[time-nuts] UPS for my time rack

Esa Heikkinen tn1ajb at nic.fi
Sat Oct 10 14:32:28 EDT 2015

Chris Waldrup kirjoitti:

> I have decided I'd like to get a UPS to put on the rack containing my
> Thunderbolt, the laptop that runs Lady Heather, and frequency
> counter. Has anyone had bad experience noise wise with the APC brand
> units like are available on Amazon and at Staples? I'd like to get
> one that doesn't generate lots of RFI. Thank you.

Get a line-interactive model which has inverter with classic iron 
transformer. Line-interactive means that the inverter is not 
continuously on when the mains voltage is OK, but the mais voltage is 
routed thru multitap transformer which gives some filtering and enables 
to fix under/overvoltage errors without turning on the inverter. When 
there's blackout and inverter is really started the transformer will act 
as a filter which reduces the HF interference caused by sine wave inverter.

You can recognize this kind of ups from treir weight. For example 2 kVA 
model should weight more than 25 kg without batteries and more than 50 
kg with batteries. You could look for example old APC SmartUPSes or APC 
Matrix UPS, which has separate inverter unit, transformer unit and 
battery units. Old SmartUPS'es may require float voltage modification 
because their charging voltage tends to increase when aging. Without fix 
it will kill the batteries too soon.

Worst case to buy is double conversion on-line model without any kind of 
transformer. These are cheap but the inverter is on all the time and 
it's output is not filtered. I have measured the output of these kind of 
UPSes with spectrum analyzer and they are really horrible interference 
sources. Not recommended if there's any kind of sensitive electronics.



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