[NANOG] Re: Small Capacity UPS

[Mark Tinka via NANOG <nanog () lists nanog org>]

On 4/14/25 08:45, Vasilenko Eduard wrote:

> Hi Mark,
>
> You are talking a lot about how damaging temperature is to the 
> battery. I do not remember you or Gary saying that 50 degrees Celsius 
> is already not good.
>
> But how could it happen in the home environment?!?
>
> People like 22+-2 – they would start to do something urgently if 
> the temperature reached 28.
>
> Home has no source for 100kWt to charge really fast, hence, the 
> current is relatively small.

In most homes with a battery backup, it is typically installed in the 
garage, shed or basement if one exists.

Climate control in these places is not often a priority, e.g., parking 
your car in your garage after being out on the road comes both with heat 
off the body of the car, as well as heat being dissipated by the engine, 
brakes, discs, exhaust pipes, e.t.c. That can easily send a closed 
garage's temperature up several degrees if the garage is not running any 
form of active cooling.

Some installations in a shed will have, at least, an extractor to suck 
warm air out of the structure. But while that may lower the temperature, 
it's often not enough to keep it at 25°C, which is the most optimal for  
Li-Ion batteries.

You don't need to charge a Li-Ion battery fast for the temperature to 
rise appreciably. Just charging an LFP battery at 0.25C (so 25A) can 
raise cell temperature by 1 - 3 degrees for every 10% of SoC gained 
assuming room ambient room temperature.

For my installation, my battery is in my garage. In addition to fans and 
an extractor, I also have active cooling with an air conditioner. Going 
into our winter now, the a/c will no longer be needed since ambient 
temperatures will peak at about 10°C - 15°C, keeping the battery cells 
between 18°C - 25°C even during a 0.25C charge rate.

But during our summer, without active cooling, the cells will live 
between 32°C - 35°C, which is too high.

Mark.
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