The solar panel kit that I bought has two solar panels and is intended for use with two 12V batteries. The system can be used in parallel at 12V or in series at 24V. The little instruction booklet explains how to connect batteries in parallel or in series. The diagram of the parallel one is fine, but I wouldn't follow their advice on the series connection, if I were you.
In fact, if you connect them like in the second picture, the batteries will not just be not included, they might well not be in one piece after a short while. And watch out for boiling acid.
Even the parallel connection is not a good long term idea.
ReplyDeleteIf one of the batteries has a failed cell then the other battery will discharge through its sick mate. This could get interesting. Lead acid batteries are "good" because they have near zero internal resistance. Best not to have the batteries inside the house, or near anything you value.
Each battery should have a beefy (capable of taking twice the maximum expected, charging or discharging current), low forward voltage drop (less wasted heat) diode just to stop the electrons going the wrong way into the battery. Such diodes should be available, two together in one enclosure from boat chandlers, caravan supplier, etc. The "diode block" should be mounted on its own heat sink to keep it cool.The
Good luck.
Addendum. No matter series or parallel connected, fit fuses. One for the series link, and one each on each battery in parallel. Fuse values to cope with maximum expected current.
ReplyDeleteGood advice Doon. There are no fuses right now, and my only defense is that everything is far enough away that even if it all explodes or catches fire, the damage will be limited. But I will get some fuses and wire them in.
ReplyDeleteHaving worked in the marine industry I wouldn't let ANY diode (even "Low Loss" Schottky types) within a mile of my batteries! They introduce horrendous loss, and that's why they need damn great heat sinks! Fuses yes, but they're no use unless the cabling can carry at least 50% more than the fuse's "Rated Current", as that's the minimum it will take to make it blow.
ReplyDeleteI agree about the risks of one battery failing (usually a single cell to start with), but it's only if that cell fails short circuit that problems will occur. You'll normally smell "rotten eggs" as the 12 volt battery tries to charge a (now) 10 volt one! I always do regular checks by isolating each battery and comparing voltages.
One never stops learning. Going to have to link to these across the way.
ReplyDeleteThank you 😊 so much for sharing this.
ReplyDelete