[time-nuts] Re: Help needed with a UPS for my GPSDO

[Shawn]

I would like to second Poul's suggestion here.

We use battery bank systems at all our communications facilities. With
the excellent efficiencies of both rectifier and DC/DC systems coupled
with excellent reliability for a rather minimal cost, simplicity of
maintenance/repair and easy customization, they are very hard to beat.


-- 
Sincerely,

Shawn Tayler

On Mon, 2023-06-26 at 20:41 +0000, Poul-Henning Kamp via time-nuts
wrote:
> Can I just interject, based on the subject line, that using a UPS
> for a GPSDO is a bad idea ?
> 
> The UPS you have scored are designed to keep a 240W load running
> for a few minutes and it is not very good at keeping a 10W load
> runing for a long time, because most of the energy in the batteries
> end up as heat in the UPS DC/AC converter.
> 
> According to the spec for the "APC backup-ups 400", holdover is
> never going to be over 90 minutes, no matter how light the load.
> 
> Ditch the UPS, float-charge the same battery, and run your
> GPSDO from that, possibly using a small DC/DC converter with a
> wattage well-matched to the GPSDO consumption.
> 
> To take an example:Â  A Trimble Thunderbolt uses 12W from cold, we
> need to design for that, so a 15W DC/DC converter is prudent.
> 
> That will have an efficiency of around 80% at the 8W which the
> Thunderbolt uses steady state.
> 
> That means that the DC/DC converter will draw 8W/.80 = 10W from
> the battery.
> 
> That means that the exact same 12V/7Ah VRLA Lead-Acid battery will
> keep your GPDSO running for at least 6-8 hours.
>