This was my first Saturday at home for almost as long as I can remember so I thought I'd get something useful done around the house.
I've installed several inverters recently for various clients and I picked a 3kW one up for myself last week along with 4 x 240Ah deep cycle batteries. Up until recently I've been using a 6KVA genny to allow me to continue working in my home office during the load shedding periods but now we've been getting power outages between 8 and 10pm and the genny is a pain to set up in the dark and it's also a bit noisy and smokey for that time in an evening so I decided something semi-permanent and more subtle was required.
I'm kinda lucky with my office because there's two sockets that were part of the original electrical installation and there's another 8 sockets that are installed surface and in trunking which are spurred off the original circuit. It sounds like a lot of sockets but they're all low load for PC's, monitors, routers, 2 smallish servers, a couple of laptops, several small chargers, an illuminated magnifier and a small domestic PABX phone thingy....oh and a small bar fridge.
I used a clamp meter with a max hold facility on the incoming circuit over a period of a few days and the absolute max current draw was 3.18 Amps and this was short duration ie miliseconds. I also wanted to run my TV and media PC which was another 1.23Amps and finally I decided that I couldn't live without my coffee machine which is supposedly 1.8kW but actually weighed in at 6.4 Amps @ 219v when I measured it.
Total current requirement was 10.81A which meant I required a 3kW inverter.
The coffee machine is obviously a heavyweight compared to the office and TV requirements but it's a very intermittant load, over a period of an hour the pressure switch kicks in and out to supply the element and the actual heating period was only around 14 minutes so the battery drain isn't as bad as I thought it might be. The total power consumption per hour works out to 1.13kW so for a 2 1/2 hour loadshed I need 2.852kWh.
The battery supply is 24V so to supply the max load (10.18A @ 230V) I'd be drawing around 104Amps at 24V so some seriously large battery cabling is needed. Over a 2 1/2 hour running time I would be draining the batteries at 47Ah x 2.5 = 117.7Ah. This is approx a 50% drain which is within the manufacturers spec and projected battery life expectancy is around 500 cycles at these figures.
Okay, enough calculations, back to my day off at home.