Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

More or less, the reasons I try recommend 5% minimum for flooded cell batteries:

• recommendation for equalization current by Rolls/Surrette (and probably others)
• enough current to equalize/mix electrolyte in tall batteries
• as Flooded Cell batteries age, they can discharge at a rate of 1-2% per day... Assuming you have 6 hours of full sun--that is 1/4 of the day to recharge the battery bank--you are looking at needing 4-8% rate of charge just to keep the old (typically forklift type) batteries charged from self discharge.

Obviously, the 1% per day losses from an old battery bank is pretty much time to time replace the bank unless you got a bunch of excess solar power available to keep them going.

Old AGM's are down in the range of 1-2% self discharge per week, never require mixing of electrolyte, and should never to equalized (at higher current/voltage like for a flooded cell bank). So--their minimum charging current can be much less.

Anyway--probably let Jesse and Kiva recharge their battery bank so they can read the posts and reply back later. We don't want to get too far ahead of them.

-Bill

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Jesse,

The 14 hours a day of a 10 amp steady state load was based on average solar power available from the sun (some days more, some days less).

It sounds like your solar panels and charge controller are working correctly--so that part is OK.

And, an MPPT controller, in your case, may increase your solar panel output a bit (~10-20%)--however, that will only be in cold weather--not during the hot summer months. At this point, I personally do not see a need for a MPPT controller unless one of your other ones fails.

And you have no need for additional PWM controllers to split the array. Will not make any difference (that I can see).

As to how long will your batteries supply your 10 amp load:

AGM: 7x 85 AH at 12 volts = 595 AH
Trojan: 8x 225 amp hour at 6 volts * 0.5 for 12 volt hank = 900 AH
==================================================
Total 1,495 AH at 12 volt

Assuming you don't discharge below 50% (longer battery life, and never discharge below 20% state of charge or you can damage your bank):

• 1,495 AH * 0.50 max discharge * 1/10 amp load = 74.75 hours or 3 days

So, yes yo have a lot of battery capacity--and if the batteries are fully charged, 3 days of a 10 amp load should not be a problem.

The max charging rate of your solar panels is around 31 amps:

• 31 amps / 1,495 AH = 0.02 or 2% charge:battery capacity ratio

That is a very low charge rate... Normally we recommend a range of 5%-13% charge rate... So, from our point of view, you have either way too little solar panels or way too much battery bank for your current solar array.

The wild cards in this are the mixture of battery chemistry and the large battery bank with relatively small amounts of solar power.

The mixed chemistry may mean that one type of battery is getting fully charged, and the other type is not.

The way large battery bank, especially with flooded cell batteries--As they age, their self discharge rates go up (1% per day) and can, in your case consume your entire solar array's output just to try and keep them charged.

What should you do??? Depends on how much money you have to spend and what other equipment you have available.

My suggestion would be to split the bank to AGM vs Flooded Cell. And get a good quality AC battery charger and genset--and recharge them to 100% state of charge (basically 14.x volts and little charging current). You could use the genset for flooded cell bank, and the solar panels for the AGM bank.

Then, place your load on each bank, and see how long you can run your 10 amp load one each bank:

• 900 AH * 0.50 discharge * 1/10 amps - 45 hours of load (pass)
• 595 AH * 0.50 discharge * 1/10 amps = 30 hours of load (pass)

You may find that the batteries are fine, or that one or more are near end of life.

At this point, your array is sized nicely to power your AGM battery bank. The Flooded Cell are just too large without using a genset to keep them up (my guess).

I guess my question is are you happy with your system--Or are you running out of power at night (what is the bank voltage at the end of the night). I am guessing you are running out of power with the blinking yellow light--so that means that your batteries are not getting fully charged, your loads are more than you think, or the batteries are aging and not able to supply as much energy as the used to.

And, if as Marc is guessing, you are chronically undercharging/over-discharging/"deficit-charging" your battery bank--then the batteries will fail sooner (3-4 years of life vs 6-8 years of life).

To help you with understanding your electrical use: Think of your solar charging system like a gas pump pumping XX gallons of gas per day... And the batteries are a fuel tank with XXX gallons of capacity (and some gas evaporate/leaks/etc. from the tank--the larger/older the tank, the more it "leaks").

Watts and Amps are like Gallons per hour, a rate. How fast you are recharging or discharging your battery bank, how much power your devices are using.

Watt*Hours and Amp*Hours are the gallons themselves (a value). How many gallons are in the tank, how many gallons did your devices use in the last day, etc.

You will see us switch between Amp and Watts, and Amp*Hours and Watt*Hours.

Traditionally, the "battery guys" used Amps and Amp*Hours.

The engineers and electrical power industry typically used Watts and Watt*Hours (and kWH for home power billing, etc.).

Both are good and have their place... But it probably will confuse you to no end... Basically Amps and Amp*Hours is just missing the operating voltage (12 volts for your battery bank. 120 volts for your AC loads).

