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bmanskiman asked

MPPT 75/10 and Smart Solar software question


I have a System set up with a 30w Solar panel, the MPP 75/10, a 100Amp hour battery and a 10 watt LED light. I am trying to better understand the SmartSolar software and it's History.


The Row named Battery shows high and low voltages for each day. Is this the high and low voltages the battery received from the Solar each day OR is it showing me how full the battery is knowing that a 14.43v is a full battery?

On this screen on Day 5 the battery was full and moved from Bulk Charge to Float charge.
On Days 4,3,2,yesterday we consumed 50+50+50+50=200Wh
It looks like solar yielded 30+0+160+190=380Wh
So it looks like we are putting more into the battery 380>200 but the battery has not yet crossed back into Float Mode meaning it's not yet full.

Why wouldn't the battery be full yet?


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2 Answers
snoobler avatar image
snoobler answered ·

30W PV for a 100Ah battery is too small. Assuming lead-acid, you need to be able to charge your battery at 5-10A.

30W is a TINY panel.

Voltage range is the voltage measured by the MPPT for the 24 hour period, high and low.

The answer to your last question is: you are using more capacity than you are replacing with solar.

The consumption numbers are what is supplied via the load terminals. This implies you are using the 10W light bulb for 3-5 hours/day based on the history.

  1. Is that correct?
  2. If you have nothing connected to the load terminals, this number is meaningless.
  3. Do you have any other loads drawing from the battery?
  4. What chemistry is the battery?

Questions numbered for answering convenience.

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bmanskiman avatar image bmanskiman commented ·

Thanks snoobler,

1. The 10w LED light on the load terminals is on from Dusk to Midnight.

2.&3 Nothing else connected

4. The battery is a BattleBorn LiFePo4 100Amp Hour battery.

So the output from solar being greater (380Wh > 200Wh) than the consumption is meaningless in this scenario?

Are there times when solar is making energy but not enough to get pushed to the battery?

Any tricks for solar panel alignment for best production?


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snoobler avatar image
snoobler answered ·

1. cool

2 & 3. Thanks

4. I was wondering if this was Lithium (LFP).

LFP batteries under low charge current need no absorption whatsoever. When you hit 14.4V @ 3-5A, you are already full. Furthermore, the jump from the 13.5-13.6V range to 14.4V range happens extremely quickly.

It may be that you're charging at such a low current and are very nearly fully charged (95%+), you're just not getting enough juice to make that final push to 14.4V/100%.

Additionally, while the MPPT is up to 98% efficient, that's not a full time thing. Most of my inverter consumption is at ~80W on a 5kW Quattro. That unit has a 90%% max efficiency, but at the extremely small power percentage, I'm running at about 70% efficient, so you may be seeing something similar.

Given the 30-50Wh/day consumption, the battery capacity and the 30W panel, assuming you get decent sun, your system should get fully charged most of the time.

The best way to orient a panel is perpendicular to the sun. Easy mode is to face the panel due South (geographic, not magnetic) and tilt it up the same amount as your latitude, e.g., if you're at 30°N latitude, face the panel due south and tilt it up 30° from horizontal. If shading is an issue, you want to factor that in. Let's say that you miss out on the last 2 hours of sun , you'd want to face your panel in a South-South-East orientation, so you're getting "perpendicular" exposure sooner than noon.

In short, the discrepancies you're seeing are likely more associated with a very low charge current, LFP chemistry, small parasitic draws and inefficiencies than from a design or deployment problem.

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