Re: Cascading UPSs

On 08-Jan-25 1:31 am, Don Y wrote:

On 1/7/2025 4:27 AM, Sylvia Else wrote:

On 07-Jan-25 5:22 am, Don Y wrote:

OTOH,  I *could* plug more than one UPS into a single (or few)
"master" UPS that effectively takes on the role of the mains
connection.  Then, I just have to keep that/those UPS running
("properly") to gain the benefits of bridging those brief glitches.
>
Any downsides to this?  If I remove the batteries from the
"slave" UPSs (i.e., don't replace them when they fail), then
I can avoid that maintenance issue but still retain the other
advantages of the UPS-per-workstation.
>
Or, maybe put some trivial "power source" in their place that
is just enough to satisfy the UPSs' expectations of a "battery"?

>
Some UPS designs cannot be turned on[*] without a battery in them, even when supplied with mains power, because they cannot energise the relay that enables the mains connection.

 Hmmm... I've found devices that can't be powered on in the absence of
MAINS voltage (which, IMO, is an annoyingly arbitrary constraint...
suitable for discard).  But, all seem to power on without a battery
(assuming mains voltage is available) though may "complain" about the
fact.
 These have the annoying habit of persistently displaying "Connect Battery"
message -- which can't be dismissed (in favor of the other status messages).
 

[*] They can stay on, just not be turned on.
>
>

 

In fairness to UPS designers, having the UPS able to start without a battery is an edge case they probably wouldn't have felt was important.
I had an old UPS (sadly, now long dead) that behaved this way. The battery side was completely isolated[*] from the mains by a transformer, which allowed hot-swapping of the batteries (a feature described in the manual). But this was the same transformer as was used to generate the output voltage. Consequently, they had to ensure that there was no danger of back feeding the mains, which rather precluded relays whose default position was to connect the mains.
Mind you, they also included an expensive component whose sole purpose was to ensure that the mains wasn't connected during an outage. This was perhaps a level of over-engineering that goes to explain why they no longer exist.
Sylvia.
[*] Which was not the case for the more recent UPS I bought to replace the old one.