In my post
https://mybroadband.co.za/vb/showth...ery-sizing?p=19223646&viewfull=1#post19223646
I stopped at the point where it becomes necessary to refine the calculations in any attempt to work out what size inverter and what size battery to get tp provide the power back up. There is plenty on the Internet about this subject much of it taking terrible shortcuts and applying formulas without understanding how and when they should be applied. And then we have the sales persons and the online sales sites selling "stuff" they have no idea about or how to sell it correctly.
One of the crucial elements in a standby power setup (forget for the moment the rather spurious argument over a UPS vs an inverter plus separate battery bank). BTW the correct way to talk about batteries is to refer to "Battery Banks" and not "strings". String is used to tie up parcels.
So this post will highlight without going into a deep explanation of anything. You can all go and read the reference I quote for yourself. Be warned though that the maths in the reference gets more and more complicated and will test even the so-called "experts" who think they know what is going on.
Batteries:
This thread has talked a lot about a few things such as:
1. "Discharge the battery to 50% of its capacity": This is not just a value, it is backed up with very sound reasoning as will be seen in the reference I use.
2. Isheed in his post suggested a "battery efficiency factor": Again he did not pluck that out of thin air, it is a pretty good estimation that can be used in a sizing calculation for ALL battery technologies.
3. Battery Banks: Plenty has been said about battery banks and whether it is a good idea to have split banks and batteries in parallel or not. The fact is that without some or other way to monitor the health of the battery banks, it is rather tricky to ensure that all the batteries will discharge at the same rate and recharge at the same rate. An essential fact when building larger systems, but I am suggesting that quite a few systems being sold "on line" to ordinary people that suggest you can do this are doing the consumer in.
4. Estimate the load properly: don't ignore anything and take all the fixed loads into account. One has to know what the ultimate loads are and have to take them ALL into account when estimating the size of the system you need.
5. How deep should one discharge a battery bank?: Well here the urban myths really kick in. What is fact is that batteries last the longest if they are either never discharged or if the discharged by more than 5% , but also never by more than 50% (at least for optimal life and usefulness over the life of the battery. The final value is a compromise between performance and battery life,
and cost.
6. The last issue I have found quite strange is that no one trotted out an application of "Peukert's Formula" yet. Again there is a right way to use this formula and most definitely a wrong way and the Internet is crawling with examples and articles written on the subject applying the formula incorrectly.
So here is a very good reference by no means the only one, BUT one of the references that is thorough and explains all you ever wanted to know about sizing of battery banks whether they are for UPS designs, inverter + battery standby systems or even alternators and a deeper understanding of what goes on a typical car electric power system.
The reference is:
http://www.smartgauge.co.uk/technical1.html
http://www.smartgauge.co.uk/technical2.html#depth
and a pretty good read on Peukert's Formula if you do not want to read the whole thing.
http://www.smartgauge.co.uk/peukert_depth.html
