Hello PowerForum Community

 

Question 1:

Does anyone know whether there is a specified MPPT max input current for an Axpert King 5K inverter?

I cannot find it specified anywhere. For comparison, my Goodwe GW5048D-ES has a specified max input current of 11 Amps per MPPT. Data sheets for both inverters attached for easy reference.

For the Axpert King 5K, max PV array Watts (4000) / max Open Circuit Voltage (145) = 27.5 Amps. This would however assume using the max Voltage. I like to know whether I can use a higher input current with a lower Voltage.

In essence, would it be feasible to use 8x JA Solar JAM78S10 455 Watt PV panels in a 2S4P configuration: 2x panels in series (max 2x 54 = 108 Volts) x4 sets in parallel (max 4x 10 = 40 Amps) for a theoretical max of 4320 Watts? This would only exceed the inverter max PV array Watts of 4000 when the PV array works at 92%+ of rated maximum power.

 

Question 2:

Has anyone used BYD U3A1-50P-A 2.5 kWh LiFePO4 batteries with the Axpert King 5K inverter and if so, is the BMS compatible or does one have to rely on Voltage measurements with setting 5, Battery Type = USE?

 

Please help me in case any of my calculations and/or related logic is incorrect. Data sheets for the solar panels and batteries are also attached.

Thanks in advance

0 |>\/\/3|<|<3Я

FCS-Axpert-King-3Kva-5Kva-Data-Sheet.pdf Goodwe_ES_Datasheet-EN.pdf JAM78S10-455-MR.pdf BYD U3A1-50P-A Battery.pdf

 

9 hours ago, 0 |>\/\/3|<|<3Я said:

Question 1:

Does anyone know whether there is a specified MPPT max input current for an Axpert King 5K inverter?

I cannot find it specified anywhere. For comparison, my Goodwe GW5048D-ES has a specified max input current of 11 Amps per MPPT. Data sheets for both inverters attached for easy reference.

For the Axpert King 5K, max PV array Watts (4000) / max Open Circuit Voltage (145) = 27.5 Amps. This would however assume using the max Voltage. I like to know whether I can use a higher input current with a lower Voltage.

In essence, would it be feasible to use 8x JA Solar JAM78S10 455 Watt PV panels in a 2S4P configuration: 2x panels in series (max 2x 54 = 108 Volts) x4 sets in parallel (max 4x 10 = 40 Amps) for a theoretical max of 4320 Watts? This would only exceed the inverter max PV array Watts of 4000 when the PV array works at 92%+ of rated maximum power.

You can certainly do what you propose.  I run my Kings each with 12 x 365W Canadian Solar panels configured as 2S6P without a problem.

Edited April 20, 20224 yr by Calvin

This helps a lot, since the max power current would be higher than what I'm planning for, thanks Calvin.

To check that I'm using the same or at least a similar panel for my calculations, from a Google search I found a 365 Watt Canadian Solar polycrystalline panel with the following specs:

Opt. Operating Voltage (Vmp) 39.8 V
Opt. Operating Current (Imp) 9.18 A

In 2S6P configuration these would run at roughly 80 Volts and 55 Amps. Does this correlate with your readings?

Those are my panels, and the reading do indeed correlate.

Thanks Calvin for your valuable input to question 1.

If anyone has experience using BYD LiFePO4 batteries with an Axpert King inverter, would be most appreciative for input to question 2.

On 2022/04/20 at 5:26 AM, 0 |>\/\/3|<|<3Я said:

Does anyone know whether there is a specified MPPT max input current for an Axpert King 5K inverter?

The King (not the King II, it has a very different Solar Charge Controller) is limited by the Solar Charge Controller's output current, and that's specified as 80 A. If the battery is at 50 V and the PV panels are at 100 V, then it will take 40 A of panel current to reach the limit of 80 A at the battery.

So it's easier to think of it as a power limitation. 50 V x 80 A = 4000 W; perhaps 10% more (4400 W) when the battery is really full and the voltage is really 55 V. It's possible to add more PV than this limit ("overclocking", so to speak), and it's generally accepted that about 20% overclocking is the limit. So 4800 W nominal, preferably 4400 W or less. 

Edit: the same applies for the Axpert MKS 5 kVA models, which have the same Solar Charge Controller.

Edited April 21, 20224 yr by Coulomb

Hello Everyone

The installation has been completed and the panels are working fine with the inverter as per above discussions. Thanks for all the input.

The 2x 2.5 kWh BYD batteries are being managed by the Axpert King (series one) with setting 5 = USE. Currently the 2.5 kWh Pylontech US2000 settings are being used, as recommended by the installer.

I do however notice differences in the battery specs between Pylontech and BYD and am curious to know if any of the experts here can let me know what values you would use for the BYD batteries instead? In the attached table, the settings in question are marked in yellow.

