Hi i have 2 x sun pays lithium batteries (48v 100AH) linked via buzz bar in parallel. i get 6 hours  on them before the inverter cuts out.

i run a double door fridge, led house lights x 5, 3 fish tank pumps and filters, wifi and tv for a few hours.

Is this a reasonable amount of hours from these batteries. i could not run BMS on both batteries as they are different. one is the newer digital touch screen while other is 4 months older.

Any advice will be appreciated.

5KVA growatt low voltage inverter

12 x 335 watt Canadian solar panels

2 x sun pays li 100AH batteries.

 

Only the power consumption of your implements will indicate the theoretical usage over a time period.
i.e. how many Watts is each one of your mentioned components? Your Inverter itself also uses around 60Watts all by itself.
Else it's a guessing game

Lets start the other way round. Let's assume your batteries are 100% OK. That means you should have around 10kW of stored energy until they cut out.
10kW divided by 6 hours would mean you would be consuming 1,6kWh if the battery is run down to zero. It probably cuts out at around 20% SOC, which means you have around 8kWh usable energy.
8 divide by 6 would be 1,3kWh.
So from that perspective you need to compare your implements stated Wattage and see how that stacks up. 
 

Edited January 31, 20233 yr by zsde

What @zsdesaid. It all depends on how much these various devices, and especially the fish tanks, consume. 

You have about 9.6 kwH of battery. Usually you will get 90% use before the BMS shuts the battery down. So that's 8.6. In 6 hours the inverter itself will consume about 0.4 kWh, so that's 8.2. If the average load per hour is about 1.35 kWh then you're getting your 6 hours worth. 

6 hours doesn't sound great to me - I get from 4pm to 7am at least on 10kWh of battery, but I don't have to run those fish tanks. If the tanks require heating then that could use a fair bit of juice.

Are you using the BMS from one battery to control the inverter? I don't think the inverter can properly charge two batteries over one set of wires. I'm guessing that when the battery that is connected to the inverter says it's had enough that charging for both batteries stops. Is there an SOC indicator on these batteries. Do the SOC indicators on the two batteries change in synchronisation with each other?


 

Thanks for the feedback and apologies for the delayed response.

Yes only  one battery is linked to the inverter for BMS as they are not identical. (as per original post) what would be a safe setting for lithium batteries before it switches back to the municipal. And what should be the set point before it cuts off completely?

 

15 minutes ago, Lazarus said:

Thanks for the feedback and apologies for the delayed response.

Yes only  one battery is linked to the inverter for BMS as they are not identical. (as per original post) what would be a safe setting for lithium batteries before it switches back to the municipal. And what should be the set point before it cuts off completely?

 

Did you get measurements on the loads? 

You have about 10kWh of battery. That's 8 to 9 kWh that you can use. Let's say it's 8. 8 / 6 = 1.33. So if you're drawing an average 1.3kW and your batteries were fully charged when you started discharging them, then 6 hours is acceptable performance. 

As to those two cut offs that you mention. The second should be taken care of by the inverter. The first you should be able to set according to your own needs and judgement. In my case the inverter will not allow the battery to discharge past 90% (that's a hard limit), and I have a setting in place so that it won't discharge past 60% whilst there is grid. Don't ask! I have no method no formula. My installer set it that way when the system was setup, and I've never seen fit to change it. I like having a bit in the bank, so to speak, in case of an unexpected outage. In usual day-to-day running I never get down to the 40% anyway.