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Thread: Saturday at home, installing an inverter

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    Diamond Member AndyD's Avatar
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    Saturday at home, installing an inverter

    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.
    Last edited by AndyD; 15-Feb-15 at 02:54 AM.
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    Diamond Member AndyD's Avatar
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    First job was to clear some space, make a hole in the counter, install some trunking and screw the inverter to the wall with 200mm clear around the sides for airflow. Easy peasy!!

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    The trunking s a bit ratty looking because I only had a second hand piece kicking around at home so I made do with what I had.

    Next was find an old piece of scaffold plank and clean it up a bit with a sander and use it as a base to place the 4 x batteries on top of. This is probably optional but it helps to be able to move the batteries all together by sliding the plank to allow cleaning behind them in future.

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    Next I installed the two 35mm˛ battery wires starting at the inverter end. A 100Amp fuse was used at the final battery terminal and link wires were made to connect the batteries together.


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    If you're ever dealing with battery installations I'd caution that the potential fault currents are enormous. Always fuse a battery installation because if there's ever a fault there's a very high likelyhood it will result in a fire and always take great care when using spanners and other tools that you never contact other terminals by accident because the results will be spectacular. Finally never leave the tops of the batteries exposed because someone will at some time accidentally short them out by placing something metallic on top of them.

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    The main supply cable to my original office sockets was removed and diverted into the inverter as the incoming supply and a new cable was installed from the inverter back to the sockets.

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    The wiring is very straight forward but the terminal blocks in the inverter were very awkward and it took several attempts to get good terminations.
    Last edited by AndyD; 15-Feb-15 at 09:45 PM. Reason: corrected measurement
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    Diamond Member AndyD's Avatar
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    Next I tested the circuit to avoid any nasty surprises and switched the inverter on. It ran immediately in back-up mode supplying the office sockets from the back-up batteries and when I restored power to the office circuit at my DB it immediately went into charging cycle.

    The inverter is seemless in the case of power fail, it takes 5mS to switch from Eskom power to battery power so all computers and other appliances keep running normally. All the inverter settings out of the box were fine except for the low battery cut-off voltage which was a bit on the low side; I'd rather not cycle my batteries as deep as they had it set because their life expectancy takes a knock so with only one small adjustment necessary I was finished for the day by 2pm.

    The inverter can also have a string of solar PV panels connected to it which is nice for future if the power situation deteriorates for example. The charging ability of the inverter is 50Amps so I could also add a second string of 4 batteries or even a third string in future if I wanted to extend the running time. I've got a very nice North facing low pitched roof so six panels would make the system completely off-grid except for maybe a few days in mid-winter.

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    Sure enough we had load shedding this evening and everything was as per plan. I ran a temporary extension lead for my TV and we watched a movie and had coffee, wi-fi and internet access for the full 2 hours.

    Tomorrow I've just got to install the permanent cable for the TV and coffee machine back-up supply.

    I'm also using the batteries to run some 12VDC back-up lighting. In every room I've installed a small 10watt floodlight with a retrofitted pullswitch. They're supplied by 2 x 12VDC circuits directly from the batteries and they're more than bright enough for functional lighting.

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    I've also got to install a short supply from my newly fitted batteries to power these two lighting circuits.

    If you've installed any back-up power systems of your own, please don't be shy, feel free to post about them below hopefully with some accompanying photos. It's always interesting to see different approaches to the same problem.
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    Wow Andy, Nice work.. and all in one day :-)
    So what does all of this cost (inverter, battery, cabling) ? What brands are you using ?
    I would like to do something like this, but then the issue of COC comes to mind

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    Diamond Member AndyD's Avatar
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    Thanks Julies, it was more like 5 hours solid installation time and would have been less if I wasn't working on my own and with secondhand bits and pieces. We do install this kinda thing for a living so I'd allow a full day if you're not familiar with this type of kit.

    I spent another couple of hours today to properly install the cable to the TV at the other end of the house and to run the 12VDC supply to hook into the existing lighting circuits so I'm finished for now and no longer need to live like a troglodyte for two hours a day, at least three days a week.

    The cost is a tricky one for several reasons, firstly I had most of the installation materials already to hand from stock. Secondly I pay dealer prices for inverters and batteries so I'm not going to workout my cost because it won't be a fair reflection of what you could expect to pay.

