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Solar charging

Started by kelkat, February 12, 2016, 11:22:07 PM

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kelkat

thanks for the info! i forgot i have a smaller panel with usb ports for my electronics.  i don't need the 12v coffee maker and have a percolate for the stove.  i have a heater buddy with propane.  the light/fan combo is the one they threw in with the camper and also have a battery operated fan light combo.   i have an older roll up panel but i can't remember the wattage.  it's 2'x4'.  i hope to get out for a couple of 1-2 night trips before my big Moab trip in April to test things out.

charliem

[font size="3"]Sounds like you're good to go so why ain't you gone yet?  8-)
[/font]
Any 20 minute job can be stretched
to a week with proper planning

Charlie
NW Florida

david

From my own experience, we never camp in places where there is any sun, period. The trailer is always shaded. In most of the USFS, SP and NP sites you would have to put your solar panel 50 feet away from your trailer and even then you wouldn't get more than several hours of sun.

We have a similar usage pattern as the OP, excluding the coffee pot, which I agree isn't a candidate for solar. We use about 15 amp hours each day. So our 70 amp hour group 27 battery can last two days or more and stay within the recommended 50% discharge level for best life.

So, given that sun is not available all day and maybe just for a few hours, I would pick a 100 watt system. With full sun all day long a 100 watt panel will put out 25-40 AHs. But figuring that shading will limit you to about half of that, then 12-20 AH of daily output should pretty well keep up.

Here is a page of 100 watt panels in the low $100 range: http://www.amazon.com/s/ref=nb_sb_ss_c_0_10?url=search-alias%3Daps&field-keywords=100+watt+solar+panel&sprefix=100+watt+s%2Caps%2C179

Also add a solar controller like this one: http://www.amazon.com/Morningstar-SK-12-SunKeeper-Charge-Controller/dp/B007NYZ5VU/ref=sr_1_8?ie=UTF8&qid=1455394472&sr=8-8&keywords=morningstar+pwm+charge+controller

The controller is totally waterproof so you can mount it near your battery outside. Wire the output of the panel to the controller by clipping off the MC4 connectors and splicing 14/12/10 gauge wire depending on the distance. Use 10 gauge for 50', the smaller gauges for shorter lengths. Then wire the output of the controller to your battery terminals with at least 14 gauge.

I have such a system on my boat. It cost about $200 and will recharge my batteries within a couple of days in full sun. I have two GC batteries with 220 AHs of capacity.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

777

I have a 8.5x22 and often camp in cooler weather and the heater works a lot at night, plus all the interior lights, etc... We would run through one battery easily. So when I replaced the one I added 2 more. I also added a 235 watt panel on the roof with a 12 volt charge controller by GoPower to charge the batteries. It works great with sun of course, but I live in wonderful NM and we get plenty of that. In good sun it will push 9 amps and fully charge batteries in a couple of hours and I'll even switch the fridge over to DC just because I can. When I run the generator in the day I flip the beaker switch so the generator isn't charging batteries as well and that helps the 3500 watt generator run the AC with less of a load. I've considered adding another panel so I can run the fridge during the day on DC and still maintain batteries at 100% for night usage. I haven't installed an inverter yet just due to the initial cost, but I plan to sometime this year.

david

777:

Some observations and comments about how you use solar power and your generator:

1. When you run the fridge on DC it runs at less cooling output than AC or LPG. It is ok to keep stuff cool, but will struggle if you put something warm in the fridge. Also it draws lots of DC current and will run your batteries down faster. Propane is cheap and it takes very little to run the fridge, and a whole lot less than the equivalent gasoline to run your generator.

2. Your 3,500 watt generator should be able to run the A/C as well as the converter just fine. The A/C draws about 1,500 watts and the converter draws about 600 watts, so the total is well below the generator's capacity.

3. 9 amps DC from a 235 watt panel is low for full sun during the middle of the day. Should be about 15 amps. Look at your wiring size and distances. I would use 14 gauge from the panel to the controller to keep the voltage drop reasonable, maybe 12 gauge if it is more than 20 feet away. But the wire size from the controller to the battery is critical. Since the controller is typically putting out about 14V when you are charging at 15 amps, if you use 14 gauge and the controller is ten feet away from your batteries, the voltage drop is 0.8 volts. That means that the controller thinks it is putting out 14 volts which is what the battery needs to charge it quickly, but due to the voltage drop the battery is really seeing 13.2 volts. That won't do much charging and may be the reason your amperage is low. I would use at least 10 gauge for the controller to battery run which will keep the voltage drop down to 0.3 volts and even bigger if it is more than 10' from the controller to the battery.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

777

Thanks a bunch! I need to reroute and do some redesign of the whole front storage bays and will run appropriate sized wire. The distance from panel to controller is only about 10 feet and uses the same gage wire that is on the panel. Again thanks for your input!

charliem

[font size="3"]Ditto everything David said. At 12V every tenth of a volt is critical. For example, 20 feet (round trip) of 12AWG at 10 Amps produces a 0.32 volt drop. The run from controller to battery should be 10 minimum, preferably 8AWG.
[/font]
Any 20 minute job can be stretched
to a week with proper planning

Charlie
NW Florida

david

Makes me feel good that this retired chemical engineer can garner words of support from a (retired) electrical engineer on an electrical subject.

