View Full Version : OT: Battery charging dilemma

04-21-2009, 08:57 AM
I recently put together a small (700 watt max output)combination solar/wind unit and planned to use some of the juice to charge regular car type batteries leaving them connected in parallel with the main battery bank consisting of two deep cycle batteries all connected in parallel.Despite leaving the parasite battery connected for days it does not seem to be charged as well as when it is connected to a small 6 amp standard battery charger connected via 12 to 120 volt inverter hooked to the system.Excess energy from the unit goes to heat sink if not used.Any explanations appreciated.

04-21-2009, 09:17 AM
A lead acid battery must charge to a voltage of at least 13.7 volts when disconnected to reach a full charge. Normal full charge systems will charge to 14.3 volts with charging voltage still applied. To reach that voltage is dependent on the current available from the supply and the internal resistance of the battery.

Measure the terminal voltage on the "parasite" battery while charging. If it doesn't reach 14.3 volts then it will not be fully charged. The most voltage that the deep cycle batteries can supply to charge the third battery in the absence of sufficient current from the generator is 13.7 which will result in about an 80 percent charge.

04-21-2009, 09:33 AM
The batteries hooked in parallel will tend to ballance their charge. So, if one of the batteries is weak it will draw the charge from the other batteries causing the whole lot to be low. It could be that the battery that is showing low is defective.

04-21-2009, 09:42 AM
I too am in the process of building a Wind Power Generator - - no solar panels - just wind. The below link has a lot of useful information, especially the Charge Controller:

The unused power would be better diverted to a dummy load when your batteries are fully charged. This load could be as simple as a few light bulbs.

A friend of mine is developing a schematic / parts list for a charge controller that allows about 14v to go either to charging the batteries OR to the dummy load.
When the schematic is complete (soon I hope) I'd be happy to post it along with any other information that may be helpfull to you - if you're interested.
In any case, I'd sure check out the link.