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Topic ClosedCharging your battery from your tow vehicle

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GlueGuy View Drop Down
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Direct Link To This Post Topic: Charging your battery from your tow vehicle
    Posted: 08 Dec 2017 at 6:58pm
Originally posted by Tars Tarkas

If we're talking about maintaining the battery for a week or more of dry camping, I guess it's a matter of choice, but I prefer a more robust solution: a generator that will recharge the battery while letting me use a Keurig or the air con or microwave.  To each his own.

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Direct Link To This Post Posted: 27 Aug 2018 at 12:37pm

WillThrill is entirely correct about this, its is by far the best way to charge the battery from the TV and it could be hooked up at all times so TV is charging the trailer battery when ever you are moving.  Maximum charging current will be limited by the resistance from battery to battery i.e. all your wiring and contacts.  

He is entirely wrong about solar panels, they are the best, easiest, and cheapest solution for so many RV power problems.  I used flexible solar panels VHB taped to top of camper, ran the wires directly to the battery box and covered the wires with permabond tape.  Used a $20 PWM charge controller placed on top of the battery in the battery box and then ran two wires directly to the battery.  It is the 1 hour $200 solar solution.  It keeps the battery fully charged at all times, required no drilling into the the camper or complicated wiring, does not add any weight to the TV or tow vehicle, makes no noise, requires no maintenance, has no ongoing costs.  I see so many people like glueguy who run their generator pretty much the entire time they camp.  It ruins the fun for everyone around them, and even the "polite" ones who run it occasionally  still make plenty of noise for everyone else to enjoy.

 My previous camper I only had a 30W panel, this time I went with 100W since the refrigerator will be pulling more power than previous ice box even running on propane.  


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Direct Link To This Post Posted: 27 Aug 2018 at 1:36pm
Greetings

Let's all calm down a bit.  If it works to charge the battery,  fine.  If it doesn't use something else.  I have used a good set of jumper cables.  Batteries don't last forever regardless of how you treat them.  Just be careful in making your connections and have good ventilation.   Wear eye protection and your sewer drain hose gloves.  


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Direct Link To This Post Posted: 27 Aug 2018 at 1:47pm
Originally posted by Kevinscamps

I see so many people like glueguy who run their generator pretty much the entire time they camp.  It ruins the fun for everyone around them, and even the "polite" ones who run it occasionally  still make plenty of noise for everyone else to enjoy.
We don't use a generator.
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Direct Link To This Post Posted: 27 Aug 2018 at 4:29pm
Just my opinion, I use my TV to charge battery while traveling all the time and I run my fridge on battery, how is that for contrary:) No issues yet and 2 different tow vehicles. I will not discuss the capabilities of the members, some really smart people here. No liars, to my knowledge. I am NOT an engineer, I spent 40 years as a troubleshooter/tester/designer on sophisticated weapon systems. I use common sense and the basic approach. IMHO.
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Direct Link To This Post Posted: 29 Aug 2018 at 6:21am
Sorry for the late reply, I've been out boondocking/offfgrid camping for the past couple of weeks.

A couple of comments:

As others here have said, unless you're using some type of advanced battery technology, using a solar charge controller to regulate voltage from the TV alternator to your trailer battery is unnecessary. Modern alternators are internally regulated to 14.4V anyway, so at best they will provide the same bulk charge regime as your WFCO. Normally it will limited to a lower charge voltage because of conductor and connection resistive losses. Flooded lead acid batteries are fine with 14.4V. In fact its good for them to see this once in awhile. And no one is going to leave their TV idling for days on end with the battery at float conditions.  The fact that a PWM charge controller "works" when used in this manner does not make it necessary to have it in the circuit. 

And as another poster noted, neither MPPT nor PWM charge controllers will boost the input voltage, PWM controllers use series FET switches, and MPPT controllers are "buck" dc to dc converters, meaning that the solar module input voltage must be above the battery voltage at all times.There is at least one company (Victron) that makes a high current "boost" dc to dc converter which can raise the output voltage above the input voltage, but its quite spendy. 

Using the TV alternator as a charging source vs. a generator has both advantages and disadvantages. I'm comparing these two on demand fossil fuel alternatives because that is an apples to apples comparison. Comparing either one of them to solar charging is an apples to oranges comparison.  More on that in a minute.  

Advantages of TV alternator as charging source:

No genny to lug around and refuel
uses by far the largest stored energy source at your campsite (your TV fuel tank)
TV engine noise at idle is typically much less than genny noise. 

Disadvantages:

Does not allow for running of air conditioner or microwave (unless you also install a large inverter).
Relatively inefficient as a charging source (although modern engines are pretty good, my Highlander burns about 0.3 gallons per hour at idle). 
Low output voltage so large conductors and careful attention to connector losses are required to limit voltage drops. This also limits the distance the TV can be from your trailer, while a genny can be located much further away for sound attenuation. 
Alternators tend to be quite current limited at idle rpm, and high output alternators can be even be more limited at idle because they have been optimized for high current output at normal operating engine speeds. 

So if you either don't use your trailer AC loads or have an inverter to run them, don't mind idling your TV for extended periods, and you are willing to put some effort into setting up a good low resistance connection, the TV alternator could be a good choice as a charging source.

