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<p>Of course not all clients are monetarily capable or willing to
oversize a Lithium based battery but many can. In my mind this is
a simpler solution. Its a strategy we're using more to avoid that
voltage cliff and reduce the likelihood of even nearing the BMS
shutting down with all of its hassle factor. This higher battery
capacity allows a little higher LBCO voltage again to keep the
system away from the dreaded BMS cutting out. With the
availability of Midnite's PowerFlo batteries at a much more
reasonable price, the added cost for an increase in off-grid
reliability may not be out of budget for many systems. </p>
<p> Gotta love the conversation about parasitic loads also, I
hope manufacturers are looking at that. <br>
</p>
<p>My $.02<br>
</p>
<p>Bill<br>
</p>
<pre class="moz-signature" cols="72">Feather River Solar Electric
Bill Battagin, owner
4291 Nelson St. (Shipping)
5575 Genesee Rd. (USPS, UPS)
Taylorsville, CA 95983
530-284-7849, 258-1641(cell)
CA. C10 Lic # 874049
Solar Powered since 1982
Home of the Sunny Side Up</pre>
<div class="moz-cite-prefix">On 2/22/2025 1:06 PM, William Bryce via
RE-wrenches wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAEQmjP4c8bqDeF3zcyTMXU53KWSK4Fn-3=tgjpuRgWTjRVOa=g@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Everyone wants to compare the AIO inverters to the
older low frequency inverters when it comes to the idle power
draw. But everyone now wants all the bells and whistles.
<div><br>
</div>
<div>Nothing is free, and if you take an older system then add
up the charge controllers draw, SCP monitoring system, Gateway
device, and then add a battery monitor to the mix you will
find the Idle draw is much higher than what the MFG says for
the inverter alone.</div>
<div><br>
</div>
<div>Feel free to check the math with a Schneider XW with 3 VH
MPPT controllers, a gateway, a SCP, and lithium batteries
running closed loop. Oh, the Schinder does not have any smart
loads like most AIO do.</div>
<div><br>
</div>
<div>My 2 cents.</div>
<div><br>
</div>
<div>Logan</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote gmail_quote_container">
<div dir="ltr" class="gmail_attr">On Sat, Feb 22, 2025 at
12:03 PM Jason Szumlanski via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true" class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div dir="ltr">
<div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">The
voltage cliff is a real issue. Even though LFP
batteries can be pretty deeply discharged without
damage, for practical purposes we need to set the
LBCO on the inverter at a relatively high voltage (or
SOC) to avoid the steep part of the cliff altogether,
rendering a good part of the capacity essentially
useless. In situations where there is a readily
available charging source at all times (auto-start
generator or grid), there really should be a way to
overcome this game of chicken between the battery
protect mode and inverter LBCO. In the off-grid world,
I don't consider that a bell & whistle, but more
of a required feature.</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">Maybe
it's not so much an inverter issue as much as it is a
needed battery feature. Imagine if there were a dry
contact on a battery BMS that told it to stay on
regardless of how it was feeling that day (subject to
safety shutdowns, of course). Then you could force the
battery to be alive with 48V DC connected when there
is generator output voltage present, for example. Of
course, there are risks with this simplistic example,
like if the inverter/charger is faulted and cannot
charge the battery. </div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">I think
the right answer is closed-loop communications that
can tell a BMS in protect mode to wake up because
there is a charging source ready to go. If Midnite
could implement this with AIO/Powerflo, it could be a
very powerful selling point. On the other hand, maybe
it's not that important as long as the inverter
reliably reaches LBCO well before the battery goes
into protect mode. That answer could be in closed loop
communication logic where the BMS sends a warning to
the inverter that it is about to shut down, so the
inverter can stop inverting on the command of the
battery, but keep the battery connected so a charging
source will charge it. </div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">In
other words, maybe it would be better for the battery
to be in command of the inverter's LBCO rather than
the inverter's own fuzzy logic.</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">The
parasitic draw issue does need to be addressed. I went
through some calculations on some typical systems I
have in the field. For example, one system has a
120kWh battery with four Sol-Ark 15Ks. I think the
inverter manufacturers prefer "idle consumption" to
the derogatory parasite comparison, but whatever you
call it, let's assume 360W for four inverters. If
the inverter LBCO is set at 12% and the protect mode
is triggered at 2%, that gives us 33 hours until the
battery reaches protect mode in theory. That is a
substantial amount of time to get a charging source on
the battery. But in practice, I have seen many
batteries enter protect mode before a "properly"
programmed inverter LBCO engages itself.</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">That
brings up another feature request. How about dropping
the idle consumption of paralleled inverters and just
keeping the primary inverter at full idle?</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">Side
note: I inherited a site where a Lithionics battery
BMS is in control of the 2-wire start for a generator.
