Opinions on my battery charging profile (solar)

[ewarnerusa]

I am curious about what others with battery charging expertise think about what I'm doing to my batteries. Am I damaging them or shortening their lifespan?

Quick background, I installed 280 watts of 12V solar panels with a fully programmable Morningstar Tristar 45 controller on our new TT in 2012. At max sun I can see 15A from the panels. It had OEM 2x12V batteries that I swapped out for 2x6V Costco GC batteries in 2013. I installed an inexpensive ebay 1500 watt PSW inverter in 2013 that does not like to operate at voltages above 14.8-ish volts. So I've utilized the programmable features of my Morningstar to accommodate this, but I'm wondering if my batteries will suffer from not enough 14.8V+ charging.

My normal charging profile has 14.4V for the bulk and absorption setpoint. It will drop from absorption to float when PMW duty cycle drops to <15% for 10 minutes. I have voltage sense wires and temperature compensation, but I have it programmed to not do the temp compensation at lower than 70 degrees F. This is because I don't want the controller charging at higher than 14.4V during normal use so it plays well with the inverter. I have also programmed an "equilization" to occur every third day at 14.9V with the same temperature compensation cutoff. So when the sun is bright I hit the batteries with up to 14.9V for 3 hours every 3rd day. My logic is that this at least gets the batteries some 14.8V+ time while hopefully minimizing the impact on being able to use my inverter. During winter storage, I change the temp compensation cutoff to much colder since the TT/inverter isn't in use. I think it have it adjust down to 32 degrees F.

Do you think my 6V Costco GC batteries are getting enough charging to stay healthy?

Thanks.

[ewarnerusa]

Thanks jrnymn7. I guess I keep thinking of the Morningstar's voltage sense readings as equivalent to multimeter readings across the posts since that's what they are designed to be. Trust but verify, sure, but since the battery compartment is currently snow covered and accessing the controller voltage readings requires hooking the laptop up to it, I'm waiting until spring... It is just these few months out of the year where daylight is at its shortest, along with snow cover, where I think my batteries may be vulnerable. But I check in often enough to not let them get below the low 12's. I also pulled the 12V fuse for the radio and propane detector, so I hope that knocks down my phantom loads to near nothing.

We had snow in the days leading up to Thanksgiving, then had unseasonably warm and sunny weather on Thanksgiving day. So that morning I brushed the snow off the panels and they basked in unobstructed bluebird sunshine all day (although at a very low angle!). After a period of absorption charging the controller went into my 14.9V cycle which with temp correction was at 15.3V. I didn't check in much more during sunlight hours but the batteries were at 12.9 V when I checked back in well after dark. We've since had several more inches of snow but even the blanketed panels had the battery voltage in the mid 13's when I checked.

[jrnymn7]

As I said, simply VERIFY all other sensors/meters. Once you know the readings are accurate, you're good to go. If not, you can adjust for any discrepancies, or upgrade. Otherwise, you're going on possibly false info. And all things must agree with, or at least relate back to, what your batteries are telling you. Until such time, they are the master, and you are the slave. Role reversal is the ultimate goal, in this case.

Case in point, the Wattage display on my xantrex prowatt 1000 is off by 18 watts. And it only displays to 10, 100, and 1000w, (0.01, 0.1, 1.0 respectively) .At some point it rounds up or down. So I can turn on a 13w light and a 7w light, and the display will read 0.00w. Imagine trying to determine Ah usage based on those numbers. I solved that issue by buying a Mega Watt.

Likewise, its Voltage display is only good to 1/10th of a volt. And it tends to round up at about 0.015v. So, if the bank is at 12.22v, it will read 12.3v. That 0.08v difference represents 30Ah on my 430Ah bank, and potentially several amps of charging current when charging. I solved that issue by buying handheld volt and amp meters, and a Trimetric.

None of this is absolutely critical, or life threatening, but it's nice to know if you ever have to do some troubleshooting (or deal with an overly sensitive inverter).