I've measured my alternator current output at idle and found that it can provide up to about 80 or 90A (its rated at 130A I believe). About 30A of that goes to run the engine and its required accessories (leaving all my TV electrical loads off). This is not at 14.4V however. So, in theory I could get 50-60A out using the TV as a charging source. In practice this is not possible because of the conductor and connector losses between the TV and the trailer battery. Best I was able to get was about 30-40A for a short period using a dedicated set of 1/0 conductors, kept as short as possible, attached to both batteries by lug terminals (jumper cables are not a good choice because they are very resistive at their clamp connections). And that was with a pretty low trailer battery voltage, I forget what it was exactly. This is about what the WFCO produces. 

So, this might be sufficient to get the job done, or you could spend the money and get a 50A Victron buck/boost converter or similar and not have to worry about the voltage drops so much. In my case I want to run my microwave and (occasionally) my air conditioner, and I already own a genny, so I've been using that.

Finally, on use of solar. At the risk of repeating myself with previous posts I will respectfully disagree with those that say that PV modules can substitute in all situations for an on demand generation source like a genny or TV alternator. I suspect that those of you who take this position tend to camp in sunny locations in sunny weather, and most likely live and camp in the West. If you live in the East like I do and your summer camping is in the deciduous forest, it is unusual to find campsites that aren't in essentially full shade. And its very common to have several days of rainy weather in a row (especially this year). Solar won't do much of anything for you under these conditions unless you have a really large array (like 1kw or more). So, either you run a fossil fueled generator, charge via your tow vehicle, or hope your battery lasts out your trip. 

With solar YMMV, with a fossil fuel source, you have on demand power available.  Apples and oranges.  I run my honda 2kw generator.  Its pretty quiet and I try to mitigate its noise further by placing it far from campsites (I carry a 100ft extension cord), running it for recharging at times when I'm using the microwave anyway, only do bulk charging from it, and leaving absorption and float charging for my return when I have access to grid power. I still plan to install solar as well, I don't always camp in the woods, especially in the spring and fall seasons.  

I would prefer a higher capacity charger than the WFCO, which doesn't come anywhere near fully loading my 2kw genny, so am considering installing a "hybrid" inverter charger like the Magnum MSH3012. That can be programmed to load the genny at its (about 1600w) continuous rating, and it will either charge or discharge the battery depending on what AC loads are on. Its capable of up to 125A output in charge mode so charging current will then be genny limited not charger limited, resulting in shorter genny runtimes. Having the inverter installed would also allow me to reconsider using the TV as my fossil charging source while still being able to run the micro and occasionally the aircon. 









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jato View Drop Down
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Direct Link To This Post Posted: 30 Aug 2018 at 6:59pm
+1 to offgrid.  In northern Michigan we can often go 3 days or more in the summer and not see any sunshine.  Spring and fall . . . well sometimes nearly a week, so solar isn't worth a hoot here.  But then again, if I were west and south it would make for an excellent choice.  It is great to have lively discussion  w/o the name calling and that is why I enjoy this forum so much.  
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Direct Link To This Post Posted: 02 Sep 2018 at 6:54am
Thanks Jato,

BTW, if we were talking about an off grid cabin in northern Michigan, and not an RV, I would still be suggesting you consider solar. Solar does still produce significant energy when its cloudy (10-20% is typical). In a stationary application you have the space for a big enough solar array and battery to get you through your bad weather periods. And solar is so cheap now that would most likely be less expensive, not to mention quieter with much less maintenance, than running a genny all the time. But for an RV application we are so weight and space restricted that that's not really an option to carry around all that extra gear. 
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Direct Link To This Post Posted: 02 Sep 2018 at 9:41am
A combination of using LED lights, judicious use of battery power, and solar can give you a quite a bit of time on battery power only.  A solar panel that you can move around a little to keep it in the sun helps, but then you have to have to mess with increasingly thick cable to connect the panel to the trailer battery the farther you move the panel from the trailer.  

If you are in a windy area, check out the marine wind generators as an alternative.  Just letting my imagination run a little wild, as it often does uncontrollably, why not build a little portable water wheel generator that you can lug over to the nearby creek if you are in a wet area of the country?  I wonder if there are any small fuel cell generators available?  Since they run on hydrogen you'd only leave water behind.  Of course, the ultimate generator would be a portable fusion nuclear reactor, but they haven't been able to build a big one so far, so the portable ones are a ways away.
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Direct Link To This Post Posted: 02 Sep 2018 at 11:53am
Originally posted by lostagain

A combination of using LED lights, judicious use of battery power, and solar can give you a quite a bit of time on battery power only.  A solar panel that you can move around a little to keep it in the sun helps, but then you have to have to mess with increasingly thick cable to connect the panel to the trailer battery the farther you move the panel from the trailer.  

If you are in a windy area, check out the marine wind generators as an alternative.  Just letting my imagination run a little wild, as it often does uncontrollably, why not build a little portable water wheel generator that you can lug over to the nearby creek if you are in a wet area of the country?  I wonder if there are any small fuel cell generators available?  Since they run on hydrogen you'd only leave water behind.  Of course, the ultimate generator would be a portable fusion nuclear reactor, but they haven't been able to build a big one so far, so the portable ones are a ways away.
Many off-grid solar panels run in the 30-40 volt range. If you had one of those, you could use smaller gauge wire, and place the controller right next to the battery.

I've seen "smaller" fuel cell generators, and they're not really that small, or inexpensive for that matter. These days, you get the most bang for your buck with solar. Silent too. Just a bit on the bulky side for decent panels.
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