Re: [time-nuts] UPS for my time rack

[Bob Camp]

Hi

One option for the “fuse” part of the DC supply system are PTC resettable 
fuses. You *do* indeed need to be careful about voltage and current ratings 
on these gizmos. If the only objective is to “not have smoke” when there is a 
short, 
that can reduce the variables to a manageable level. If your wire will handle 
20A for 
long enough to get the gizmo to limit and your load is typically < 5A there are 
parts you can find. 

A few cautions: 

The trip points are very temperature dependent. If you need to handle -20C in 
the winter 
and +40C in the summer, that will narrow things down quite a bit. 

Mounting matters quite a bit. If you go with SMD parts, be careful of traces 
that act as
heatsinks. This is one case that the part needs to get hot. 

There are to many variables on most of the spec sheets to simply pick one and 
move on. 
The only good way to do it is to get several and run repeated tests on them Min 
carry current
will occur at your highest temperature. Worst case trip will occur at your 
lowest temperature. 

Consider that the “carry current” may not be the real limitation. Resistance in 
the supply lead 
of an OCXO is a bad idea. This may limit your current well below the point that 
the fuse actually 
trips. 

This sounds like a pretty scary list. To some degree it is. These parts do have 
their place. That
does not mean they work everywhere and anywhere. 

Bob

> On Oct 13, 2015, at 2:54 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message <4FD0F30EBAEF49609DF207E3EE61C15B@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.

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Re: [time-nuts] UPS for my time rack

[Poul-Henning Kamp]

In message <1444701906.379459.408467601.5676d...@webmail.messagingengine.com>, 
Bill Byrom writes:

>Anything can (and will) fail, [...]

The interesting thing is that several sources in that business have
reported to me that about 30-40% of all power related downtime is
caused by Battery, generator and UPS failure, in that order.

Many sites simply have lower uptime after they install UPS systems.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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Re: [time-nuts] Trimble Thunderbolt and David Partridge divider boardquestion

[Bryan _]

 I believe the author was looking into modifying his circuit to use a LTC6957 
as a frontend. Not sure if he ever got around to it.
https://www.febo.com/pipermail/time-nuts/2015-May/092138.html

-=Bryan=-

> From: t...@leapsecond.com
> To: time-nuts@febo.com
> Date: Mon, 12 Oct 2015 08:31:17 -0700
> Subject: Re: [time-nuts] Trimble Thunderbolt and David Partridge divider  
> boardquestion
> 
> For those of you who want to follow the link Chris provided without his 
> personal google search metadata, the correct URL is:
> http://www.perdrix.co.uk/FrequencyDivider/Frequency%20Divider%202.pdf
> 
> /tvb
> 
> - Original Message - 
> From: "Chris Wilson" 
> To: "Discussion of precise time and frequency measurement" 
> 
> Sent: Monday, October 12, 2015 7:08 AM
> Subject: [time-nuts] Trimble Thunderbolt and David Partridge divider 
> boardquestion
> 
> 
> >  12/10/2015 14:58
> > 
> > I have had my Trimble and Dave's divider board for many years and it's
> > on 24 hours a day, seven days a week, no problems.
> > https://www.google.com/url?sa=t=j==s=web=1=rja=8=0CB4QFjAAahUKEwjr27ewjb3IAhVMVhQKHVmJALI=http%3A%2F%2Fwww.perdrix.co.uk%2FFrequencyDivider%2FFrequency%2520Divider%25202.1.pdf=AFQjCNHiXeXt-NZksvMBKYHfkJPf5mn_Fw=YJooGHWI_easGkSZHUVPJgThe
> > Trimble uses a mushroom roof mounted aerial. I have recently built up
> ...
> 
> 
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Re: [time-nuts] Trimble Thunderbolt and David Partridge divider boardquestion

[Chris Wilson]

Hello,

on 13/10/2015 14:41  you wrote:





>  I believe the author was looking into modifying his circuit to use
> a LTC6957 as a frontend. Not sure if he ever got around to it.
> https://www.febo.com/pipermail/time-nuts/2015-May/092138.html

> -=Bryan=-

Hi Bryan, now sorted, I have done some `scoping and the LF signal *IS*
getting into the divider. I added a splitter I bought from a US member
some  time  ago (thanks for the SMA TO BNC adapter cable!, and now the
sine  wave  is  clean  from the Trimble splitter. The signals from the
divider are still dirty when TX'ing though, but that's not an issue as
I rarely use them. Thanks for the info.


-- 
   Best Regards,
   Chris Wilson.

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[time-nuts] Symmetricom 58534A-H01, NOS surplus (eBay)

[Gregory Beat]

Surplus Ericsson GPS Timing Antennas (58534A), new in box, have appeared on 
eBay -- 
at a significant reduction in price (compared to used units sold from China).
Item number: 111702246202
Seller is located in Austin, TX (USA)

Symmetricom 58534A GPS Timing Antenna (circa 1998)
Integrated GPS Timing Receiver (for outdoor mounting)
Data Sheet
http://www.microsemi.com/document-portal/doc_view/133397-58534a

Symmetricom 58534A : Option 001 (circa 2000)
GPS Antenna Evaluation Kit
User's Guide
ftp://ns2.tangerine.co.ug/james/097-58534-02-iss-1.pdf

The 53534A has a 30.5cm cable (12-conductors, 6 twisted pairs, shielded)
terminated with a 12-pin round (circular) connector (Deutsch MMP 21C-2212P1).
This 12-pin circular connector is used with similar "all-in-one" 
receiver/antennas by
Motorola, Trimble, and Accutime.
The Mating Connector is: Deutsch MMP 26C-2212S1 composed of a 
molded back-shell (6810-204-2001) and 12 socket terminals (6862-201-22278).
Deutsch Connectors are now part of TE Connectivity (old Amphenol connectors),
check with your TE Connectivity electronics distributors. 

Synergy SYSTEMS (San Diego) may have those connectors available.
http://www.synergy-gps.com

PHOTOS are available of what is "inside" this 58534A GPS Timing Antenna (circa 
2008).
Includes schematic diagram for a DIY Interface box (5060-0184)
to convert the RS-422 to RS-232 and provide a 1 pps output.
http://home.catv.ne.jp/ff/y226/1/1-12/GPS/sub1-12-GPS.htm#58534A

A DIY interface box could be changed to USB (computer connection) 
with the proper substitution of a Silicon Labs or FTDI  -- UART (TTL) to USB 
bridge chip,
for the Maxim 232 device.

enjoy.

greg
w9gb

Sent from iPad Air
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Re: [time-nuts] UPS for my time rack

[Poul-Henning Kamp]

In message <4FD0F30EBAEF49609DF207E3EE61C15B@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
p...@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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Re: [time-nuts] Symmetricom 58534A-H01, NOS surplus (eBay)

[Poul-Henning Kamp]

In message , Gregory Beat writ
es:

>Surplus Ericsson GPS Timing Antennas (58534A), new in box, 

>to convert the RS-422 to RS-232 and provide a 1 pps output.

I've used Synergy GPS's version for some NTP servers and there is
one little detail they don't mention too much:  The RS422 circuitry
has a significant tempco.

The PPS signal moves more than a microsecond as a result of this
in danish weather, in particular in clear winter weather.

Other than that, it's a quite convenient way to get GPS on a
roof, since you can use anything from phone-wiring to CAT7
for the cable.

Do think about lightning protection, if nothing else, tie a
knot in the cable right outside the hole into the building.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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Re: [time-nuts] UPS for my time rack

[Tom Van Baak]

I found this UPS article fascinating, because it echoed what I eventually found 
in my own lab:

http://www.theplatform.net/2015/03/13/how-this-battery-cut-microsoft-datacenter-costs-by-a-quarter/

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.

Consider that many Rb/Cs standards and even some Qz standards have internal 
batteries. Even if one chooses not to use their internal batteries, most of 
these instruments still feature dual power inputs. In addition to power 
redundancy it also makes it easy to move equipment or cables around without 
power loss. Most importantly, local backup like this avoids the possibility of 
single-point lab-wide power failures.

Recently, as some of my gear works from 5 VDC, those ~2600 mAh mobile phone USB 
backup power bricks make an excellent mini-UPS. The ideal models are those 
without LEDs or on/off buttons so they discharge and charge/float seamlessly 
without manual intervention, even if fully drained.

