[time-nuts] UPS for my time rack

Mark Spencer mark at alignedsolutions.com
Tue Oct 13 16:28:03 EDT 2015


Sorry for a somewhat Non time nuts posting but this topic seems to have drawn a lot of interest.

I found the Microsoft article fascinating.   Thanks for sharing.  

Re DC power.   I've seen some computing equipment that ran from -48 volts DC but to expand on the comments from PHK about DC power it never really seemed to catch on in the Enterprise space.   The need to deal with actual wiring issues vs simply plugging in an AC power cord was a major obstacle in my view, but there were others as well in my view.

(Years ago I did a quick assessment of building a data centre that would have largely used -48 volt DC power.   We didn't proceed with the project.)

To return to a time nuts focus:
One of the things I like about much of my time nuts gear is that it runs from 24 Volts D.C.  At this point though the only gear I have powered by my backup battery system is gear that already has a backup 24 Volt power connection.   

I've toyed with the idea of constructing a simple change over system to quickly switch from the AC line powered supplies to the backup battery system for the gear that doesn't have backup power inputs.   

(I briefly considered running the gear from the batteries full time but I'm concerned that some equipment really wants to see 24 volts not the 27.5 thru 28 volts or so that is required to charge the batteries.  My BVA oscillator is a particular concern for me in this regard.)





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Sent from my iPhone

> On Oct 13, 2015, at 11:54 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> In message <4FD0F30EBAEF49609DF207E3EE61C15B at pc52>, "Tom Van Baak" writes:
> 
> 
>> I used to rely on one massive UPS (along with natural gas generator)
>> for my entire lab. Eventually I found it more reliable and convenient
>> to have localized power backup. By local I mean backup for a single
>> shelf, or even a single instrument.
> 
> The big gain is avoiding the DC->AC conversions.
> 
> AC->DC conversions are covered under EnergyStar and similar programmes,
> so they're generally 90% efficient or better.
> 
> But DC->AC conversions, for instance in inverters and UPS's are not
> covered, the argument going that they are only run very seldomly,
> and therefore capital cost would be wasted.
> 
> In the professional segment, UPS's which require a forklift,
> efficiencies are good, in some cases very good, because power costs
> money at that scale.
> 
> But anyting you can fit into a rack will typically have horrible
> losses, the smaller the UPS the worse.  I've personally measured
> sub 50% efficiency in one case.
> 
> The argument against running stuff on 12 or 24V DC is the short
> circuit currents, and the absense of an affordable standarized
> connector.
> 
> For the short circuit currents the only cure is fuses and caution,
> and for connectors there seems to be no hope of a standard - ever.
> 
> China forced USB through as the standard for mobile phones, but
> despite several valiant attempts nobody has ever managed to get
> anything above 5V/5W standardized.
> 
> Here's the website of the IEEE WG which came out with a standard
> (IEEE 1823:2015) this May:
> 
>    http://grouper.ieee.org/groups/msc/upamd/
> 
> It will cost you $160 to see the full standard, which is a very
> good and strong reason why adoption will be slow, and nobody
> I've talked to expects it to go anywhere ever.
> 
> At the same time USB has come up with 100W power concept
> which is not compatible, since IEEE uses CANbus and different
> connectors.
> 
> I've not heard any rumours that China man nail this one.
> 
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
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