[ewarnerusa]

Do those of you who are instructing me to check battery voltage with a multimeter doubt the accuracy of the voltage sense readings? I don't refute the ultimate accuracy of a multimeter reading across the posts; however, the purpose of the voltage sense wires is to have a continuous reading of voltage across the battery posts that the controller can monitor to ensure the proper setpoint voltages are being realized at the battery. This acts to compensate for any voltage drop and loss issues due to wire lengths, resistance, etc.
From the manual,
"A battery voltage sense connection is not required to operate your TriStar
controller, but it is recommended for best performance in all charging and load
control modes. The battery voltage sense wires carry almost no current, so the
voltage sense input avoids the large voltage drops that can occur in the battery
power conductors. The voltage sense connection allows the controller to measure
the actual battery voltage under all conditions."

also,
"Battery Voltage Sense: Connecting a pair of voltage sense wires from the
controller to the battery is recommended. This allows a precise battery
voltage input to the controller and more accurate battery charging."

[Crabbypatty]

To answer your question you need to look at the costco battery specs. I think that they are made by interstate. I have Trojans with a charge wizard. The charge wizard only goes to 14.4 and I have had my first pair of Trojans for 11 years. Ill be doing solar in the spring as we dry camp and the last outing our generator had an issue, so I would like less work and more automation.

[jrnymn7]

Oh, O.K., I see now, that unit comes in both versions.

Well, in that case, good thinking! 🙂

I noticed on page 18 of that version's manual, section 4.1.1, EQing coincides with Float mode, so again, it's only to be done once Abs charging is complete. So that's a good confirmation of how Morningstar understands when to EQ.

[ewarnerusa]

It is a pwm controller. I built with expansion in mind, I just haven't expanded (yet).

[jrnymn7]

Once you've established what constitutes FULL for your batteries (notice I said 'your batteries', not someone else's) then you can establish what it takes to get them to FULL on a regular basis. At which point, you'll know when to stop charging simply by the amps accepted at a particular voltage... say 2a at 14.8v.

And it may not take 14.8v. It may only take say 14.6v. What is important is that there is a slight gentle bubbling going on (not a rolling boil, but tiny bubbles every few seconds or so). This is an indication of gentle gassing going on. This, like EQ'ing, is where many folks get tripped up. They get gassing, while charging, mixed up with gassing during prolonged float mode. There is a huge difference, and your manual touches on this. No, you do not want your batteries gassing, while in float, for weeks on end, unattended. But this does not negate the need to bring your fla batteries up to gassing voltage, to achieve a FULL charge.

It's easy to just throw numbers around, and then argue over them. What is really needed, is one's attention to what their batteries really need, and not what someone else 'believes' is best, based on how it makes them feel. And once you establish the facts, charging will be much more predictable, and require less attention to every detail; although you will need to 'check in' once in a while.

[jrnymn7]

o.k, thanks. I recommend doing just the opposite. During the summer, they are getting lots of solar, so much less likelihood they are not getting to full. But in the winter, they are clearly not getting the FULL charge they need.

You also need to verify that the batteries are indeed FULL, when the controller says they are. Trust what your batteries say, and nothing else, until all devices have been verified as being accurate.

You need to supplement the (lack of) solar with gen charging in the morning, if possible, followed by solar for the remainder of the day. In fact, one of the guys here does a gen charge both am and pm, to supplement his solar.

If you haven't already, you need to establish your baseline SG for those batts. To do this, they need a NEAR FULL charge at say 14.8v; followed by a TOP charge (to truly 100% FULL) at say 15.2v , followed by a short EQ at 16v, (or better, at 8v per individual battery). Take SG readings every hour, until SG no longer rises. Let them sit for a couple days with absolutely no loads, and take SG readings, as well as voltage readings, for each individual 6v batt. If all is well and equal, (cuz you can't spell equalize without 'equal'), this is your baseline for future reference.

--- It is very important that you keep the batts very well ventilated when doing Top and EQ charging ---

And I hate to say it, but you could have gone with a much less expensive pwm controller with those 12v panels... mppt is for 24v... and spent more on your innverter. But as BFL often says, you've got it now, so try to make use of it the best you can. 🙂

[ewarnerusa]

In the summer while parked at home it's daily. Right now in winter I peek in there less frequently, maybe a couple times a week. Sometimes it's in float, sometimes not. Daylight is short and we've had snow several times.

[jrnymn7]

Please define "often", thanks.

[ewarnerusa]

Yes, I often see that the system is in float.

[jrnymn7]

So, the obvious question is, are the batteries being FULLY charged daily, or at least every other day?

