Wrong(?) Voltage settings mt50

hcohen · July 2020

Hi,

I'm getting a confusing reading from my system and trying to understnd it.

Got 2x120W panels connected in series to a battery bank of 2x190ah EFB type.

The CC is EPEVER 20A.
The open voltage is a nice 40V at the entrance to the CC, BUT, when i connect it I'ts dropping to 15V-13V.

Next, the wires leading to the battery never show a voltage higher then 12.7, even in mid day. The amp is almost 10 but the voltage is low.

All the load is going directly from the battery and not from the load terminal at the CC.

Any idea how to troubleshoot the system?

Thank you

Photowhit · July 2020

Well, I'm guessing you have the batteries hooked up in parallel? For a 12 volt battery bank?
So a 12 volt 380 amp hour battery bank, and you are sending 10 amps or about 2.5% into the system, and you also have loads?

Typically you would want to be able to send 10% of the battery capacity to the battery or 38 amps.

What loads do you have running?

mike95490 · July 2020

Looks like you have a PWM controller, and you should have your PV panels wired in PARALLEL, for 20V, not series.

hcohen · July 2020

Its a MPPT one and I'm drawing couple of pumps and a smal fridge

Photowhit · July 2020

hcohen said:

Its a MPPT one and I'm drawing couple of pumps and a small fridge

You are seriously under paneled.

On good days, you might have enough to keep the fridge going. Over cast days will bring you negative. A small fridge will use around a kWh or 1000 watt hours a day. You might expect 150-160 watts charging during the hours around solar noon from 240 watts of array. Add in the pumps (motors even small will use a good bit of wattage) and the amount of energy to keep your inverter going (some can use a surprisingly large amount of energy) and you don't have a well balanced system.

I'd suggest telling us your loads with a higher degree of accuracy and let us help you design a balanced system. If you want to figure out the amount of energy an AC load is a Kill-A-Watt meter can help a lot. you can plug the appliance/load into the meter and the meter into the wall. For things like a fridge, that go on and off. It can measure the load cumulatively for 24 hours and up to a week (I think). They are ugly expensive. Around $20.

hcohen · July 2020

Its a sailing boat configuration, so the fridge is a 12v really efficient and small, 30cm3.
The pumps only work for a short bursts every now and then.

Are the.voltage readings I'm getting normal?

petertearai · July 2020

A 12 volt system will need 14.2 to 14 .4 volts to charge . If your panels arnt big enough then your charge controller will struggle to raise the voltage to this required bulk voltage .is this a new system that has worked well in the past ?

hcohen · July 2020

This is a new system, hasn't been fully tested.in the past.

I simply have a hard time understanding the voltage readings.

The MPPT lowers the PV voltage to 14.4 with 4Amp, but, the cabels going into the battery are reading 11.8. I would expect the reading over the battery WHILE charging will be higher.

There is a voltage difference of ~3v between the minus of the PV and the battery.

hcohen · July 2020

hcohen · July 2020

Image: https://us.v-cdn.net/6024911/uploads/editor/su/p4b7egwjtmm0.jpg

i'm reading the voltage from the terminals here.

And thank you all for taking the time to help

BB. · July 2020

You should have a volt meter to confirm the readings on your MT50... An AC+DC Current Clamp DMM (digital multi-meter) is really nice to have (very quick, easy, and safe to measure current):

https://www.amazon.com/Uni-T-B4Q094-UT210E-Current-Capacitance/dp/B00O1Q2HOQ (inexpensive, good enough for our needs)
https://www.amazon.com/gp/product/B019CY4FB4 (mid-cost meter)

Note there are AC only clamp meters too... Perfectly good meters, but not useful for measuring current on DC battery wiring.

At 11.8 volts charging--Your battery bank seriously under charged. Getting the batteries on AC charging for many hours (basically get to 14.2 to 14.4 volts typically for AGM/Sealed Lead Acid Batteries), and hold 14.x volts for 2-6 hours for full charge (for deeply discharged lead acid batteries, holding for ~6 hours is usually needed).

On the panels. Are both panels free of shadows (no shading from lines on boat, facing roughly towards sun)? If there is any shading on either panel, it is very easy to see ~1/2 or more of the panel's output voltage lost (due to shading).

You might try connecting one panel at a time to the charge controller on a sunny day... And make sure that both panels perform the same (ideally, Panel Voltage should be ~15-17.5 volts for cool to warm sunny day, no shading). And the current should be under optimum conditions (full sun, panel(s) pointed at sun, near noon, etc.) somewhere between 50% to 100% of Imp rating for panel/array. Under less than ideal conditions, seeing less than 50% of panel rated current is no surprise.

Of course, how much current is drawn from the panel is dependent on the battery state of charge. In your case, battery bank is discharged and should draw all available power/current from array+charge controller. One batteries get >~80% or so state of charge, the batteries start to limit their current draw.

Trying to debug poor Vpanel input voltage to your MPPT controller can be a pain sometimes. Especially if it never has worked as expected...

Panel(s) can be bad, wiring connections loose/corroded, connections to charge controller loose, mis-configured charge controller, or even a "bad" charge controller can cause any of these issues.

One other suggestion. Solar Charge Controllers generally get their "operating power" from the battery connection.

When connecting a solar charge controller, always make the battery connection first, then connect the solar array. And when disconnecting the controller, disconnect the Array first, then the Battery bank.

