Need Help Finishing Solar Array

pebbledropper

I have a 2008 38' Country Coach w/ 2 OE Lifeline 8D's and a 4-yr-old Xantrex 3000 PSW inverter. All the fuses, breakers, cables, auto switchover, and 50A shore cord are 7 years old OE.

I bought a Magnum 3012 Hybrid inverter, Magnum battery sensor, & ME-ARC remote controller.

I intend to replace the old 8D's with 6-6CT's from Lifeline. These AGM's wired in series to make 3-12V batteries are rated when new at 300Ah, or 900Ah together, which is 450Ah @ 50% SOC. Therefore, I shouldn't ever need to replenish the bank with more than 450 Amps per day.

The current coach electrical system can charge the house bank from its alternator when driving down the road, shore power, and an 8,000W Onan generator. I presume all that is wired into and through the auto switchover; but I have not explored that, yet.

From a project I never did I own 3, still-in-the-box, GO 160W panels from AM Solar as well as a 100W also from AMS. The 3-160's each have a Vocc of 22.2, Vmpp of 18.7, short circuit Isc of 9.32, and Impp of 8.55.

Until convinced otherwise, I plan to buy a FlexMax MPPT 80 solar controller by Outback.

I have room on the roof for 6-160's. My plan was to wire each set of 3 panels in series for 36V and hook them in parallel to go down to the controller, which I hope would be magically changed from 36V to the 12VDC nominal I need for my battery bank.

The run from the likely location of my combiner box to the controller is about 15'.

However, AM Solar is currently out of the 160W. I donno when they will get more. ILO waiting for the matching 160's to come in, I have room for 2-250W or so panels from somebody. That would give me about 980W in the array, 1,080 if I include the single, still-in-the-box 100W.

MY QUESTIONS BEGIN WITH should I hold out for the other 3 matching 160W panels from AM Solar, or buy 2 off-grid, higher voltage panels and somehow wire the disparate parallel strings together, or do something else?
I realize the "something else" may be to buy a controller for each of the disparate strings; but what sizes?

FWIW: I'll be taking the cables from the controller(s) to a high capacity bus bar where all the other devices wanting to be connected to the batteries with also be connected. From the bus bar, I'll go through an APL fuse (pos) and shunt (neg) with 2 cables to the batteries.

Jerry Lewis
McK TX N of Dallas

BB.

OK--Lots of questions here--Sort of makes it difficult to figure out a coherent set of replies--But I will give it a shot.

You tell us what you have, but not really how much power you need and if you are/were happy with the old system or not (more power/more power than you needed/etc.).

In general, getting much more than ~1,200 to 2,000 watts from a 12 volt battery bank is difficult. The amount of current and size of copper wire needed to support those high currents with 0.5 volts or so maximum voltage drop can be quite difficult.

Your choices are to design for that high of AC power output--Really a 24 or even 48 volt battery bank--Or revisit your loads and figure out what you need to run from solar and, if you need short periods of large amounts of AC power--Look at using a genset for those loads.

I really like to suggest designing a "balanced" power system that supports the loads you need. So I will see how I can help with some answers that don't lead you astray.

pebbledropper wrote: »

I have a 2008 38' Country Coach w/ 2 OE Lifeline 8D's and a 4-yr-old Xantrex 3000 PSW inverter. All the fuses, breakers, cables, auto switchover, and 50A shore cord are 7 years old OE.

I bought a Magnum 3012 Hybrid inverter, Magnum battery sensor, & ME-ARC remote controller.

A basic rule of thumb to start a design--You need roughly 400 AH of 12 volt Battery Bank per 1,000 watts of AC inverter and solar array. So, for a 900 AH @ 24 volt battery bank, a maximum of ~2,250 Watt (useful) AC supply and solar array would be about the maximum for that size battery bank.

Now, AGM batteries do support much higher surge currents than flooded cell lead acid batteries--So, for your AC output, you could support your 3kWatt (or larger) AC inverter--Assuming you can keep the cables short and heavy from the Battery bank to the AC inverter:

• 3,000 watts * 1/0.85 inverter eff * 1/10.5 cutoff voltage = 336 Amps typical peak 3,000 Watt AC load current

For a typical off grid cabin design, a 2 day storage and 50% discharge is usually recommended as a cost effective solution... For an RV will little space and to keep weight down, sometimes those systems are designed for 1 day of storage and 50% maximum discharge.... Anyway, assuming two days of "no sun":

• 900 AH * 12 vots * 0.85 inverter eff * 1/2 days storage * 0.50 maximum discharge = 2,295 Watt*Hours of AC power per day

You can see that a 3kWatt AC load would use up your daily ration in about 46 minutes... That it why knowing loads are so critical. To match the battery bank capabilities against your loads.

I intend to replace the old 8D's with 6-6CT's from Lifeline. These AGM's wired in series to make 3-12V batteries are rated when new at 300Ah, or 900Ah together, which is 450Ah @ 50% SOC. Therefore, I shouldn't ever need to replenish the bank with more than 450 Amps per day.

