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k4fcp View Drop Down
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Direct Link To This Post Topic: dual batteries
    Posted: 13 May 2013 at 12:33pm
I've been doing solar powered camping for 12-14 years and everyone makes good points; however,
I do have some suggestions from my experiences.

Mounting panels on the roof is a terrible idea except for maintenance charging.  I attach mounts to my panels so they are portable and can be directed towards the sun and also placed in position to get the most from the sun.  This alone will result in a 30-40% gain.

There are two types of charge controllers PWM and MPPT .  The PWM has a problem and results in your solar panels actual power being reduced by 30%  (ie an 80w panel is effectively reduced to a 56w panel).  The MPPT is more efficient and enables your 80w panel to put out it's rated power), actually a little more.

LED's are the way to go with lighting.......ooops, I have  an appointment in 20 min so I'll post and add later as I can't see a draft function
Rich
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Direct Link To This Post Posted: 25 Apr 2013 at 9:21pm
Called the dealer.  They supply an Interstate 12v 24 group 'marine-grade' battery.  Looked online and it seems there were two models.  Have to ask which one they are supplying.  Still a better option to add the golf batteries, given the greater AH they will provide.
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Direct Link To This Post Posted: 25 Apr 2013 at 7:33pm
I guarantee its the cheapest one they could buy.  If you go with dual batts get two 6 volt batts wired in series, it cuts down on potential issues.
Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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Direct Link To This Post Posted: 25 Apr 2013 at 12:59pm

I appreciate everyone's collective knowledge and the good discussion.  I'm learning alot - and certainly have food for thought.  We wouldn't be able to use the solar, even for maintenance, at home, since we live in the fog.  But I have shore power for that.  Camping on the coast will also limit the amount of direct sunlight.  Perhaps a combination of the two would work, for those trips inland where there is more sun, and the generator for the cloudy/foggy days.  A dual battery would sounds like it would at least give us enough power for the long weekend trips nearby.  Seems like I'll be checking with the dealer and see if the 'free battery' they throw in is quality or if we just buy a good pair.

I love the idea of human power - eco-friendly!
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Direct Link To This Post Posted: 24 Apr 2013 at 10:07pm
I can end this discussion about solar versus gen sets. get an old bike, rig a 30 amp alternator to the rear wheel. (alternators need excitation) get the grill hot. grill some brats, dogs, burgers etc, when the downwind kids show up, put them on the bike, hold out a grilled treat in front of the bike and tell them "ride for a dog" I bet it could work. it would be good activity for the kids, and charge the battery
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Direct Link To This Post Posted: 24 Apr 2013 at 9:10pm

1% every other day in the winter, 1% per day spring/fall, 2% per day hot summer.

Agree, it is feasible.  As long as the panels are in the sun, since just a small amount of shading on a panel will drop its output greatly and not much more shading will drop the output to near zero.

One more option to discuss - the poor man's battery charger.  If you rarely dry camp so a generator or solar system or 2nd battery wouldn't make sense, use the TV.  Every other day hook up jumper cables and run the TV engine for an hour.  Since lead-acid batts charge faster the more discharged they are, waiting for every other day puts more amps in, faster.  Not very efficient in the short term but much more efficient than buying a generator for a few hours of charging time every year. 

Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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Direct Link To This Post Posted: 24 Apr 2013 at 3:38pm
Originally posted by techntrek

Actually most lead-acid designs self-discharge at 2% per day in warm weather

How warm are we talking here? The 4%/week that I mentioned is at 80F...

We could argue about the exact figures all day, but the bigger point is that many people successfully charge their trailers with solar panels and it could work for bodie55 also.

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Direct Link To This Post Posted: 24 Apr 2013 at 2:58pm
Actually most lead-acid designs self-discharge at 2% per day in warm weather, which is why you must top them off at least once a month during the summer.  AGMs have a lower discharge rate but they are rare compared to the usual flooded lead-acid used on most campers.
 
Off-grid solar systems come out to about a 52% efficiency of the solar panel's rating after you take into account the things that furpod mentioned plus the PV derating due to heat, battery losses during charging, etc.  However, that just gives you a rough hourly figure.  Then you need to take into account the "solar insolence" factor, which is roughly 4.5 to 5.5 hours of equivalent sun in most of the US.  So an 80 watt panel * .52 * 4.5 = 187 watts available per day.  That comes out to about 15 amps per day. 
 
