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swtrcloud9 asked

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. screenshot-20240717-081559.jpg

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
screenshot-20240717-081559.jpg (303.7 KiB)
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pwfarnell avatar image pwfarnell commented ·

@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 avatar image swtrcloud9 pwfarnell commented ·

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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pwfarnell answered ·

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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swtrcloud9 avatar image swtrcloud9 commented ·

So, I think on that basis I can assume:

  • That the batteries now need to be replaced probably due to undercharging in the Winter months. Probably go with AGM instead of Gel.
  • Overcharging should not be occuring via solar through the MPPT controllers or via the generator thourgh the MultiPlus so long as they are configured correctly.
  • The engine alternator may be a source of overcharging so need to check the voltage on that.
  • Need to install a shunt for proper measurement.
  • Need to ensure that the batteries regain charge each day either by reducing consumption when its overcast or having another energy source such as wind.

The current battreies are a Turkish brand. I contacted the manufactuer at the time to verify the listed charging voltages becasue it seemed odd to me that the Absorption voltage was lower than the Equalisation voltage. Maybe that is normal, it just seems odd.

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pwfarnell avatar image pwfarnell swtrcloud9 commented ·

That is a good summary. A full charge is not required every day, I will go max 3 days without a full charge on my AGMs from time to time, but not routinely.

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nickdb avatar image
nickdb answered ·

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


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swtrcloud9 avatar image
swtrcloud9 answered ·

@nickdb Here are the trends for the three MPPT units.screenshot-20240717-104610.jpgscreenshot-20240717-104707.jpg

screenshot-20240717-104747.jpg

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.


screenshot-20240717-104610.jpg (312.1 KiB)
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nickdb avatar image nickdb ♦♦ commented ·

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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pwfarnell avatar image pwfarnell commented ·

@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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