1 of 3 MPPT not always starting

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swtrcloud9 asked 7 hours ago

1 of 3 MPPT not always starting

I have 3 x 455W solar panels each connected to its own SmartSolar MPPT 100/50 (for redundancy) on my boat. The three mppt units are then conneted in parallel to a set of 3 x 260Ah GEL batteries. There is also a multiplus conected to the same batteries. No external A.C. supply.

The first two panel/mppt combinations are ok.

But mppt #3 sometimes doesnt come back on in the morning - the staus stays off. Even though #1 & #2 are both on and at the bulk status. This screen shot is a short time after the first two panels have started.

Unplugging the panel from the mppt unit and plugging it back it in gets it going again.

I have checked that all three panels are producing approximately the same voltage at each of their respective mppt units and that the battery voltage at all three mppt units is the same.

Any clues? The whole setup is just over a year old and has been working perfectly up till now.

MPPT SmartSolar

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pwfarnell commented · 7 hours ago

@swtrcloud9 Not related to your issue I notice thst your battery voltage is very low, did you have a large load on your system when you took that screenshot. If not your are discharging your batteries overnight much more than is ideal.

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swtrcloud9 pwfarnell commented · 5 hours ago

Yes, that is another issue I am trying to resolve. The main loads overnoght are the fridge and computer charging. Working through a process of elimination in the first instance. I suspect my computer as the voltage was well over 12 when I got up at 0430 and only 11.1 a couple of hours later. The only thing that changed was using the laptop.

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Answer 1 · 2024-07-17T07:05:47Z

nickdb answered · 7 hours ago

you will need to show trend charts for each so we can see the battery/pv voltage over the period.

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Answer 2 · 2024-07-17T08:54:48Z

swtrcloud9 answered · 5 hours ago

@nickdb Here are the trends for the three MPPT units.

So, there is a significant dip in the battery voltage around 0500 which was when I got up, turned on one led light and opened my laptop.
The second dip at around 0930 may have been when my wife attempted to make a cup of coffee (not sure).

Note that I have used a load tester on the batteries which show that 2 of them are working at full capacity and the other one has a 15% reduced capacity. They are less than 18 months old.

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nickdb ♦♦ commented · 5 hours ago

One LED and a laptop shouldn't do that to healthy batteries.

What charger settings are you using on each mppt?

Are they networked?

Firmware up to date?

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swtrcloud9 nickdb ♦♦ commented · 4 hours ago

@nickdb The laptop and the light were the only things that changes. The fridge/freezer was running all night and I presume it was cycling correctly.

VE.Smart Networking configured for the 3 controllers and the battery sensor.
Synchronised charging
MPPT Firmware v1.64
Battery Sense firmware v1.13

The charging settings for all three controllers are the same. (GEL batteries) From memory, these were set based on the info written onthe side of the batteries.

As mentioned, I borrwed a load tester to test the batteries and two were indicated as good and one slightly less.

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pwfarnell commented · 1 hour ago

@swtrcloud9 Are you possibly UK based canal boater, just asking out of interest as I am also one.

Anyway, you are using your batteries as deep cycle domestic batteries and load testing is not suitable for testing these. They can be well down on capacity and still have enough ommph left in them to pass a load test, but if you do a long discharge you find that they have been degraded. The most common way is by undercharging them, i.e. Not getting them up to absorption voltage of 14.x Volts for several hours until the current is below around 15A in your case. You ha ve 780Ah, you should be using about 150-200Ah daily depending on use, that is around 2000Wh your solar or alternator needs to put back. You really need a SmartShunt in your system to calculate the power you use each day and how much you charge and give you the battery SOC.

i am sorry to be the bearer of bad news but it looks like you have pushed your batteries too far without fully charging them often enough.

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swtrcloud9 pwfarnell commented · 1 hour ago

Thanks @pwfarnell We are a sailboat about to exit the Med and cross the pond to spend time in Panama. I do like the idea of living on a canal boat one day though.

I will install a shunt as soon as we are in one place long enough.

So, is there a way of testing the batteries for their intended use,or is the SmartShnt the best/only option?

Regardless, looks like new batteries in my future...

...but, would the depleted batteries be the cause of the same controller not turning back on in the mornings sometmes when the other two are fine?

Here is the history of the 3 mppts over the last 11 days. Sometmes absorption lasts for 6 hours sometimes ony 1 hour, but every day all controllers are spending time in float. So, how would I force them to spend more time in absorption? It looks to me like the 3 panels combined are generating around 3kW per day. So, what to do given reaching float every day and more than 2000wh?

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Answer 3 · 2024-07-17T14:32:44Z

pwfarnell answered · 7 minutes ago

OK, it looks like the under charging is not the total issue then as your history shows you are getting to float so you are not under charging them now, but at times in the past maybe, I still stand by the batteries being degraded and low on capacity. With UK canal boaters it is the most common issue given how little sun we get st times. The only way to test if the batteries are fit for purpose is to have a shunt on them then monitor the Ah used and watch the battery voltage, but checking the voltage is ideally at rest. You have 780Ah, you use 200Ah so you think you are at approx 75% SOC. However, your voltage is 11.1V, which from a gel battery voltage chart is less than 10% SOC, so your actual total capacity of the batteries is only 220Ah, 73Ah each. Gel are also known to have problems from overcharging, I do not know your batteries but nnormally thought that they should charge at 14.2V, but manufacturers do vary. Do you have temperature compensation set up on your mPPTs from Smart Battery Sense, if they are above 25degC they should have a lower absorption voltage.

I can not answer why the MPPT is not starting, they will not start if the battery is too low and you have had some very low minimum voltages but the others have started up. It could be to do with this, the one may be more sensitive to battery voltage.

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