Inverter and batteries

Anyone know where I can get this at a reasonable cost:

NPW45-12 its a 12V 45W 8.5A/H lead acid in an RCT UPS (x2 batteries)

I was gonna just replace the batteries and use the UPS again but all i'm finding for that battery is R845 each RS-Online. At R1690 i'm pretty sure its just easier to buy a new UPS..?
 
Dairyfarmer said:
So doing a bit of reading up I've come to the following conclusion:

3kva/3kw inverter (R6200 delivered)
4 x 102ah batteries = 408ah connected parallel/series 2 x 2 (R6800 delivered)
Average load of 1500w (peak max of 2000w, generally around 1000w)
1500w = 75Amps DC @24v
3 hours = 225ah @ 100% DoD, therefor 450ah at 50% DoD
or 100 mins @ 400ah

In 6 month's time I hope to have added another 2 x 102ah batteries to increase it to 150 mins. Further to that I hope to have added 2 x 250w pv panels. During the day, when Eskom is down, I can then add 2 hours? to the system.

The aim to to not have to run the generator at all during the day. In the evenings the generator would run around 90 minutes, so I would get more than 3 to 4 hours of available power.

On the battery front, I can get Exide 102ah batteries @ R1700 from a reputable battery place that supplies our local tractor dealership. so no shipping costs. And easy warranty returns. I hope that I can maybe shave R200 off each battery price.

I have a spare fuse box and a few circuit breakers laying around. Will need a new earth leakage though (R600) and a dc circuit breaker (R200).
Click to expand...
Do the inverters also charge the batteries?
 
2 x 12V batteries in parallel deliver 12V and have a total A-H capacity of X x AH rating of the batteries, whe X = the number of batteries in Parallel. ie, 102 x 2 = 204AH
2 x 12V batteries in series give you 24V but the AH rating is then still 102AH.
Two series-parallel combinations then will give you 24V at 204 AH.

4 x 102 AH in parallel give you 12V at a total of 408AH.
 
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Dairyfarmer said:
So doing a bit of reading up I've come to the following conclusion:

3kva/3kw inverter (R6200 delivered)
4 x 102ah batteries = 408ah connected parallel/series 2 x 2 (R6800 delivered)
Average load of 1500w (peak max of 2000w, generally around 1000w)
1500w = 75Amps DC @24v
3 hours = 225ah @ 100% DoD, therefor 450ah at 50% DoD
or 100 mins @ 400ah

In 6 month's time I hope to have added another 2 x 102ah batteries to increase it to 150 mins. Further to that I hope to have added 2 x 250w pv panels. During the day, when Eskom is down, I can then add 2 hours? to the system.

The aim to to not have to run the generator at all during the day. In the evenings the generator would run around 90 minutes, so I would get more than 3 to 4 hours of available power.

On the battery front, I can get Exide 102ah batteries @ R1700 from a reputable battery place that supplies our local tractor dealership. so no shipping costs. And easy warranty returns. I hope that I can maybe shave R200 off each battery price.

I have a spare fuse box and a few circuit breakers laying around. Will need a new earth leakage though (R600) and a dc circuit breaker (R200).
Click to expand...

I am at the battery stage my self and been checking prices (bang for bucks ) and the prices vary seriously for the same batteries , i am not in a rush because i am still gathering all the bits and pieces and soon going to make the mounts for the solar panels i bought .
I bit the bullet and bought the Axpert 5KVA nearly 10 grand .
 
phil77 said:
Do the inverters also charge the batteries?
Click to expand...
Some do. The 3Kva/3kw Axper has a built charger. Basically you plug in your pv panels and Eskom/generator and batteries. You can then set it to prioritise. So if you have pv panels it can use those first with Eskom/generator when the solar drops. Nice if you install Eskom prepaid or just want to save some Eskom usage during sunny periods. Also if the drain is too much it can bypass the inverter and go straight to Eskom/generator.
 
Ok the inverter has arrived. I have a new DB box that I will use for those things isolated from the inverter. I'll be getting batteries next week.