Multiple units can be placed in series for additional, if slightly inefficient, 
capacity. A good self-test is:

http://leapsecond.com/images/perpetual-USB-power.jpg

/tvb

- Original Message - 
From: "Poul-Henning Kamp" 
To: "Discussion of precise time and frequency measurement" 
; "Bill Byrom" 
Sent: Monday, October 12, 2015 11:44 PM
Subject: Re: [time-nuts] UPS for my time rack


> 
> In message 
> <1444701906.379459.408467601.5676d...@webmail.messagingengine.com>, 
> Bill Byrom writes:
> 
>>Anything can (and will) fail, [...]
> 
> The interesting thing is that several sources in that business have
> reported to me that about 30-40% of all power related downtime is
> caused by Battery, generator and UPS failure, in that order.
> 
> Many sites simply have lower uptime after they install UPS systems.
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@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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[time-nuts] UPS for my time rack

[Tim Shoppa]

A winning way to do 12v and 24v wiring up to 45Amps are Anderson Powerpole
connectors. Many sources sell fused distribution panels.

For larger currents (up to 350A) the SB "Storage Battery" series is broadly
used in Forklifts and solar applications

Tim N3QE

On Tuesday, October 13, 2015, Poul-Henning Kamp > wrote:

> 
> In message <4FD0F30EBAEF49609DF207E3EE61C15B@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
> p...@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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> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] Rohde & Schwarz GPSDO

[Magnus Danielson]

Hi,

On 10/07/2015 04:06 AM, Bob Benward wrote:

If anyone is interested, a Rohde & Schwarz GPSDO:

Rohde & Schwarz GPS RECEIVER ED170MP MEINBERG 2105.5504.00

http://www.ebay.com/itm/262081245211?_trksid=p2055119.m1438.l2649
=STRK%3AMEBIDX%3AIT


Ok, who is the lucky winner that out-bid me with a whooping 5 USD?
455 USD is a good price. :)

Yes, I was being a bit cheap only setting 450 USD for it, but never the 
less. I currently waste my money on 8th Symposium on Frequency Standards 
and Metrology 2015.


Some time-nuts friends is here, and various friends from NIST, PTB, SP, 
FemtoSecond etc.


Cheers,
Magnus
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Re: [time-nuts] UPS for my time rack

[Mark Spencer]

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  wrote:
> 
> 
> In message <4FD0F30EBAEF49609DF207E3EE61C15B@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
> p...@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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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 
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Re: [time-nuts] UPS for my time rack

[Florian Teply]

Am Tue, 13 Oct 2015 18:54:58 +
schrieb "Poul-Henning Kamp" :

> 
> In message <4FD0F30EBAEF49609DF207E3EE61C15B@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.
> 
Definitely, avoiding unnecessary conversions is key to achieve good
efficiency. And in most cases equipment actually converts to DC
internally, so converting AC to DC (for the battery), then back into AC
to power the equipment, which in turn converts to DC to power internal
circuitry is bound to be inefficient. DC-DC converters with very
good efficiency exist for quite some time now. I've converted most of
the stuff I regularly use to run off common 12V and/or 48V rails
generated by two "central" power supply blocks.

> 
> 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.
> 
Umm, around here, at least for ham radio operators, it seems many
standardize now on PowerPole connectors for 12V DC. They are pretty
affordable, running at below 2 Euro for a single pair. Sure, it's not
as cheap as an USB connector, but they are designed to handle
significant currents (15, 30, 45 amps which are freely interchangeable,
versions rated for 75 or 120 amps exist also).

Now of course if you want to mix voltage levels, things might become a
bit more complicated, as most 12V equipment doesn't like to be supplied
with 24 volts, so it might actually not be the brightest idea to use
identical connectors in such circumstances. Don't ask how I know... ;-)

Of course, short circuit currents are the same as before, so properly
rated fuses and/or circuit breakers are a must, but that would be
recommended for mains powered equipment as well.

Best regards,
Florian
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Re: [time-nuts] UPS for my time rack

[Brooke Clarke]

Hi Poul:

I really like Power Pole connectors.  Unlike cigarette lighter plugs and sockets where the spring causes them to 
separate on their own the Power Pole connectors "snap" together.


The Amateur Radio Emergency Services (ARES) used to use car trailer connectors but long ago switched to Power Pole 
connectors in a specific configuration that maintains their Hermaphroditic  
nature.  That's to say unlike conventional electrical extension cords that have a male and female end, in this system 
both ends of the cord are identical.  The ARES configuration is

"Red on right
A reads right"
http://www.prc68.com/I/PowerPole.shtml

The PP15 series plastic shells used for ARES can accept contacts rated at 15, 30 or 45 Amps, so they can handle quite a 
bit of power.

