Battery and Solar

[Hilldweller]

Do you have any amp numbers on your 12 volt items? Or are you saying that for most of them in use you can go 3 days in warm months (no electric blanket use?)? Does your trailer have a fridge in it now?

Right now it's just an Edgestar-43 and a few lights. The Edgestar uses more juice than the ARB will.

The electric blanket isn't a given yet. Right now we use a propane heater --- but the tent on the Conqueror is huge. The heater works great; it would cook us alive in a teardrop trailer.
Still thinking about how to get/stay warm.

 

[teotwaki]

Right now it's just an Edgestar-43 and a few lights. The Edgestar uses more juice than the ARB will.

The electric blanket isn't a given yet. Right now we use a propane heater --- but the tent on the Conqueror is huge. The heater works great; it would cook us alive in a teardrop trailer.
Still thinking about how to get/stay warm.

I've tried a Mr. Heater "Little Buddy" for my RTT and it did great at pre-heating the tent before going to bed and before rising. Got it on sale through Gander Mountain

 

[Hilldweller]

I might just get a smaller one that runs off a 1 lb bottle.
The electric blanket is cheap and I can mess around with it. Since I'll only need it for short bursts when the fridge isn't pulling amperage, I think I'll be okay.
Funny how the fridge doesn't drain the battery too much in January in the mountains here... :ylsmoke:

 

[dwh]

Most of our camping is in wooded areas...That's why I was looking at jumbo panels....The idea for solar is to avoid the genny use entirely...

Looking at the pic you posted, there is a major problem - dappled sunlight.

Because of the way PV modules (solar panels) are built with strings of very low voltage (like 1/2v) cells wired in series, getting shade, even partial shade, on some of the cells, cuts the output of the string of cells dramatically. Basically, the cells are either making power or using it, and if some cells in the string are making and some are using, the total output of the string drops. If half are making and half are using, then the output is nothing.

It also causes hot spots in the PV module, because the cells that are using power have now become little heating elements, so manufacturers rig up some diodes to bypass around shaded sections and prevent the hot spots. But because the cells are wired in series, cutting some of them out drops the voltage. To charge a battery, the voltage of the PV module has to be higher than the battery's voltage, so if you cut out a section of the series string and drop the voltage - you might not have enough voltage available to charge the battery. So even though the PV module may be "technically" making some power, it might be doing it a voltage that is too low to be usable for your purpose.

Because of that, dappled sunlight (a.k.a. partial shading) can make the harvest of a solar panel into a complete crapshoot - you might get something, you might not. You probably won't.

It's a common problem with solar and RVs - if you want power, you gotta park in the sun, but who wants to park in the sun? This is one reason why smaller panels can be better - you can park in the shade, run an extension cord to the solar panel and set it up in the sun. You can also aim it so it gets the maximum harvest, and move it around so you can get a good harvest all day instead of for only the few hours that a fixed panel will get.

In that sort of arrangement, a smaller panel can (usually will) harvest greater watts in a day than a large fixed panel on an RV parked in partial sun.

There are various issues with the smaller movable panel, which can all basically be summed up under the category of, "It's a hassle". For your situation, the hassle is probably worth it.

 

[teotwaki]

I might just get a smaller one that runs off a 1 lb bottle.
The electric blanket is cheap and I can mess around with it. Since I'll only need it for short bursts when the fridge isn't pulling amperage, I think I'll be okay.
Funny how the fridge doesn't drain the battery too much in January in the mountains here... :ylsmoke:

"Little Buddy" uses one pounders :sombrero:

 

[teotwaki]

A lot of this has been hashed and re-hashed on the forum so I did a bit of searching for ARB/Engel info. Apparently there was an article in Expo Journal if you have been receiving that.

The "older" MT-45 fridge runs from 20 to 28 amp hours per day if set on "REF", if it is moderately full inside and when equipped with an external insulated cover. The newer ARB pulls less current if I recall correctly but we can use this as a starter.

 

[Hilldweller]

Thanks, dwh; that's somewhat along the lines I had been thinking and what had me considering the folding flexible panel. The weight and pack-ability along with the ability to move it.

But, then again, it's very convenient to pilfer, isn't it? :costumed-smiley-007


I was thinking 20 amps or less/day for the ARB, teotwaki. My Edgestar is doing that now and I was hoping for an improvement.


Something happened today that put me on the fence anyhow. I need a beer.

 

[teotwaki]

Thanks, dwh; that's somewhat along the lines I had been thinking and what had me considering the folding flexible panel. The weight and pack-ability along with the ability to move it.