    If you were to order such a system as a customer I'd expect the inverter would be around R10K. Obviously this inverter is a pure sine output plus it's a 50Amp intelligent PWM battery charger and it's a solar PV controller with monitoring software all in one so it's considerably more expensive than a cheap inferior camping type inverter.

    The batteries are also not cheap, for a single 230Ah battery of recognised brand you're going to pay in excess of R2200.00 so for a similar 3kW setup to run a smallish office for 2-3 hours as outlined above you're in for >R20K I'm afraid and that's before there's any installation labour and sundries which would also vary depending on how much cabling etc is required for your particular installation.

    I suppose compared to a decent Honda 3KVA self start, silent generator with a nice built-in AVR the price is in the same ballpark. Both the generator and inverter options have their own advantages but for a small office environment I'd chose the inverter any day. Generators aren't seemless unless you add a UPS into the equation and inverters don't carry the ongoing maintenance and fuel costs that a generator does. The inverter is also scaleable so it will adapt better to changes in requirements in the future. On the flip side an inverter setup isn't portable, the batteries do require some very light maintenance every few months (which you can do yourself) and the batteries will need replacing in 5-7 years if load shedding continues at the present rate.

    As for compliance, the system I've installed will be compliant once I've finished tidying it up with a battery cover, some labelling etc and I can issue a Coc for it if I need one. There's no reason an inverter or a generator can't be installed to be compliant to the electrical installation regs if a competant installer is used.
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    nice Andy.i wish i had your energy.
    i would also like to know which brand you use and what supplier?
    i have been looking at ACDC but i know they are not shy to sell cr@p.
    i want to start installing for customers.
    what is the advantage of an inverter over a UPS with external batteries. i'm guessing the easier connection to solar.
    what battery charger are you using?

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    ok ,after reading your post again,i see the inverter has a built in battery charger.
    it looks as if the batteries are connected in series.are they 6v batteries as you say you have 24 volts in total?

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by bergie View Post
    nice Andy.i wish i had your energy.
    Lol, my get up and go....got up and went many years ago

    Quote Originally Posted by bergie View Post
    i would also like to know which brand you use and what supplier?
    i have been looking at ACDC but i know they are not shy to sell cr@p.
    i want to start installing for customers.
    ACDC do have some lines that are not my favourites but they also have some lines that are very respectable, guess it's a matter of knowing which is which. They have started selling the Victron range recently which are absolutely superb pieces of equipment. We were installing Victron stuff about 6 or 7 years ago and I've loved it ever since. The only downside is the cost, for a 3kW Victron Multiplus you're going to part with about 18-20K just for the inverter but like I say you do get what you pay for in this case.
    Send me a PM with the type of system you're thinking about and I'll give you suppliers details.

    Quote Originally Posted by bergie View Post
    what is the advantage of an inverter over a UPS with external batteries. i'm guessing the easier connection to solar.
    what battery charger are you using?
    Battery charger is built into the inverter. Scaleability and the ability to handle multiple power sources is one advantage. The inverters can be supplied by a combination of wind turbine, generator, solar PV and Eskom power for example and different power sources can be set in order for priority of use. You'll struggle to find a UPS with a 50A PWM intelligent battery charger built into it. With some inverters you can link them together to provide a single larger output or even link 3 x single phase inverters to provide a 3-phase output so they're a lot more flexible than a UPS.

    Quote Originally Posted by bergie View Post
    ok ,after reading your post again,i see the inverter has a built in battery charger.
    it looks as if the batteries are connected in series.are they 6v batteries as you say you have 24 volts in total?
    Yes, built-in charger and the batteries I used are 4 x 6v deep cycle in series to give 24VDC. At present I'm tapping off the middle of the battery bank and both ends to give me 2 x 12VDC supplies for the lighting circuits but this isn't ideal because they're unlikely to be perfectly balanced loads so I'm going to fit a 24-12 DC converter across the entire bank sometime next week so the lighting load is pulled evenly from all the batteries.
    Last edited by AndyD; 15-Feb-15 at 07:12 PM.
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    thanks andy. i will pm you.
    so once you have your solar panels all you will need is the grid tie inverter. i cant see it being long before we can feed back into eskom.

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    Andy I need one in Cape Town. Please give me a price installed ?
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