Charging your battery from your tow vehicle - R-pod Owners Forum

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offgrid

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Joined: 23 Jul 2018
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Posts: 5290

Topic: Charging your battery from your tow vehicle
Posted: 02 Sep 2018 at 12:40pm

I'll put in my pre-order now for a Mr. Fusion as in the Back to the Future Delorean. Takes care of camp garbage cleanup too. Or better yet, can I plumb my black tank to it and eliminate that little chore?

Kidding aside, if you want to do portable solar and your back is up to it, GlueGuy's suggestion is a good one. Buy a standard Chinese 60 cell (40 lbs) or 72 cell (50 lbs) PV module. This will be in the range of 290-350 watts nominal. Then, permanently mount an MPPT controller for it near your batteries. 10 gauge wire should be good up to about 50 ft for that with < about 3-4% voltage drop.

And the standard residential/commercial modules are the lowest cost ones you can get. The controller will probably cost almost as much as the module will. They're big though about 65x40 inches for the 60 cell modules and 75x40 for the 72 cell modules.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

lostagain

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Joined: 06 Sep 2016
Location: Quaker Hill, CT
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Posts: 2587

Posted: 03 Sep 2018 at 11:54am

offgrid, I love your idea of using the methane from the black water tank. We normally avoid it's use, but now, thanks to your insightful suggestion, we'll have to revisit that practice. Heck, we could hook it directly to our Champion duel fuel generator. Approve

We use a flexible 100W panel with about 20 of 8awg wire and can move it to follow the sun pretty well. It really cranks out the power and keeps the batteries nicely topped off. It takes just a few minutes to set up. But, then while camping, time doesn't matter and tinkering with stuff like that is fun.

Never leave footprints behind.
Fred & Maria Kearney
Sonoma 167RB
Our Pod 172
2019 Ford F-150 4x4 2.7 EcoBoost

offgrid

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Joined: 23 Jul 2018
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Posts: 5290

Posted: 03 Sep 2018 at 12:19pm

Here ya go:

https://www.youtube.com/watch?v=KyO1iQk-zDw

You could mount the 55 gal drum in the rPod wet bath, raise the john on top of it, put in a ladder and cut a hole in the roof to make headroom and get the drum in there. Then you could stop on the way to your campsite at dairy farms to get cow manure to get it started. But be sure to stay at least two weeks so you can get a whole water jug full of methane which would probably run your furnace or stove for about five minutes on your last camp day. LOL

I think I'll stick with my propane bottles, at least until Mr. Fusion is ready for sale....

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

poston

podders Helping podders - pHp

Joined: 28 Mar 2018
Location: Nevada
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Posts: 195

Posted: 03 Sep 2018 at 12:20pm

Originally posted by lostagain

But, then while camping, time doesn't matter and tinkering with stuff like that is fun.

My philosophy exactly!

It's a good feeling being totally self-sufficient, even just for a few days or a week or more.

I appreciate all the good information flowing from you all! Thumbs Up

--
Jim
Virginia City, Nevada
2016 R-pod 180
2015 Nissan Xterra Pro-4X

Olddawgsrule View Drop Down

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Location: New Hampshire
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Posts: 1014

Posted: 03 Sep 2018 at 12:49pm

Okay, re-charging from your TV to methane production.. Oh My.. LOL

Loved the banter, but really?

Start a new thread and I'll add some input on my thoughts!

Can you re-charge your batt's from your TV was the original question. Answer has been proven as yes.

Is it the best way? Open for discussion.

Is it a solution to an issue while Boon-docking? Does look like yet another simple choice.

Me, I would not just use jumper cables and hook direct. That's me..

I do like the idea of using a Solar Controller in the mix.

Byways no Highways
2017 Tacoma
Truck Camper Build
2004 F150 My Overlander

GlueGuy

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Joined: 15 May 2017
Location: N. California
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Posts: 2629

Posted: 03 Sep 2018 at 2:13pm

Originally posted by Olddawgsrule

Okay, re-charging from your TV to methane production.. Oh My.. LOL

Loved the banter, but really?

Start a new thread and I'll add some input on my thoughts!

Can you re-charge your batt's from your TV was the original question. Answer has been proven as yes.

Is it the best way? Open for discussion.

Is it a solution to an issue while Boon-docking? Does look like yet another simple choice.

Me, I would not just use jumper cables and hook direct. That's me..

I do like the idea of using a Solar Controller in the mix.

For the amount of time that would be involved; maybe an hour or so is the longest I would try. It should not harm either the TV or the TT or any of the batteries. I wouldn't expect a full charge, and I don't like idling the TV for excessive amounts of time, but in a pinch, it wold work nicely.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

offgrid

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Joined: 23 Jul 2018
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Posts: 5290

Posted: 03 Sep 2018 at 2:59pm

Olddawgsrule,

Ok you're right on the methane, we got way off topic. Embarrassed

At the risk of restarting an argument I'd really like to better understand the fear folks seem to have of charging their house batts from the TV. And what they expect a solar charge controller to do to improve things.

Do your house batts get charged that way while you're driving? If so, what's the difference? Most all class A, B, and C RV's charge that way too. Always have.

You need a solar charge controller for two reasons. First, nominal 12V solar modules have an open circuit voltage of 18-20 volts or more. That's just the way PV devices work in order that their max power point voltage is in a good range for battery charging (around 13-14V). As the battery voltage rises their current output reduces until it reaches zero at that 18-20-ish open circuit point.

Second, people leave their solar modules connected to their batteries more or less permanently. So, when you leave a solar module connected to a battery for a long period with no load or charge controlller on it the battery voltage will keep increasing until the current output by the solar module drops to a level that matches what the battery can accept just floating. That is typically a very high voltage and results in excessive generation of hydrogen and oxygen consuming the water in the battery. Not good.

In contrast, your TV will never be left running and connected to your house batteries for long periods. And, car alternators are self-regulated to 14.4V. So neither condition requiring the use of charge controllers in solar applications applies.

Also, the chemistry used in your TV start battery is essentially the same as in a flooded lead acid golf cart battery. So if getting charged from your TV alternator was going to be a problem for the trailer house batteries then it would also be one for your TV start battery. That doesn't happen. This all supposes that you are not using some exotic battery chemistry in your trailer of course.

So, the problem with charging from your TV isn't that you risk battery damage, its that your TV alt has trouble putting out enough current at high enough voltage to be an efficient charge source when being spun by a big engine. You can partially get past the need for higher voltage by running big conductors, but we're talking about a lot of copper.

If you turn the TV around nose to nose with the trailer you can get to maybe a minimum 10 ft conductor run. 1/0 would give you a voltage drop of 0.2A at 100A, if your alt could put that much out at idle. And to that you need to add connector losses at both batteries and at whatever mating connector you use between the batteries. The connector losses from using jumper cables are too high because of the limited connection surface area, terminal lugs should be used like on any other battery connection.

Then there is the inrush current when you initially hook up the two batteries at different voltages (the additional current will come from the TV battery, not the alt).

BTW, all these same considerations will apply to a solar charge controller in the same circuit. How do you keep from finding out where they hid the smoke in your solar charge controller from the excess current when you first connect up? Batteries are essentially an infinite current source while solar modules are current limited. That's what I'd be worried about.

Welding cable is good for this application because its flexible, try to bend normal 1/0 sometime and you'll see what I mean. Ampacity (ability to handle current without overheating for 1/0 welding cable is about 200A, which I think would be safe considering the inrush current when you initially connect up the two batteries. So I think 1/0 would be the way to go. I would use mating high current Anderson connectors so you can't accidentally mix up the battery polarities. They're rated for hot connection too. Conceal the set on the TV behind the front bumper or somewhere else accessible. Have the mating connector and its cable looped and strapped to the the trailer tongue. Anderson also makes nice rubber boots for these to keep the road crud out of them.

If your TV alt doesn't put out enough current to make this worthwhile the car audio industry has a solution that the folks installing giant amps in their vehicles use. There are several companies that will wind you a custom alternator. Just be sure to tell them that you want to maximize output at idle, not at normal engine rpm. You can also try a smaller diameter sheave/pulley on your existing alt.

So charging directly from the TV is a perfectly viable solution, I'd do it with no qualms at all, but it doesn't address my need for an AC source for the air conditioner and microwave. So I still lug my generator around, for now. But if you already have a large inverter or don't need to run your AC appliances, then TV charging is a great way to go.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

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Posted: 03 Sep 2018 at 4:17pm

Originally posted by GlueGuy

For the amount of time that would be involved; maybe an hour or so is the longest I would try. It should not harm either the TV or the TT or any of the batteries. I wouldn't expect a full charge, and I don't like idling the TV for excessive amounts of time, but in a pinch, it wold work nicely.

My $.02

I have done this many times over the years.

However, a few years ago, it was the last camping trip of the season and cold. As I sat by the campfire, listening to the V8 of my new truck idle, in a flash of crystal clarity, it came to me:

"You know, that's a damned expensive battery charger AND I need it to get home."

I purchased a inverter generator before the next season.

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Posted: 03 Sep 2018 at 4:38pm

Here is another potential way to "skin the cat", that I have not seen mentioned:

My truck (with it's towing package) has a tray for a second battery under the hood. I've not investigated if it has any sort of isolator in the circuit.

One thought I had was to take a second battery and install an isolator, if needed. This way, one battery would always be in the truck charged and could be swapped with the depleted battery on the camper. The depleted battery would get charged during normal running about/sight seeing. (Swap/rotate batteries, as needed)

One could install a second battery tray, along with a battery isolator, if not already equipped. ( an isolator "isolates" the second battery from the main vehicle starting battery - so as to not cause problems with the starting battery)

lostagain

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Location: Quaker Hill, CT
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Posted: 03 Sep 2018 at 5:52pm

Good grief, you guys are making me tired just thinking about all the work necessary to realistically charge from the TV, apart from the charge you get while driving. I think I'll stick with my little 100A solar panel and its controller and the inverter generator I recently got that runs on propane. If I can't keep the batteries charged with that, then I'll just have to find a place where I can plug into AC.

And, Jim - poston - I didn't see you at the VC Labor Day Parade Confused

I was the grumpy old man with the white t-shirt with blue writing on the back.

Never leave footprints behind.
Fred & Maria Kearney
Sonoma 167RB
Our Pod 172
2019 Ford F-150 4x4 2.7 EcoBoost