I also bought a "Kill-A-Watt" device so I can get an idea of what devices are actually using over a period of time as well as their peaks. You will be amazed at what some can things draw and what they can peak at. For example my double door fridge/freezer draws a constant 190w. When I open the door it drops to 5w (the globe died a long time ago and haven't replaced it). I then disconnected the fridge from the mains. Let it sit for 10 minutes and then plugged in in. It spiked at nearly 900w for a few seconds then dropped to about 220w. After a few minutes it was back at 190w. Opening and closing the door a few times didn't push it over 200w.

The batteries were another story. I have finally settled on Exide Excis 100 (12v/102ah) at R1700ea. A company in PMB sends a truck up my way every week. So no delivery charges. Also the company is close enough that I easily do returns. I get 2 batteries next week and will order another 2 after pay day. That will give me 24v/200ah or 90min @ 1500w with a 50% DoD. I expect, at least, 500 cycles from the batteries. Over the next few months I will have a total of 6 or even 8 batteries. 8 batteries = 24v/400ah or 190min @ 50% DoD. More than enough to deal with load shedding. backup is mainly for evenings.

I will just have to be careful when adding more batteries to check they are all charged to the same capacity before connecting to the inverter. I will charge the first set using the inverter, then disconnect that bank and charge the second set. Only when both are fully charged will I combine them.

I will be adding solar panels later this year to try keep the batteries topped up
 
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Nice. Please document everyhting. I love reading htis stuff.
 
I'll photograph the install once done. First set of batteries arrive this week. So I'll be building a table for them and doing a temp install on my veranda.

This weekend I spent in a hot roof space sorting out electrical cables. I how have everything sorted out on the DB. Stuff that will remain connected directly to Eskom (Laundry, geyser, kitchen plugs) are all on their respective breakers. Everything that is going on the inverter are on their respective breakers. Once the inverter is in, it is just a matter of sending isolating the inverter breakers onto their own main switch and earth leakage.

The watt meter is a must. Dishwasher came in at just under 2200w on it's highest setting. The washing machine was close to 2800w at it's max. I would expect higher readings in winter when the cold water is a lot cooler and more energy is needed to heat the water. But they are definitely not on the system. I haven't even bothered with the tumble dryer, but it is so seldom used.

Everything that is going on the inverter has been calculated and is less that I expected which is great. I still have 2 or 3 lights to change from tube to led. But they are all less than 50w as they are. So no hurry.
 
Bear in mind the Axpert inverter isn't a grid tie inverter.
It cannot dynamically draw power from the grid (and feed back into the grid)
 
@PUP Backup
PUP Backup said:
Bear in mind the Axpert inverter isn't a grid tie inverter.
It cannot dynamically draw power from the grid (and feed back into the grid)
Click to expand...
Not trying to feed back into the grid. And it can draw from any connected source dynamically as per the setup of the inverter.

The inverter is a hybrid. meaning that it can take power from multiple sources (utility, generator, pv, wind) to charge the batteries and supply power. The user can set the inverted to prioritise the source.
 
I bought 8 100ah batteries and they only lasted about two years. There were two or more bad ones in the bank and it ruined the whole bank. That's R24k that could have gone into lithium, which I went for in the end.

I think if you go the lead acid route you should invest in some sort of battery balancing and monitoring solution so that you can spot if one starts going and act. But honestly I think lithium like the blue nova or freedomwon ones will costs less in the long run.

Also I don't think it's best practice to add more batteries after your bank has been used, it will age the new batteries. And remember from that 204ah you will only realistically get about 80ah@50% dod when you factor in efficiencies.
 
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oober said:
Also I don't think it's best practice to add more batteries after your bank has been used, it will age the new batteries. And remember from that 204ah you will only realistically get about 80ah@50% dod when you factor in efficiencies.
Click to expand...

