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SmartSolar MPPT 75/15 drops charge twice per day

My SmartSolar MPPT turns the solar charge off twice per day if I am consuming power during the day this drives my battery down to nearly empty without the charge kicking back in to compensate - I have written off 2 batteries like this. I don’t understand why does the charge suddenly drop before the battery gets to float state anyway and why doesn’t the charge kick back at some point to lift the battery state back up before the battery is killed?img-5583.pngimg-5582.pngin the 2 photos attached I’ve shown solar power and voltage against battery voltage.Overnight the night before I plugged the battery into a mains charger that took the battery to 13+ volts when I unplugged that the battery voltage dropped to 12.7 volts as the solar was kicking in which lifted the battery voltage back up - so far so good. Then the charge suddenly drops as there was no load on the battery it stayed at a decent voltage all day but still no charge until @5pm when we get a small blip that then drops. So any ideas why I get the same sudden drop twice a day? As this is the second battery in 2 years I can’t see how the battery is to fault?

MPPT SmartSolar
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img-5582.png (287.0 KiB)
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trustytriumph avatar image trustytriumph commented ·
Thanks @Alexandra it is a lead acid battery it’s a yuasa l36 100 - so I think you are saying it’s the panel that’s faulty? When I get power through it’s charging fine and even though we’ve had full days of clear blue skies full sun it’s still drops twice a day around the same time which was more what made me think it was an MPPT issue? Unless the panel can only handle so much charge / heat and then cuts out ? But why then does it wait until @5pm to come back on?
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Alexandra avatar image Alexandra ♦ trustytriumph commented ·
It will charge later on as the battery voltage has fallen and the panel voltage is enough to kick on again. Also your rebulk offset might be around there?

I have never used that panel brand. What is its VOC?


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Alexandra avatar image
Alexandra answered ·

@Trustytriumph

If that is agm or any of the lead based ones. I can totally see that being a charge issue. But not the mppt so much as insufficient panel voltage and charge power.

Lead batteries like at least least a C10 charge in bulk with full absorption length dropping back into float, if you are cycling. If you haven't been doing that religiously, then it is insufficient charging killing the battery.

Otherwise you are barely offsetting its own self discharge and charging too slow for the battery to stay healthy.

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trustytriumph avatar image trustytriumph commented ·

another couple of photos and a day I plugged the mains charger in as the battery was nearly dead again

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Alexandra avatar image Alexandra ♦ trustytriumph commented ·

You would be better off with a pwm charger for a single 100W panel

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