In theory, this should work, but in practice, the
owner often finds the BMS in protect mode with the
generator not started. I haven't dug too deeply into
this issue yet, but direct BMS control of the
generator is another interesting option. But then you
would want to build in all of the quiet time, charge
percentage/voltage limits, exercise, and other logic
that typically an inverter handles. This is an example
of how a BMS is in control of the charging source, but
it would be better if the BMS was telling the inverter
what to do in terms of AGS and LBCO. </div>
</div>
<div>
<div dir="ltr" class="gmail_signature">
<div dir="ltr"><br>
Jason Szumlanski
<div><span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Principal
Solar Designer | Florida Solar Design Group</span><br
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">NABCEP
Certified Solar Professional (PVIP)</span><br
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span
style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Florida
State Certified Solar Contractor CVC56956</span></div>
<div><font color="#333333"
face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif">Florida
Certified Electrical Contractor EC13013208</font></div>
</div>
</div>
</div>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Feb 22, 2025 at
11:17 AM Steve Higgins <<a
href="mailto:steve@surrette.com" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">steve@surrette.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>Hello all... <br>
<br>
The first issue is that inverter/charger parasitic
loads have increased exponentially in the past 20+
years. When the LBCO cuts out, the inverter may shut
off, but it does not remove itself or any other
DC-connected device from the battery. These
devices still draw a parasitic load. In the 1990s,
the Trace SW would pull about .3 to .4 amps of
current from the battery when connected to it.
Today, many manufacturers use cheaper transformers,
and the high-frequency inverters draw a much higher
current. Some of these all-in-one inverters draw 1-2
amps of current from battery banks, just connected
and not even turned on. <br>
<br>
What's important here is that the battery voltage is
already very low when you trigger an LBCO shutdown
(it's not a disconnect). For a 48-volt system, this
is 44 to 47 volts, depending on where you set the
LBCO. When a Lithium battery is this low, the
voltage dropoff is much higher. With a lead battery,
the voltage dropoff is much more linear, but with
Lithium chemistry, this voltage dropoff is more like
a cliff. This is why it's important for many of
these Lithium systems to set the Battery cutouts a
bit higher so people have more time to fix the
situation before the BMS shuts down. Ideally, the
customer should be educated not to over-discharge
the bank, which would help. Many of these customers
want turnkey systems that they don't want to think
about but don't want to pay for it or do the work
that is required to maintain it. <br>
<br>
Now, if the battery had gone into "Protect" mode and
the BMS had shut down, the battery is outputting
very little votlage... the inverter/charger needs
voltage to run. There used to be a line of
inverters in the marine and RV market that would do
what we called "Dead Battery Restart". This meant
there was a parallel circuit in the power supply so
that when you supplied AC to the input, a secondary
power supply bypassed the regular battery power
supply and would power up the inverter and allow the
charger to run. Most of the inverter manufacturers
got rid of this circuitry because it was not cheap,
took up space on the boards, and was just another
circuit that could get damaged with generator/shore
power surges. I don't know of an inverter today
with this dead battery restarting circuit. </div>
<div><br>
</div>
<div>With this, you need to be very careful. If the
customer has cratered the battery voltage and drawn
down the voltage so low that they have damaged the
cells, jumpstarting the battery can create a
charging hazard, and that could cause the cells to
swell internally. If that happens, the battery will
get warmer and warmer under charge, and eventually,
you could have a cell rupture. This can happen
quickly with Li-ion, but with LFP, it's much harder
to create this problem. Usually, in LFP, cells will
swell a bit, and the current interrupter on the
individual cell will open up and drop that string,
and you will lose capacity. </div>
<div><br>
</div>
<div>Like everything else, it's a race to the bottom
on cost; this affects quality and features...
Everyone wants the "Bells & Whistles," but they
don't want to pay for it. </div>
<div><br>
</div>
<div>Steve Higgins <br>
</div>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Feb 22, 2025
at 5:08 AM Jason Szumlanski via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="auto">I have been thinking a lot recently
about the reasons off-grid systems can shut down,
and working on strategies to prevent these
nuisances that require manual intervention.
<div dir="auto"><br>
</div>
<div dir="auto">Ideally, a BMS should never shut
down due to low voltage/SOC because a properly
programmed inverter should reach it's cut off
well before the BMS decides it needs to protect
the battery, especially where there is closed
loop communication. But let's say that happens,
where the BMS does make the DC battery output go
to zero.</div>
<div dir="auto"><br>
</div>
<div dir="auto">It seems to me like the inverter
should be able to start a generator, and then
signal to the BMS that a charging source is
available. But I'm not aware of any system that
actually does this. The inverter should be able
to wake up the battery. I can see this being
particularly possible where one manufacturer is
writing the code (I'm thinking Midnite
AIO/Powerflo).</div>
<div dir="auto"><br>
</div>
<div dir="auto">Of course, the inverter would have
to have power in order to do that, so if it's
nighttime and there is no PV, the inverter power
would need to come from somewhere. I have two
thoughts. First, someone could manually start
the generator, waking up the inverter, but they
would not have to reset the BMS if the inverter
told it to wake up. The second way would be for
the inverter to somehow close the 2-wire start
circuit upon inverter shutdown, restoring power
to the inverter automatically. </div>
<div dir="auto"><br>
</div>
<div dir="auto">If those are not options, an
external NO relay powered by the inverter output
could be added to the 2-wire start circuit,
perhaps with a time delay to return to the NO
position to allow the generator to remain
powered until the inverter does it's thing and
starts charging the batteries.</div>
<div dir="auto"><br>
</div>
<div dir="auto">Anyway, my question is whether any
inverter/battery combination out there works in
a way that the inverter tells the battery there
is a charging source available to wake up the
BMS and reconnect DC power. And if not, why?</div>
<div dir="auto"><br>
</div>
<div dir="auto">Jason Szumlanski </div>
<div dir="auto">Florida Solar Design Group </div>
</div>
<br>
<br>
</blockquote>
</div>
</blockquote>
</div>
</div>
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