But, then again, it's very convenient to pilfer, isn't it? :costumed-smiley-007


I was thinking 20 amps or less/day for the ARB, teotwaki. My Edgestar is doing that now and I was hoping for an improvement.


Something happened today that put me on the fence anyhow. I need a beer.

No problem! All disagreements aside, DWH, myself and others just want to help you out regardless of the final outcome.

 

[ken78cj5]

If you want to increase your battery useage, connect 2 6V in series for a total of 12V. For all you engineers out there ohms law states that the current is inversly proportional to the voltage. Half the voltage = double the current capacity.

 

[dwh]

that's somewhat along the lines I had been thinking and what had me considering the folding flexible panel. The weight and pack-ability along with the ability to move it.

But, then again, it's very convenient to pilfer, isn't it? :costumed-smiley-007

Yup, those are some of the issues. Another is voltage drop from a lengthy run of wire between the panel and the charge controller.

My only problem with folding panels is they tend to be bloody expensive on a cost per watt basis.

 

[TreeTopFlyer]

teotwaki asked me to re-publish some of my data logging files from when I was running tests on my Norcold Fridge.

I don't have MS office on this machine right now so I am guessing at the files. I think these two files are with the norcold set at #3 and #4 temp settings. The fridge was "full".

I am doing a 3 day camp this weekend. I will try and run some new logs this weekend and detail how it goes.

One thing that was surprising was how using the fridge at a cooler temp avg'd less amps even though the fridge ran more.

I tried to get ARB to send me an insulated cover so I could do some benchmarking with a cover and without, but no dice on that.

 

[Hilldweller]

My only problem with folding panels is they tend to be bloody expensive on a cost per watt basis.

At the end of the day, overall savings and value are moot if it doesn't work due to shade...

The reality of the use is that 48 weeks a year it will be in shady areas but time in the field will be 3-day weekends or standard weekends. That makes it easy to get by on 2 batteries.
Then there's the 2 (or so) 5-day trips like Thanksgiving; that stretches 2 batteries but can still be done with nothing else.
Then our annual 2-week roadtrip. And those are often "out west" where we'd get more sun.

Hence my position on the fence.

A hard panel is so appealing for ease of use. It's just there, ready, willing, screwed to the shell.

My Honda genny does a fine job but there's the bulk factor, noise (although very minimal), fuel requirements, and the general Zen-less nature of it.

.

Fridge decision might also come down to dimensions.
My Edgestar works great; it would certainly be better if it had a blanket like some other brands have.

 

[dwh]

If you want to increase your battery useage, connect 2 6V in series for a total of 12V. For all you engineers out there ohms law states that the current is inversly proportional to the voltage. Half the voltage = double the current capacity.

Well...no.

Both 6v and 12v batteries are just 2v cells wired in series. If you take two 6v batteries and wire them in series to get 12v, you still end up with the same thing as a 12v battery - 6 2v cells in series.

If you take two 6v batteries that have a 100ah capacity and wire them in parallel, you'll have 200ah capacity - but still at 6v.

If you wire them in series, you'll have 12v - but still only 100ah capacity.

Watts is the same either way.

6v x 200a = 1200w
12v x 100a = 1200w


If you can get 10 hours out of one battery before it's dead and then you hook up two of them, you'll get more than 20 hours out of it. That's the Peukert Effect:

http://en.wikipedia.org/wiki/Peukert's_law

 

[teotwaki]

.

Fridge decision might also come down to dimensions.
My Edgestar works great; it would certainly be better if it had a blanket like some other brands have.

Maybe look at having a custom cover built for the Edgestar since Engel/ARB/Norcold covers are not cheap. It could use dense foam, canvas and velcro to keep it cheap. No fancy zippers or mesh screen inserts.

 

[dwh]

At the end of the day, overall savings and value are moot if it doesn't work due to shade...A hard panel is so appealing for ease of use. It's just there, ready, willing, screwed to the shell.

Yea. I wasn't really talking about folding panel vs. solid fixed panel. What I meant was more like folding portable panel vs. non-folding portable panel.

If you look at teotwaki's pic of his setup, he's using solid panels in a non-fixed way. Those panels are a far less expensive on a cost per watt basis than a fold up made of webbing and velcro.

I just have a natural preference for that sort of setup because of how much the foldups cost per watt.

The issues with the non-folding panel are bulk and weight, and the possibility of breaking the glass. On the plus side, you can drill a hole in the aluminum frame to padlock it to something.

I suppose another way would be to fab up some lockable quick-release mounts and use a couple of smaller solid panels. Then they could be fixed on the top of the trailer, but one could pop them off and set them in the sun if needed.