When an SLA battery is under load, they say not to go below a certain value to avoid wear. So, don't go under 30% State of Charge (SoC), which is also a certain Open Circuit Voltage (Voc), say 11.8V .
So, here both values are linked, one value means the other, independent of the load rate.
Under load, however, you can't just guess the Voc . So ok, no problem, we have graphics of voltages and state of charging with different load rates (ignoring existing wear, let's keep it simple).
So far, so good.
But here comes my problem โโ Although I can't find much documentation on this, there are two opinions!
- You can't go under a certain State of Charge (SoC)
or- You can't go under an absolute voltage (V, not Voc!!).
I made two graphics to make this clear. Only the colors are different. Yellow and red mean: avoid (resp. at all cost) to avoid fast wear.
So, 2 possibilities:
- (Top)
Best not to go under 30% state of charge. The voltage under load depends on the load (current).
E.g. on a load of C/3, you can go to somewhere between 10.3-10.7V. - (Bottom)
Best not to go under a certain absolute voltage.
E.g. on a load of C/3, you can go to 11.8V, but you would still have 95% state of charge left!
And it gets even weirder. Some say that voltage should be the Voc that correspond with the 30% Soc. Others just take a random voltage.
Me, personnally, I bet on number one, and number two is from people that were a bit confused. Although this is how not too intelligent controllers's cut off is set.
But can someone with deep knowledge confirm or correct me? Possibly with some explanation. ๐๐ Thank you. ๐๐