[time-nuts] backup power (was BVA has been sold)

[jimlux]

On 9/25/20 11:07 PM, Poul-Henning Kamp wrote:
> --------
> Bill Notfaded writes:
> 
>>
>> Can't I just use a high quality APC backup power system like we use to
>> power racks of gear in our Telco and compute closets?
> 
> Very few UPS's are good at long-run applications, they are typically
> built to run a heavy load for minutes, not a tiny load for hours
> or even days on end.



> 
> That means low efficiency, 75% net efficiency is considered good,
> and it goes totally south the further you are from the name-plate load,
> because the constant overhead is large.
> 
> Some UPSs dont even have a thermal design allowing 24*365 operation.


As people have found when modifying those inexpensive $100 UPSes to use 
an external battery.  They're *cost sensitive* so the electronics just 
gets to maximum temperature as the designed in battery runs out.  It 
might be cheaper to add mass than a (noisy) fan, for instance.




> 
> If you want to power mains kit from batteries, it is usually better
> to get a "real" inverter which is built island-grid applications.


They do make UPSes for long term running but not as a static inverter - 
typically you can identify them because they come with options for 
external batteries. Or,you choose which battery pack to add.



> 
> But for powering small loads, OCXO's, GPSDO's, Rb's, fire alarms,
> emergency lighting etc, the overhead of going from battery voltage
> to mains voltage and back is just a unnecessary loss.
> 


There is, also, the Tesla PowerWall approach..
13.5 kWh, 7kW peak, 5 kW avg, $6500

You can keep a lot of oscillators humming for quite a while with 13.5 
kWh, even at reduced efficiency.