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[aprssig] UPS

Tapio Sokura oh2kku at iki.fi
Wed Dec 27 01:36:38 UTC 2006

Michael Hatzakis, Jr MD wrote:
> I'll try to be helpful here... First, most UPS's do not run on 12v, they run
> on 48v for the older and larger units and the newer one's use a lower
> voltage, but still much higher than 12v required for TNC's and radios, so
> you simply cannot use a UPS to keep batteries charged to run a TNC/Radio if
> this is what you were thinking...

It depends. Many, I'd even say most of, today's small and affordable 
UPSes (well under 1 kVA) use a single 12 volt sealed lead battery. 
Higher VA versions use several batteries connected in series, for 
example I have one under my desk that eats five (60 volts) and another 
at work that has eight (96 volts). The bigger you go in kVA, the higher 
the voltage, generally.

I agree that directly plugging into a UPS's battery for 12 volts for 
radios, TNCs, and such isn't necessarily a good idea. Use the UPS for 
those devices that need "house current" and use a power supply with a 
battery for 12V. Some just use a big sealed lead battery and a smart 
battery charger permanently connected together. If you want to spend 
some money, the pwrgate works fine as well.

If you absolutely have no use for uninterruptible AC, then by all means 
use it to power the DC equipment. But keep in mind that many small 
off-line UPSes aren't designed to continuously run on/charge batteries. 
So if you continuously "steal" 12 volts from the battery, you might fry 
something up, especially on a higher load. On-line UPSes always convert 
all power going through them to DC, so they should handle continuous DC 
loads better.


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