If you start off with a charged battery and use 15 amps each day AND get full sun each day, you'll have a charged battery by the late afternoon.  Since you can go down to 50% state-of-charge (and 30% SOC on rare occasions), the typical 100 amp deep cycle battery would allow you to draw out 15 amps for over 3 days if you got no sun at all.
Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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Direct Link To This Post Posted: 24 Apr 2013 at 10:14am
Let me defend solar a bit...

Originally posted by Keith-N-Dar

About six months if you are lucky.  Unfortunately for the cost solar is not a good option if you really want to recharge a battery like on a Pod.  You would need a much larger array than one of the portables.  You can recharge a cell phone or computer, but the smaller arrays may not even overcome the internal resistance in a car type battery. 

No facts or figures here at all... so lets add some: I'm assuming you're talking about the self-discharge of a lead acid battery since the internal resistance is not difficult at all for any charger (20 milliohms)... lead acid batteries self-discharge at a rate of about 4% per week. For a 80AH battery, that's just 3.2AH/week. Even if your 80 watt panel only charged half of it's rated output (40 watts) that would only take an hour of sunlight to overcome (PER WEEK). If you're really concerned about that, get an AGM battery and it's almost a non-issue. As to the cost/watt of course it's going to be more than a generator, but that's not the only factor. Solar panels are silent, maintenance free, can be "running" while you're away, don't cost anything to run, and are extremely light and portable. All of those factors are worth different amounts to different people.

Originally posted by furpod

With a solid mount panel, no tracking mount, you will probably see an average of 1/4 or the panels rated capacity over the course of a clear day.

Not sure where you're getting this figure from, but solar production is usually calculated using solar insolation hours, which depend on the season. For a fixed installation it's around 4-5 solar insolation hours per day. That means with an 80 watt panel you're getting up to 33ah out of the panel. You'll lose about 25% due to efficiency losses, which gives you about 25ah to the battery. That's almost 1/3 the capacity of a group 24 battery.

Originally posted by furpod

So, if you can keep your 12v use low, LED's for lights, no inverter action to run the TV/DVD etc, that 80 watt panel can extend your off grid time, but it's not going to stay ahead if you need to say, run the heater. The heater blower can pull near 30ah a night from your battery(s) all by itself..

The furnace uses about 3 amps when it's running. You would have to run it continuously for 10 hours to get that 30ah figure. Even on a really cold night I'd say my heater is only running an hour or two total. That's only 6ah at most.

Originally posted by furpod

I have not been to the website you mention, but there isn't very much real estate on a pod roof..

They fit a 200 watt system on it...




Originally posted by furpod

Now.. again, there is no doubt that they can, and will extend your off grid time. But for the $$ a small, good genny is the answer. The Honda inverters are the gold standard.

You're right, even a nice honda is only $0.50/watt, which is 1/4 or less the cost/watt of a solar installation... but that's not the only factor. As I mentioned above, there are many advantages of a solar setup that aren't captured in a purely financial comparison.



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Direct Link To This Post Posted: 24 Apr 2013 at 8:31am
Well.. other people are way smarter than me on this but.. IF (and I say IF because it ain't going to happen), but if, you really could get "80 watts" out of your panel, that's a little over 6ah. Real battery talk revolves around amp hours. Real solar talk revolves around actual production, not rated capacity..

With a solid mount panel, no tracking mount, you will probably see an average of 1/4 or the panels rated capacity over the course of a clear day.

so 12 hours times 6.5 or so amp hours at 12v+/- is 78ah a day. HEY IT WOULD WORK!! except.. you will never see any where near that number. Maybe 20ah in real use.. and then there are resitance and conversion losses.. I would bet 15ah available to the battery over the course of the day. Couple cloudy days and you are sunk.

So, if you can keep your 12v use low, LED's for lights, no inverter action to run the TV/DVD etc, that 80 watt panel can extend your off grid time, but it's not going to stay ahead if you need to say, run the heater. The heater blower can pull near 30ah a night from your battery(s) all by itself..

I have not been to the website you mention, but there isn't very much real estate on a pod roof..

Now.. again, there is no doubt that they can, and will extend your off grid time. But for the $$ a small, good genny is the answer. The Honda inverters are the gold standard.
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