HELP! Lifepo4 16.5kwh in, only 12.5kwh out

[costa]

Hi, got a new battery box with claimed 16x280ah Hithium lifepo4 cells.
I did around 4 full charge / discharge cycles to test the capacity.
I have a 5kwh hybrid inverter what can show the solar charging input and the generated power to keep the house running.
The output (lower number) in kwh is identical with an energy meter what collects the power usage from the whole house.



The battery capacy test I start from 100%, all cells are over 3.375v (54.2v) and stop when the bms or the inverter turns off. That is around 42.3v
The maximal of power I can draw is 12.5kwh.
To recharge to 100%, the charge is up to 56v when the bms ovp kicks in and the balancers do their thing, 16.5kwh are used from the solar cells. The system has a tdt bms-6032with an additional red active balancer. After good an hour passed, the battery is down to 54.2v and the balance is down to 20mv cell difference.

The MF-OMEGA-UM5kV3 inverter has a claimed peak efficiency of 93%

From all the test I see, the charge and discharge should be identical.
Why 16.5kwh in and only 12.5kwh out? are the losses so high?

 

[Brucey]

Couple things to take into account.

The zero load power consumption of the inverter (how many W it uses just to stay powered up).

The inefficiency in its grid battery charger.

The efficiency curve of the inverter over its load range, while it may claim 93% that may be at say for example 60% of total max load and if you are idling along at 10% load your efficiency could be very much worse than 93%.

 

[AshleyL]

Couple things to take into account.

The zero load power consumption of the inverter (how many W it uses just to stay powered up).

The inefficiency in its grid battery charger.

The efficiency curve of the inverter over its load range, while it may claim 93% that may be at say for example 60% of total max load and if you are idling along at 10% load your efficiency could be very much worse than 93%.

Exactly this.
A good example is PC PSU when doing conversion from AC to DC. (technically it is the same as solar inverter as the conversion to DC - AC or AC - DC use the same hardware)


Notice the abysmal efficiency at low load? Not even 90% efficiency at 10% - 20% of rated load.
If you take a look on https://www.cybenetics.com/index.php?option=psu-performance-database on PC PSU , almost all the report indicate 60% - 75% efficiency at 10% to 20% of the rated load.

Not to mention the inverter itself requires power in order to produce power.

(12.5kwh/16.5kwh) x 100% = 75.75% overall efficiency. Pretty good efficiency if your household load is less than 50% of the inverter rated load.

 

[goldserve]

The biggest problem I see for most inverters or bms is the ability to track low current usage by the inverter when the sun goes down. For example, the Midnite AOI MM15 draws 33w as reported by a victron smart shunt. Let’s say in the winter, we only have the sun for 6 hours so the rest, 18h the inverter is drawing 33w. 18h x 0.033W = 0.6kwh. I know 33w is on the efficient/low end so check your inverter.

 

[Solar Guppy]

It's bet except for a single data point that inverter is running high 70's to mid 80's in efficiency which seems typical for a low end budget hybrid, so a reported 77% is what I would expect.

 

[Quattrohead]

Sounds about right, those voltronics based inverters run incredibly warm so they are wasting rather a lot of energy.

 

[costa]

manual states, the inverter has no load power consumption of <55w
as far as I can read it right it is shown in the differenz between the green marked values, what are often above 250w near identical, but sometimes not.



The inverter has variable speed cooling and below 250w it is often silent and just hand warm.

But my main question is: is it possible to determine the real capacity of the battery just with the inverter or bms data or is there a shunt what logs the data, like the Victron SmartShunt, necessarry?

oh, and thanks for your input

 

[Brucey]

You can see that your load percentage is only 4% so it would be normal for efficiency to be well below 93%.

 

[AshleyL]

manual states, the inverter has no load power consumption of <55w
as far as I can read it right it is shown in the differenz between the green marked values, what are often above 250w near identical, but sometimes not.

View attachment 276193

The inverter has variable speed cooling and below 250w it is often silent and just hand warm.

But my main question is: is it possible to determine the real capacity of the battery just with the inverter or bms data or is there a shunt what logs the data, like the Victron SmartShunt, necessarry?

oh, and thanks for your input

Victron Smartshunt, too expensive for your taste though.
The accuracy is undisputable.

 

[costa]

@AshleyL
80 euro / $ for the 300a model is not too bad
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so when I noticed that the battery bms needs to pass 4585.99 watt so the inverter can produce 4115 watt, that is not a faulty bms but the actual inverter loss what I see here?

 

[Solar Guppy]

Those numbes

so when I noticed that the battery bms needs to pass 4585.99 watt so the inverter can produce 4115 watt, that is not a faulty bms but the actual inverter loss what I see here?

You maybe surprised by this, but there is no standard for accuracy in reporting operational parameters for these products, its a complete unknown how close to actually the reported values are. It is highly likely at best you might see values within 10% for these budget products.

Reporting an efficiency of 89% seems actually an optimistic value, but there is nothing that can be done about just learn there are reasons there are more expensive inverter options and a key improvement is better efficiency.

 

[AshleyL]

Those numbes


You maybe surprised by this, but there is no standard for accuracy in reporting operational parameters for these products, its a complete unknown how close to actually the reported values are. It is highly likely at best you might see values within 10% for these budget products.

Reporting an efficiency of 89% seems actually an optimistic value, but there is nothing that can be done about just learn there are reasons there are more expensive inverter options and a key improvement is better efficiency.

And hence most of inverters such as Growatt, Solis and Deye set the default 20% "back to grid"..............

 

[Quattrohead]

A shunt is the only way to know for sure, remember many of these inverters don't account for their own power usage.
The efficiency on these voltronics inverters is terrible, you mentioned the fan doesn't turn on until it's doing 250 w of conversion, the luxpower based EG4 18k PV doesn't use it fans until it's processing over 6000 watts of energy.

 

[costa]

Those numbes


You maybe surprised by this, but there is no standard for accuracy in reporting operational parameters for these products, its a complete unknown how close to actually the reported values are. It is highly likely at best you might see values within 10% for these budget products.

Reporting an efficiency of 89% seems actually an optimistic value, but there is nothing that can be done about just learn there are reasons there are more expensive inverter options and a key improvement is better efficiency.

well, if I turn on a 2kw heater and my house power meter shows that the usage jumps from the idle usage of around 150watt to 2150watt and my inverter shows around 2150watt also I assume they have near identical tolerances and report correctly, since I checked the heater before with a plug in meter.
when the inverter and the home power monitor shows I used 8.2 kwh in 24 hours then I assume they are both correct since they measure on two different places with two differnt electronics.
And, yes the MasterPower MF-OMEGA-UM5kV3 is one of the cheaper models compared to Victron. But for a simple all in one inverter it did it´s job for 2.5 years and counting. Also with 650$ it is not a bargain basement model.

 

[costa]

Victron now has a 300A smart shunt what is around 80 €/$
According to the Victron Smart Shunt, my 16 Hithium 280AH cells have a capacity of 297AH each and the total battery can store 15.3KWh.
The TDT BMS displayed incorrect values because the capacity was set to 280AH.
The TDT BMS shows a 0.15V lower voltage than Victron.
53.15V to 53.30V
So my system has a loss of 10% when storing and around 15% when generating normal current over 24 hours.