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Inverter not maintaining battery's at float charge voltage


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Posted

Hi,

I noticed that my inverters is not keeping my battery's fully charged. I have 2 Axpert 5kw inverters in parallel, connected to 2 Narada 48v 100ah batteries(connected parallel). The system is 2.5 years old. In the morning the inverters charge the battery's to 54v, but then one or both stop charging, never the same inverter. The one inverter starts charging, but not enough, so the battery's voltage starts dropping. Then they work stop/start. They always used to idle, keep battery's full and supply enough power for my house. Now one switch off, till the voltage drops to about 48 v then both run full blast( set at 60A each) till battery's is full, then the cycle repeats. Now, the soc shows 100% at 54v, and drops slowly to about 96% (+-49v), then the inverters kicks in and charge them till 100% soc. I don't know why. It looks like the inverters uses the soc to charge, and not the voltage.

Posted (edited)
56 minutes ago, Oros said:

In the morning the inverters charge the battery's to 54v, but then one or both stop charging, never the same inverter.

54.0 V is the disconnect voltage for Pylontechs; it's likely to be the same or very similar for Naradas, as I believe that they are also 15S LFP. 54.0 V is 3.60 VPC, usually considered the upper limit for LFP cells.

Are your inverters connected to the BMS via an RS-485 cable? Or are you using battery type = USE?

56 minutes ago, Oros said:

Now, the soc shows 100% at 54v, and drops slowly to about 96% (+-49v), then the inverters kicks in and charge them till 100% soc.

My guess is that the BMS is sending the "do not charge" signal to the inverter at around 100% SOC, which is why the battery voltage drops. At 95% SOC, they probably remove the "do not charge" signal, so that the inverter charges the battery again.

I agree that it's not ideal behaviour. What should happen is that at 100% SoC, the inverter should go into a float mode, where it ignores the voltage suggested by the BMS, or at least subtracts a percentage or a fixed voltage from it. Then the battery can remain at near 100% SoC, so then a few surges from big loads turning off, or a few sags from big loads coming on, would not cause these wild swings in SoC. This would reduce or nearly eliminate the unnecessary micro-cycles on the battery, improving longevity.

Voltronic have had years now to get this right, and they don't seem to be improving much if any, unfortunately.

Edited by Coulomb
Posted

I actually bought a comms cable for the narada to ICC raspberry pi. The soc is now a nice smooth graph. Not eratic from the inverters. On the icc software, on the battery settings page was a setting for soc controlled charge. I enabled it, but was not happy because with 100% soc the mppt stopped charging, but the voltage was no near the 54v full voltage. So I disabled it, but it looks like the inverters is stuck in that mode. I even disconnected the comms cable, but it did not made a difference. I think I must, on the inverters, go through all the settings and change it back to what it was set at when the system was installed. I just hope it is a setting. Only thing is, when i went through the manual, I did not see such a setting that looks at the soc for charging.

 

Posted
16 hours ago, Oros said:

I did not see such a setting that looks at the soc for charging.

My understanding is, if you use battery type PYL and a cable from the inverter to the BMS, then it will always use the SoC provided by the BMS. When ICC reads the SoC, I'm not sure how it works; I suspect that ICC sends PBMS commands or the like directly to the inverter, replacing the logic in the removable display.

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