Can I use main breaker as battery disconnect?

in a previous RV i went to the auto parts store and bought a battery mounted disconnect and put it on the main NEG/grd cable post

with this RV i have not bothered since we full time
and i only temporarily disconnect when testing or servicing the batteries and cables

however i have two of them in my electrical supplies, just in case i need one

The biggest problem is that the 120 VAC breakers are only rated for a few amps, and they are rated at VAC, not the direct current, that tends to ark when exposed to high amperage fault.

Your home is limited to the fault current that can go through the typical #6 wire going from a 10 KW transformer to the home, and it limited to about 25,000 amps maximum fault current. A truck battery can supply more than 25,000 amps for a couple of seconds, and typically will require a fuse to make sure that the device does trip in a high amperage fault.

The 480 volt rated Square D circuit breakers are also rated at 48 VDC, and you could use that type of breaker, but they are the larger frame 'I line' breakers, about 1.5" wide and 6" long. Many times a electric car conversions will have a I-Line circuit breaker in it, rated at 300 amps or so.

You can find DC rated circuit breakers at a place like West Marine. I would rather use a automatic reset circuit breaker like found at Napa Auto, or your local auto parts store. They come in 15 amp to 60 amp ratings with 5 amp steps. Only about $3 - $10 each. In my RV, the generator starter wire is protected by a pair of the 30 amp breakers with a bussbar between them, so it is rated at around 60 amps. You can gang them together.

Good luck,

Fred.

RoyB wrote:
TURBOJIMMY - I originally installed my four position BLUE SEA SWITCHES for other reasons but it turned out they made GREAT BATTERY DISCONNECT switches in the positive side of things.

I like that switch a lot. I don't have a switch to manually put my chassis battery and coach batteries together. This would work nicely, I think.

Thank you for the posts and the diagrams. I definitely will install the switch. I plan to pull the negative cable and see if anything is still powered up to decide which terminal to place the switch.

TURBOJIMMY - I originally installed my four position BLUE SEA SWITCHES for other reasons but it turned out they made GREAT BATTERY DISCONNECT switches in the positive side of things.

ALot of folks like to install the BATTERY DISCONNECT switches in the NEG path but either way works just fine. In the AUTOMOBILES where everywhere is very congested with possible cable short to frame ground areas it makes sense to mount the switches in the NEG PATH so that the wrench you are using on the POS SIDE terminal doesn't touch any frame Ground. My trailers were never that congested so I never worried about that problem.

I was always able in the past finding cheap DONUT TYPE CURRENT TAPS so always used the POSITIVE SIDE cabling for that. Now those type of CURRENT SAMPLE DEVICES are very expensive making one to use an actual HIGH CURRENT SAMPLE LINK which always makes sense to be mounted in the NEGATIVE BATTERY CABLE side. Even this has small wiring going to panels etc so you have to individually fuse those as well to prevent accidental touching a small LCD meter wire to frame ground and burning out the wire. I like the Hall Effect Current Sensor (DONUT TYPE) much better. Then the remote meter panel wiring is all low voltage - low current requirements.

RoyB wrote:
If you are going to work on the 12VDC cabling turn off the converter/charger unit and pull the battery terminals.

After thinking about it, my post was a bit of a brain fart. Pulling the converter fuses stops the 12V from the converter to the fuse panel, but not from the batteries to the fuse panel. As you said, you'd have to disconnect the batteries AND the converter (unplug from shore power) in order to kill the 12V voltage completely.

Mine has circuit breakers (the auto-resetting type, not what you would envision as a 120V breaker) where the 12V comes into the rig from the batteries. I had thought about putting a disconnect switch there to prevent parasitic battery drain while I'm parked but never got around to it.

If you are going to work on the 12VDC cabling turn off the converter/charger unit and pull the battery terminals.

Both the CONVERTER/CHARGER unit and the BATTERY TERMINALS feed the same point on the 12VDC Distribution wiring panel.

Here is an simplified 30AMP WIRING BLOCK diagram that may be of some help for you..



My present used 12VDc UPGRADE looks like this which I am in the process of starting a bigger and better upgrade to get more AHs and use some solar panels for daytime charging of the batteries. My game plan here is to use my 255AH battey bank to run all the 120VAC items we want to have from an INVERTER and 12VDC items direct connected to the battery bank. Then will use my 2KW Honda Generator connecected to the trailer shore power cable each morning around 8AM when allowed to run my generator here on the East side of the US to recharge the battery banks back up to their 90% charge state using the on-board PD9260C Converter/charger unit running off the generator 120VAC. This takes around three hours using the SMART MODE charging techniques...

Once re-charged to the 90% charge state then we are good for the next day/night run off the batteries.



Roy Ken

No, the main breaker is 120 volts. Battery is 12 volts DC.
You get various styles of battery terminal disconnects at most auto parts stores and walmart.
Ones like this mounted in battery box works easier then the knife switch style on battery post.
Battery switch

The main breaker is for the 110V not the 12V. There should be a main fuse for the 12V side of things - mine's on my converter.