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Old 12-04-2011, 12:27 PM   #1
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class for solar

reading the thread on SOLAR THAT REALLY WORKS, got me to thanking, I use 2 large solar panels and not sure if I am getting all that I can. In the past several dealers in Quartsite had classes on solar, does anyone know if they are still doing them? we are heading that way soon.....thanks
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Old 12-05-2011, 10:51 AM   #2
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don't get suckered!

certainly solar works. The real question is "for what?"

As for "getting all that you can" ... that is a matter of chasing after smaller and smaller returns. Those returns, in a complete perspective, are rather small to start with so the tendency is towards a whole lot of effort and expense that is needed for very small returns.

Then there is the 'classes' approach. That is a shotgun approach that should be considered more for entertainment than for guidance IMHO. If you have a particular question to guide your efforts, you'll often find the answer in these discussions. The real knowledge comes from experience.

In understand that my views do not fit either the desired ideology nor the 'common wisdom' and I also understand what that means in terms of response. Take care, watch out for intellectual integrity, learn, and reason carefully.
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Old 12-05-2011, 05:36 PM   #3
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Don't be fooled. The solar dealers in Quartzite are in need of schooling themselves. Re-read "Solar That Really Works". Go to the wire sizing site that is listed and see if your wiring is the right size or one size larger.

Do you have a battery moniter as Handy Bob suggests? That will tell you if the solar is working and how well.

Do you have a battery temperature sensor on the controler?

Are the controler settings adjustable?

Are your batteries getting 14.8 volts @ 80 Deg. F for several hours?

The cooler your batteries are the higher the voltage should go. Mine goes over 15 volts when good and cold. No harm done either.


Is the controler as close to the batteries as possible without being in the same compartment?

Solar is all about the batteries. Or rather getting the power your expensive panels are generating INTO the batteries.

I posted "Solar That Really Works". I renovated my system so it does really work and used Handy Bob's directions, that you read, to do it. You can do the same thing to check out your system.
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Old 12-08-2011, 08:37 PM   #4
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OK here goes with what I have and what little I know;
we are hooked up to shore power at this time, but are heading to Quartzsite soon
I have been using solar for about 4 years when we are out in the boonies during the winter
I have 2 130 watt panels
4 trojan 106 golf cart batteries
blue sky controler mounted 3 ft from the batteries with a moniter in the house. I dont think they are adjustable
panels are mounted on a 20 ft extension cord so I can park the motor home anywhere I want and than put the panels where they will get the most sun. the extension cord is one place I may need to upgrade as it is 16 gage..
temp is mostly about 65 o most of the time in Az where we are
I guess I will have to just keep doing little thing till I get it done the way I want
Have changed some lights, and am loooking at others when I can find what I want
thanks for the input, really helps
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Old 12-08-2011, 09:50 PM   #5
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What model Blue Sky controller do you have?

Since I redid my solar like Handy Bob suggested, I barely use my generator when boondocking. What a difference from my original setup. I set my Blue Sky Solar Boost 2512ix to 14.8 volts when charging and increased wire size to 4ga, shortened wire runs and like you put the controller close to the batteries.

I think with replacing you 16ga wire and increasing charging voltage, you will see a huge difference.
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Old 12-09-2011, 03:11 PM   #6
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16 gauge wire is no where near big enough for that 20ft run. You need to be using 8 or even better 6 gauge wire from panel to controller. Find yourself a long set of 6 gauge battery jumper cables to use (cut clamps off and wire them to your system). Pluggable connectors used in the snow plow / winch arena could be used to connect/disconnect your cables at the controller.

You should be using around 4 gauge wire from controller to battery.

Goal here is to reduce the voltage loss of the cables such that you benefit from all the current (energy) that is available from the PV array.

Please note that voltage loss in the battery charging context is expressed in 10ths of a volt with a normal bulk charging range between 14.4 and 14.8 VDC. You can set the better solar charge controllers for 14.8VDC however if you loose 0.2 VDC due to wire loss then only 14.6VDC is seen by the battery. Some controllers have a seperate monitor wire used to measure the voltage at the battery so that it can set the level such that it compenstaes for wire loss. In this case, the 6 guage wire (panel to controller) is making sure all the maximum amount of energy available from the array is being seen by the controller. The "short" 4 gauge wire is making sure the controller is seeing actual battery voltage (not .1 to .2 volts above the actual battery voltage). So, for solar to be effective, and you feel like the $ investment was worth it, you have to have all the pieces working together.

