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Inverter and batteries



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  • Inverter and batteries

    Ok so it's time to get a backup system for our power outages. Load shedding is ok as we can plan for it. We do have a 100kva generator that we run when we expect long power outages, but the dairy takes priority as it doesn't have the capacity to run the dairy and houses.

    I wanted something that I could run my lights (all led now), tvs, router, etc. I will not be connecting geyser, chest freezers, dish washer, oven, microwave and laundry to it. I have a gas hob so even the kettle will not be connected. I am undecided about the fridge. It's 400w I can do without for now. I am looking for 2 hours of 3kva backup. 3 hours if we are careful.

    So looking around I have decided that an Axpert MKS 3kva/3000w/24v pure sine inverter is my choice. I chose this one because the budget is right, it is 3000w not 2400w, 24v not 48v. I have decided not to go for a system that can have multiple inverters. What I like about this inverter is it has an inbuilt charging system and can get power from any source. My plan later is to add panels to supply the load during the day (maybe then connect laundry) and use Eskom as a source at night. During extended outages I would run the generator for 2 hours and then get another 2 hours from battery.

    I do have 3 phase. So I plan to isolate everything that would run on the inverter onto one phase and everything that will run from Eskom or generator onto another phase (will just cost another earth leakage). That way no one can accidently turn the dishwasher on when there is no Eskom/generator.

    The batteries are where i am getting a bit stuck. I have worked out that if everything is on I'll be just over 2000w but conservative I expect around a 1500w draw when there is no Eskom (a tv, router, android box, pc and a few lights). 2 x 105ah batteries should give me an hour (to 50%) or 4 batteries for 2 hours. Mostly we are not home during the day so charging from solar would not make much difference. I don't want to be short on batteries because it's not ideal to add new batteries to old ones. But batteries are expensive so I don't want to end up with hours of backup I don't need. We can be more mindful of power consumption during power outages.

    The inverter cost around R7k (seen it for less than R6K) and a 5kva I have seen at R8-R9k. So it is so tempting, but then the batteries needed starts going up pretty quickly. R2k for good batteries (3000 cycles). I want to try keep the cost below R15K without panels.

    If you have some serious comments please post them.