Standard alternator vs Balmar Marine alternator with and without Victron current limiting devices. The original source for this video was from one of my RV blogs. This is presented as a planning tool for those considering converting to lithium batteries in their RV. Be aware that changes to your system will be required to make the conversion.
I know this video is from Victron and thus it is not unbiased, but I found it interesting in that it described some types of charging that are dangerous for alternators when connected to Lithium batteries. And while the Victron DC-DC charger is mentioned it is not the center of the tests.
Typical Lead Acid batteries (SLA) tend to have their internal resistance
rise tremendously as they approach a full state of charge - which means
they accept less and less current, and hence not overdrawing the engine
alternator.
But LiFePO4 batteries do not, and will accept most of the current given
them when charging - which is as you noted - can be very hard on stock alternators
trying to pump out all that these batteries are willing to accept. On
one hand this is one of the great benefits of Lithium batteries - they
charge up must faster - especially beneficial when charging from a solar
system or when running a generator. But as noted if and when connected
to the engine alternator for charging it can over tax it.
This is why there are DC-DC chargers made. These devices specifically
limit how much amperage charge is given to the house batteries - both by
design as well as by switchable parameters in the unit itself. These
are made in different amp ratings. I am considering a 20 or 40 amp
Renogy model -
Amazon but there are many of these types of devices from other manufacturers-
https://www.amazon.com/dp/B07Q4SVX3M...ding=UTF8&th=1
These DC-DC chargers not only limit the amperage draw on your engine
alternator, but they can also be set for your specific house battery
chemistry, set to differing charging modes, and can be set to a maximum
voltage, at which point it greatly reduces the amount of charge coming
through it into your batteries - making life much easier on the
alternator.
Someone mentioned that the downside of these is that they only transmit
power 1 way - which is true - as they are designed to only allow current
flow from the engine into the batteries. But you can still use the
dash battery connect switch (found on many RVs) which connects the house
batteries to the engine battery momentarily in order for the house
batteries to assist a discharged engine battery (theoretically from not
being used) - it depends on how the DC-DC charger is wired in. The dash
switch utilizes a solenoid to connect the 2 battery systems due to the
high amounts of current the engine starter draws. But properly wired
the DC-DC charger should never be connected through that solenoid at
all. They have their own on-off remote switching and when off they are
automatically isolated from the solenoid connection switching.
BTW - I would like to have 400Ah of Lithium batteries. They would make all the difference in using my RV
as I add a solar system, I hardly would have to
use the generator any more, and they would really enabled us to boondock
much more enjoyably than fighting with my old SLA
batteries. Also saved several hundred lbs of battery weight too.
So it is good to recognize a potential problem when using
Lithium batteries which may be connected directly to the engine
alternator - possibly overly stressing it. But there are simple
solutions, and the benefits of Lithium batteries are many.
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