Battery Isolator

[rappar]

If I missed the answer with my search, I am sorry for the question coming up again.
When I pulled a larger trailer, I always had a battery isolator installed. Now, i am in the process of purchasing a teardrop. It will have some 12v and 110 outlets, not many. Should I invest in an isolator or do most just unplug from the TV to avoid the problem of running down the TV battery?
If my TV battery is new and in good shape, do I need to unplug when I stop for a lunch break and have nothing on in the trailer?
Thanks
Ron

[eamarquardt]

A simple relay, powered only when your ignition is on (most cars have a wire leading to the radio that can be tapped into), in the wire leading from the tow vehicle battery/alternator to your trailer connection is all that is required to isolate the two batteries. I'm not sure why an expensive (and I've heard somewhat unreliable) battery isolation device is required.

Cheers,

Gus

[dave_dj1]

If you are just stopping for lunch or shopping I don't think you will have any issues at all. If the TD battery is in good condition and you don't go crazy on usage while stopped I think you will be fine. I have hauled campers for years and have never had a battery isolater.

[PcHistorian]

if nothing is on then don't worry about it. It won't pull any power. If you are charging a trailer battery from the tow vehicle then an isolator should be used. (and possibly stronger wire.) Truthfully, right now the 12v dc accessory systems in my trailer are completely separate from the trailer's traffic lighting system. (running lights, turn signals, brake lights.) So I would never have that problem, the two systems are independent.

[bdosborn]

I ran the teardrop without an isolator, I just unplugged from the truck when we camped. I didn't unplug when we stopped for lunch and never had a problem. The trailer battery and start battery will be wired in parallel and will tend to discharge each other when the car isn't running but not fast enough for anything bad to happen in an hour or so.

Bruce

[PcHistorian]

@bdosborn: do you have your trailer +12vdc for the battery connected to the tow vehicle's battery or to the alternator output wire, or some point in the ignition switch like an accessory or ignition circuit? (I'd go with ignition, then if you use the accessories on the key switch, you won't connect and drain both batteries. And when ever the car is on and running, then that will be powered to charge the trailer battery.

[bdosborn]

@bdosborn: do you have your trailer +12vdc for the battery connected to the tow vehicle's battery or to the alternator output wire, or some point in the ignition switch like an accessory or ignition circuit? (I'd go with ignition, then if you use the accessories on the key switch, you won't connect and drain both batteries. And when ever the car is on and running, then that will be powered to charge the trailer battery.

I have a pickup with the factory tow package so I use the factory charge line. It comes off the main fuse block under the hood and it's not switched. I had a lot of charging problems (as in no charging) due to voltage drop until I replaced the factory 14# wire with a 6#. The Boxcar is a lot bigger electrical load than the teardrop was so I've installed an automatic combiner. It combines the trailer and truck whenever the voltage is over 13.3 or so. The truck charges trailer via alternator when its running and the trailer charges truck via PV panels when the sun is out.



http://www.yandina.com/c100InfoR3.htm

Bruce

[PcHistorian]

car batteries are 12.76 vdc when freshly charged and idled (no connection). I don't know what the deep cycles are at freshly charged and idled, but it should be at least 12vdc. You'll probably need a digital volt meter to test the deep cycle to the hundredths of a volt. but if you hook the two in parallel the one with the greater idle voltage will discharge into the lesser one, but both should be over 12.00 vdc. (provided both are healthy batteries.) I have not had a problem with tv batteries that still had 12.25 vdc in them. so if the deep cycle idle charged level is over that then there should be no problem. Ideally the deep cycle would be the greater voltage.
I should check on some current limiters and maybe some alternator diodes, just to play with things. That way both could get an equal chance at the alternator (get alternator diodes rated at that alternator's current flow) and nether would back-flow into the other with no loss of voltage or current.

[absolutsnwbrdr]

http://www.yandina.com/c100InfoR3.htm

Bruce

Bruce, I think we've talked about this Yandina thingamabob before. I think it was a thread based on the Sure Power battery isolator. Anyway, after your positive experience with this thing, I decided to bite the bullet and order one . Can't wait to get it installed.

[bdosborn]

Cool, make sure and post a review! Don't forget to add the DPDT center off switch so you can have manual control over the combined.
Bruce

[absolutsnwbrdr]

Cool, make sure and post a review! Don't forget to add the DPDT center off switch so you can have manual control over the combined.
Bruce

Why would I need the manual control? The instruction sheet mentions that green remote wire can be connected to a SPDT center-off switch, but is usually left unattached for automatic operation.

[zipz71]

Why would I need the manual control? The instruction sheet mentions that green remote wire can be connected to a SPDT center-off switch, but is usually left unattached for automatic operation.[/quote]

In case you ever want to move the trailer with out the battery installed.

[bdosborn]

Cool, make sure and post a review! Don't forget to add the DPDT center off switch so you can have manual control over the combined.
Bruce

Why would I need the manual control? The instruction sheet mentions that green remote wire can be connected to a SPDT center-off switch, but is usually left unattached for automatic operation.

Several reasons:

-When I don't want to charge the start battery from the solar panels or battery charger and just charge the trailer battery.
-When I want to force the batteries to combine, say because the start battery is dead and I want to use the trailer battery to help.
-Because I want to turn on the trailer running lights at the trailer plug with a jumper.

Bruce

[droid_ca]

is there a schematic that somebody could post

[absolutsnwbrdr]

Bruce, a schematic would definitely help. I've been scratching my head trying to figure it out, and I'm about to wear a hole in my head doing so.

Hmmm... DPDT...