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I have a solar charge controller connected to a solar panel (30w), also connected to the charge controller are a 12v battery (4.5Ah) and a raspberry pi Zero (5v, draws approx. 200mA).

This evening the charge controller is showing the battery voltage as 10.7v.

I turn on the load switch to supply power to the Raspberry Pi but as soon as it draws current the controller switches power off again.

So my question is, should my 12v battery be able to supply enough power to the raspberry pi (5v & 200mA ) when it is only charged to 10.7v?

If not, why not? I would have thought 10.7v being far higher than 5v so it should be well capable.

Battery details:

12volt/4.5Ah Constant voltage charge(25C) cycle use: 14.5 - 14.9V Standby use: 13.6 -13.8V Initial current: 1.35A

Charge controller details:

Anself: https://www.amazon.com/Anself-Controller-Regulator-Overload-Protection/dp/B01A0D18MU?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-ffab-20&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B01A0D18MU

Schema:

30w solar panel----charge_controller/Battery(USB interface)---raspberry pi

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    \$\begingroup\$ Read the charge controller's datasheet. 10.7V is probably close to its undervoltage cutoff, to try to protect the battery. Add some drain and it falls below that, so the charge controller disconnects the load. Assuming the load is connected through the controller... \$\endgroup\$
    – user16324
    Oct 16, 2016 at 18:54
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    \$\begingroup\$ Can you provide more details about the charge controller and how everything is connected? A schematic or block diagram? The battery is very nearly fully discharged. The charge controller may be designed to disconnect the load at 10V (this is a common cut-off voltage for lead acid batteries). Incidentally, your battery will last much longer if you avoid discharging it below 11V or so. Discharging to 10V is kind of hard on a battery. \$\endgroup\$
    – user57037
    Oct 16, 2016 at 18:55
  • \$\begingroup\$ Besides the battery state, how exactly did you connect the RPi to the battery? Are aware that 10.7V is far too high for an RPi? \$\endgroup\$
    – marcelm
    Oct 16, 2016 at 23:01
  • \$\begingroup\$ Hi all & thanks for the comments, I've edited my post to include battery details and schematic. \$\endgroup\$
    – Tullio_IRL
    Oct 18, 2016 at 22:34
  • \$\begingroup\$ The description for the charge controller in Amazon indicates that the over-discharge cutoff is 10.5V. This means that @BrianDrummond has probably pointed out the most likely answer to your specific question. As soon as the battery tries to supply power to the load, the voltage drops from 10.7 to below 10.5, and the charge controller disconnects the load to protect the battery from over-discharge. \$\endgroup\$
    – user57037
    Oct 19, 2016 at 4:42

2 Answers 2

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Consider that the lead acid battery is 100% resting at 12.5V and near 0% @ 11.5V and charging should be in the range of 13.5 to 14V.

Your "mileage will vary" with flooded vs SLA from battery chemistry differences slightly and deep discharge marine batteries.

Below 11.5V starts to rise in series impedance quickly so any load drops the voltage more easily than in the normal charge voltage range. 12.0V is midpoint or around 50% SoC .

All it takes is one bad cell to spoil the pack. If you think it is fully charged and it drops to 10.7 then my guess is one cell is self shorted partially and should be 1.5V higher or 12.2V

Take readings after adequate settling time with some loading following charger off.

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  • \$\begingroup\$ Stewart Thanks Tony. Although I've good knowledge of electricity my knowledge of batteries is very poor, \$\endgroup\$
    – Tullio_IRL
    Oct 18, 2016 at 22:48
  • \$\begingroup\$ Tony, any suggestions on where to learn about batteries or could you explain? Best regards Paul \$\endgroup\$
    – Tullio_IRL
    Oct 18, 2016 at 22:52
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If a lead-acid battery shows 10.7V, it is very likely that at least one of its elements is damaged/faulty, and develops a large internal resistance, and the entire battery cannot hold voltage and supply even 200mA of current. The controller cuts it off. I bet that if you try to charge it, the voltage will rapidly increase to >15V, and the controller will think that it is fully charged, and will stop. This (one cell failure) is a typical fault that has developed over time. You need to replace the battery.

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  • \$\begingroup\$ To add, the other cells are near-faulty in that stage, too. \$\endgroup\$
    – Janka
    Oct 18, 2016 at 22:48
  • \$\begingroup\$ I think it is possible that the battery is still good. It really depends on its past charge history, which we don't know. If it was only discharged down to 10.7V once and didn't stay there for too long, it may still be good. But for sure, discharging it to 10.7V repeatedly will kill it in no time. \$\endgroup\$
    – user57037
    Oct 19, 2016 at 4:47

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