When wiring out your battery bank, you need to make sure the parallel current paths through the three sets of batteries are equal resistance--So that each string carries about 1/3rd of the charging/discharging current. See this website for help:

http://www.smartgauge.co.uk/batt_con.html

The current coach electrical system can charge the house bank from its alternator when driving down the road, shore power, and an 8,000W Onan generator. I presume all that is wired into and through the auto switchover; but I have not explored that, yet.

You really need to investigate the coach's AC alternator and wiring/isolation relay (if any--Do you have a separate engine start bank?). A lot of vehicle alternators tend to only supply high current when they are cool (engine first started) and once they warm up, their output current falls (by 1/2 or more?). Heavy duty truck or marine type alternator systems may be needed it you plan on charging at ~100+ amps for several hours on end (as the you drive).

An 8,000 Watt generator is pretty large, and the Magnum 3012 will only draw about 18 amps @ 120 VAC for charging (~2,160 Watts)--For an 8 kWatt inverter, its efficiency (assuming gasoline genset) will tend to drop below ~50% of rated load (below ~4,000 Watt load). So the "match" between the 8kW genset and ~2kW charging current through the inverter is not great--If you can run other AC loads at the same time (microwave, washer/drier/refrigerator) while charging the battery bank will be a bit more fuel efficient.

From a project I never did I own 3, still-in-the-box, GO 160W panels from AM Solar as well as a 100W also from AMS. The 3-160's each have a Vocc of 22.2, Vmpp of 18.7, short circuit Isc of 9.32, and Impp of 8.55.

Until convinced otherwise, I plan to buy a FlexMax MPPT 80 solar controller by Outback.

I have room on the roof for 6-160's. My plan was to wire each set of 3 panels in series for 36V and hook them in parallel to go down to the controller, which I hope would be magically changed from 36V to the 12VDC nominal I need for my battery bank.

Yes, 3 series * 2 parallel will work fine with the Outback FM 80... However, the Outback will be more efficient if you run 2 panels in series * 3 parallel when charging a 12 volt battery bank. The Outback will need good cooling air (don't install in unventilated closet). And the cooling fans for the FM 80 will be fairly loud during the day when charging (don't put the FM 80 next to your daytime work space if the noise will bother you).

The run from the likely location of my combiner box to the controller is about 15'.

Should be OK... Depending on how you wire the panels (3x2 or 2x3), you will have to look at the cable size. Keep cable form FM 80 to battery bank short and heavy.... You don't want more than a ~0.1 voltage drop from controller to battery bank if you can avoid it (more accurate charging voltage feedback to FM 80).

However, AM Solar is currently out of the 160W. I donno when they will get more. ILO waiting for the matching 160's to come in, I have room for 2-250W or so panels from somebody. That would give me about 980W in the array, 1,080 if I include the single, still-in-the-box 100W.

Mixing/Matching solar panels (old/new, 140 Watt vs 250 Watt, etc.) is always a pain. If you can match Imp for panels to make a string, and match Vmp of panels for parallel connections (panels Imp and Vmp should match within 10% or better for optimum and safe operation). In some cases, it can be almost impossible to mix&match panels (i.e., Vmp~18 volts for some panel and Vmp~30 volts for others) and connect them to a MPPT charge controller).

You are left getting new panels that will match or get a second charge controller or other solution. Details matter here.

MY QUESTIONS BEGIN WITH should I hold out for the other 3 matching 160W panels from AM Solar, or buy 2 off-grid, higher voltage panels and somehow wire the disparate parallel strings together, or do something else?
I realize the "something else" may be to buy a controller for each of the disparate strings; but what sizes?

There is no "right answer" here... You should do several paper designs and see which is the most cost effective for you (many times, you can sell panels on Craig's List for a pretty good price). Or even use one or two the the smaller panels to keep the vehicle batteries charged, etc...

Just to give you some idea of total panel wattage using rules of thumbs design... 5% to 13% rate of charge for off grid solar... 10% or greater for full time off grid solar (i.e., cabin/home) recommended (and minimizing generator run time).

• 900 AH * 14.4 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 842 Watt array minimum
• 900 AH * 14.4 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,683 Watt array nominal
• 900 AH * 14.4 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,188 Watt array "cost effective" maximum

Note that even a 10% rate of charge on a 900 AH is 90 amps, more than the FM 80 is capable of... So if you choose to install a larger array (over ~1,500 Watts), you should look at a second solar charge controller.

FWIW: I'll be taking the cables from the controller(s) to a high capacity bus bar where all the other devices wanting to be connected to the batteries with also be connected. From the bus bar, I'll go through an APL fuse (pos) and shunt (neg) with 2 cables to the batteries.

Sounds correct... But the details matter. Cable AWG, current draw, fuse/breaker ratings, etc....

-Bill