June 12, 20224 yr Hi All, I am a bit of a noob but need some help. I have 2 x RCT Axpert MX2 8kVA 8kW 48VDC Inverters and 4 x HUBBLE AM-2 5.5KWH LITHIUM BATTERIES and panels. The batteries wont start their discharge in the afternoon/evening if they are not charged up to 48V. They will go into idle mode for the night if they don't reach 48V. There is a setting on the inverter "Back to discharge Voltage" but the minimum the setting allows me is 48V. Is there anyone that knows if its possible to override change this setting? Also have a Riot Cloud Link device for what its worth but the PV information is not available, any help?
June 12, 20224 yr 48 V on a 15S LFP battery is pretty much dead flat. Why isn't the battery charging to higher than that? "48 V" is the "nominal" battery voltage, it goes back to the days of lead-acid when a nearly empty cell had a voltage close to 2.0 V. To answer your question, the inverter isn't using the battery when it's that low to try and protect the battery from excessive discharge. This again goes back to lead acid days, when over-discharge was very bad for a battery.
June 12, 20224 yr 59 minutes ago, Coulomb said: 48 V on a 15S LFP battery is pretty much dead flat. Why isn't the battery charging to higher than that? The Hubble is a 13S NMC, so LV cutoff is 42V.
June 12, 20224 yr Author Well, they charge up to a maximum of 53V i think on a good day(low household consumption and long direct sun on panels) but on some days they don't reach 48V they go into idle and don't discharge after sunset. They sometimes don't reach 48V because that depends on the consumption from other appliances during daytime hours when the panels are suppose to be feeding appliances and charging batteries. The cut-off is set at 45V/44V.
June 12, 20224 yr 3 hours ago, P1000 said: The Hubble is a 13S NMC, so LV cutoff is 42V. Oh, they must be NMC then; 48.0 V would be 48/13 = 3.7 VPC. 48.8 V can't be a particularly high state of charge.
June 12, 20224 yr 1 hour ago, RSM said: they charge up to a maximum of 53V 53/13 = 4.08 V, that makes them NMC or similar nickel based chemistry. It's unfortunate that Hubble made these 13S; 14S would have suited these inverters much better. You really don't want to be using a 64 V inverter model with these batteries, and unfortunately nearly all of the new models are 64 V models with a 1:7 transformer. That means that they start clipping their output (when in battery mode) at 48.1 V (when generating 230 VAC). If you are stuck with such a model, consider setting it to 220 VAC output. Edited June 12, 20224 yr by Coulomb
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