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Lithium batteries, the care and feeding of

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starfire:
For anyone interested......
Last year my lead acid batteries died, so decided to spend big on Lithium, or LiFePo to be exact, this flavour of chemistry seems the safest and most forgiving of them all. $4500 later, they arrived.
First problem was the placement. Like me, these things dont like low temperatures, we are talking minus something, so I placed them inside the hovel to keep them warm. The generator shed being 30 feet away gave voltage drop issues with the 100 or so amps charging current. This caused havoc with the alternators seeing over 18 volts at their output terminals.
I cured this by running independent sense wires, directly from the battery terminals back to the power shed, allowing the over voltage regulator to work correctly, it now reads the  actual battery voltage and not the alternator output.
The maximum  terminal  charge voltage of the batteries is 14.7 volts, anything higher will damage the chemistry.
Here I simply designed a high voltage cutoff using a LM311 voltage comparator that switches off the alternator field current when the battery voltage reaches 14 volts... plenty, as the Lister is only used as the  backup when the solar fails..
The main charging voltage comes from 800 watts of solar panels. The MPPT controller will switch of at 14.6 volts, this means the bank is full.
Here is the schematic  of the car alternator control when I remember how to do this picture posting thing.....
These old car alternators are modified by removing the internal regulator and connecting one brush to ground, the other to a wire into the controller.
I then wondered about these Battery Management Systems built into these Lithium packs.
After reverse engineering one sample, I could not see how they can "balance" each cell with just a 100 milliamp draw, when each  cell has a capacity of 600 amp hours..... it would have zero effect.
Firstly, I decided to establish if these Lithium cells actually do get out of whack with each other, they cannot be equalised as a lead acid bank can, this would overcook the highest cell. Is this an actual problem, or just an internet theory, steeped in myth and confusion.
I removed the BMS.
After nearly a year, the cells are within 3/10ths of a volt, highest to lowest, so unless I am extremely lucky, very unlikely, the balancing thing appears not to be the issue its made out to be. So, to simplify matters, we leave out the BMS.
It it also important not to  discharge these LiFePos to less than aound 10.7 volts. This apparently causes permanent damage.
This requirement is easily met , almost all inverters will automatically disconnect at around 11 volts.
The difference with Lithium to lead acid is night and day, with a charge absorption efficiency approaching 95 percent, no sulphation or gassing..... no watering, no stress, just set and forget.

mikenash:
Mr Starfire.  You're back.  Excellent.  I was just talking about you . . .

I'm interested to hear how the lifepo's will go long-term.  I just killed my (cheap, 2nd-hand) AGM by neglect and absenteeism and am mulling over replacements

Cheers

starfire:
Yes Mike,, and many thanks for the kind words......
I can honestly recommend these LiFePo batteries. I used to worry and stress over the lead acids..... how much charge I had to leave in for longevity reasons,  periodic equalising, are they sulphating, much like a woman, you are never sure you are doing the right thing, and the costs of not doing so can be crippling.
Lithium are bloody expensive, but the full capacity can be used, they cannot be damaged by long periods of partial charge, in fact, they will exceed the rated 2000 full cycles if "mistreatred" like this.

mikenash:
 Cool.  Thanks

The Bay of Plenty property where I spend a bit of time has lots of sunshine but I'm only there for the odd weekend or long weekend. To save using a noisy generator just for a few watts (lights, electric blanket - to keep that woman happy lol, small fridge - etc) I spent $300 on a panel (200W I thinK?  I forget, AGM 100 A/H battery and a cheapie PWM controller & inverter.

Due to some bad planning I let it get down to about 50% and I think it's on the way out - so I need to think about replacement

The thing that bothers me with the lifepo's is the cold.  I THINK it's OK for them to get cold, but not to be charged when it's cold

Will have to do some more homework

Well done on the battery upgrade  :)

starfire:
Yes Mike, its the charging issue when cold is the bugaboo. Unless this is another internet myth? Anyway, cause the sun always shines on frosty mornings,making the panels active,  its probably a good plan to prevent, rather than cure. Ive been lucky with lead acids, the scrap price had risen dramatically over their useful lifetime, so the scrap value almost equalled the initial purchase price, but no more unfortunately. Solar panels are about the cheapest they will be now I reckon, 1$ per watt for a quite decent panel.
Until you retire, I would wait.... Lithium is bound to get more affordable with time.

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