Nochmal was zur Spannungsdifferenz. Die nur ca. 2V hat man natürlich nur, wenn die Sonne keinen Strom liefert, der 50Ah Akku gerade entladen wird und seine Spannung dadurch bei ca.52V liegt Aber irgend einen Kompromiß beim Zusammenschalten muß man bei dieser ungewöhnlichen Konstruktion ja immer eingehen.
Die Ruhespannung eines nicht ganz leeren Akkus, sollte durchaus noch bei ca. 50V liegen.
Der Innenwiderstand einer LiFePo Zelle ist abhängig von der Kapazität. Je kleiner diese ist, um so höher ist der Widerstand. 0,001 Ohm sind für eine 50Ah Zelle also ein guter Wert.
Das mit dem Innenwiderstand sehe ich genau so wie du, darum hab ich mal als Beispiel meine reellen Messwerte von größeren 280Ah Zellen (da näher an den 314Ah hier) angegeben.
The power supply can remain connected permanently, and the approximately 0.6 W input at 12 mA won’t cause any problems. A diode in series should protect the power supply against higher voltages when the mobile batteries have finished charging.
I don’t know how often you intend to do this, but I’d simply connect a cable with an additional resistor of around 25 ohms to the positive bus and, before connecting the positive cable each time, hold it against the battery’s positive terminal for a few seconds to charge the capacitors. The negative terminal of course needs to be connected beforehand.
I just tested this with a 24 V MP. In this case, with a 12-ohm resistor, so a maximum of 2 A. The capacitors were fully charged in about 1 second. During the test with around 4 A, you can already see a very small spark, but it’s still harmless.
I’ve got something like this fitted to my batteries as well. I might only need it once a year for the ESS battery, but I need it regularly for my caravan/mobile battery, and it works brilliantly.
From the recent posts, I’ve learnt quite a bit about LFP batteries and their construction and behaviour. Thanks everyone
Do you have a link for me?
After all the posts, I think I’ll stick with the pre-charge circuit after all. The question that remains is which design is better: a power supply or a resistor that is switched out again after a few seconds?
Andy’s video provides hardly any useful insight. Two batteries with almost identical voltages (13.3 V and 13.4 V) are connected in parallel — naturally, nothing happens. A battery at 11 V and one at 14 V is a completely different matter; in that case, a BMS will kick in. See the following video:
Simply Connect a Lithium / LiFePO4 Battery in Parallel Full to Empty
