Morningstar MPPT Charge Controller slow charge

darklyte27

Hi Folks, I have a 25 amp MPPT charge controller. When  I First connected it it would charge at full current of my two 135watt panels of 8 amps each. for a total about 10-12 amps because im running 100 ft wires.

After the first day, My batteries are drained maybe 20-30% and the following day it would only charge around 4 amps or so. If I reset the controller it would charge at full current again 10-12 amps. Is this right? Could it be my batteries are too old and causing resistance and fooling the charge controller? I had swapped the unit from morningstar and even updated the firmware and it still does the same.

The batteries are 5 or 6 years old, sunxtender AGM 104 amp. I use to use the 30 amp PWM charger from morningstar.

Photowhit

So are you using a MPPT type charge controller or a PWM?

Are the panels in series or parallel?

What stage of charging is the charge controller saying when you see 4 amps and at what stage is it in when you see 10-12 amps? How long does it stay at at the 'full charge' before switching back to the 4 amps?

darklyte27

I use to have a PS-30M connected. https://www.morningstarcorp.com/products/prostar/

Then switched to the MPPT charger last year. In all modes, bulk or absorb and charges at the slower rate. The only time it charges at 10-12 amps is when I reset the controller and will charge at that state until the sun goes down. Then the following day I see its back to its slower current charging. I have a 2000 watt inverter and connected to it is a mini fridge that pulls 55-80 watts for a few minutes.

I also used a battery monitor, xantrex link pro but just switched to a victron smart bmv.

Im going to guess my batteries are just too old and cant hold a charge.

Photowhit

I wouldn't give up on the batteries too quickly, I would think if reset the charge controller would see the same things and reduce the current. 

I don't know what MPPT controller you are using, perhaps it's been set for current limiting?

(Sorry about asking about the PWM controller, I didn't read that you 'use to use')

darklyte27

Ok, My new mppt chg controller is also a Morningstar PS-MPPT-25M ProStar MPPT 25 Amp.

I just reset it this morning, it was charging at 4 amps or so, after reset it charges at the higher current 10amps. I also saw the batteries sunxtender 104ah i have are now 305$

While sams club has these duracell platinum agm 94ah for 150$

Estragon

Are the panels connected in series or parallel?

Raj174

@darklyte27
What is your battery voltage and PV voltage coming in the the controller?

darklyte27

2 x 135 watt kyocera in parallel.
Voltage is 13V+ during the day, after sun goes down 12.5 or so, morning before sun rise 12 or even below. Could the mini fridge be dawing too much and hurting the batteries? 4x 104ah 12v

Is my system sized correctly?
Can my 2 panels charge the batteries enough in a day to support the mini fridge?
I sometimes turn on the cfl light but not long.

BB.

Starting with a rule of thumb design for a full time off grid system... Guesses:

• 288 kWH per year for a "mini fridge"
• 288,000 WH per year / 365 days per year = 789 WH per day

Assume battery bank supports 2 days without sun, 50% maximum discharge (typical for flooded cell lead acid batteries):

• 789 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 maximum discharge * 1/12 volt battery bank = 309 AH battery bank @ 12 volts nominal

You have a 4x 104 @ 12 volt battery bank for 416 AH @ 12 volts... Typical 5% to 13% rate of charge for FLA battery bank from solar.. 10%+ recommended for full time off grid power.

• 416 AH * 14.5 volts charging * 1/0.77 panel+controller deraings * 0.10 rate of charge = 783 Watt nominal array (based on full time off grid battery bank of your size)

Then there is how many hours of sun you get for your location... Say San Jose California with a fixed array:
http://www.solarelectricityhandbook.com/solar-irradiance.html

San Jose
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.81	4.54	5.69	6.53	6.70	6.80
Jul	Aug	Sep	Oct	Nov	Dec
6.60	6.54	6.29	5.72	4.40	3.57

Say you are OK with using a genset during winter... 4.54 Hours of sun per day (Feb) for "break even" month:

• 789 WH per day * 1/0.52 off grid system eff * 1/4.54 hours of sun = 334 Watt array minimum

Generally, for a full time base load like a refrigerator (you cannot turn it off during bad weather), you should plan on using ~50% to 65% of "predicted system output:

• 334 Watt array minimum / 0.50 base load derating = 668 Watt array nominal (based on loads and hours of sun).

Your system is (guessing) producing around:

• 2 x 135 Watt array * 0.52 off grid system eff * 6.29 hours of sun per day (September) = 883 Watt*Hours per day (Sept long term average)

So, your system today is probably way under paneled (5-6 year old batteries are probably not in very good shape. Get 4x 6 volt @ 200 AH "golf cart" batteries--Relatively cheap and rugged--Set up 2x series by 2x parallel batteries for 12 volts @ ~400 AH).

Note that your 2,000 Watt AC inverter is pretty large for such a small battery bank/system. A 2,000 Watt inverter can draw 10-20 Watts just turned on (not drawing any power). 20 Watts * 24 hours per day = 480 WH per day -- Or about 50% of what your refrigerator draws.

Your charge controller does not sound like it is working correctly... Something is not right (reseting controller should not change its charging behaviour). You need to check your wiring too... Too light/too long of wiring from controller to battery bank (high voltage drop) can slow down charging dramatically (for a 12 volt battery bank, ~0.05 to 0.10 volt drop from controller to battery bank suggested maximum drop).

