[RE-wrenches] midnite AIO

Sun Feb 23 07:21:46 PST 2025

Jay,

Prepare to be even more impressed:
https://www.youtube.com/watch?v=BQF4peNdtlY

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

On Sat, Feb 22, 2025 at 6:20 PM Jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi Logan.
>
> I am super impressed with what the AIO can do.
>
> Question. What happens if something breaks inside. Is it field repairable?
>
> Thx
> Jay
>
> On Feb 22, 2025, at 2:07 PM, William Bryce via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> 
> 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.
>
> 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.
>
> 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.
>
> My 2 cents.
>
> Logan
>
>
>
> On Sat, Feb 22, 2025 at 12:03 PM Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> 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.
>>
>> 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.
>>
>> 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.
>>
>> 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.
>>
>> 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.
>>
>> That brings up another feature request. How about dropping the idle
>> consumption of paralleled inverters and just keeping the primary inverter
>> at full idle?
>>
>>
>> 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.
>>
>> Jason Szumlanski
>> Principal Solar Designer | Florida Solar Design Group
>> NABCEP Certified Solar Professional (PVIP)
>> Florida State Certified Solar Contractor CVC56956
>> Florida Certified Electrical Contractor EC13013208
>>
>>
>> On Sat, Feb 22, 2025 at 11:17 AM Steve Higgins <steve at surrette.com>
>> wrote:
>>
>>> Hello all...
>>>
>>> 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.
>>>
>>> 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.
>>>
>>> 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.
>>>
>>> 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.
>>>
>>> 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.
>>>
>>> Steve Higgins
>>>
>>>
>>> On Sat, Feb 22, 2025 at 5:08 AM Jason Szumlanski via RE-wrenches <
>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>
>>>> 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.
>>>>
>>>> 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.
>>>>
>>>> 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).
>>>>
>>>> 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.
>>>>
>>>> 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.
>>>>
>>>> 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?
>>>>
>>>> Jason Szumlanski
>>>> Florida Solar Design Group
>>>>
>>>>
>>>>
>
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