The 14.8VDC value comes directly from the Trojan RV deep cell battery documentation. It actually represents a trigger value the charging voltage must achieve in bulk mode (constant current mode). Once this trigger value is meet, a 3 stage charger will transition to absorbtion mode. In absorbtion stage, the current is ramped down as the battery charging evolution is completed where it transitions to float mode. While some may say I am stating this incorrectly, all you have to do is go look at any 3 stage charger documentation and you will see it says exactly that (Powermax, PD9200 series, Morningstar PWM Tristar, Morningstar MPPT Tristar, Battery Tender, etc.). The difference is in level settings. The methodology is the same in all of them. Yes, even the Morningstar MPPT Tristar controller uses the 3 stage approach. Boost applies during bulk mode only.

All of this is a balancing act between how high of a charging voltage a wet cell battery can accept (without damage or excessive gassing) for a given state of charge condition (SOC). Using a 14.8VDC trigger value is about as high as you can go (at 80 degrees F) without causing excessive gassing (generation of hydrogen and oxygen gasses from the electrolyte). That however comes with a price in that you must keep an eye on battery water level and add water when necessary. This is where confussion sets in because marketing design for the masses comes into play for the converter/charger market. They design, rather dun down, converters to the 14.4 (bulk), 13.6 (Absorbtion), 13.2 (float) values to prevent complaints from consumers that their converters are burning their expensive batteries up. These levels also work better for the AGM battery market. Can a battery obtain 100% SOC at these reduced levels? Yes. However, it comes at the cost of long charging times (i.e 36hrs). Not convinced? Again, go read the documentation and pay attention to the length of time is required to obtain full charge. Given that the vast majority of RVr's pull into a camp ground and then connect to shore power this is an acceptable marketing stratagy. However, due to short sun availability times, the boondocker that wants to be off grid extracting the utmost from his solar array must tune his system to squeeze all of the energy he can from it (absolute minimum wiring loss and absolutely no opsy shading of the array by A/Cs and such) and get that energy into the battery bank by using the maximum settings available (without damage). That, in my opinion at least, is the real purpose (intent) behind Handy Bob's recommendations. However grasping an understanding of all that is involved to do this can be a challenge. It requires grasping an understanding of battery design and requirements, solar cell array capabilities, wiring impacts, and controller capabilities. Die hard racers understand tuning for maxiumum performance at the track. This is just tuning for maxiumum performance of your energy generation and storage system.

PLease note the 14.8VDC value is only valid at 80degrees F. A quality controller monitors the temperature of the battery so that the battery trigger voltage is higher at colder temperatures and lower at higher temperatures. This sort of thing is not new. The regulator controlling the alternator (or in some cases generator) in your car has being doing this since 1950's and earlier.

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Old 12-09-2011, 06:36 PM   #7
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The herein mentioned 14.8 volts @ 80 deg. F should be measured at the battery terminals not at the controler or anywhere else.
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Old 12-09-2011, 09:06 PM   #8
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Some things I should have also addressed before:

Ralper's statement of it should stay at 14.8VDC for several hours might not be understood. The absorbtion mode voltage setting his morningstar MPPT controller uses is the same as the trigger voltage (14.8VDC). Additionally, his controller is designed to stay in absrobtion mode for at least 2 or more hours. Net result is it is at or near the set voltage for several hours. While he has 400 Watts of solar array capability (approx 30 amps), the max available amperage is only supplied to the battery during bulk mode. During absorbtion mode, the voltage is maintained at 14.8VDC however the amperage is ramped down untill the battery is 100% charged. For reference, normal 3 stage charger operation is such that the SOC is around 90% when the charger transitions from bulk to absrobtion mode. Even though the voltage level is maintained in absorbtion mode, the amperage has to be ramped down the closer it gets to 100% SOC. This prevents damage to the battery and reduces gassing.

