Battery Disconnect: Between TT and TV

travelingjw · 02-23-2018, 01:44 PM

Once again I forgot to disconnect my umbilical cord and drained the battery on my tow vehicle. I am looking for a simple way to install a disconnect switch so I don't have to unhook the umbilical when attache; I want to mount the switch in plain site. I want to make sure this is a high quality installation as I am not happy about adding another potential failure point between my tow vehicle electrical power and my TT brake lights, etc. Thanks for any comments or suggestions.

I have viewed the "disconnect" discussions but they all seem to focus on disconnecting the travel trailer battery from the trailer itself...maybe I am missing something basic. Won't be the first time

.

(FYI, tried searching forum for this but could not find; though I am sure it must have been covered before).

GrumpyDad · 02-23-2018, 04:40 PM

I suppose any of the normal battery disconnect switches would work, although I've never heard of anyone doing this. Isn't it easier to just pull the plug out of the 7-way, or am I not understanding this properly?

This is the type I've used before for battery disconnects. Easy to mount and use.

**Mustang65** · 02-23-2018, 07:06 PM

If you forget to unplug the TT from the TV, you are going to forget to use the disconnect switch. Put an reminder in your phone to disconnect the cable and have it remind you everyday at the same time, this way you do not have to remember to reactivate the reminder.

You could hang a big cardboard sign in the TT doorway, so you hit your head on it when you enter the TT. If you put the sign up each time.

If you know anything about electronics, you can build a circuit that would cut 12VDC power to the TT when the ignition is turned off. Easy project!

Parts
1 - 12VDC 30 amp automotive relay ($5)
1 - 20' length of 16AWG wire
1 - Package of female wire connectors for the relay wiring

The ignition wire will activate the relay and your TT will have power, turn off the ignition and relay loses power... cutting power to the TT.

The last one would make life sooooooo much easier.

Don

My Registry

RVing with SOLAR

RayPayne · 02-23-2018, 09:24 PM

I take the relay approach. Cut the constant power on your 7 pin and pass it through a relay fed by ignition switched power. The only way you can flatten the TV is if you leave the ignition switch on.

Cranetech · 02-23-2018, 10:04 PM

Try looking at something like this.... When the voltage reaches a certain voltage it will shut off preserving battery.... Low voltage dissconnect..Low Voltage Disconnects - Littelfuse

**Mustang65** · 02-24-2018, 06:37 AM

Quote:

Originally Posted by RayPayne

I take the relay approach. Cut the constant power on your 7 pin and pass it through a relay fed by ignition switched power. The only way you can flatten the TV is if you leave the ignition switch on.

The problem with these setups is that the voltage monitor will slowly drain your battery also, something like the parasitic drains in the TT's.

Don

My Registry

RVing with SOLAR

mjlaupp · 02-24-2018, 07:42 AM

Install a battery isolator in the TV: https://www.etrailer.com/Accessories.../TR118665.html

Bassdogs · 02-24-2018, 08:15 AM

Also have to ask, why not just remember to pull the pigtail?? Forget one, forget the fix. Easier to just train yourself to pull the pigtail. I would also suspect you might have an inadequate TT battery that is causing such a rapid drain on the TV battery. Don't see any reason you would be having this problem with just one overnite unless you are dealing with below 0 temps. The biggest draw on the 12v is the furnace fan. A few lights for the evening and other 12v uses isn't going to drain either the TT or the TV battery unless one or both is already weak. After a tow of 150 miles or more, your batteries should have topped off. How old are your batteries??

Advice: have your batteries checked and train yourself to unplug the pigtail. Problem solved!

RayPayne · 02-24-2018, 10:23 AM

Quote:

Originally Posted by Mustang65

The problem with these setups is that the voltage monitor will slowly drain your battery also, something like the parasitic drains in the TT's.

Don

I've had battery isolators that leaked enough power to slowly flatten the battery, but not the relay. The relay with the trailer on the normally open circuit only draws power to bridge the trailer power when the ignition is on. If you install it properly, it should have a zero draw for the trailer wiring when the ignition is off, regardless of how long they are connected.

retiredtech · 02-24-2018, 11:26 AM

That so-called charge wire on the 7 pin trailer connector is kind of a joke. It's there to supposedly keep the trailer battery charged while on the road. But it's never going to put out a sufficient charge voltage, because the truck's charge system is in control and monitoring its own battery which is always going to be fully charged. At best, it will only float charge the trailer's battery.

