How to Fault find is it issue with MPPT, the Solar Panels or the Battery?

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Mike Kolling asked May 5, '21

How to Fault find is it issue with MPPT, the Solar Panels or the Battery?

I have a strange situation and I am not sure how to do the fault-finding.

I have 2X 150W Solar Flexible Monocrystalline Panels connected to a Victor MPPT Smart Controller 75/15.

Admittedly the panels were cheapies off Ebay for £50 each.

Together with the Victron they connect to 4X Trojan T-105 6V Cells which form a 24V set.

I am using default factory settings for the Victron as the numbers seemed pretty close to the Trojan requirements

It has all been working for about 3-4 weeks and I have been impressed with the system.

This shows the history, all good

Suddenly this weekend, the MPPT is not able to charge the batteries up high enough to transfer from Bulk to Absorption so it just sits there trying to charge.

In this image, this is the highest I could get the battery to (27.06V) I couldn’t get it any higher?

I am concerned that this will damage the batteries as it is still pumping amps into them.

Previously the Max voltage I got out of the two panels was approx. 44-45V, but now it seems to only run at 35V.

My path so far

I disconnected the MPPT, connected a battery charger and charged the batteries up, then left over night and they held good charge which makes me think its not the batteries
When I bought the panels I also got cheap PWM controller with them. I swapped out the Victron with the PWM and it appeared to be doing the same ie still runs at about 35V on the Solar and wont get the battery volts any higher
This leads me to believe I have developed a fault with the Solar Panels.

Am I running enough grunt in the solar panels to do the job?

The Panels are rated at

Specification:

Optimum power : 152W ± 0.25W

Working voltage: 18.1V±0.3V

Working current : 8.1A ± 0.15A

Short circuit current : 8.3A ± 0.15A

Open circuit voltage: 21V±0.8V

Times Two as they are in Series to drive enough volts to charge 24V system.

The Rating for the Trojan batteries is the 24V column: -

Do I need more panels? AM I short on required power?

Is 150W X 2 enough or do I need higher rating? Or do I just need better quality Panels?

Thanks in advance

Mike

MPPT Controllers MultiPlus Quattro Inverter Charger

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Answer 1 · 2021-05-05T18:55:37Z

dazey77 answered · May 05, 2021 at 06:55 PM

From what I see, it doesn't really look like you have a fault. Your panel specs are 18v working voltage, so 36v which is near-as-dammit what you are seeing. With no load, you should see your panels go back up to 42v. You can test this by turning the charger off in the app and seeing what your panel voltage does. If it still sits at 36v then perhaps there is an issue.

from what you show, the panels and system are still generating and charging the battery, OK you didn't get out of bulk this period but that could be extra loads, worse weather, shading, whatever.

for 2x £50 150w panels, 124w output is not bad most of the time, if its in full sun at midday with panels pointed at the sun, its not great.

The most I ever got out of a 200w semi flex system was around 150w (UK, flat roof). Had 200w from a 250w rigid with no issues and in only a few months vs a few years for the semi-flex. 200w is roughly the limit of my 75/15 which is at 12v.

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Answer 2 · 2021-05-05T19:01:24Z

dazey77 answered · May 05, 2021 at 07:01 PM

Your settings don't look right to that table. Why is your max battery voltage not hitting 29.64v as trojan table. The MPPT is going into float (the other days) at too low a voltage? The table shows a max battery voltage of 28.8 and trojan says you should be buk charging to 29.6. Can you share your charge settings?

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