Brand new battery

jimmerz · 05-03-2020, 04:05 PM

So i finally bought a new battery and installed a battery disconnect switch so i get more life out of this battery. My question is, when connected to shore power can i switch my battery off?

I know this is mostly for storage, just curious.

Thanks

Aceallenk · 05-03-2020, 04:22 PM

Yes. and your DC stuff like the lights, water pump, etc, will still function because of your charger

Rrizz · 05-03-2020, 04:38 PM

But doesn't that mean the battery will not charge while on shore power as well? I'm not sure how the battery disconnect works....

woodwalker · 05-03-2020, 04:46 PM

Quote:

Originally Posted by jimmerz

So i finally bought a new battery and installed a battery disconnect switch so i get more life out of this battery. My question is, when connected to shore power can i switch my battery off?

I know this is mostly for storage, just curious.

Thanks

Leave it on except when storing, it will not charge when plugged in if it is wired properly

Rrizz · 05-03-2020, 04:52 PM

Just looked at one. It appears it is a simple line break on the negative side of the battery.
This means when it is off, battery will not charge from tow vehicle OR shore power. Depending on the make/age of your rv, some of your 12v items may not work either.....

Monday blues · 05-03-2020, 04:57 PM

Hey guys, the only thing I would add is don't plan on your tow vehicle keeping the battery charged. It has been explained to me from a tech at a trailer company that the " charge line " on your tow vehicle doesn't really " charge " the battery. I was having issues with batteries going bad on my dump trailer and that is what I was told. If you are going to shut the batteries off I would advise to run a battery maintainer on them. Did this on the dump trailer and the results were astounding.

Hope this makes sense and helps!

backcountrycamp · 05-03-2020, 06:08 PM

That's not true. If you have a properly wired 7-pin connector, and the +12V "Aux" line is connected to VCC on your vehicle (which it should be) and likewise on your trailer, then the tow line will absolutely charge your battery. I've had plenty of road trips where that was my only charge source and I ended with a full charge. Your battery will charge any time the voltage on the bus exceeds its internal voltage by enough to overcome its internal resistance. Your vehicle voltage is whatever your alternator is putting out. It's enough to charge your vehicle battery and definitely enough to charge your trailer.

What it WILL do is charge it fairly slowly. It's a long wire run from the alternator back to your trailer, and usually it's not much more than 12AWG so there's going to be some loss. Don't plan on running your vehicle for an hour to charge your trailer battery after a day's use. Shore power, a generator, or solar are always going to "win" over that source. But it will do it, if it has enough time to work.

You can prove this is true if you have a simple multimeter. Jumper from your vehicle ground to your trailer ground. Jumper from your vehicle AUX pin to your trailer AUX pin through the multimeter, with the switch set to "ammeter" mode. Make sure the range can handle 10+ amps - some cheap meters only go up to 1A. Your meter will show you how much current is going into the trailer. If you have nothing else turned on, that's your charge current (at that moment).

For reference, I did this once while diagnosing a wiring issue and was reading 5.5A. If you have a 100Ah battery 50% (more or less "fully") discharged, it would take 9 hours to charge fully assuming that charge happened at a constant rate (which it won't). This won't be a very accurate calculation because charge rate will vary over time, temperature, and other factors, but it'll at least give you a rough ballpark.

I firmly believe EVERY RV owner should invest in a cheap multimeter. Even a $10 harbor freight special is worth having. There's so much you can diagnose with it.

backcountrycamp · 05-03-2020, 06:11 PM

PS - didn't mean that to sound combative. If you're only hauling for a few hours and your battery needs 9 hours to charge, that's definitely not "enough". As Monday_Blues pointed out, some time of charge maintainer (float charger) is a great thing to have while your trailer is in storage. I'm just pointing out that batteries are pretty brainless devices. They don't know where the power is coming from, and if your vehicle is supplying 13.5+V then everything connected to it will charge. Just maybe slower than you'd like!

jimmerz · 05-04-2020, 11:08 AM

Thank you all!

Thomas Walch · 05-10-2020, 02:19 PM

Check if there is power at the 12volt leg of the outlet. The manufacturers usually don’t put power to this leg. Normally there is a fuse not installed a relay or in some cases both may need to be installed. I had to install fuses or relays on my 2002 Avalanche my 2010 F150 and my present truck aToyotaTundra. From the factory manufacturers do not power up this leg in the trailer hookup. After hooking up power to this line I never had issues with my battery going dead.
Mechanic Transportation Technology Teacher.

MartyinSC · 05-10-2020, 03:57 PM

Leave the battery connected on shore power. It has a buffering or stabilizing effect on power fluctuations that make it through the converter.

Thomas Walch · 05-10-2020, 04:15 PM

Definitely true. Your car can run with the battery disconnected but it is really hard on the charging system. The battery buffers the system. Rv’s can work without a battery but it’s definitely harder on the convertor. Any high amperage draws like slides are hard on the convertor. Batteries have no problem with higher amperage draws (within reason). Not a good idea to disconnect the battery when hooked up to shore power.

TerryH · 05-10-2020, 08:50 PM

Quote:

Originally Posted by jimmerz

So i finally bought a new battery and installed a battery disconnect switch so i get more life out of this battery. My question is, when connected to shore power can i switch my battery off?

I know this is mostly for storage, just curious.

Thanks

But the you are NOT charging battery

jacinda · 05-11-2020, 11:38 AM

Quote:

Originally Posted by MartyinSC

Leave the battery connected on shore power. It has a buffering or stabilizing effect on power fluctuations that make it through the converter.

nice advice

Aceallenk · 05-11-2020, 03:13 PM

The only time you really ever want to use the disconnect switch is when you want to prevent your battery from draining itself when your trailer is not in use for any length of time, rather than have to manually disconnect the battery cable. I use to also have to do that before adding the disconnect switch, but that turned into a serious pain in the a$$ quick...and if I didn't disconnect my battery it would be almost dead in 8 days. Like many said, as soon as you connect to a power source make sure your battery is connected. I now added a few solar panels and ''never'' disconnect my battery....and never fear my battery being drained to under 12V or dead. Todays new trailers a disconnect switch is probably standard equipment, and if it isn't, it should be, as there's just a few things that never turn off killing the battery...

**dagst1** · 05-11-2020, 03:15 PM

Also be sure to check the water level in the battery every other month or so.

backcountrycamp · 05-11-2020, 06:39 PM

I'm mixed on the disconnects. The idle/house load in our camper was much higher than I expected, about 350mA with everything off. I spent some time tracking it down and found 250mA of that was just the radio. The remainder was about 80mA to the fridge (even when off) and the rest was the DC converter itself.

In my opinion even if you can't afford a full solar rig, a small solar "maintainer" is so cheap that it's a smart option for almost anybody. In that case I'd never bother disconnecting the battery in storage. However, I still like having a disconnect (I added one to mine) for when I want to do any kind of wiring. It's SO much easier than having to get out to open up the battery box and disconnect a cable...

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