[time-nuts] UPS for my time rack

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Sat Oct 10 18:07:28 EDT 2015

On 10 October 2015 at 14:20, Chris Waldrup <kd4pbj at gmail.com> wrote:

> Hi,
> 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.

There's one issue with them that I don't see anyone mention.

I was thinking of doing the same a while back, and intended getting a UPS
and adding a large external battery pack, so if the mains failed late at
night, I could run the GPS receiver and a few other things overnight, and
consider starting the generator in the morning.  I contacted a dealer on
eBay, who specilaises in UPSs. He told me that the smaller units with built
in batteries will die if you put large external batteries on them.
Essentially the charging circuits are not designed to run as long as needed
to charge big batteries. Even on ones designed for external batteries,
there's a recommended limit on the size of them. So if you think you might
want to increase runtime by adding some batteries, buy one designed for
that service.

I've had two here which were HP/Compaq 5 kW units. These were different to
the normal, in that the batteries added up to over 300 V, so could produce
240 VAC with no need to step it up. Both these blew up on me, for reasons I
never worked out. The load was never anywhere near 5 kW.

Lots of people mention sine wave. Of course, if you keen enough, you could
make a class A amplifier and sine wave oscillator. The problem is that the
pure sine wave inverters tend to be very inefficient.

As with most things, there are a lot of things to balance - runtime, cost,
quality of output, audio noise, RFI  etc etc.


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