The main difference between his controller and a 120VAC 3 stage converter/charger is the voltage values. He has his morningstar set for Bulk - 14.8, Absorbtion 14.8, and Float - 13.4. A typical converter is set for Bulk - 14.4, Absorbtion 13.6, and Float - 13.2. Again, the standard consumer converter is designed for typical RV consumer use, not off grid boondocking. Ralper's setting allows quick recharge within the short solar availability window where the converter extends charging out of many more hours.

Reviewing battery mfg charging data can be either hit or miss or even confusing. Trojan provides good data for their batteries. http://www.trojanbattery.com/pdf/TRJ...UsersGuide.pdf

The data for the popular Interstate battery is somewhat confusing: Interstate Batteries FAQ :: How do I charge certain deep cycle 6-volt and 12-volt batteries?. The bulk trigger voltage listed is lower than the absorbtion voltage for all popular batteries. The absorbtion volatge is much higher than all other mfgs for equivalent batteries. Now combine that with the fact no one really makes a charger that even comes close to matching these values only makes you suspect the validity of the data.

Dave
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Old 12-09-2011, 10:57 PM   #9
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Dave,
Well put. I set up my charging system as in your, and Handy Bob's, description and went from a mediocre to a fantastic solar system.

Also, about 12 years ago I started using Water Miser battery caps. At first I was skeptical, but soon learned outgassing was eliminated, as was terminal and cable corrosion.
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Old 12-10-2011, 08:58 PM   #10
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An additional thought. As per DiHard batteries, any battery should not be charged at more than 10% of its amp/hour rating. My 6 Trojan T-105 batteries have a total amp/hour rating of 675 amps. That means my charging rate should not be higher than 67.5 amps. My solar rarely goes up to 26 amps. (panels flat all the time and dirty half the time). That is about 39% of the maximum rate it should be.

My point is that solar is basically a trickle charge and it would be rare indeed if the batteries were damaged during charging unless the controler malfunctioned.
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Old 12-11-2011, 09:19 AM   #11
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Quote:
solar is basically a trickle charge and it would be rare indeed if the batteries were damaged during charging unless the controler malfunctioned.
a lot of folks don't seem to get this ... ;-)

As for damage, the maximum charge current is mostly a heat thing - you don't want your batteries to suffer a steam explosion or to get too hot during charging. The heat is due to the charging current going through the battery resistance.

But there are other ways to damage things. The 14.8v is good for pushing charging current but can be rather hard on the stuff you have attached to the battery in your RV. (for the kneejerkers: yes, most 12v appliances can handle 14.8v but the issue isn't total catastrophic mandatory meltdown but rather one of risks and benefits)

Another potential damage source common with older solar systems and many RV converters is overcharging over time. That can be seen by electrolyte loss and unseen in plate corrosion. It is why the old trickle or float maintenance charger is not optimum for battery life during storage maintenance.

Then there's the 'vigorous charge' issue. That is a charge that will do a good job of mixing the electrolyte and getting the lead sulfate back into solution. The C/10 charge rate mentioned appears to be a good goal for this level of charging current.

The wire gauge bit is another topic that could use a bit of analysis IMHO. That, too, is a cost versus benefit consideration. An error often made is to use peak current levels for the loss calculations rather than typical current levels. Then there is the problem of just how hard to squeeze the efficiency and what it is going to get you for the effort. I mean, big wire like 4g is nice but really, for a 200 watt peak power RV system at 12v?

It seems to be rather easy to over-engineer RV low voltage systems. Take care!
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Old 12-11-2011, 09:55 AM   #12
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a lot of folks don't seem to get this ... ;-)
The wire gauge bit is another topic that could use a bit of analysis IMHO. That, too, is a cost versus benefit consideration. An error often made is to use peak current levels for the loss calculations rather than typical current levels. Then there is the problem of just how hard to squeeze the efficiency and what it is going to get you for the effort. I mean, big wire like 4g is nice but really, for a 200 watt peak power RV system at 12v?

