MPPT Problem

[Safariwest]

Hi gang!

I'm new here and sort of new to solar panel systems. I apologize in advance if this turns out to be a long post. I recently installed a solar system on my remote property and it looks like I'm having issues.

Here's the system
Four 170w 12v panels connected in parallel on a sun tracking bracket
Two #2 cables running 140 feet to the controller (I wish it was a shorter run but it is what it is)
The controller is a 60A MPPT
From the controller it goes through a shunt before the batteries. I have a data acquisition unit connected to the shunt to read the amps and to the batteries to read the voltage
24 12V GNB Marathon M12V90 batteries hooked up in parallel

Here's the issue
The MPPT is having issues when it's sunny. When the sun is out the amp readings jump from around 32A to zero. At times it will stay at 32A for a few minutes then it will jump up and down constantly. It's rather frustrating as the batteries aren't getting a good charge. It's fairly stable when it's cloudy but will still jump down to zero amps every so often. After exchanging a number of emails with the manufacturer of the MPPT, he suggested that I put the panels in series. He was thinking the MPPT wasn't getting enough voltage. He says the MPPT can handle the voltage and that should fix the problem. I explained to him that I was seeing the volts coming from the panels on the MPPT display was getting to over 21V. He still thinks this is the solution. So he is saying that the MPPT will still put out the correct voltage for the 12V batteries but the input would be 48V. It just doesn't sound right to me. What do you guys think?

Here are some screen shots from the data acquisition unit. It is set to take readings every 4 seconds. The top line is the amps from the solar panels. The third line down is the amps my equipment is drawing. The bottom line is the battery volts.

Sunrise on a sunny day

Sunrise.jpg

Part way through the day

Mid Day.jpg

Sunset

Sunset.jpg

Cloudy day

Cloudy.jpg

Not sure if the images uploaded correctly. Sorry, I'm new

[Mike90250]

Welcome

You have a couple problems

First, MPPT controllers down-convert and watt match higher voltage arrays to lower voltage batteries. Generally with only 2-5% losses.

For charging a 12V battery, you need to supply it with at least 22V, so putting your panels all in series, should be FINE. Putting 2 in series, and then the 2 series strings in parallel, would be even finer, but that's likely only a 1% gain.

What's NOT fine, is you have listed 680 watts of panels, to try to charge 24 parallel, M12V90 12V batteries. ARGGGG !!!

That's 2160Ah of battery being fed with 48A of charger. That's not even a trickle charge! Best tell us more of what you are wanting to do, and don't buy anything else yet.

[Safariwest]

Mike,

Thanks for the fast reply! Well, I figured I was doing something wrong. I will put two in series then the two pairs in parallel. Thanks for that. It just didn't sound right.

The good news is I didn't pay a nickel for the batteries. I work in the telecom industry and the batteries (and cabinet) were snagged from a decommissioned cell site. The batteries are installed in a sea can and run a computer, 4 security cameras, lights and a few other things. As the weather gets warmer it will run some fan to cool off the container. I know the amount of batteries were overkill for the amount of equipment I am running. The thought behind it was since I had all the batteries, I may as well use them and keep them charged. The other factor was the panels will get covered in snow and there are many days or even weeks without direct sun in the winter. I figured as long as I am putting in more amps than I'm using, I should be fine.

[Amy@altE]

Please give us the model of the charge controller and the panels. Not all MPPT can take a high input voltage. Most can, but some cannot.

[Safariwest]

The MPPT is an Enerpo EC-MPPT60 I can attach the manual. It does say in it "Maximum 150 Volt dc solar input voltage". I have a photo of the info on the panels. Not sure of the make.

EC-MPPT60 user manual V2 0.2（2013 11 20）第三版.pdf

Solar Panel Info.jpg

[sensij]

For charging a 12V battery, you need to supply it with at least 22V, so putting your panels all in series, should be FINE. Putting 2 in series, and then the 2 series strings in parallel, would be even finer, but that's likely only a 1% gain.

Why would two parallel strings of two panels be better than putting all four in series?

Voltage drop through 140 ft of 2 AWG for 2 and 2 (35 V, 19.4 A) would be 2.4%

Voltage drop through 140 ft of 2 AWG all four in series (70 V, 9.7 A) would be 0.6%

Am I missing something?

[Sunking]

The MPPT is an Enerpo EC-MPPT60 I can attach the manual. It does say in it "Maximum 150 Volt dc solar input voltage". I have a photo of the info on the panels. Not sure of the make.

[ATTACH]5824[/ATTACH]

[ATTACH=CONFIG]5825[/ATTACH]

Look at the panel spec Voc and multiply by 1.25 and then multiply x 4. If the answer is 150 or less you can connect all 4 panels in series. Otherwise 2 x 2.

[Amy@altE]

I agree, wire all 4 in series for nominal 48V charging the 12V battery. The output current will be under the 60A limit, and the input Voc will be well under 150V.

[Safariwest]

All 4 in series then. I'm out of town so I'll get my brother to do that on the weekend. I'll let you know how it goes and maybe post some good charging data. Thanks to all of you for the help. This is my first MPPT controller and I never would have thought to feed it with 48V from the panels for 12V batteries. Live and learn. Or maybe read the manual and do research eh

[Amy@altE]

RTFM?!?!?! Why didn't I think of that?

[Mike90250]

Why would two parallel strings of two panels be better than putting all four in series?

Voltage drop through 140 ft of 2 AWG for 2 and 2 (35 V, 19.4 A) would be 2.4%

Voltage drop through 140 ft of 2 AWG all four in series (70 V, 9.7 A) would be 0.6%

Am I missing something?

Yes. The MPPT converter looses efficiency as the PV string rises above the battery voltage. You have to trade the heat loss in the MPPT vs loss in the cable. Different models of MPPT have different loss curves.

When I first replied, I did not know the Controller model and site cold weather temperatures, and said "likely only a 1% gain."

It's a phenomenon I'm well aware of, with 2 world class controllers, one on a 80V string, other one on a 170V string (Classic 200v). The thermal difference in controllers is quite striking .

[Safariwest]

I got my brother to put the panels in series and everything is working great. Lots of steady power coming in. Thanks for all your help!!