Peter_n_Margaret wrote:

---

No, I will need to manually look after the alternator. Now it can operate full auto.
We can bake bread at any time now, including at night to have it fresh for breakfast, so no change there.
In fact, if the sun does not shine, 400Ah of AGMs will run a compressor fridge drawing 3.5A for longer than 400Ah of lithiums because 400Ah of AGMs can run down to 10.5V and will provide in excess of 400Ah (at that low current draw). The lithiums are typically capped at 90% and you can not flatten them without risk of serious damage, so they will only provide something like 300Ah in real life.

Horses for courses Terry.
Each battery system has its own strengths and weakness and which is right for each individual will depend on their priorities at the time.
Right now, spending an extra $4,000 to change to lithiums is not justified, for me.
Maybe next time, if I live long enough?

Cheers,
Peter

---

 No idea who fed you that nonsense but it is nonsense none the less. The 400Ah is measured at a 200 amp load, not a 3.5 amp load, you will get a lot more than 400 Ah out of 400Ah of lithium before it drops below 12v or 3v per cell. As far as the 90% cap, more nonsense, the safe discharge limit is measured at cell voltage level not state of charge, do I need to provide a cell logger graph to show the number of hrs a 400 Ah lithium battery can supply 3.5 amps before a cell drops below 3v to prove it to you? I'm happy to do that if you post the graph for 400Ah of AGM batteries before an battery in the bank drops below 12v. You can't show actual cell voltage unfortunately because that is simply not available so the risk of a cell dropping below the lead acid safe threshold is all your responsibility but you are the one who put up the comparison after all.

What price for your 400Ah of AGM you intend to use for this test?

T1 Terry

Peter_n_Margaret wrote:

---

So are you are saying that Peukart applies to Lithium?
So how long will 400Ah of Lithium run a fridge drawing 3.5A?
And it is rubbish to suggest that an AGM can not or should not be discharged below 12V.
Cheers,
Peter

---

Peukert's law applies to all batteries developed at the moment, it is just the percentage it effects the advertised capacity that needs to be taken into account. The graph I posted previously shows both chemistry batteries and using a bit of reverse maths to clear up what is hidden in the Full River graph you can see how much of the advertised capacity at a given load will effect how long the battery can supply that load.

As an example, the Full River chart for a 105Ah battery at a 105 amp load shows a 1CA load graph line and following Full Rivers dotted graph line that shows completely discharged it intersects the time line at around 30 mins. 105Ah divided 60 mins = 1.75 amp mins x 30 mins = 52Ah capacity at that load, the Peukert effect displayed in chart fashion , albeit rather disguised in the manner it is presented.  

Now let's look at the Winston graph. It doesn't try to hide the Peukert effect but rather clearly shows the effect a high current discharge effects the advertised usable capacity is a percentage graph along the bottom line. 

Unfortunately the chart does not show any load less than 0.5CA or 50 amps per 100Ah of battery capacity so there can not be a direct comparison of a 0.05CA or C20 discharge rate as shown in the Full River chart in the line marked 5.3 amp load.

So, neither chemistry battery can give a tested result of the total capacity available under a 3.5 amp load for a 100Ah battery and most certainly not a 3.5 amp load for a 400Ah battery, so that would need to be actually tested and the test repeated a min of 3 times to get an average result ... are you up for it Peter, I can provide the workshop and test equipment if you want to supply the new 400Ah of AGM batteries and the end of test battery voltage, after all, you probably don't want to wreck a brand new set of AGM batteries do you ... but it would answer your second part of the question when the average over the 3 tests were shown and it there was any difference between the first test and the last test as this would show battery damage wouldn't it.

T1 Terry

Hi Terry 

Again why do I step in ?? Just a masochist I guess  But another technical rant that seem to present not much useful information ? but issues a challenge to Peter to test his new batteries to ultimate discharge to prove your point at his expense ?? Hmmmm seriously ?

However my point is the two graphs are not directly comparable, for those who may be interested in the comparison. Peter talked about discharging his batteries at 3.5A The Fullriver graph has a line for 5.3A so that will do for some comparison perhaps. 

The Winston graph has a normal linear scale along the bottom so double the distance is double the capacity. As expected ! But the Full River graph is a log scale along the bottom. A common maths trick to compact the information into a shorter graph. So that means that double the distance represents four times the time. So going from full at 105A to discharged at ~30 min (0.5Hr) compared to 5.3A to discharged at ~20 hrs are ratios of current 20/1 and the time is a ratio of 40/1.  At a lesser rate of 3.5A it would be about double the time again ~40Hr. I guess that is what Peter was saying about his LA batteries running his fridge !!

You might sensibly choose to end the discharge at the end of the flat line part of the voltage graph which gives the same ratios and roughly halves the times. 

Just saying  "Lies, damm lies and statistics" is another old saying.

Jaahn

PS what might be of interest from that Full River graph is the reason why a volt meter reading is not useful for determining the state of charge or anything else of much use while the battery is charging or discharging. However with some experience you can "get the feel of what is happening" under the usual charge/discharge cycle.