Battery‐Tipps
Since we are all experimenting with the DPL SOC percentages, this may be interesting:
The 20%-80% SOC myth for LiFePO4 Batteries https://www.youtube.com/watch?v=DQeUYJoTpzg
The maximum charge and discharge current is limited to 25A, but the Pylontech data sheet tells me the maximum is 100A
The maximum current is limited to keep the battery healthy and reach the 10 year guarantee.
**US2000C: **Charge/Discharge Current: 25 A (recommend), 50 A max In off-grid, the inverter can draw more than the 25A limit to run the loads, make sure you have sufficient batteries installed to keep the load per battery around this limit.
So, if you want to keep the 10year warranty of your Pylontech Battery, with one battery you should not exceed 25A x 48V = 1200W with 96% Efficiency = 1152W Limit of your inverter 😇
With two Pylontech batteries, you should not exceed 2 x 25A x 48V = 2400W with 96% Efficiency = 2304W Limit of your inverter 😇
and so forth....
Accordingly,
US3000C: Charge/Discharge Current: 37 A (recommend), 74 A max
US5000C: Charge/Discharge Current: 50 A (recommend), 100 A max
The maximum charge voltage of 53.5V (15 cells) and the maximum peak current of the system must not be exceeded.
At 54.0V the overvoltage protection is triggered and at 44.5V the undervoltage protection.
Deep discharging or overcharging can lead to cell imbalance and subsequent balancing (1-2A charging current) can take several days.
To ensure that the battery system is optimally charged and discharged, a communication (RS485 or CAN) with the charger/inverter is recommended.
The charging voltage should not be set above 52.5V without RS485 or CAN communication.
More Details under: https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom (especially 9. FAQ and Known Issues, My system only charges the battery to 52.4V )
Feedback from a user who tested a GOBEL GP-SR1-RV150 Battery (2022 model) is that the CANBus (in DEYE Configuration) is working with OpenDTUonBAttery.
I know it is boring but, it is invaluable: spcqike's comments about 12V, 24V, 25V, 48V, 51V batteries and battery Lead vs LiFePo4 cells:
A single Lead cell has a nominal voltage of 2V, but can have a real voltage of 1.75V to 2.4V, depending on its charge state. That said,
- a 12V battery can have 10.5V to 14.4V (as it has 6 cells)
- a 24V battery has 12 cells and
- a 48V battery has 24 cells, giving a total of 42V-57.6V, depending on its charging state.
A single LiFePo4 cell has a nominal voltage of 3.2V, a minimal voltage of 3V and a maximum voltage of 3.4-3.45V.
- So you need either 4, 8, 15 or 16 cells to get a 12.8/25.6/48/51.2V battery.
- In case of 16 cells you get a voltage range from 48V-55.2V with a nominal voltage of your mentioned 51.2V.
- So, a „51.2V“ lifepo has a lower (maximum) voltage than a 48V lead acid battery. And in terms of 12/24/48V, it’s a 48V battery. Not a 51.2V one.
The HOYMILES requires min 22V to start working (Anlaufspannung)
then it works until Voltage drops below 16V (Betriebsspannungsbereich)
The HOYMILES has poor performance at 24V The higher the production (above 500Watt), the worst is the performance of the Hoymiles at 24V. You can only notice this by monitoring the Amperes the 24V battery delivers.
Thus, the above leave the 48V as the only sensible option (for significant power generation e.g. above 300W) A very lengthy (german) discussion about this is here: Nach 6 Monaten Trial & Learnings - Meine 51,2V / 100Ah / HM-1500 onBattery Anlage
The shortest night has approx. 6,5 hours with no light, ca 22:30h - 5:00h.
The longest night has approx. 15,5 hours with no light, ca 17:00h - 8:30h.
You can calculate the "average" hours with no light: 6,5 hrs + 15,5 hrs = 22 hrs / 2 = 11 hours on average day
...which is of limited use. A better average is the monthly one:
Apparently you should not! Opinions differ on how much you should use. You should form your own opinion on this (and read the manual of your battery).
Nevertheless, all say that you should not drain your battery down to zero 0 % percent and that you should avoid charging it to 100% percent.
OpenDTUonBattery can master both situations (under and over charging).
Remember that your battery provides power to a HOYMILES, which also has an efficiency rating, let's say 96% percent.