The contacts are also self wiping.

I've come up with a 24 Volt configuration that does NOT mate with the 12 Volt ARES standard, but retains the 
hermaphroditic feature.

I don't like the systems that only change the plastic shell color because they 
mate with the 12 Volt system.
http://www.prc68.com/I/PowerPole.shtml#24VP

There are a number of companies making DC outlet strips and various other power management devices all based on Power 
Pole connectors.

For example: 
http://www.powerwerx.com/powerpole-power-distribution/rigrunner-4005.html

Mail_Attachment --
Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Poul-Henning Kamp wrote:


In message <4FD0F30EBAEF49609DF207E3EE61C15B@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.




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Re: [time-nuts] UPS for my time rack

[Brooke Clarke]

Hi Tom:

The Li-Ion 18650 size cells (18mm dia x 650mm long) are used in most laptop computer batteries and Tesla cars because 
they are made in such high volumes.
The referenced article shows a single 18650 cell, but with about 3.7 Volts per cell you need to connect them in series 
and/or parallel to get the typically needed 12 or 24 Volts (and needed amp hours) for backup power.  The big problem is 
these cells can easily catch on fire and/or explode if they are mistreated either during discharge or charge.  To 
prevent that a protection circuit needs to be incorporated for each individual cell.  The easiest way to do that is to 
buy a battery pack with internal protection circuits and matched charger.  Then this can be connected to the external DC 
input on an individual piece of equipment.  For example:

http://www.batteryspace.com/li-ionpacks37-89v.aspx
My first precision oscillator was a rack mount Gibbs 5 MHz standard that I got for a very low price because the internal 
lead acid battery had vented acid fumes which etched away many of the copper PCB traces inside the oven.

http://prc68.com/I/office_equip.html
http://www.prc68.com/I/rack1.html
Mail_Attachment --
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Tom Van Baak wrote:

I found this UPS article fascinating, because it echoed what I eventually found 
in my own lab:

http://www.theplatform.net/2015/03/13/how-this-battery-cut-microsoft-datacenter-costs-by-a-quarter/

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.

Consider that many Rb/Cs standards and even some Qz standards have internal 
batteries. Even if one chooses not to use their internal batteries, most of 
these instruments still feature dual power inputs. In addition to power 
redundancy it also makes it easy to move equipment or cables around without 
power loss. Most importantly, local backup like this avoids the possibility of 
single-point lab-wide power failures.

Recently, as some of my gear works from 5 VDC, those ~2600 mAh mobile phone USB 
backup power bricks make an excellent mini-UPS. The ideal models are those 
without LEDs or on/off buttons so they discharge and charge/float seamlessly 
without manual intervention, even if fully drained.

Multiple units can be placed in series for additional, if slightly inefficient, 
capacity. A good self-test is:

http://leapsecond.com/images/perpetual-USB-power.jpg

/tvb

- Original Message -
From: "Poul-Henning Kamp" 
To: "Discussion of precise time and frequency measurement" ; "Bill 
Byrom" 
Sent: Monday, October 12, 2015 11:44 PM
Subject: Re: [time-nuts] UPS for my time rack




In message <1444701906.379459.408467601.5676d...@webmail.messagingengine.com>,
Bill Byrom writes:


Anything can (and will) fail, [...]

The interesting thing is that several sources in that business have
reported to me that about 30-40% of all power related downtime is
caused by Battery, generator and UPS failure, in that order.

Many sites simply have lower uptime after they install UPS systems.

--
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@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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[time-nuts] UPS for my time rack

[Mark Sims]

How could anybody possibly accept/consider/use a VAX/Unix as a solution to any 
real computer problem?  The manual set only takes 3 feet of shelf space.   
Anybody knows that a real (IBM) computer requires 80+ feet of documentation.  
Or so I was once scolded by the management of a Very Large Company...  that 
shortly thereafter had its lunch served to them by a much smaller competitor 
and went belly up.
Somewhat time-nut related...  the project main application needed millisecond 
consistent (not necessarily accurate) time stamps on a world-wide network.  
That was in the pre-gps, pre-fiber, pre-historic before-times.  I don't think 
that they ever quite got there.



  
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