Morning guys,

 

I have installed a Voltec MKS 5KVA Inverter (Axpert) as a backup (No Solar)

 

The batter is a Pylontech US200 2.4Kw

 

I have used the settings as what is recommended for the combination being

Program 02 -20

Program 05 - USE

Program 12 - 48V

Program 13-  51V

Program 26 - 53.2V

Program 29 - 47.5V

The problem: The inverter sees the battery is fully charged, the Battery SOC (Indicator LEDS) shows full.

During power failure, the inverter shows loads to be 270Watts.

After 20 minutes, the Inverter gives low battery warning of (04)

Please help. I think these settings maybe too conservative and the battery does not reach full SOC nor does it reach full 80% discharge.

Any help is appreciated.

 

 

 

My guess (I don't know this inverter so all these "programs" mean nothing to me), is that it has to do with the chemistry of the battery and the number of cells. The LFP chemistry has a very flat voltage curve, unlike lead acid. It spends most of its live in a small voltage band. You can't judge state of charge from the voltage (not really with lead acid, and even less with LFP), so whatever the inverter is telling you can simply be ignored, it means nothing. Additionally, this battery has 15 cells in series which means it lives on the low end of the voltage range (48V-53V).

Now, again I don't know how this inverter does it, but typically a low voltage alarm is raised when you get "close" to some lower end. For an LFP, this happens really easily, because of the flat voltage curve. If the inverter is running lead acid programming (for the Voltronics that is always the case, there is no factory LFP firmware as far as I am aware?), it may well complain too soon.

So... hopefully others can give you more accurate numbers, but if the inverter doesn't switch off, and the LEDs on the battery itself indicates a good charge level... I would simply ignore the warning.

Thanks for the reply. In all the documentation i've read, it is syggested that a cutoff voltage be set in the inverter to 47.5v. This is the point that the inverter starts complaining. Also, when I run a small load of 1000watts, the low voltage alarm comes on when voltage drops to 47.5 volts. It is strange that a battery capable of delivering sagely 1200 watts has such a large drop in voltage.

If setting 29 is set at 47.5 v the alarm will go off off at 49.5 v . Run this setting at 46.5 v and t will be much better . The alarm will then go off at 48.5 v . The inverter will now switch off at 46.5 and your batteries will be safe . Just remember that you need 3 *3.5 kW Pylontech for the 5 kW inverter to keep your guarantee . If you have only one 2.4 kW you should try and get some more batteries .

1 hour ago, Chris Louw said:

Just remember that you need 3 *3.5 kW Pylontech for the 5 kW inverter to keep your guarantee .

Please explain the technicalities of this, I also only have 2 3.5kw on a 5kw inverter.... 

1 hour ago, Chris Louw said:

If setting 29 is set at 47.5 v the alarm will go off off at 49.5 v . Run this setting at 46.5 v and t will be much better . The alarm will then go off at 48.5 v . The inverter will now switch off at 46.5 and your batteries will be safe . Just remember that you need 3 *3.5 kW Pylontech for the 5 kW inverter to keep your guarantee . If you have only one 2.4 kW you should try and get some more batteries .

So I gather that the Inverter cutoff voltage must be set higher than the low cutoff of the Pylontech?

1 hour ago, Cozy35 said:

So I gather that the Inverter cutoff voltage must be set higher than the low cutoff of the Pylontech

At 44.5 v the battery protection will turn on . You don't want that to happen . Yes the inverter cutoff must be higher than that off the Pylontech .

2 hours ago, FixAMess said:

Please explain the technicalities of this, I also only have 2 3.5kw on a 5kw inverter.... 

I think it is because the 5 kW inverter can draw 100 amps . The recommended discharge is 37 amps per 3.5 Pylontech . I'm  not a electrical man , correct me if I'm wrong .

15 hours ago, Chris Louw said:

If setting 29 is set at 47.5 v the alarm will go off off at 49.5 v .

The low battery warning will come on at 49.5 V. The warning has the buzzer sounding one short beep every second, showing 04 in the middle two digits of the LC Display with the ⚠ symbol beside it. Power will continue to the loads.

Quote

The inverter will now switch off at 46.5 and your batteries will be safe .

This is the low battery error / fault. You will see 04 in the middle of the LC Display, with ERROR beside it. There is no power to the loads.

On 2020/02/15 at 3:47 PM, Chris Louw said:

At 44.5 v the battery protection will turn on . You don't want that to happen .

why would the bms protection coming on be a bad thing?

If the battery protection disconnects the batteries while the inverter is supplying load the inverter can be damaged . Best to always switch off the load first, then switch off the inverter before disconnecting the batteries .