I have got 4 x 102ah batteries to start with. Any ones added will be within a week or 2 of commissioning the system. Once I have data regarding usage, peak, average etc. My whole plan is based on a 50% "draw" (i.e. 1500w) as my constant and a 50% DoD over a 3 hour period (initially 120 till I can get some data)

PUP Backup said:
I have been following the 4x4 Community posts on this subject and the Axpert inverter is often the subject of a post.
See: https://www.4x4community.co.za/forum/showthread.php/309748-Axpert-Mecer-3000VA-use-as-grid-tied
I have seen how projects disappoint as buyers, having bought a system, find out that it is limited in some unexpected way.
The 4x4 Community forum I have found the most informed on RE.
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I have based my setup on total off grid systems that have been running for 2 years or more. So I have used actual data. I have explained that it is not being used as a grid tied system. I am going to use the inverter as it is designed to be used. It is designed to be a hybrid inverter meaning that it accepts multiple inputs of power, can prioritise charging of batteries for any of the sources and deliver regulated power. People have varying ideas on what grid-tied means. That is where confusing comes in.

In order of importance:
To get a constant voltage as rural power fluctuates badly.
UPS for times when we have short power outages between 20 seconds and 5 minutes which happen, at least twice a day as Eskom balances city power by rerouting rural power.
UPS for extended outages of 1 hour or more, due to loadshedding, storms, cable theft (whole district goes out until they can isolate the affected branch). Part of the time a generator will be used until critical farm applications have completed their cycle (between 1 hour and 3 hours, but no more within a 12 hour period).
In the future the addition of pv for daytime charging of batteries (when draw is minimal and around 500w) to reduce usage of Eskom.

The system is not designed to be utility independent. it will not be used for intensive power consumption (laundry, microwave, oven, geyser) of over 1000w peak per device and 300w average per device. I have spent the last two weeks logging appliance usage using a watt meter to get peak and average consumption.

I have spent a lot of time reading where people find problems and how they have solved them. I have spent time with people that have been running off grid for 2 years+, so they have had time to troubleshoot, adapt and let everything settle. I could also have spent R70k and had a 10kw total off grid system, but i have worked around what I need and what I can afford. So I will have tv, internet, lights, fans and fridge in my whole house for 2 hours minimum.
 
Dairyfarmer said:
In 6 month's time I hope to have added another 2 x 102ah batteries to increase it to 150 mins. Further to that I hope to have added 2 x 250w pv panels. During the day, when Eskom is down, I can then add 2 hours? to the system.
Click to expand...

Dairyfarmer said:
I have got 4 x 102ah batteries to start with. Any ones added will be within a week or 2 of commissioning the system.
Click to expand...

Cool just going on what you mentioned earlier. 6 Months vs 2 Weeks is a big difference.

With your initial setup you should be able to draw 1500 Watts for about an hour and a couple of minutes to reach 50% DoD you won't get near 3 hours@1500W draw without killing your batteries.
 
oober said:
Cool just going on what you mentioned earlier. 6 Months vs 2 Weeks is a big difference.

With your initial setup you should be able to draw 1500 Watts for about an hour and a couple of minutes to reach 50% DoD you won't get near 3 hours@1500W draw without killing your batteries.
Click to expand...
sigh!
 
Just about there. Mounted the inverter and built the table for the batteries. This week I will run a 4mm 4 core cable from my DB to the inverter. Two wires for Eskom in and two wires for inverter to load. I did consider using the armouring as earth, but I did find some earth cable. This cable comes from a pump section of cable we changed for aluminium at one of the pump houses. They kept stealing the copper between the transformer and the pump. Cheaper than buying panel flex.

A friend is going to help me with soldering and crimping the battery cables this week. I have to make sure that all the cables are exactly the same length. This will be my battery setup:
alt118.png
Can I just bridge the positive terminals P1 and P2 then run Y from P1? Or must the length between P1/Y and P2/Y be equal? The same obviously for N1, N2 and Z. I did consider inserting P1 and P2 (25mm2) cables into a single 8x50mm2 ring terminal and then onto the fuse. Else I will run equal distance cables from P1 to fuse and P2 to fuse terminating each cable in an 8x25mm2 ring terminal (duplicated for N1 and N2).

Fuse is 100a in this style. That way I don't need a bus bar, yet. Further battery additions will probably see me getting one):
Mega_Fuse_holder_CIP000100001_1800x1800.jpg
 
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