June 19, 20206 yr Hey guys, Is it possible to run two independant inverters from the same battery bank? The situation is there is an existing Goodwe 4.6kw inverter installed but client wants additional circuits added to the backup (circuits which would overload the backup output), is it possible to now add an additional inverter (perhaps like an Axpert?) to the battery bank to supply these additional loads? So basically the DB board would be split in to 3 (on grid loads, backup loads on Goodwe and backup loads on the additional inverter). Now, the additional inverter will have nothing to do with the PV or charging of batteries it will exist purely to supply the additional loads with backup power in the event of grid failure.
June 19, 20206 yr 12 minutes ago, Sammyigt said: Now, the additional inverter will have nothing to do with the PV or charging of batteries it will exist purely to supply the additional loads with backup power in the event of grid failure. Done like this it might work, the problem with systems like this is when both are trying to charge ext. If they have Pylontechs, they would know the true SOC of the batteries even if some other divice is using some power from it. The only problem comes in when the combined loads exceed the allowed discharge current of the Batteries. If exceeded, the batteries will just switch off and the client will be without power in any case. You have to ensure that you have enough batteries to supply loads like that.
June 19, 20206 yr Jaco already touched on this, but usually it is no problem as long as 1) you don't overwork or overcharge the battery, and 2) you'll have to deal with any SOC tracking the system might have. Some inverters can track the amount of Amp-hours going into and out of the battery and do good SOC tracking, while others do no SOC tracking, or they use voltage (which is terrible), and in those cases the SOC of such an inverter (or both of them) will be off since they won't know what the other one is doing. In cases where you have a battery monitor (such as the Victron BMV) or a BMS that SOC tracking, then you won't have that problem (the extra draw of the second inverter is accounted for), but then you may have a problem that the BMS (if it communicates via CAN-bus cable or RS485 to the inverter) would not be able to control both, so the BMS won't be able to stop charge/discharge on both.
June 19, 20206 yr Author 7 minutes ago, plonkster said: Jaco already touched on this, but usually it is no problem as long as 1) you don't overwork or overcharge the battery, and 2) you'll have to deal with any SOC tracking the system might have. Some inverters can track the amount of Amp-hours going into and out of the battery and do good SOC tracking, while others do no SOC tracking, or they use voltage (which is terrible), and in those cases the SOC of such an inverter (or both of them) will be off since they won't know what the other one is doing. In cases where you have a battery monitor (such as the Victron BMV) or a BMS that SOC tracking, then you won't have that problem (the extra draw of the second inverter is accounted for), but then you may have a problem that the BMS (if it communicates via CAN-bus cable or RS485 to the inverter) would not be able to control both, so the BMS won't be able to stop charge/discharge on both. So I'm looking to provide probably the cheapest solution. As mentioned there is a Goodwe 4.6 ES currently with 2 x us2000 Pylontechs so comms for true SOC exist between those two. Additional batteries will be added to this as well to prevent the batteries from overloading. Can I use an Axpert inverter (or are there better alternatives for a +/- 5kw battery inverter?) for the additional load? I know they get their SOC info from the voltage of battery so they will need to be told to stop discharging at around 47.5v? The Axpert will as mentioned have nothing to with charging the batteries and wont be discharging them in the evenings, it will remain in bypass mode unless there is grid failure (so this will allow the Goodwe to continue running in self use mode without hindrance from the Axpert.
June 19, 20206 yr I don't see a problem with what you suggest. The second inverter is just another "DC load", and DC loads are common in many applications. You can configure the second inverter with a voltage to disconnect at (Say 3.1V per cell, times 15, that.s 46.5V), but the BMS will also disconnect if the battery goes too low. US2000 battery recommended max discharge is 25A per module, so just remember to size it with enough modules to cater for the extra "DC loads".
June 19, 20206 yr Author 3 hours ago, plonkster said: I don't see a problem with what you suggest. The second inverter is just another "DC load", and DC loads are common in many applications. You can configure the second inverter with a voltage to disconnect at (Say 3.1V per cell, times 15, that.s 46.5V), but the BMS will also disconnect if the battery goes too low. US2000 battery recommended max discharge is 25A per module, so just remember to size it with enough modules to cater for the extra "DC loads". Yeah I'm aware of the 25a discharge current on the battery. I was just not sure about running an additional inverter as a DC load on the battery but thanks for clearing up 👍
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