question

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traveller asked

The battery loses capacity within the range of a few days, whereby the potential of available sunlight is not used to recharge the battery. Any suggestions?


Dear community

I’m a total newbie to solar power, so please excuse my non-knowledge and the questions related to it. I looked at the wiring-manual, but couldn’t find a matching systemdescription.

The situation: Campervan, 12V car battery; daily electrical usage roughly 10-15Ah or 120-200Wh

  • Battery: 12V, 90Ah, (C20) – 8 weeks old, never discharged below 12.1 V, range of temperature 5-15°C
  • Solar panel : 85W
  • Charger: SmartSolar MPPT 75/10 on Factory settings (GEL VICTRON DEEP DISCHARGE (2))(Absorption: 14.40V, Float: 13.80V, “Ausgleichsspannung”: 16.20V

Problem:
The battery loses capacity within the range of a few days, whereby the potential of available sunlight is not used to recharge the battery. Any suggestions?

  1. Presently the battery is at 12.2V (which I equal with 30-40%), meaning 50-60Ah have been used and should/could be recharged – correct?
  2. 50-60Ah resembles roughly 600-700Wh at 12V – correct?
  3. After only 50Wh of charging the (battery)voltage is already at 14.4V, and the charger switches from “bulk” to “absorbtion” and at 110Wh to “float”-mode. The maximum charge in one day with ample sunlight is only between 120-160Wh – resulting in observation 1.
  4. Is the factory setting appropriate for a regular lead-acid liquid battery, or what would be the correct battery settings?

If anyone’s willing to share some insights regarding the insufficient charging, I’d deeply appreciate it – thank you.

MPPT Controllers
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5 Answers
marekp avatar image
marekp answered ·

To me it looks like everything is working properly.

The lead battery should not be discharged below 50% of its capacity, and MPPT controller is acting accordingly.

This battery is a regular starter battery or a traction battery?

If it is a regular starter car battery, the loss of capacity is to be expected with deep discharging it.

The loss of capacity can be also low temperature related.

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traveller avatar image traveller commented ·

Thanks for your reply
I thought about the temperature relation but it seems an awful lot..?

And no, not a starter battery.

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klim8skeptic avatar image
klim8skeptic answered ·

Your SmartSolar Mppt along with Victron Connect is quite useful at providing clues.


Post a screen shot of your battery/controller history to see that they are up to...


screenshot-2020-02-03-21-36-43-375.jpeg (1.0 MiB)
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JohnC avatar image
JohnC answered ·

@traveller

The assumptions you've made in your Q#1 are misleading you. No doubt google will tell you whatever you care to read, but delve deeper. All batts are different, so you need to find your own 'level'.

Your charge V's are ok, and if the charge algorithm is reaching Float level, then look at your Tail current. While steady at 13.8V (+/- temp comp), look at your charge current. It will flatten off to a point where you can't envisage it going much lower. For you, maybe less than 1A or ~10W. Your batts are charged.

And if you've charged (say) 160Wh over the day, apply an 85% charge efficiency to calculate you've only drawn them down 136Wh (not 700Wh).

These calcs are a bit rough of course, but you may find you're in a much better position than you think you are..

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michelg avatar image
michelg answered ·

Hi, you may have electrical leaks or any device consuming energy somewhere in the middle. Connect an Ampmeter at the battery when everything is "disconnected" and check how much is drawn at that moment.

Michel.

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traveller avatar image traveller commented ·

Thanks for that thought, and no - the consumption displayed at the MPPT (momentary and over a days range) reflects accurate the actual consumption.

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traveller avatar image
traveller answered ·

Thank you much for replying

@JohnC (..the "missing" 700Wh were assumed to have cumulated over the days of non-proper-charging.)

The reason why I believe something to be odd is that between 12.74V (measured 4hrs after ending a charging cycle) and 12.36V lay only a consumption of 80-100Wh.. and the waterpump (3Ah) makes the light (.04Ah) already flickering.

As proposed by clim8skeptic I add a screenshot.


screenshot-2020-10-05-17-11-18.png (83.8 KiB)
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