Lithium batteries and new solar charger

BFL13 wrote:


What would the table for a 100AH that is really 100AH say is zero%? Still 10v?

I am chosing to answer this one seperatly as it is a little trickey.

cheep cells, factory seconds and such yes 0 would be 10V, but most batteries actualy have higher than there rated capacity. this is a tip for people building there own batteries also, you want to get matched cells. this isnt an issue though as when you buy from reputable companies they do exactly that. buying factory seconds or "B" cells can save you a lot of money but capacity wise you will get whats advertised and nothing more usaly. so a 280AH cell might test out around 281 or 281AH. an "A" grade cell might test out at 285 or 290. this isnt the only difference if a termanal is stripped or there is a scratch on the metal shell it becomes a "B" grade and might have the higher testing capacity.

normal batteries are like this also we have two places in town , one will do a capacity test and the higher rated ones get sold for more money, the other place will not accept and returns any battery that tests below a spicit point. but most companys sell the ones that test higher as a "premium" battery.

but I digress, to get back to your original question ya the true 0% capacity point will be 10V. that is why with LiFePo4 set ups I am an advocat of not going below the 15% mark, not because it will hurt the battery as they are rated for 3000 cycles (some up to 5000) at 100% depth of discharge so thats that many times you can tke it down to 10V from 100%. quite a long time. my concern is mor to that 10V isnt enough to properly run stuff in the RV. if you go a bit large bank then set your bottom end at 12.5V your still using what 86% of the capacity and you will get no cut out alarms or anything from inverters or other equipment.

how much of your capacity can you use and stay above 12.5V in any other battery. SiO2 drops below 12.5V bettern 75 and 70% capacity
and Lead acid drops to 12.5V below 90% of capacity. so if you look at usable capacity above 12.5V on 100AH batteries for each type you get 85AH on the LFP, say 33AH on the SiO2, and 10AH out of the regular old Lead acid.

now 12.5 is rather harsh so lets look at 12.0V LiFePo4 will let you use 91AH before it hits 12V, SiO2 aproximatly 65AH, and a normal Lead acid about 50AH.

where this stuff becomes realy important is people that need to run CPAP or other mediacal equipment or use there inverter regulary . a lot fo the previous discussions never realy went into the use of them just the data differences in capacity and charging/discharging temps, I feel that is only part of the discussion as there are ways to elemininate the cold tempature issues with LiFePo4 batteries if your willing to do it and they arent that difficult. to me its the way they actualy preform during use that is the important part. thoes LFP batteries will run a inverter at full blast with no alarms for the full 91% of there capacity, no other battery SiO2 or normal is going to get close to that with out alarming.

Steve