Many controllers use the battery bank voltage to select 12/24 volt operation, and get a "clean boot" from the battery connection. And in some cases, it is possible to damage a solar charge controller by connecting the array first, then the battery bank (it is probably a rare failure, but possible).

-Bill

mike95490 · July 2020

According to the meters on your controller pic, your controller is operating in a PWM mode and not MPPT
If it was operating in MPPT, your panel voltage would be about 34V with more amps going to the battery,

Or you have a bad panel

hcohen · July 2020

Thanks Bill.

Yes, there is some shade but I cant really avoid it so I do expect some lower output.

Maybe its the MPPT that confuses me, at another project I had PWM and I simply saw the voltage.

I just don't understand why the charging voltage is low. I would expect to see something like a 14 over the wires leading to the battery.

The battery is going up a bit but i would still expect to get a higher reading when charging and the readings are 12/11.9

I went over the lines yesterday and replaced corroded parts.

petertearai · July 2020

If the battery is severely discharged , then the battery will keep to voltage low .

hcohen · July 2020

But when I'm charging with the motor i'm reading 13,

I'm starting to think to controller is bad

BB. · July 2020

Your panels at 2x 120 Watts = 240 Watts. The typical best harvest (you might see a couple times a year, around noon, on a cool/clear day) is around 77% of rated output:

240 Watts * 0.77 panel+controller derating = 185 Watts "real" best harvest
185 Watts / 11.8 battery voltage during charging = 15.7 Amps "best" harvest (what MPPT is supposed to do)

Even on average days (a little haze in the sky, panels not pointed within 10 degrees of the sun, etc.), a bit less than 8 amps is not "bad".

Connect the two solar panels in parallel--Did the MT50 numbers change?

The solar charge controller appears to be operating in MPPT mode... Notice that you have (slightly) higher V-array and lower I-array. While the battery has lower Vbatt and higher Ibatt. That is what the MPPT controller is supposed to do (take higher voltage and lower current from the array, and efficiently down convert to lower voltage and higher current to the battery bank).

On the above picture, you have ~42 Watts in to the controller, and ~42 Watts out to the battery bank (Power = Voltage * Current).

Shading is a "killer" for solar panel production. Even the shadow from a single line crossing a panel can easily cut the power production by 1/2 or more.

For battery charging, 5% rate of charge is about the minimum you want. And 10% to 13% rate of charge for solar is a good number.

For your 2x 190 AH battery bank, if it is 50% state of charge (and it could be even less), it will take:

2 * 190 AH batteries * 0.50 state of charge = 190 AH
190 AH / 2 amps average solar charging current = 85 hours to charge
85 hours / 5 hours of "sun" per day = 42.5 days of "average" sun and charging current to recharge bank

At this point--If you have shading on panels, and/or cannot point the panels at the sun (i.e., under sail, at anchor with random pointing), you probably are getting the best you can.

And at:

2 amps average charge / (2 * 190 AH) = 0.005 or ~0.5% rate of charge

you are at best, just float charging the battery--And not much more (float charging is typically around 1-2% rate of charge.

If your panels and system where working optimally:

15.7 amps actual charging current / (2 * 190 AH battery bank) = 0.04 ~ 4% rate of charge

Still not a great charging source if not "helped" by your engine alternator/generator/shore power charging.

At this point--Your battery bank is severely discharged (probably less than 50% SoC), and you need to get it fully charged soon. The longer it sits at less than ~75% state of charge, the faster the bank will sulfate and eventually fail.

And your present solar charge controller is not really up to the task of fully/quickly recharging your battery bank.

Charging at 38 Amps from your engine would take (very roughly):

2 * 190 AH * 0.50 state of charge = 190 AH to charge
190 AH / 38 amps charging = 5 hours
actual time on charge would be 5 hours + ~6 hours absorb = 11 hour "on engine" minimum charging time

And you have to watch the actual charging current. Many alternators when the get "hot", tend to reduce their output current... So it may even take more time/fuel to fully recharge.

Even getting your battery >~80% SoC would be a big help at the moment.

-Bill

BB. · July 2020

And regarding "EFB" batteries:

https://www.rbbattery.com/articles/2019/4/29/efb-battery-guide-everything-you-need-to-know-about-efb-technology

What Is An EFB Battery?

EFB stands for Enhanced Flooded Battery. It is typically an improved version of a wet battery.

What a wet battery? A wet battery is a rechargeable battery that contains a liquid electrolyte. For vehicle batteries, the electrolyte used is sulfuric acid. If you are not conversant with battery terminology, kindly have a look at this article for a basic guide to batteries.

Depending on which country you live in, this type of battery also goes by the terms Improved Wet-Flooded Battery (IFB) and/or Advanced Flooded Battery.

These batteries come specifically designed as a lower option to the Absorbed Glass Mat (AGM) batteries in terms of durability and output. As a result, EFB often gets mistaken for AGM and standard wet-flooded batteries.

You may be able to check your battery with a hydrometer (if the battery is not sealed)... However, I guess you need a specific gravity chart for you EFB to accurately estimate the true State of Charge (according to the link above?).

https://www.solar-electric.com/search/?q=hydrometer

-Bill "learn something new everyday" B.

mountainman · July 2020

I used to have a epever 30 mppt charge controller and a bird could fly over and it would get lost tracking.
It would hang up at a low array voltage until I reset it.
It would only work on a cloudless day.

Wrong(?) Voltage settings mt50

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What Is An EFB Battery?

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