Good suggestions. Also, if you have 12V charging the relevant battery, you can
power 5V stuff with a cheap, off-the-shelf UBEC. In a system I built recently,
I powered a Wandboard, an SSD (SSD's typically only use their 5V supply) and an
8 port GigE desktop switch with one that puts out 5@5V:
http://www.robotmarketplace.com/products/0-DYS30055.html.
There are lots of UBEC's out there in the robotics and radio control suppliers.
Motors and batteries like to be higher than 5V, and the electronics and small
servos like 5V. You could design your own, but why bother...
On Sunday, June 29, 2014 11:45pm, David Lang da...@lang.hm said:
On Sat, 28 Jun 2014, Joseph Swick wrote:
On 06/28/2014 12:28 AM, Dave Taht wrote:
One thing that does bug me is most UPSes are optimized to deliver a
large
load over a short time, a UPS capable of driving 5 watts for, say, 3 days
is
kind of rare.
I think this is something that's in need of a new approach/disruption.
For low power devices like NUCs and RasPi servers, running them off of a
traditional UPS is hugely waste-full, since you're going from your Line
voltage (120VAC or 240VAC in many places) to 12 or 24VDC (Or 48VDC for a
bigger UPS). Then when the UPS has to kick in, it converts the battery
voltage back to your line voltage.
A better approach would be to have a UPS that had a good intelligent
charger for your deep-cycle type battery that coming off the battery,
you kept it at the correct DC level for your NUC or Raspi. Which for
many of these devices is 5 or 12VDC. So in a sense, it becomes your
low-power device's power suppy, it just happens to have the added
benefit of having a built-in backup battery.
Coming from a Ham Radio perspective, some hams run their base stations
off of deep-cycle marine batteries with some form of charger keeping
them topped off. This way, the radio operator can operate his or her
station for days just on emergency power. Since a lot of ham gear is
designed to operate off of 12VDC (with some notable exceptions like your
high-power amplifiers).
It shouldn't be hard to develop a decent grade Low-power UPS for home or
small office use that can run these low power devices for days at a time
with out all the inefficiencies of converting VAC to VDC and back again.
And there's probably a bunch of Raspi (or similar low-power computer
boards) enthusiasts who already have for their own personal use.
I think a lot of people are just using li battery packs with USB output to run
their Pi type computers, with a wall charger into the battery pack.
it may not be the best thing for the batteries, but it's off-the-shelf and
cheap.
for 12v computers, it's easy to just float a gell-cell on the output of a
power
supply. If you want to be a purist, have some sort of current limiting
resister
so that when the battery is extremely low you don't overload the power supply,
but in practice, the power supplies are cheap (getting hold of an old PC power
supply is probably free, and they tend to have a fairly heafty 12v output),
and
gell cells are pretty forgiving of abuse, so you can get away with the
dirt-simple PS - battery - device the vast majority of the time.
It helps that 12v equipment tends to actually be speced to run off of
automotive power, which is about the ugliest power source you can deal with.
David Lang
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