[jrnymn7]

This is straight out of the owner's manual:

page 33
TriStar MPPT Operator’s Manual

FLOAT Stage
After the battery is FULLY charged in the Absorption stage, the TriStar MPPT 150V reduces the battery voltage to the Float voltage set-point. When the battery is FULLY recharged, there can be no more chemical reactions and all the charging current is turned into heat and gassing. The float stage provides a very low rate of maintenance charging while reducing the heating and gassing of a FULLY charged battery. The purpose of float is to protect the battery from long-term over charge. The green SOC LED will blink once every two (2) seconds during Float charging.

Once in Float stage, loads can continue to draw power from the battery. In the event that the system load(s) exceed the solar charge current, the controller will no longer be able to maintain the battery at the Float set-point. Should the battery voltage remain below the Float set-point for a cumulative 60 minute period, the controller will exit Float stage and return to Bulk charging.
The Float set-point is temperature compensated if the RTS is connected.


EQUALIZE Stage:

WARNING: Risk of Explosion; Equalizing vented batteries produces explosive gases. The battery bank must be properly ventilated.
CAUTION: Equipment Damage; Equalization increases the battery voltage to levels that may damage sensitive DC loads. Verify all system loads are rated for the temperature compensated Equalize voltage before beginning an Equalization charge.
CAUTION: Equipment Damage; Excessive OVERCHARGING and gassing too vigorously can damage the battery plates and cause shedding of active material from the plates. An equalization that is too high or for too long can be damaging. Review the requirements for the particular battery being used in your system.

page 34

Operation

Certain battery types benefit from a periodic boost charge to
stir the electrolyte, level the cell voltages, and complete the chemical reactions. Equalize charging raises the battery voltage above
the standard absorption voltage so that the electrolyte gasses. The green SOC LED will blink rapidly two (2) times per second during equalization charging.
The duration of the equalize charge is determined by the selected battery type. See table 4-1 in this section for more details. The Equalization Time
is defined as time spent at the equalize set-point. If there is insufficient charge current to reach the equalization voltage, the equalization will terminate after an additional 60 minutes to avoid over gassing or heating the battery. If the battery requires more time in equalization, an equalize can be requested using the TriStar Meter or push-button to continue for one or more additional equalization cycles. The Equalize set-point is temperature compensated if the RTS is connected.

WHEN TO EQUALIZE:

The ideal frequency of equalizations depends on the battery type (lead-calcium, lead-antimony, etc.), the depth of discharging, battery age, temperature, and other factors. One very broad guide is to equalize flooded batteries every 1 to 3 months or every 5 to 10 deep discharges. Some batteries, such as the L-16 group, will need more frequent equalizations. The difference between the highest cell and lowest cell in a battery can also indicate the need for an equalization. Either the specific gravity or the cell voltage can be measured. The battery manufacturer can recommend the specific gravity or voltage values for your particular battery.

WHY EQUALIZE?

Routine equalization cycles are often vital to the performance and life of a battery - particularly in a solar system. During battery discharge, sulfuric acid is consumed and soft lead sulfate crystals form on the plates. IF THE BATTERY REMAINS IN A PARTIALLY DISCHARGED CONDITION, the soft crystals will turn into hard crystals over time. This process, called “lead sulfation,” causes the crystals to become harder over time and more difficult to convert back to soft active materials. Sulfation FROM CHRONIC UNDERCHARGING of the battery is the leading cause of battery failures in solar systems. In addition to reducing the battery capacity, sulfate build-up is the most common
cause of buckling plates and cracked grids. Deep cycle batteries are particularly susceptible to lead sulfation.

NORMAL CHARGING of the battery can convert the sulfate back to the soft active material IF THE BATTERY IS FULLY RECHARGED. However, a solar battery is seldom completely recharged, so the soft lead sulfate crystals harden over a period of time. ONLY A LONG CONTROLLED OVERCHARGE, or equalization, at a higher voltage can reverse the hardening of sulfate crystals.

... context is everything. If the OP's bank is being chronically undercharged, doing a 14.9v abs charge every few days is not going to remove the sulfation buildup / stratification. If they are being fully charged regularly, then unequal SG readings and/or unequal individual battery voltage readings are an indication a proper EQ'ing is in order.

[BFL13]

ewarnerusa wrote:
Do you think I should ditch my 14.9V every 3rd day idea and go back to a more typical 15.5ish volt equalization on a 30 or 60 day basis? Or maybe even just on demand?

Set the controller to 14.8 and when the batts get there, confirm batt V with a multi-meter. Adjust controller V so that Vbat is 14.8 at the batts.

Then anytime you want to use the inverter, turn off solar, start the inverter, and then turn solar back on.