Battery And Tv (tow Vehicle) Output

Discussion in 'Electrical & Mechanical Issues' started by AlCat, Mar 1, 2017.

  1. AlCat

    AlCat Junior Ranger Donating Member

    Hi. I have had some issues with our battery not lasting as long on a camping trip as I think it should (and not charging very well from the TV), so I wanted to explore this a bit before running to a local repair shop. I recently went to a trailer service shop and they said the battery was just fine and the TV is just fine, but the battery doesn't charge well from the TV. Frustrating.

    another poster wrote that the problem may stem from the TV simply not putting out enough juice to charge the TV battery, and that this is common on modern cars (I use a 2004 Volvo XC90).

    What do folks think?

    Perhaps more importantly, what's the right kind of business to troubleshoot this? The local trailer place did not address this to my satisfaction, so I am wondering if a battery place may be better....
  2. AlCat

    AlCat Junior Ranger Donating Member

    This is one comment on this issue that I wanted to explore:

    My TD "doesn't put out high enough voltage to fully charge an AGM battery. These batteries need a specific charging profile to get *fully* charged. This includes a voltage of 14.6 or so. I doubt most cars do this."
  3. fernlane

    fernlane Novice

    Alan - I'm the one who wrote that, and since I installed the trimetric battery monitor last summer I've got observational data that has convinced me that it's true, at least for my VW tow vehicle.

    Trojan recommends (for deep cycle AGM batteries) 14.4 volts for bulk charging, 14.1-14.7 for absorption and 14.7 for the finish charge. My TV just puts out a constant voltage of around 14 so it doesn't come anywhere near matching the desired charging profile.

    I really got into this issue early last summer when I had the same complaint you've got now - the battery just didn't last as long as it should have. I had it tested twice and it tested fine, but under load in the trailer it wouldn't do the job.

    I had a good email exchange with Craig who pointed me in the direction of suspecting the problem was the TV voltage. He explained that while the TV may come close to fully charging the battery, it just can't, so in time the battery effectively develops a memory (according to Craig) which continues to decrease the battery capacity.

    In our first year of owning the 550 we had been on several long trips where I was dependent on the TV for much of the battery charging - just not enough sun for full charging with the solar panel. I was also guilty of thinking that a day of driving was fully charging the battery. I think those trips pretty much did in that battery. It still had decent capacity but not enough for dry camping with the dometic.

    Solar panel use is the cure for this problem but you've got to have good sun pretty consistently, something not always available in the shady east.

    The trimetric has really helped me understand what's going on. It's not perfect, and there's a learning curve for sure. I'm much more aware at all times, however, of the battery state of charge. Since we depend so much on it this is only as it should be.

    Robert Dickson
    Evan and AlCat like this.
  4. AlCat

    AlCat Junior Ranger Donating Member

    Hi, Robert. Thanks for the thoughtful reply. I've had a similar experience (and we do use a solar panel, when we can, which is often, but not enough), but I'm also a novice when it comes to batteries and charging, and I'm sure I did more to abuse my battery than you did.

    In the end, what is your solution re the battery? A generator?

    When you have a depleted battery and then drive a day in the sun, there's not much sun left to charge the battery when I get to the next site. So I need the car to work....

    Do U.S.-brand SUVs/trucks have the same output issue?

    Or is the solution to buy a new battery every three years? (not the worst thing)

    If I could convince my wife to replace the fridge with a second nice cooler, the battery issue would be much less.

  5. AlCat

    AlCat Junior Ranger Donating Member

    I need to modify my comments on this topic. We bought our TD in 2011, and I thought we had replaced the battery a couple of years ago. Turns out we have NOT replaced the battery, so we are running with a 6-year old AGM. So some of my power issues may be the result of abusing an AGM battery over 6 years not 3 years.

    I am feeling a bit more confident that a new battery combined with better battery-handling practices will result in better results.