My point is an RV has its own charge system, unlike utility trailers. If I couldn't remember to pull the cable when camping, I think I know what I would do...

Bassdogs · 02-24-2018, 12:02 PM

Quote:

Originally Posted by retiredtech

That so-called charge wire on the 7 pin trailer connector is kind of a joke. It's there to supposedly keep the trailer battery charged while on the road. But it's never going to put out a sufficient charge voltage, because the truck's charge system is in control and monitoring its own battery which is always going to be fully charged. At best, it will only float charge the trailer's battery.

My point is an RV has its own charge system, unlike utility trailers. If I couldn't remember to pull the cable when camping, I think I know what I would do...

Understand your logic, bit my real world experience says otherwise. On our multi day road trips we overnite about 99% of the time at a WMart or similar retailer lot. We generally drive about 300 - 350 miles per day and leave home with a full charge. Most of our longer drives are done during winter months and many times face overnite temps in the teens or lower. The furnace pretty much runs most of the nite. Under these circumstances I unplug the pigtail so that in a pinch I can plug it in if the onboard battery is down. With 2 good 6v's that is rarely necessary and after another day of driving we stop with a 90% or higher charge on the TT batteries.

GrumpyDad · 02-26-2018, 10:56 AM

Quote:

Originally Posted by Bassdogs

Understand your logic, bit my real world experience says otherwise. On our multi day road trips we overnite about 99% of the time at a WMart or similar retailer lot. We generally drive about 300 - 350 miles per day and leave home with a full charge. Most of our longer drives are done during winter months and many times face overnite temps in the teens or lower. The furnace pretty much runs most of the nite. Under these circumstances I unplug the pigtail so that in a pinch I can plug it in if the onboard battery is down. With 2 good 6v's that is rarely necessary and after another day of driving we stop with a 90% or higher charge on the TT batteries.

Wonder if different trucks charge at different amperages? My experience is that two hours of driving doesn't do much at all to charge my two 6V deep cycle batteries.

I guess like a lot of things, "it depends" is the real answer. I say for anyone who isn't sure, you shouldn't rely on your tow vehicle to completely charge your batteries while driving. Plan on a charge from shore power or a generator every three days or so, less in cold weather.

Bassdogs · 02-26-2018, 02:14 PM

Quote:

Originally Posted by GrumpyDad

Wonder if different trucks charge at different amperages? My experience is that two hours of driving doesn't do much at all to charge my two 6V deep cycle batteries.

I guess like a lot of things, "it depends" is the real answer. I say for anyone who isn't sure, you shouldn't rely on your tow vehicle to completely charge your batteries while driving. Plan on a charge from shore power or a generator every three days or so, less in cold weather.

Note my example talked about a drive of 300-350 miles not 2 hours. Two hours charge on just about any charger isn't going to recharge a discharged battery. My trucks have been Silverado 1500 and now a 2500HD.

GrumpyDad · 02-26-2018, 03:54 PM

Good call, I wasn't reading closely, and I was thinking about my own situation where the drives are shorter. I guess depending on your speed that would be six hours or so. I don't travel that far often in one day.

Jagiven · 02-26-2018, 05:28 PM

Not sure about a Chevy, check your owners manual. On my dodge all I have to do is move a fuse. One position the aux is always hot. The other position, it is only hot, while the engine is on.

I have heard, on Ford's you have to install a relay.

Atlee · 02-26-2018, 05:31 PM

Maybe Ford changed, but in 2014, all I had to do was install the fuse that Ford had in a plastic bag in the glove box.

Didn't have to add anything else. Also, with the Ford, if the key is off, the connection between the chassis battery and the plug is dead. Turn on the key, and the connection is live again.

Quote:

Originally Posted by Jagiven

Not sure about a Chevy, check your owners manual. On my dodge all I have to do is move a fuse. One position the aux is always hot. The other position, it is only hot, while the engine is on.

I have heard, on Ford's you have to install a relay.

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