@Coulomb was hoping you would perhaps be able to provide guidance, especially on the optimal Voltage settings, since it seems you know these Axpert inverters well.

Also attached is the spec sheet for the BYD batteries that will remain in use with this inverter.

Thanks

0 |>\/\/3|<|<3Я

 

BYD U3A1-50P-A Battery.pdf

10 hours ago, 0 |&gt;\/\/3|&lt;|&lt;3Я said:

was hoping you would perhaps be able to provide guidance, especially on the optimal Voltage settings

While maximum charge current per battery module is 50 A, recommended seems to be half that, so I'd use 25 A x 2 = 50 A for setting 02, maximum charge current. The x2 is because you have two battery modules in parallel, so each would get a maximum of about 25 A.

Manufacturers continue to recommend far too high voltages for bulk/absorb and float. The forum has settled on 52.5 V and 51.8 V respectively, but that's for 15S, and you have 16S. So I'd use 52.5 x 16/15 = 56.0 V and 51.8 * 16/15 = 55.3 V. (Personally I use 55.2 and 53.7 for my 16S LFP home-made system). For back to utility, I'd use 51 V; I recommend a fairly high voltage for South Africa with the frequent load shedding. 53 or 54 V for back to battery. Low DC cutoff you might need to fiddle with; 46 V x 16/15 = 49.1 V should work OK. This will actually make the effective back to grid voltage 49.1 + 2.0 = 51.1 V, which is fine. Battery equalisation voltage should be whatever you use in your bulk/absorb setting. This is only needed to work around the premature float bug. If you have timed absorb, you a\may find that slightly easier to use than equalisation. To make equalisation work, you need a bunch of other settings (e.g. eq enable, equalise every day or 2 days, eq time about an hour or 1.5 h). With timed absorb, you can just set it to 60-90 minutes and that's it. Leave equalisation off if using timed absorb.

Much appreciated, thanks @Coulomb.

You mention: "So I'd use 52.5 x 16/15 = 56.0 V and 51.8 * 16/15 = 55.3 V. (Personally I use 55.2 and 53.7 for my 16S LFP home-made system)."

What is the reason you are opting for the lower voltages on your 16S system and would you do the same with these BYD batteries?

 

I'm noticing that Victron specifies the following for these same batteries:

https://www.victronenergy.com/live/battery_compatibility:byd_b-box

Your absorption voltage aligns with theirs. They have the float voltage at 55, which is only 0.2 less than the absorption voltage. Is this fine?

Currently mine are now set as per the yellow section:

It's worth mentioning that I'm not using these batteries unless the utility power goes out. There isn't enough capacity to use in the evenings and then make it through loadshedding. The aim is to keep the batteries full and use only during loadshedding here in South Africa. I would of course want them to provide maximum runtime without voiding a warranty or causing damage beyond standard degradation.

Are there any risks associated with using 56V bulk like I'm doing now? Should I also lower to 55.2 and if so, could my float be the same or 55 like Victron suggests? Could you please help me understand why your float voltage is at 53.7?

18 hours ago, 0 |&gt;\/\/3|&lt;|&lt;3Я said:

What is the reason you are opting for the lower voltages on your 16S system and would you do the same with these BYD batteries?

Just one reason: longevity of the battery. Two things shorten battery life (all battery types): temperature, and high cell voltage. One is kinetic energy of particles, the other is potential energy to enable them to overcome chemical barriers. You keep your cells as cool as practical; no direct sunlight for example. The other thing is to keep the cell voltage low.

LFP has a relatively flat voltage characteristic, but with two hockey sticks at either end, i.e. at very high and very low states of charge. You have to charge up to about 55.2 V to fully charge the battery; there  is no working around that. You can charge it to higher voltage, but that reduces life for very little extra energy stored. Once it's fully charged, you can let the battery relax to a lower voltage. This will lose a little state of charge, about 1%. That's not wasted; you can power loads with that 1%. But then you keep it at that level (think of it as 99% of usable SoC), and the lower voltage (bottom end of the hockey stick) means that the particles don't have as much potential energy to enable the bad, irreversible reactions that reduce capacity.

I don't know if you can achieve float voltage without using the battery for loads. Mine power loads almost all the time, so it's no problem to achieve float voltage. It happens automatically for me. You can probably figure out a way to achieve it and get maximum battery life. Probably SUB output source priority or the like would do it. My system is old and doesn't have SUB output source priority.

14 hours ago, 0 |&gt;\/\/3|&lt;|&lt;3Я said:

Are there any risks associated with using 56V bulk like I'm doing now?

Yes, your battery won't last quite as long. How much life is affected depends on how long the battery stays at that voltage.

Much appreciated, thanks @Coulomb. The inverter is indeed set to SUB as you suggest.

As for the battery voltages, for now I've settled on the values in green.