  6. Inn42

    Inn42 Junior Ranger

    Just to add to fernlane's comments: It seems our alternator puts out 14.4v, which is only 14.0v by the time that it gets to the 7 pin connector, so I suspect it is a bit lower at the camper battery. So I suspect he is correct that few newer tow vehicles will be capable of fully recharging the AGM battery.

    In other threads, a couple of items caught my eye, which seem to be relevant here. Cosmo had made a comment along the lines that too low of voltage will shorten AGM battery life. In another thread, Cary had recommended setting the Dometic to medium: the thread made it clear that the high setting will drain the battery too quickly, and I suspect the low setting may reduce the battery voltage to a point where over time it could reduce battery life. I don't know if I am connecting these dots correctly, but there seems to be a correlation.
  7. fernlane

    fernlane Novice

    here are a couple of charts from the Trojan (battery) user guide. I'm pretty sure there's no vehicle out there that doesn't come with an AGM battery that can match the needed charging profile. I think this is a pretty typical AGM battery charging profile.
    This is why our AGM batteries don't charge well on the road. I watch my battery's voltage and amps on the trimetric while it's charging (plugged in or solar panel) and there's just no way my car can do what the on-board charger or solar panel can do.

    Screen Shot 2017-04-10 at 8.40.48 PM.png

    Screen Shot 2017-04-10 at 8.39.46 PM.png
    Tour 931 likes this.
  8. SethB

    SethB Newbie

    A late addition to this thread...

    Not all TV wiring is capable of delivering the volts AND amps to charge a camper battery. There are a couple issues:

    1) As posted above, best battery charging and longevity comes from charging at various voltages like what fernlane posted from the Trojan docs. A DC/DC, also sometimes called a 12v/12v charger is a smart charger that will take what your TV’s alternator puts out, and regulate charging voltage. Soemthing like this: CTEK (56-677) D250S 5-Step, Automatic DUAL 12 Volt 20 Amp Battery Charger: Automotive
    Will put out voltages for the different battery charge states. It’s really just like the smart charger CI includes in the trailer, but, starts with what your alternator puts out.

    2) My Nissan Frontier TV has 10 gauge wire on the charging line that goes to the factory 7-pin connector. That’s common. This has two results that aren’t optimal for charging. First, there’s a voltage drop. Second, it will only pass so many amps in a given amount of time. Your alternator may put out upwards of 100a at 14v, but you might only get 10a at 13v at the hitch!

    I ran an FWC (Four Wheel) camper in the bed of my pickup for the last few years. There’s a very active user forum, and that camper has a big following of boondockers. It is a design for off-roading... Here’s a typical thread about getting the most charging out of a TV. Hit post 12 on the second page
    Wire Upgrade from Truck to Camper - Four Wheel Camper Discussions
    Lots of FWC owners add 6ga cable for charging, some go to 4ga. It’s a little different than a towed TD - the wiring runs to the bed of the pickup are shorter, and, it’s easy to use high capacity connectors like Anderson Powerpole.

    A lot of those owners are doing jeep trail in the desert southwest, so, solar is very popular. They do seem to like refrigerators with freezers for ice cream and ice in their drinks :) All of which takes a lot of power!
    Evan and Tour 931 like this.
  9. TimeCapsule

    TimeCapsule Newbie

    I just got a CTEK D250s for Xmas, but won't be able to install it and check it out until things warm up a bit in Minnesota. They are a bit expensive, but in theory it should be a good solution for charging from the TV and it is supposed to have a good MPPT solar charger. I probably will add a battery monitor at the same time. Adding a smart charger between the TV alternator and the battery that will boost the voltage should do wonders for the battery.
  10. SethB

    SethB Newbie

    Please post back about your experience with the D250s, I’m pretty sure one will be part of our next camper... a CI!

    I didn’t quite get to charging and storage upgrades before we sold our FWC Eagle, but we’re mostly without shore power, in the shade, and frequently under clouds camping in the Pacific NW, so, I’m pretty interested in all power solutions that will prolong battery power for a CPAP.

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