[NANOG] Re: Small Capacity UPS

[Javier J via NANOG <nanog () lists nanog org>]

I agree. The cheap solar batteries in my shed have gone down to the point
the BMS turned them off. So I added a second solar panel, then I added 3
more batteries in parallel. I just recently (with the help of my
landscapers awesome shovel) moved the panels to a more optimal location and
buried the DC cable to the shed. Now I never get lower than 70% SOC. I'm at
100% by 1pm on sunny days. It's a test off-grid system to power poe cams,
smart bulbs, watch what wild animals try to eat my chickens etc. But really
it is to see what location is best because I won't be cutting down trees I
don't own, or don't want to.

Going strong since 2013.

Some of these batteries now have bluetooth, I added a bluetooth module on
mine.
BMS protects the cells, keeps them balanced etc, just to add to that.

I couldn't find the video but Will Prowse on youtube has a solar powered
gate opener operating for years, battery exposed to the elements in las
vegas, going strong after years. I don't think I will ever buy a lead acid
based battery again.



On Thu, Apr 10, 2025 at 1:13 AM Mark Tinka via NANOG <nanog () lists nanog org>
wrote:

> On 4/9/25 14:27, Gary Sparkes wrote:
> > Long term storage, of course, is different, but that's a much easier
> solved problem, and design specs are often in the -30c to 25c range for
> optimal capacity retention over long term storage. But operationally,
> 25-50c is perfectly fine. Past ... above 5c, I think, you're looking at a
> 10% capacity fluctuation in that 5c to 50c range.
>
> Yes, most LFP batteries will work even at 60°C, but that does not mean
> you should do it if you want to get the most out of your investment.
>
> The biggest issue is battery aging, and keeping it within recommended
> temperature values will ensure they last longer than if you don't.
>
>
> > While true, heat is the enemy of lithium batteries of any type, deep
> discharging is the second worst enemy (BMS prevents actual cell damaging
> deep discharge, but you really should never go below 30% of rated capacity
> if you can ever help it - this is the most stressful zone), then charging
> too rapidly - too high rate of charge.
>
> The point of the BMS is to prevent you from operating your battery in
> dangerous territory.
>
> 30% is not a reasonable floor to stop discharging a Li-Ion battery. All
> you are doing there is limiting your available capacity. The recommended
> floor to stick to is 20%. However, it is perfectly fine to go as low as
> 10% without any appreciable loss of overall capacity. And in an
> emergency, you can even go to 5% and still maintain good long term
> capacity.
>
> This is where Li-Ion outshines LA by a mile.
>
> Limiting your capacity by not discharging to, at least, 20% SoC, is
> quite pointless based on all the information we have so far, because
> calendar aging is still going to get you either way.
>
> Mark.
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