Below table gives an example of a 4,8kWh (48V, 100Ah) battery that should not be drained below 15% and not charged above 95% It gives you the available battery capacity and shows how many Watt p. hour your Hoymiles would be able to deliver during the night hours:
Easy answer and difficult at the same time.
Let's suppose you have a base consumption (Grundlast) of 160W per hour at night:
Then, even during the long winter nights, you only need a 2,4kWh battery! Right?
Not quite!
-
First, the above calculation is based on using 100% of the battery. But as we explained earlier, it is not recommended to use 100% of your battery's capacity. The examples above showed us discharging the battery up to 10% percent and charging it up to 95% percent thus, 85% percent of the total battery capacity is only being used. Below is the battery size needed if you only use 85% of the total battery capacity:
-
Second, 160W per hour maybe the case during night time (when you are sleeping). During the long winter nights though, you will probably be at home watching TV or cooking during the some night hours so, the consumption will probably be much higher (at least for some hours).
Keep in mind, during the day you need solar power to cover your daily needs AND charge the battery.
Also, the charging process has some losses. If we take for example a 90% efficiency of the charging system, then the table below shows how much energy we need to send to the battery:
(The number of hours with sufficient light for your PV Panels is lower than the number of daylight hours shown on the table)
Well, Yes and No:
- We have never heard (yet) of anyone having destroyed his inverter due to inrush of current from the battery.
- However,
- Your Inverter Manual as well as panels advice to never connect/disconnet the cables while there is solar power to the panels
- It is documented everywhere that one must pre-charge the capacitors before connecting a battery
- It is actually "piece of cake" you can achieve this using a 3EUR resistance or even with a 230V incandescent light Bulb!
There are many videos explaining the reasons and how to do it: https://youtu.be/ZlrtmJRfSP8?t=72
One with a 48V light bulb: https://www.youtube.com/watch?v=DOrJ5AH9yjM
... and one with a 230V light bulb: https://youtu.be/0M_7s39E3Ds?t=313
If you need a permanent solution and want to look "elegant", member DDvO has a good solution:
If you have a battery without "Soft-Start" function, it is important to know this:
If the BMS cuts the connection to protect the battery, e.g., because of overcharging, you will need to pre-charge, unless your charge controller is still alive and outputs a respective voltage/current to feed the inverter. This is a tricky problem. The consensus is to avoid BMS intervention (for a couple of reasons) whenever possible. I had the BMS reconnect the battery after some problem went away by itself, and the fuse blew. Not ideal.
Note that you must remove the resistor after pre-charging the capacitors. After a disconnect, I use a fuse/switch to connect the inverter to the battery with a resistor (~1Ohm) in series. Pre-charging does not take long (give it two seconds). I then enable another fuse/switch, which establishes the direct connection. The pre-charge-switch must be disconnected afterwards.
rs3hc made some testing and shared his thoughts:
We all agree that the problem with connecting the battery directly is the high charging current of the electrolytic capacitors. This results from the "internal resistance" of the Hoymile, the cable connection and the internal resistance of the battery.
Wir sind uns einig, das Problem beim direkten Verbinden des Akkus ist der hohe Ladestrom der Elkos. Dieser resultiert aus dem "Innenwiderstand" des Hoymiles, der Kabelverbindung und dem Innenwiderstand der Batterie.
The only thing we know halfway is the cable resistance and that of the battery.
Das einzige was wir halbwegs kennen ist der Kabelwiderstand und der der Batterie.
A proper AGM battery has an internal resistance of 10-30 mOhm. (0.03 Ohm for better arithmetic)
with 4 batteries (48V) you have 120 mOhm (0.12 Ohm).
With a 48V system and fully charged batteries you have a voltage of approx. 54-56 V.
Eine ordentliche AGM Batterie hat einen Innenwiderstand von 10-30 mOhm. (0,03 Ohm fürs bessere Rechnen)
bei 4 Akkus (48V) hast du 120 mOhm (0,12 Ohm)
Bei einem 48V System und voll geladenen Akkus hast du eine Spannung ca 54-56 V.
Now let's assume a reasonable but short cable path.
2m at the plus and 2m at the minus with a good 6 qmm.
This gives you a line resistance of only 11.3 mOhm (0.0113 Ohm).
Jetzt gehen wir mal einem vernünftigen aber kurzen Leitungsweg aus.
2m am Plus und 2m am Minus mit gutem 6 qmm.
