MPPT controller not calibrated correctly?

Bandit

New to this forum, but reasonably astute re solar.

I've set up an off-grid 400Ah 24V primary bank (2x200Ah 12V deep cycle in series, x 2 groups in parallel, about 10 Kwh total, and all batteries hold perfect balance after 6 months in the Philippine jungle, www.pernilla.org). I've got 4x265w24V panels in series, about 120V panel series output in the sun, and 40A+ at 24V+ controler side We chose a 45A (max 150V) EP Solar industrial iTracer MPPT controller. Finally, a good 220V, 1000W pure-sine inverter powers everything from fridge to computers. It's a really solid solution accounting for our needs and budget. We have a 5Kw genset for backup but almost never need it.

My problem:
Despite the specs matching our needs for the most part, the last weeks we've been slamming the batteries nearly daily, with a construction project and lots of power tools. At dawn they may be at 11V, probably less than 10%. When the sun comes up we get our expected bolt from the panels, climbing steadily to near 40A at about 11am as expected. Then, inexplicably (to my reptile brain) our 'smart' controller decides that the batteries are at 75% and starts stripping amps. Clearly the batteries, despite 'optimistic' voltage readings which I think spook the controller, cannot possibly be more than 25-50%. So I suspect we are throwing away up to several Kwhs/day as the result of a 'dumb' smart controller...

I've tried every adjustment, and even tried to 'trick' it by setting other battery types (they are flooded) but no help. I wrote the company and no response. I'm stumped. Any of you folks have any suggestions?

In any case, good luck to you all with your own projects, BR/Tom!

mike95490

Generally, batteries control their charge amps. 
 The controller supplies the volts. 
   You program a target voltage and it goes there,
If you have been slamming the batteries, they may need a bit of EQ to fix things up.  Or by taking older batteries down to 10%, you have broken their backs.    Get your volt meter out, and see what the voltage at the battery terminal is, while charging hard, does it agree with the measured voltage at the controller ?  Could be a poor connection causing the slow charging.  

mcgivor

Do an EQ and see if the current increases, some EPever controllers do an auto EQ on th 28th. day of each month, no manual option, if this is the case adjust the date to the 28th. to fool it.

Estragon

+1 on the EQ.

Another thought is to turn the controller off and back on to start a second absorb cycle.  If the bank really is full, it should get to Vabs prwtty fast and current will taper naturally.

Photowhit

+2 on Equalizing...lol. If you can, If they are 200 amp AGM then read from your manufacturer about conditioning/equalizing type charge AGM/VRLA can only 'outgas' once and then they are dead...

Things / setting that may help. Increase the length of time in absorb and increase the voltage in absorb to near the max before the are steady out gassing. The higher the voltage the longer it will be before the batteries accept less amperage. Imaging 2 cups of water and the voltage as how high you are lifting one to allow water to run to the other. In deed equalizing is lifting the voltage much high to allow a slight over charging of the battery bank.

BB.

11 volts (resting voltage) is pretty near dead for lead acid batteries... And taking Lead Acid batteries to near dead is usually not going to give them a very long life (sulfating--which makes the battery AH capacity drop and increases internal resistance).

And if you are taking them near dead, generally it takes at least 2 days of charging (and little in the way of loads) to bring your bank full again.

What is the charging voltage? It should be around 29.6 volts (for FLA batteries at ~25C). And it should hold that for ~2-6 hours (2 hours for shallow charging, ~6-8 hours for very deep cycled batteries). A 10% rate of charge, it will take at least 7 hours to get to 80% state of charge, and another 6-8 hours of Absorb charging at 29.6 volts to bring the batteries to near 100% state of charge... You are looking at 13+ hours of charging, and most places you are lucky to get much more than 6-8 hours of sun per day (actual sun shining on the solar panels).

At this point, don't know if the batteries are not being properly charged (problems with solar/charge controller) or you are simply drawing more energy than the system can provide.

Just to give you some really rough numbers (based on reliable system configuration--a bit on the conservative side)...

• 2 parallel strings * 2 batteries in series * 12 volts * 200 AH * 0.85 AC inverter eff * 1/2 days of backup power * 0.50 maximum discharge = 2,040 Watt*Hours of AC power from battery bank per day for 2 days maximum (no sun)

Then there is how much energy you can harvest from your solar array; 4x265W=1,060 Watt array, fixed (not tracking array), 
http://solarelectricityhandbook.com/solar-irradiance.html

Cebu City Philippines
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 80° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.79	5.19	5.43	5.44	5.48	4.85
Jul	Aug	Sep	Oct	Nov	Dec
4.49	4.37	4.57	4.74	4.72	4.61

This is mid December:

• 1,060 Watt array * 0.52 off grid system eff * 4.61 hours of sun per day (December) = 2,541 Watt*Hours of AC power per day

That is about the maximum you should use, and using less (variable sun/weather) is normal for 'base loads'. Your maximum base loads would be something on the order of 65% of predicted usage:

• 2,541 WH per day (Dec) * 0.65 =1,652 WH per day maximum base load support (suggested base load for Solar in December)

-Bill