Battery charge by solar panel.

Hi,

I have a Lead–acid 12v battery and [0v-12.5v] solar panel for recharge it. If the panel is supplying 6v for example because aren´t sun during much time, this can damage the battery?

Edit: Or when is evening and suply 2v.

greetings.

dgdeivid: f the panel is supplying 6v for example because aren´t sun during much time, this can damage the battery? Edit: Or when is evening and suply 2v.

Insufficient charging of a lead acid battery can cause sulfation which coats the cell plates and will reduce the battery capacity. Typically a charge system for 12V lead acid car batteries will consider the battery discharged soon below 12V, and will use 13.8V up to 14.4V to charge it. Solar panels for 12V systems are often 18V and more, using a regulator to bring the charge voltage down to these levels. It's possible you could trickle charge your battery using your solar panel with a boost converter to increase the voltage but you won't charge the battery with 6V (you need to have greater potential on the charge side, or the battery will attempt to charge your solar cells).

Cheers ! Geoff

Always use a blocking diode with an array of PV cells to prevent the battery discharging through the panel (a commercial panel may already have this, but check). If you have a blocking diode the only issue with lack of sun is that the battery isn't being charged.

Never let a lead acid battery discharge below the lower limit (about 1.65V per cell). This totally ruins the battery (capacity and live reduced by large factors). You need to store lead acid batteries fully charged to prevent them deteriorating too.

A silicon PV panel to charge 12V lead acid system will typically have 36 cells and generate around 18V under load in full sun. Some of that voltage will be wasted in the blocking diode and charging regulator - the voltage overhead allows the panel to still charge when it is overcast (when the panel only gives about 15V). 12V lead acid batteries charge at 13.8 or 14.4V.

A sealed (valve regulated) lead-acid battery -- a Gel cell or AGM -- should not be continuously charged above the float voltage (13.7 V or so). A charger may well charge it at up to 14.8V or so during bulk charge, but this would be when the charger is minding the current flowing into the battery and the charger would back-off the charge voltage when the battery nears full charge.

Continuous float charging above 13.7 V will cause the water in the electrolyte to be electrolyzed into gaseous H2 + O2 faster than the battery can catalyze them back into water. This will result in gradually venting the electrolyte and eventual drying out and destruction of the battery. A flooded battery can be topped off, but there is no way to add water to a VRLA.

If your solar array can generate much more than a few dozen mA, you should have a charge control circuit to avoid over charging.