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Hi!

I (still) need some help with building a solar charger...

I want to charge a Nickel-Cadmium battery (1.2V) with solar cells from a garden light. Unfortunately these cells give me 5V in full sun...

Will the battery take the 5 Volts without damage?

The amperage is fine, so no questions about that...

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The voltage makes a current flow. If the current is very high, it will damage the battery for sure, by overheating, Without active control of the charging, the rule is that the charging current should be between 1/10th and 1/14th of the capacity of the battery - so a 2800mAHr battery is charged at something LIKE 280mA.

I suspect though that you have measured your panels with no load on them. You will be horrified by how little voltage they deliver on load, probably just enough to charge the battery.....

Yes, I measured without a load...but I know the cell was used to charge a 2.4V battery (2x 1.2V in series) so I assume it delivers at least 2.5V...
The current is 140mA in full sun (without load), the battery I want to charge has 1200mAh...
As long as the current from the solar cell is between 1/10th and 1/14th of the capacity of the battery a voltage between 2.5 and 5.0 is fine?

Ni-Mh need current, not volts to charge. Looks like you'll be fine. 140mA into a short circuit, and 5V open circuit means there is effectively a 5/0.14 Ohm resistor in series with the solar panel - its "internal" resistance, 35 Ohms.

I reckon everything's fine.