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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Redundant power supplies
Date: Mon, 28 Oct 2024 22:42:34 -0000 (UTC)
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Lasse Langwadt <llc@fonz.dk> wrote:
> On 10/27/24 07:54, Don Y wrote:
>> Most of my boxes have dual power supplies.ÿ Most
>> don't give me an option as to how they are used/configured;
>> one shits the bed, the other is there to cover the load.
>> 
>> I have always *assumed* they were configured to SHARE the load.
>> 
>> I picked up another box that gives me the option of NOT operating
>> them redundantly (what the hell does the "extra" one do, just
>> sit around??).ÿ And, when in the redundant configuration,
>> allows me to choose which is the "primary".
>> 
>> This suggests one is carrying the load and the other is switched
>> in (even if passively) when that one fails.
>> 
>> Is there any advantage to this over a "sharing" configuration?
> 
> I would guess if you wanted to power one of them from a "preferred" 
> powersource and the other from a another source that you don't want
> to load unless you have to
> 
> 
>> 
>> And, why would I ever want to *disable* PFC?
>> 
> 
> when you have an UPS that doesn't have sinewave output, they don't 
> always play nicely with PFC
> 

The two best things about equal sharing are that the supplies run cooler
and that you always know that the backup supply is working. 

Otherwise you risk cascading failures a la Three Mile Island. 

Cheers 

Phil Hobbs 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics