Battery Question

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Battery Question

Postby Belmo » Wed Jul 17, 2019 3:01 pm

I am building my TD, and though I'm not at the wiring stage yet, I've been thinking about it (a lot. I'm obsessed like everyone else here. :D ).

I'm leaning toward a battery-powered 12-volt system, because the places we like to camp mostly don't have hookups. I'm also leaning toward a very, very basic electrical system: I'd run the roof vent and some lights, and (maybe) a cell phone charging port through the battery -- that's it. I don't want a beer fridge, or air conditioning -- we go camping to get away from all that stuff.

This leads me to a question, though, that those with more experience might be able to answer: if I get a decent 12V battery (I'm assuming a deep-cycle marine battery), how long will the charge last when I'm out in the field? This would be pretty light use: the use of a few lights at night, and the roof vent when/if needed.

Will a good battery power this stuff for a day before it needs to be charged? A week? A month? 12 hours? I have absolutely zero idea how long one will last -- and I think this will help me figure out what I want to do with the electrical system in my TD.

What are the experiences of you 12-volt people out there in Teardrop Land?
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Re: Battery Question

Postby Pinstriper » Wed Jul 17, 2019 3:38 pm

It isn’t possible to answer this question without getting into the numbers, ie. what is the draw from the fan, how many lights and how many hours you want to run them, how big a battery.

As a gross generalization, if you had a deep cycle in the 35ah range, like riding lawn mower size, if all you were running was a few led lights and a cell phone charger, I doubt you could measure any drop in a weekend. The fan....the fan probably eats, say, 1/2 an amp/hour. So, running it all night to drown out road noise or the sounds of bears and lions cavorting in your kitchen, say 2-3 days of that ? Maybe less.




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Re: Battery Question

Postby friz » Wed Jul 17, 2019 3:58 pm

For condensation reasons, plan on running the fan all night. I would suggest a fan with infinite speed settings. I started out using a three speed and I did not have enough fine control. I have a 100 amp hour agm battery. I never run it below half. I have a couple nights of use with out a charge. I have a 50 watt solar charger. Just need a few hours of sun to top it off.

On my last weeklong trip, I came back with a full battery.

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Re: Battery Question

Postby tony.latham » Wed Jul 17, 2019 4:41 pm

For condensation reasons, plan on running the fan all night.


Fritz: You must live (and camp) in the jungle. Or at least someplace with high humidity. :frightened:

We always have our vent open at night with both windows open to one degree or another and seldom run the fan for more than a half-hour. (But boy-howdy, when it's needed, it surely is sweet.)

Today's a humid day here at 22%. A couple of days ago it was 9%.

But we live in the Rockies. When it's hot, we go up.

A Fantastic fan uses about 2.5 amp hours, maybe less. Another couple of amps for the phones and the LED cabin light about nothing.

We're downsizing from a Group 27 marine (50 useable amps) battery to a Group 24 AGM (40 useable amps) with this new build. It'll have 100 watts of solar on the roof to help us slush through.

The bigger the windows, the less you'll use that fan though.

But to answer your question, with our Group 27 in our current 'drop (and me sucking on a CPAP device) three nights is about it. But even with our existing system, the 80 watts of solar that we can put out gives us a somewhat indefinite length of stay.

I like Pinstriper's suggest of a little wheelchair battery. (35 amp/hour battery has about 18 useable amps.) If I didn't use my sleep machine all night, I would be leaning that way.


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Re: Battery Question

Postby Belmo » Thu Jul 18, 2019 7:53 am

Pinstriper wrote:It isn’t possible to answer this question without getting into the numbers, ie. what is the draw from the fan, how many lights and how many hours you want to run them, how big a battery.

As a gross generalization, if you had a deep cycle in the 35ah range, like riding lawn mower size, if all you were running was a few led lights and a cell phone charger, I doubt you could measure any drop in a weekend. The fan....the fan probably eats, say, 1/2 an amp/hour. So, running it all night to drown out road noise or the sounds of bears and lions cavorting in your kitchen, say 2-3 days of that ? Maybe less.




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This is a perfect answer -- thank you!
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Re: Battery Question

Postby KTM_Guy » Thu Jul 18, 2019 6:50 pm

I did a test of all the 12v devices in my teardrop when I was building and put the values in a spreadsheet. Then I would try to guess what I think we would have on for how many hours to get and idea how much power I would use. We went with a Maxxair roof fan for two reasons very low power draw on the low speeds (10 settings) and it can fe full open even in a downpour. We run the fan all night no matter the temp outside at speeds 1,2,3, maybe 4. And that is the biggest draw we had at 2-3 amps. The next big draw was the USB chargers, and I would say don't skimp on them they are cheap and put them everywhere. We have them in the galley and in the cabin and use them all depending where we are. They will draw up to 2 amps. When we drive we will try to charge everything we can so when we get to camp everything should be charged. LED lighting is next to nothing and on a few of my lights I have dimmers so that cuts a lot of power usage. 2-5 amps a day. In summer you have less need for light than in the winter. Winter camping uses more power than summer.

For use worst case power usage was 10-12 amps a day without worrying about usage. If we really needed to conserve we could be in the 4-5 amps a day range.

We went with a 125 AH battery and could go for a week without a problem. Probably longer if we had to.

Since we have added a fridge/freezer (it is a game changer well worth the cost, we never camp where there is power and it might be 2-4 hour drive to get ice) but it is a pig on power. We have since added a DC to DC charger and a 100 wall solar panel. Still in the testing phase to see if that will be enough. I don't think my wife would ever go back to a cooler and ice.

Now is the time to to put the devices in, it's a lot easier than later.

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Re: Battery Question

Postby Shadow Catcher » Sat Jul 20, 2019 10:18 am

Plan on more than you think you want! Our tear is at the far end of elaborate admittedly. There are 5 duplex 120 AC outlets inside and four outside and they all get used. there are 6 12V outlets inside and 4 outside. We use two 120 mm three speed case fans in place of a big fan. Cell/laptop chargers...
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Re: Battery Question

Postby Homebrewer25 » Wed Jul 24, 2019 9:48 am

Since we are talking batteries right now, I've got a question on 6v vs 12v systems.
I'm planning on having 2 batteries ... either 2 12V in parallel or 2 6V in series.

Here are 2 Duracell deep cycle batteries I found at Batteries Plus:
SLI27MDC 12V 90AH $100
SLIGC110 6V 215AH $115

2 12V in parallel should give me 180AH capacity
2 6V in series should give me 215AH capacity (assuming 2 x 215AH @ 6v = 215AH at 12v)

Is this correct?
It's 5 o'clock somewhere ... time for a :beer:

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Re: Battery Question

Postby Socal Tom » Wed Jul 24, 2019 12:26 pm

Your math is right on the 6v. Weight and capacity and size are the the legs of the compromise equation here. I use an 85ah Walmart marine/deep cycle. I routinely draw down to about 40% (11.8 volts). So battery life is not maximized( they last about 5 years). It’s good for a normal weekend without a recharge. For longer trips I bring solar panels or a 1kw generator. So rather than hauling 150 lbs of battery everywhere. I take 75 every where and add 50 lbs of generator when needed.


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Re: Battery Question

Postby TimC » Wed Jul 24, 2019 8:47 pm

If you are still looking for input on battery and its use I'll give you my experience.

I'm in a TD with about 130 cu ft of interior cabin area.

-I have two 45 cfm 12v case fans, 120mm size (4"). They each pull about .15 amps, so .3 amps per hour. Running eight hours each night that's 2.4 amp hours (ah). These fans turn over my air in the cabin about once every two or three minutes. I run both all night with my windows cracked no matter the temperature and often have to throw a blanket on in the middle of the night (far north midwest camping).

-I have one 130 cfm 12v case fan, 200mm size mounted in a frame. It pulls about .25 amps per hour. In eight hours blowing directly on my sleeping area (though rarely over four hours before I get too cold) it burns 4ah.

-I have four LED lights mounted in the TD, They use .35 amps each per hour. A liberal guess of usage would be 3 hours total, so, that calculates to 1.05ah.

-Total average use may be as much as 7.45ah each night. That's without conserving power. It took my 40 watt solar panel (ten years old) about 2+ hours to recharge that battery on a sunny morning.

That's it for 12 volt usage in my TD if you don't consider the emergency 12v blanket I have never used and a couple LED porch lights that I might turn on in the middle of the night for a minute to see what went bang outside.

I started out with one of Mighty Max's 18ah AGM SLA batteries (11.9# each and small enough to stick in a very small spot; 7.1" x 3" x 6.5"). The rule of thumb I go by is never deplete your amp hour capacity by more than 50%, so, I'll call the 18ah batteries 9ah usable. I was running my battery down to maybe within 1.5ah of 50% depletion. I added another Mighty Max 18ah battery doubling my usable power to 18ah just in case I was out and wanted two nights of battery reserve in the event of rain/cloud cover. When conserving power due to cloudy camping I have never run the batteries below 50%. I'm prepared for the worst case with a couple small LED lanterns that operate on disposables.

I'm hoping I will make some extended trips to warmer climates where I will likely have fans blowing on me all night. I may run into a stretch of as many as four cloudy days in a row or more. To prepare I have ordered two additional MM 18ah batteries and upgraded my 10 year old 40 watt solar panels with a new 50 watt panel. This addition will give me a reserve power of about 36ah (72ah rating). That's enough for close to five nights if I conserve. I'll also back up my lighting and ventilation with additional LED lanterns and fans operating on disposable batteries.

I have nothing against the Fantastic Fan. If I had the money I would probably have installed one. However, it is overkill for me. And at 920 cu ft/minute on high it is sucking juice from your batteries at break neck speed.. On high speed that's about 8 complete air changes per minute in my TD. The ventilation of the two 120mm fans and the air movement of the 200mm blowing directly at me are more than sufficient to let me sleep comfortably. It was 80 and humid this past Friday night in Marquette, MI when I crawled in. No problem over night. I actually turned the 200mm off in the middle of the night when it got "cold". In the morning it was 73 inside and outside the camper. With two bodies generating heat it might have been warmer inside, but I doubt it.

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Re: Battery Question

Postby Homebrewer25 » Thu Jul 25, 2019 8:06 am

Thanks, Tim and Tom.

I think I'll go ahead and start out with one Duracell 12v 90AH, which is $118 with core charge & tax from Batteries Plus.
I will have room to add another if I decide I need one.
And I will have a 100W solar panel/system for keeping the battery charged.

My electrical needs are not yet fully determined, but at a minimum I will have:
Fan (Maxxair or Fantastic)
white LED lights (exterior door, interior ceiling and reading, galley)
blue LED lights (under body both sides, galley)
charging stations (interior and galley)

and probably will have:
12v TV/DVD (for really bad weather)

and may add at some point:
12v Dometic refrigerator.
It's 5 o'clock somewhere ... time for a :beer:

Steve
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Re: Battery Question

Postby rkanz » Thu Jul 25, 2019 9:09 am

I have a Maxxaire fan, lights, and phone chargers. I run a 35 ah agm with a 50 watt solar panel. I bought a Grape Solar panel and charge controller on sale frame Home Depot for $80. With this system I never run out of juice.Image


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