So to convert back and forth--just multiply or divide by the voltage you are talking about:

• Watt = Amps * Volts
• Watt*Hours = Amps * Hours * Volts

-Bill

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Anima Center wrote: »

I either need to sell the Trojans, or run 2 separate systems.

As Marc says above--we still don't know/understand your daily load... The initial calculations seem to indicate that you are right on the edge of more load than the solar panels can reliably output for you (if you get a cloudy/hazy stretch of weather especially).

You may want/need the larger battery bank if you get more solar panels--but mixing the AGM+Flooded cell on one bank is not a great idea. Using the A/B switch may sort of help--especially if you get additional power sources (genset or more solar panels).

Trojans will require a gen for equalizing, if I keep them. The AGMs may not require a gen.

Or more solar panels... Regarding the genset--Your needs may decide if you need one (especially for days/week of bad weather) or not.

Most of a solar off-grid system is pretty bullet proof... However, the batteries are the one thing that will die early if treated badly.

Having a small(er) genset with 10-20 gallons of fuel (and fuel stabilizer for up to ~1 year storage if kept reasonably cool) is usually good insurance and pretty handy at times too.

There is no dual bank controller larger than 25amps.

Most PWM controllers (not MPPT) can actually share a solar array... You could increase the size of your solar array and use one controller to charge your AGM bank and a second controller to charge your flooded cell bank. The two banks (and controllers) would share a common negative ground connection between them.

I have enough panels already for the 7 AGMs, but need more wattage if I have more storage.

More or less correct... The other big issue is your daily load requirements (Amps times Hours). I really recommend some mix of one or more of the following:

• Battery Monitor (not ideal with mixed battery bank)
• Accurate DMM (Digital Mult-Meter)
• Kill-a-Watt meter (nice for 120 VAC loads)
• DC Amp*Hour / Watt*Hour meter
• DC Clamp Current Meter (use to debug your solar panel/battery wiring)
• Hydrometer + thermometer (for flooded cell batteries).

Each tool has its place. A Battery Monitor (especially with AGM's) is a really nice tool to have since you cannot measure specific gravity.

If I keep the Trojans for a separate system, I need about 30 amps of panels to keep it properly charged.

To charge and use them... If you are just keeping them in "storage"--You could get by with 1/2 that amount of solar panels or less and just charge/equalize them once every month or so (as needed).

If you where going to be "using the bank"--yes, I would go 45 amp minimum of solar panels (45a*17.5v=~800 watts of solar panels)--the 5%-13% of rated capacity rule of thumb.

If I use 2 systems, I either use the Blue Sea switch or dedicate different loads to each.

It is difficult to know what would be good for your installation. I am not an advocate of manual switching of battery banks... I assume that it will get old and eventually people will stop doing it.

The low watt panels should be pulled out of the systems regardless.

No, as you have them wired right now--they are not hurting anything and (hopefully) are contributing to your energy production.

I don't need to make strings of matched panels, or jump up to 24volt (there is only 30 feet of wire between the arrays and the batteries).

I should never have the weaker panels between the strong ones and the controller.

Not a clear way of stating the problem/solution... Basically, for parallel connections, the Vmp's should be close (within 10% for MPPT controllers, > 15 volts for PWM controllers on a 12 volt battery bank). If you have a Vmp=17 volt and Vmp=34 volt on one controller in parallel--it is, at the very least, a waste of 1/2 the energy of the Vmp=34 volt panel.

For series connections (you are not doing any at this time)--you would not put a 12 volt car battery and motorcycle battery in series for 24 volts--The smaller battery will get damaged/destroyed if there is a heavy or sustained load (car battery >>> motorcycle battery).

However, you could put a 12 volt car battery in parallel with a 12 volt motorcycle battery and it will work (not great or recommended, but it will work--just like your system is working so far with AGM+Flooded cell in parallel).

At this point, your system is still "small"--so unless you need 24 volts for something--I would wait and define your needs first.

Regarding the 30 feet from solar panels to charge controller--what gauge wire are you running? Too small of wire and long distances will give you lots of voltage drop--and 12 volt systems (especially) do not tolerate voltage drops very well.

If so, which is more practical: Buying 30 amps worth of panels, a controller, wire, switch etc for the Trojans, and maybe another panel for the AGMs.... or else, trying to sell the Trojans and stick with one system, with more AGMs, more panels and a 45 or 60 amp (non MTTP) controller??

In general, define/measure your loads first (amps/watts and time/hours)--then define/build your system.

It is very difficult for us to guess at what is optimum for you without knowing your loads.

And, as you can see, it is possible to put a system together out of bits and pieces--but it becomes very difficult to service/understand/get good life out of the batteries.

In the end, it sounds like the system is sort of meeting your needs right now--but the batteries are either not getting charged (not enough solar panels + too much loading + no backup generator/charger).

Measuring your daily load (amp*hours of DC use) would be a good start. Just connecting to your AGM bank for now, possibly another good thing to do (assuming the AGM's are still good--Not known at this time).

Getting a full charge on all of your batteries (generator, put 1/2 your bank on an outbound truck for charging at home/office) and then seeing how the hold up with a known load--will tell you a lot.

-Bill