It seems to be rather easy to over-engineer RV low voltage systems. Take care!
That is what I thought when reading this thread. The OP has 260 W of panels. That should mean a bit less than 18 Amps at 14.8 Volts. He is being advised to go to 6 or 4 guage wiring. Conventional calculations of ampacity would suggest that 10 guage would be adequate. Here is my question: Has anyone here actually checked the real voltage drop in such a system with different sized wiring? i.e. put a current of say 20 amps through various sized conductors over time and measured the actual voltage drop over time.

I'm not trying to stsrt an arguement, just trying to see if "real world" data is available because I prefer real world hard data to hypothetical.

Thanks.
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Old 12-11-2011, 10:37 AM   #13
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Originally Posted by bluepill View Post
That is what I thought when reading this thread. The OP has 260 W of panels. That should mean a bit less than 18 Amps at 14.8 Volts. He is being advised to go to 6 or 4 guage wiring. Conventional calculations of ampacity would suggest that 10 guage would be adequate. Here is my question: Has anyone here actually checked the real voltage drop in such a system with different sized wiring? i.e. put a current of say 20 amps through various sized conductors over time and measured the actual voltage drop over time.

I'm not trying to stsrt an arguement, just trying to see if "real world" data is available because I prefer real world hard data to hypothetical.

Thanks.
Ampacity tables are created with "temperature" as the critical factor. This is to prevent fires. With solar charging "voltage drop" is the critical factor. Use the tables to provide a safe installation and "voltage drop calculations" for peak performance.

Anderson Power Poles are a good choice connecting heavy gauge cables for a plug in connection.
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Old 12-11-2011, 02:17 PM   #14
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re: "I'm not trying to stsrt an arguement, just trying to see if "real world" data is available because I prefer real world hard data to hypothetical."

see Stealth 316 - Wire Resistance and Voltage Drop Calculator to play with numbers. Keep in mind that the panel rating ("260 W of panels. That should mean a bit less than 18 Amps at 14.8 Volts") is peak and rarely encountered. Using probably half or two thirds of that peak for efficiency considerations will probably provide a good comparison.

Voltage drop is one consideration but the real issue is power loss as a percentage of power delivered over the time of day that that power can be delivered.

As for current capacity and temperature and whatnot, a good reference is that the 10g RV umbilicals are rated for 30 amps

10g is easy as its resistance provides a millivolt drop per foot per amp. A 20' run would have 40' of wire. Say 10 amps current; That comes to 400 mV drop - near a half a volt. The power used to heat the wire would be 0.4v times 10 amps or 4 watts. A 14 volt system would be running at 140 watts power so the loss represents 4/140 or about a 3% loss.

Figure that a change of 3 in wire gauge is a factor of 2 in resistance. Do that twice to go from 10 to 4 guage wire. That runs the voltage drop in the above scenario down to 100 mV, the power loss to 1 watt, and the loss rate at a bit under 1%. So you've maybe gained a bit but consider, for a 5 hour solar day and 3 watts not lost to heating the cable, your upgrading from 10 to 4 gauge gained you maybe 15 watt hours out of the 500 watt hours collected.

Take controller and battery efficiencies into account (80% each probably a good value to use) as well in doing your cost to benefit considerations.

The Anderson connectors recommendation is a good one I think. I use the type and configuration standardized for Amateur Radio Emergency Service use. They handle up to 10g wire and 45 amps. You'd need to use the larger version if you want bigger wire or more current. see Powerwerx: Online Shopping for Anderson Power Products Powerpoles, Wouxun Radios, Wire & Cable, Adapter Cables, Powerpole Power Splitters, West Mountain Radio RIGrunner & more for one vendor.

This is all simple algebra. If you want to have more fun, go find the models for solar insolation by altitude, time of year, panel inclenation and whatnot so you can do a proper integration of solar power input over time. Then apply the panel efficiencies for maximum power impedance versus angle of radation, temperature and so on and a few other variables to really have a good time. It might improve things so that instead of talking about efficiencies within a few percent, you can hone it down to a few tenths of a percent! (and I'm reasonably sure you can find papers on this on the web as it appears to me to be a good engineering grad student paper topic).

numbers can be fun! ;-)
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