But seriously, I have lived with this stuff on a boat where unless you have a genset (and marine gensets are $10,000+) you have to carefully manage your DC usage and production. And since propane refrigeration won't work on a sailboat (needs to be kept level to work) the DC requirement is much higher since it has to cover refrigeration. Some boats have several hundred watts of solar panels and several hundred or more amp hours of battery capacity to make it all work out.

I installed my first solar panels on my boat about 15 years ago and every boat since has had solar panels, some with enough capacity to fully cover my DC needs (400 watts) and others to just keep the batteries topped up. (100 watts).

RV DC management is exactly the same as boating use with the exception that boats use 5-10 times more amp hours to provide for refrigeration. Another difference is that RVers call their AC battery charger a converter for some reason. Always made me suspicious that they weren't real three stage chargers, but I read the specs on the one in my CL and it says that it is.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

david

777:

I just reread your post and looked up Go Power solar charge controllers. Their solar controllers are all PWM (pulse width modulation) that work with nominal 12V panels. If you have a single 235 watt panel, then it is almost certainly a nominal 24V panel.

The Go Power PWM controller (if that is what it is) is wasting about half of your solar panel's output. You need a MPPT (maximum power point tracking) controller that will convert the 24+V input to the 12+V output that your batteries need.

That is why your amperage is so low if you really do have a PWM controller.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

777

How do I check the voltage from the panel, to insure it's the 24v

david

A simple test is to disconnect your panel from the controller. Then measure the voltage from the panel with nothing connected but your voltmeter while it is pointing towards the sun. If it is a nominal 24V panel, the voltage will be 30+, maybe as high as 40V, the so called Voc (open circuit voltage). If it is a nominal 12V panel, the voltage will be 15+, maybe as high as 20V.

I have never seen a nominal 12V panel at a wattage of 200 or more. The largest 12V panel I have seen is 150 watts.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

777

Sounds good, I'm sure it's 24v. Bummed I wasted money on the wrong charge controller. Any brand recommendations for MPPT controller?

charliem

[font size="3"]Until David wakes up and has his coffee I'll make a suggestion  ;)   . My choice would be the Morningstar Sun Saver MPPT

[a href="http://www.morningstarcorp.com/wp-content/uploads/2014/02/SSMPPT_ENG10_1111.pdf"]http://www.morningstarcorp.com/wp-content/uploads/2014/02/SSMPPT_ENG10_1111.pdf[/a]

Although it's rated at 200W max it will handle your panel without damage and the times when you would actually get 235W from your panel are rare. It's available from Amazon and Northern Arizona wind and Solar. Designed in the USA, manufactured in Tiawan (not PRC) and warranted 5 years!

That said I'll yield to David's hands on experience if he has additional suggestions.
[/font]
Any 20 minute job can be stretched
to a week with proper planning

Charlie
NW Florida

david

Well, I am up, awake and on my second cup of coffee and agree that the Morningstar controller noted above should work fine. It is listed for $228 on Amazon: http://www.amazon.com/Morningstar-Sunsaver-TrackStar-Charge-Controller/dp/B006H9VPL6/ref=sr_1_1?ie=UTF8&qid=1455719327&sr=8-1&keywords=morningstar+sunsaver+mppt

I have used Morningstar PWM controllers in several applications and they always worked fine. Can't say the same for Chinese made controllers. Well in reality the Morningstar one is probably made in China but it is engineered and QC managed from the US.

FWIW here is what they say about power and current specs: Input power can exceed Nominal Maximum Operating Power, but controller will limit and provide its rated continuous maximum output current into batteries. This will not harm the controller (reminder: do not exceed Voc).

Interestingly that means that it will limit output power to 15 amps if you hook it up to more wattage. The chances of that ever happening with your 235 watt panel are slim in any case as Charlie noted but it is nice that the controller won't be harmed if it somehow happens.

Your Voc should be fine, but you probably should measure it as I described above to make sure. It is very unlikely but they do make nominal 48V panels where the Voc should be above 75. But if you had one of those, you wouldn't even make 9 amps when connected to a PWM controller and it would probably toast the controller.

David
David M

16TBS towed with a 2013 Nissan Pathfinder

charliem

Quote from: @david" timestamp="1455720340" source="/post/18775/threadWell, I am up, awake and on my second cup of coffee and agree that the Morningstar controller noted above should work fine.

Can't say the same for Chinese made controllers. Well in reality the Morningstar one is probably made in China but it is engineered and QC managed from the US.

David
[font size="3"]Good morning. Morningstar is mfg'd in Taiwan, not mainland China. I've had plenty of bad experience with Chinese junk; not so with Taiwan. Chinese products are usually warranted for 5 minutes or 5 miles, whichever occurs first.  :( [/font]
Any 20 minute job can be stretched
to a week with proper planning

Charlie
NW Florida