4x4 electrical box. Connect cable to the Disconnect Switch
7. Push the black battery negative cable through the other hole in the 4x4 electrical box. Connect the cable to the disconnect Switch.
8. Mount the cover with the switch to the 4x4 box
9. Install the 30Amp main fuse
10. Turn on the TT interior lights and hit the switch, if all works as planned continue to item #11, else (put the fuse in)
11. OK, now you can open that beer and admire a "JOB WELL DONE
12. Paint the box black to match the frame.

You could mount the switch to the battery box, but I am not a big fan of having the battery bump against the bolt threads of the switch if/when the battery shifts because of a nasty bump, and the less number of contacts in the battery box the better.

This project should take you about 30 minutes.... an easy job!

Don

My Registry

RVing with SOLAR

[DJL1967]

Thank you very much for the detailed explanation. Much appreciated. This is the way I will go.

[01tundra]

Makes absolutely no difference whether you break the positive or negative side.

All the talk you read about online about breaking the positive side will cause "sparks" is just talk from people who don't have a great grasp of 12VDC systems. If there's any load on the battery, breaking either side "could" cause sparking.

Break whatever side is physically easiest to break, I always break the positive side, but breaking the negative side will work as well......makes zero difference.

I did not break the emergency brake positive wire through the switch though, that way if I ever forgot to turn the switch on I'd still have brakes. If you broke the ground your emergency brake switch would not work if the TT got away from the TV and the master switch was turned off.....that's why I break the positive side, less the break away switch lead.

[RoyBraddy]

Be aware what the disconnect switch does. I have one on my setup in the POSITIVE leads but even when it is activated I still have DC connections going to the tongue Jack and Breakaway switch assembly. These two items have a ON-OFF control switch and will not drain my batteries...

I did not want to have my BATTERY DISCONNECT switch activated when traveling over Public Roads and also have my Break-Away Switch function disabled that would apply DC Voltage to the Electric Brakes if the trailer became disconnected when in travel mode.

Installing the disconnect switch in the Negative Path of the battery will most likely remove all 12VDC operations for your trailer. The work-around if you go this route is to have these functions you want AVAILABLE all the time wired directly to the battery terminals both Positive and Negative terminals...

Just be aware...

Roy Ken

[01tundra]

^ exactly my point. And it will render the e-brake box unfunctional if the switch is accidently left off while traveling and the negative side of the battery is broke through the diconnect switch.

The even goofier reason I see people stating why to break the negative side is because "they tell you to always remove the negative side of the battery first".....apples and oranges. It is recommended to pull the negative side first when removing a battery from service because if you pull the positive lead and accidently drop it on the chassis it will short out because the negative side of the battery is still connected and completes the circuit. If you remove the negative first and accidently drop it on the chassis no short will occur - has absolutely nothing to do with which lead to break on a disconnect switch.

[Mustang65]

The main reasons for my choosing the NEGATIVE cable for the Disconnect Switch on the negative cable is the convenience. You only have to purchase a Marine switch and a 6" automotive battery cable. I had the disconnect switch for another project so I needed to put it in a 4x4 PVC electrical box which I caulked the cover plate to the box before screwing it on. Has been on for 5 years now with no issues.

The only other connection to the batteries NEGATIVE post is the Emergency Break-away switch and the inverter.

With the gasses produced by the charging batteries in the enclosed battery boxes, and depending on the type of switch selected, I do not want to put any additional connections, so I chose the frame mount.

Don

My Registry

RVing with SOLAR

[01tundra]

If breaking the ground wire, one could always run a dedicated ground wire from the E-brake switch to the negative terminal on the battery and not break it though the switch.

[DJL1967]

Thanks everyone for your well informed responses. I made this box up last night and will go ahead and install it this week. Again, thanks for all the help.