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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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
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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:

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 <phk@phk.freebsd.dk
javascript:_e(%7B%7D,'cvml','phk@phk.freebsd.dk');> wrote:

Am Tue, 13 Oct 2015 18:54:58 +0000
schrieb "Poul-Henning Kamp" phk@phk.freebsd.dk:

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.

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

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 http://www.prc68.com/I/PowerPole.shtml#Herm
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

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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:

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

Depending on your actual power throughput needs- PTCs can be a challenge as
Bob mentions.  You will have a tough time meeting the power requirements of
a Thunderbolt with many you'll see.  Now efuses (think TPS24/25xxx)  or
mosfets with a controller (think LTC43xx) can be a good choice but don't
hesitate to use a real honest to god fuse that blows out and waits for you
to come replace it if that is what you would need

I personally do as suggested in the thread above to some degree- I do AC to
DC conversion once for all my time and frequency stuff then have batteries
local to important gear and (in older stuff) a diode(s) or (in newer stuff)
a real hotswap controller.  But whenever something is really important
there's whatever fuse is needed.

Finally if you are of the type to be adventuresome -
http://cds.linear.com/docs/en/datasheet/4110fb.pdf  or

• Google for Freescale's, ON Semi's or TI's offline UPS Reference
  designs.  Yes they invert DC to AC, but you can drive the inverter gates
  with a microcontoller's PWM output. meaning no matter how jagged your
  utility's wave may be you can create a perfect, beautiful 50 or 60 Hz sine
  of your own - devoid of most noise.

NS

On Wed, Oct 14, 2015 at 12:01 AM Bob Camp kb8tq@n1k.org wrote:

In message 20151013225202.1e70abe8@aluminium.mobile.teply.info, Florian Teply
writes:

The one I just put in my HP5065A does 60W with 90+% efficiency
in a 2x1x.5 inch package:

http://phk.freebsd.dk/hacks/HP5065A/20150930_dcdc/index.html

They're quite neat, but I wish there were something a little less
heavy-duty for the 1-2 Amp range.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@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.

How did you find the units that will act as a UPS, without buying
everything on the market and testing them?

I just checked all of those bricks in our house, and none will do it.
There are a couple of PNY units that do not provide output power until a
button is pressed, and don't charge until input power is connected while in
idle mode.  Then there are Tp-Link and Mophie units that switch on the
output automatically when a load is connected (or perhaps the output is
just always powered), but which disable the output and switch to charge
mode when input power is provided.  None of them seem able to pass through
5V power without discharging.

• Dave

On Tue, Oct 13, 2015 at 2:07 PM, Tom Van Baak tvb@leapsecond.com wrote:

I’ve used Anderson PowerPoles in mixed voltage environments successfully. A visual indication can be obtained by using other colors for the connector shell; e.g., red for +13 Vdc and blue for +25 Vdc…

One can also re-orient one of the connectors in each pair by 90º or 180º to create a physical incompatibility. This takes some care as the cable ends are no longer interchangeable, but it does provide protection against connecting to the wrong voltage.

— Eric K3NA