For a 400 AH @ 12 volt battery bank, a 1,000 Watt AC inverter is about the maximum size inverter for FLA that that bank can support. For a typical AC refrigeration pump, need around a 1,200 to 1,500 Watt AC inverter (also supports a few lights, cell phone charger, etc.). Refrigerators are not small loads--They are large enough to push an off grid solar power system into the "mid size" range. A 24 volt battery bank is probably a better choice (smaller DC wiring, less voltage drop, etc.).

A couple of suggested tools:

https://www.solar-electric.com/kiacpomome.html (kill-a-watt AC power meter)
https://www.amazon.com/gp/product/B07546L9RT (inexpensive DC clamp Digital Multi Meter)
https://www.amazon.com/gp/product/B019CY4FB4 (better DC clamp DMM)
https://www.solar-electric.com/catalogsearch/result/?q=hydrometer (hydrometer for FLA specific gravity measurements)

Probably enough typing for the moment... Comment or questions?

-Bill

Estragon

> @darklyte27 said:
> 2 x 135 watt kyocera in parallel.
> Voltage is 13V+ during the day, after sun goes down 12.5 or so, morning before sun rise 12 or even below. Could the mini fridge be dawing too much and hurting the batteries? 4x 104ah 12v
>
> Is my system sized correctly?
> Can my 2 panels charge the batteries enough in a day to support the mini fridge?
> I sometimes turn on the cfl light but not long.

I would try rewiring the panels to series for the new mppt controller. There's a pretty good chance the voltage is too low in parallel, especially after the panels warm up in full sun, for the mppt controller to operate properly.

Pwm controllers just pass panel voltage through, so as long as wire is short and/or heavy enough, voltage from a nominal 12v panel can be enough. Mppt controller are designed to "buck" convert higher sting pv voltage down to charging voltage, and need some voltage headroom to work properly. Mppt can give higher output than pwm in cold weather, but can have issues in warmer weather unless pv string voltage is high enough. Two of your panels in series would likely have a Vmp of 30ish volts, which should be good for charging a 12v bank with mppt.

darklyte27

Thank you both for the useful info,

darklyte27

There should be a fuse between the panels and the charge controller right? I have a 20 amp blade type fuse on both positive and negative. Also is it an issue if the panels, batteries arent grounded? Its an off grid system. I measured the voltage from the panels at it was about 16.3 volts into the charge controller with about 8 amps going in at the moment in parallel, kind of partly cloudy today.

Is 100 ft wire run a long run?

Estragon

You don't really need to fuse a single string, or even two in parallel, but some sort of disconnect (my preference would be DC rated breaker) can be handy.

A 20a fuse may be too big for the panel (often spec 15a max). I'm also not a big fan of using blade fuses in this application, as they're often designed for periodic lower current loads, as opposed to running for hours at near rated current.

To figure out if 100' is a "long run", you could check an online voltage drop calculator with your wire size.

Mppt controllers generally like at least 20-30% voltage overhead. 120% of ~14.5v charging voltage is 17.4v. At 16.3, you may be too low for proper operation. Rewiring to series is a simple way to fix, and the higher voltage / lower current will have less loss than in parallel over the 100' run.

darklyte27

Thanks, I will try series. Since its 12v battery system it will charge better than parallel?

BB.

With Vmp-array closer to 18 volts or less (remember that Vmp falls as the panels get hot in the sun), the mppt controller can really only operate like a pwm controller.

With Vmp-array over 20 volts (when panels are hot), it will operate as an mppt controller.

Vmp-array at ~35± volts (standard test conditions), you mppt controller should be very happy (working optimally).

Bill

darklyte27

I did not know that Bill, thanks. I put my panels in series, lets see how it does tomorrow. The system is still a 12 volt system, solar input is now 24v and should be charging better correct?
I didnt realize with these mppt controllers you can input 12 24 36 48v and they will still charge a 12v system. since the batteries are wired as 12v I leave my dip switch setting as is 12v system.

I orig had a 1000wat inverter but went to the 2000 watt for my air compresor.

BB.

Think of a pwm controller likea fixed gear bicycle. Under the proper condition (speed, conditions), they work well, lightweight, and inexpensive.

Mppt controllers are like an automatic transmission between the peddles and the tire. Adjust the gear ratio for optimum power from the human and optimum power to the rear wheel.

Set the output voltage& charging conditions (I e., 14.75 volts absorb set point, 13.8 float voltage, etc.).

The controller itself figures out the answer to pmax=Vmp*Imp every few minutes (out multiple times per second) for the solar array.

As long as the Varray is within the Vpanel input range of the controller, all is automatic.

Bill

darklyte27

I think you guys solved it, The last 2 days were partly cloudy so I wasnt able to see if it was getting a better charge except coming home to see the voltage higher. Today I came home and the meter is reading the batteries at 12.81V, The max voltage was 14.23

So because of the 100 ft cable from 1 side of my yard to the garage where the batteries are that voltage drop must be hurting the charge. Since Monday when I changed the panels in series it looks like its doing a better job. Ill confirm when  I get a full sunny day.

Unfortunately my backyard is the only spot that can fit the panels, and the garage is at the front of the home.

The panels sit on a ground mount as well which is why I have to use the 100 ft mc4 cables.

thanks again folks for your knowledge.

As for the battery setting, its set for AGM, Bill

http://support.morningstarcorp.com/wp-content/uploads/2017/07/PS-MPPT-IOM_v2.6_EN_WEB.pdf