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Small detail, but I think you misspoke. :-)
"So as the batteries approach 100% SOC, the batteries naturally
take less current."
I think you meant "So as the batteries approach absorption charge
voltage, the batteries naturally take less current."
Without DVCC or some other SOC current limiting device/software,
charging is based on a voltage level generated by a charger.
BTW - love your work.
On 2022-05-06 4:12 am, Scott SV Tengah
Dean, small detail, but I misspoke - high voltage disconnect
occurs at 4v per cell. Further, I only charge to 28.4v, so 3.55V
per cell. Victron seems to believe the additional capacity above
that voltage level is not worth the stress on the batteries.
I do not use the DVCC but rather simply a VeBUS BMS with the
Victron Smart batteries. I installed my system in 2018 so I'm not
sure DVCC was available then?
In any event, here's what I think happens. Please correct me if
I'm wrong. The lifepo4 batteries draw as much current as necessary
to charge themselves. So as the batteries approach 100% SOC, the
batteries naturally take less current. In other words, even when
my 200amp chargers are connected to a nearly fully charged Victron
Smart lithium battery that is going into top balance mode, the
batteries only demand 1-3 amps and I can see, through bluetooth,
that the batteries are being balanced. This can continue for
hours. But usually if I want to top balance, I'll run the
generator for a bit to take the batteries to 90-95% and let the
Victron MPPT do the rest. No use in running in the generator to
provide 25-50watts of power!
I don't know what is going on behind the scenes, but my ve-bus BMS
is connected to my Quattro charger via ethernet. With respect to
my other charging sources (Skylla-i 80amp, Victron MPPT and
Mastervolt 110amp alternator), the ve-bus BMS, through an on-off
signal, turns off charging in a safe manner. I reiterate, for
others, that it does not disconnect the batteries from the
charging source, but rather turns off the chargers safely.
As aside, for my MV alternator, I have it set at a very low
absorption voltage. This is for two reasons (1) prevent holding
the batteries at high SOC if I am motoring for a long time (2) let
my solar do its work as a I have an aversion to "wasting" solar
energy. To be honest, more often than not, I turn off my
alternator because we simply don't need that charging source. This
is done through an additional manual switch installed inline with
the "reg-on" wire.
On Thu, May 5, 2022 at 03:53 AM, Dean Gillies wrote:
You mentioned about charging at 200A causing your overvoltage
protection to trigger at 3.7V. Does your system use Victron's
DVCC? This allows your BMS to control the charging voltage and
current directly, and is particularly important in the situation
you mention. By way of example, my BMS disables my alternator
and Mastervolt charger when the SOC reaches 95%. That leaves my
Victron MP and MPPT as the only charging sources when the system
is above 95%. The BMS then uses DVCC to exert fine control over
the charging voltage and current at the top-end. When the first
cell reaches 3.45V, the total charge current is reduced
significantly by the BMS which starts to balance the cells in a
controlled manner using DVCC to control the MP and MPPT. As the
cell voltages increase and come into balance then the charging
current is ramped down and reaches zero when the cells are all
at 3,58V. Balancing currents are small, in the order of 1A, I
don't believe you can effectively balance a LFP battery with a
free-running 200A charger. Maybe your Victron BMS can do more
On the subject of alternator protection, my system turns-off the
alternator (Using the RegON signal) whenever the SOC exceeds 95%
and turns it on again when it drops below 90%. My Mastervolt
charger is also controlled in this way. So my normal operation
is to cycle the charging. If all that fails then my AGM
batteries will act as a fail-safe sink as you mentioned.
2007 A54 #69