Advice needed please, I have recently acquired a small load shedding setup using a Victron Multiplus 12/800/35 with a Blue Nova BN13V-108-1.4k lithium battery. I have the charging set up according to Blue Nova recommendations as follows:
Bulk – 14.2V
Absorption – 14.2V
Float – 13.8V
The Multi is set up for lithium with settings as follows, some of which are default:
State of charge when bulk finished – 85% (default)
Charge current – 26A
Repeated absorption time – 1Hr (default)
Repeated absorption – 7 days (default)
Absorption time – 8Hr (default)
I am finding that with stage 4 or 5, when outages are more frequent, the battery does not seem to get to float and 100% SOC before the next bout of shedding. My understanding is that lithium’s can get to max charge within a very short time in comparison to lead acids.
My questions here are, should I increase state of charge when bulk finished higher to 90-95% and should I reduce absorption time to 1Hr or less? Blue Nova don’t provide recommendations for these.
That’s a 110Ah battery. You can easily charge that at C/2 (which would be 55A) without any problems. Your Multi can do 35A. So yes, you absolutely can increase the charge current to 35A, which should be enough to get the battery from empty to full in a little over 3 hours.
Please note though that the Multi derates when it heats up, so you may well get a little less than 35A if it is charging continuously for a long time, and especially also if your ambient temperature is on the higher side.
I would also increase the “SOC when bulk finished” to 95%. It doesn’t do anything about the actual SOC, it merely helps the Multi to make a better estimate. All batteries experience what is called “SOC drift”, where the estimate doesn’t match what is happening in the battery. The way to get around drift, is to reset it to a known value when a certain voltage is reached. Some BMSes may even have multiple “waypoints” to help them estimate their SOC better. The Multi uses the point where Bulk ends (and absorption starts) as that point. This is the point where it reaches 14.2V, and at that point the battery should be >95% charged. On my SmartLithiums I reach absorption around 98% SOC.