@ NewCatBee
Nice to meet a fellow DIY solution seeker with real hands on experience
I can only base My DIY on smaller projects using mostly 18650 are some few packs for
Electric bikes and
motor bike starting batteries and jump starts for Inboards and outboards when the main battery is down .
These 18650 replaced the earlier
AGM, FLA, NiCads , NiMh and later LiPo solutions .
So far the 18650 have proved to be very tough
However feed back from those who have done larger projects is the risks from DIY packs is reduced in larger packs with planning ahead replacement solutions for when some or any cells go bad
In larger packs reducing capacity from say 400 amp hours down to 395 Ah with swapping out some faulty cells is mostly just the time to do it but can keep the main packs assembled in sub section packs going for another few years
The only major risks come from
charging at below 0 degrees C which can wreck all types of Li-Ion or from overcharging in high heat and causing plating .
(Link below explains this temperature issue for batteries )
http://batteryuniversity.com/index.p...w_temperatures
Its how the packs are built and how the BMS are doing their jobs that are important
The 18650 dont like to do too many cycles without balancing systems solutions and really are not suited to using without really good BMS solutions
Building with the sub assembly packs in smaller sizes often require more BMS than the larger Prismatic cells .
However prices for good BMS solutions are dropping especaily with some open source solutions selling kits that can be soldered together to save even more costs
However when a larger Prismatic cell goes it harder to figure solutions for the rest of the pack .
The cost of the 18650 cells is dropping at a exponentially faster rate than Prismatic cells
A few years back The prismatic cells were probably the best solution in there time easier to connect and certainly well priced for their time but Lithium Ion
price wars are changing the story rapidly .
I know its hard
work putting together packs of several hundred or thousands of cells but payback is less risk to lose the entire pack if there is some local issue like one BMS went wrong and takes out ten cells or some local shorting takes out few cells .
Over many years losing many good smaller packs especaily Lipos and NiMh bigger packs the 18650 solution when you got all the bugs sorted is hard to beat if you sorce the cells at low enough prices
then the 18650 projects turns into combine together as many typically 6 to 10 cell packs grouped in parallel and assembled into the desired voltage and AH and respecting the C discharge rates
That often means keeping below 1C discharge rates where those 18650 cells preform best or for short peak loads of 2C .
really big fairly
cheap domestic battery solutions in the 200 to 400 Ah can be with DIY solutions surprisingly low costs even compared to drop in AGM solutions
I am the first to say for big
propulsion solutions I cant see too many DIY solutions in this time in 18650 cells that for the most adventurous type
I think you will go stir crazy joining together 10,000 to 100,000 plus small typicaly 2 AH 18650 cells
Then trying to find any faulty cells there would be a interesting challenge without some sort of computer system that keeps track of all the cells.
Those computer solutions exist in the top end market drop in 18650 battery solutions like Tesla but are not really available and proven to
work to the Open source market in this time .
This you tube with " Robert Murry-Smith " ultimate DIY battery egg
head is a battery and capacitor inventor using home brew graphene and carbon solutions
Presently this week he is making a carbon battery solution for the
electric car Twizzy all from scratch
It might be worth checking out as cost wise and safety wise it looks to be the real cost effective solution if it works as predicted it will work from smaller trial batches
For those who want more info about the
LiFePO4 solutions this below Youtube is from narrow
boat user who did it
He explains the benefits for him doing the Vectron LiFePO4 drop in solutions
and tonite our Califorian " jehugarcia "battery maker covers many issues about the 18650 cells packs in larger sizes that are in this post