Da hast du einen Leitungswiderstand von nur 11,3 mOhm (0,0113 Ohm).
I'll leave the resistance of the load breaker or fuse to one side :D
Den Widerstand vom Lasttrenner oder Sicherung lasse ich jetzt mal gekonnt bei Seite :D
This means that, apart from the Hoymiles, we only have 0.1313 ohms to oppose the 54V.
Das heist, abseits vom Hoymiles haben wir rechnerisch den 54V nur 0,1313 Ohm entgegenzusetzen.
This gives us a short-circuit current of 426.5 A!
Hier kommen wir zu einem Kurzschlussstrom von 426,5 A !!
I went to my HMS-600-2T and measured the electrolytic capacitors --> 11.85 mF
Ich bin mal zu meinem HMS-600-2T gewandert und habe mal die Elkos gemessen --> 11,85 mF
Then I measured the resistance of a PV input.
The resistance increases with the charging of the electrolytic capacitor and the supply of the control electronics behind it.
Dann habe ich mal den Widerstand eines PV-Eingangs gemessen.
Der Wiederstand steigt mit der Aufladung des Elkos und der Versorgung der Steuerelektronik dahinter.
I had the first measured value after approx. 0.5s with 28.54 Ohm and after one second already over 150 Ohm and after 3 seconds over 380 Ohm.
Den ersten Messwert hatte ich nach ca 0,5s mit 28,54 Ohm und nach einer Sekunde schon über 150 Ohm und nach 3 Sekunden über 380 Ohm.
But here you have to take into account the inertia of the measurement technology, even though I had already preselected the range. Hier muss man aber die Trägheit der Messtechnik mit einbeziehen und das, obwohl ich die Range schon vorgewählt hatte.
I am sure that the initial resistance will be much lower.
In the first nano/milliseconds, the resistance is in fact close to zero.
Ich bin mir sicher, dass der Anfangswiderstand um einiges geringer sein wird.
In den ersten Nano/Milli-Sekunden ist der Widerstand faktisch nahe Null.
I therefore think that the initial charging current should easily be over 100A, but I can't prove that without a high-current clamp with inrush measurement.
Daher denke ich dass der Anfängliche Ladestrom locker über 100A liegen dürfte, dass ich aber ohne Hochstromzange mit Inrush-Messung nicht nachweisen kann.
I have uploaded the video here in Drive
Das Video dazu habe ich hier in Drive hochgeladen (Link)
03_x265.mp4
I found a few photos of the inner workings of the HM-800, including the electrolytic capacitors.
Ich habe im Netz noch ein paar Fotos vom Innenleben samt Elkos des HM-800 gefunden.
The 800 has 4x 2,700 uF per input for 63V, resulting in 10,800 uF. This corresponds to the measured and the +-20% rating.
Beim 800er sind je Eingang 4x 2.700 uF für 63V, ergeben 10.800 uF. Das deckt sich mit dem gemessenen und dem +-20% Rating.
In the photos you can see that the electrolytic capacitors come directly after the solder joints of the string inputs.
Auf den Fotos sieht man schön, dass nach den Lötstellen der String-Eingänge direkt die Elkos kommen.
I think there is a lot of luck involved if you connect the battery without precharging.
Ich denke da ist viel Glück dabei, wenn man die Batterie ohne Vorladung zuschaltet.
In any case, it really affects the durability of the electrolytic capacitors.
Auf jeden Fall geht es sehr auf die Haltbarkeit der Elkos.
Conclusion - Fazit
With AGM batteries, I would proceed as follows:
Bei AGM Akkus würde ich wie folgt vorgehen:
- Den WR an den Victron MPPT schalten - Connect the inverter to the Victron MPPT.
- Die PV Strings am Victrom MPPT zuschalten - Connect the PV strings to the Victrom MPPT.
- Jetzt fährt der MTTP hoch und startet sanft den WR - Now the MTTP starts up and gently starts the inverter.
- Bitte in der App des Victron SmartSolar MPPT prüfen welche Systemspannung eingestellt ist!!! - Please check which system voltage is set in the Victron SmartSolar MPPT app!!!
- nun die Batterie zuschalten - Now connect the battery
Note: If you have a battery that has a "Soft-Start" function, you do not need to do the above
Hinweis: Wenn Sie eine Batterie mit einer "Soft-Start"-Funktion haben, müssen Sie die oben genannten Schritte nicht durchführen.