Re: Powering ATX Motherboard on 12V Battery
davy
The +12V and -12V are relative to ground. Take two 12V batteries,
connect them in series, if the middle connection is grounded you will
have a +12V live and a -12V live.
If you are using car batteries, then use a DC to ac inverter..... this
will step the 12V DC up to 120~240V ac and you'll be able to run the ATX
power supply as if it was connected to the wall socket in your home.
You'll need consider how long the inverter will be in use for, because
they draw a heavy current and you'll need to recharge the car
batteries.... forget it if you are thinking of dry type cells.
davy
Drycola
Hello everyone,
I need to run an old ATX motherboard on 12V DC batteries instead of the
powersupply. I need that for a robotics project.
I know that power supply provides +12V, -12V, +5V, & -5V DC to the
motherboard and other components, but I'm little confused about the +12
and -12 issue, I mean can these be directly connected to the + and -
output of the 12V battery??
My question in simple words: *How can I run motherboard on 12V
battery?*
Paul
Look in the "Intelligent Vehicle PSU kit" section here. There is a
ready made solution. More than the mini-itx store carries these,
so have a look around.
http://www.mini-itx.com/store/?c=10#int
The DC-DC converters come in two types. A narrow range one,
expects a regulated input. An example of a power source for
a narrow range adapter, is the "150W AC Universal Adapter 12V 12.5A".
Since the spec on the input is tight, no conversion is
needed on the 12V rail, and the adapter has one fewer
regulator circuits on it.
12V +/- 5% -----+------------------> direct to motherboard 12V rail
|
+--- 3.3V reg ----->
|
+--- 5.0V reg ----->
|
same for 5VSB, -12V etc
A "wide range" adapter, handles DC input voltages which
are unregulated. The car battery might vary from 14V to 12V.
The DC-DC converter board might look like this. This is
the kind you'd be interested in.
wide range -----+--- 12V reg -----> to motherboard
|
+--- 3.3V reg ----->
|
+--- 5.0V reg ----->
|
same for 5VSB, -12V etc
Power conversion circuits come in different switching conversion
types. A buck converter would handle 14V to 12V. A boost converter
would handle 6V to 12V. A buck-boost converter handles
6-24V wide range input, to 12V output (i.e. handles voltages
both above and below the desired output voltage). Different
architecture switching conversion solutions, is what makes
possible all the different ranges. A converter architecture
must be designed for the right span of voltages for the job.
If you buy a converter designed for 14V-12V to 12V output,
it isn't going to work off 6V necessarily. It's important
to match the right DC-DC converter to the job, and
make sure you know what you're buying. Look for a datasheet
from the component manufacturer, to try to get as many
details as possible on it. Or contact them directly,
for applications information.
It helps, if the adapter is designed specifically for vehicles,
since you should really have "low battery" protection. You want
the DC-DC converter to cut off, while there is still some
charge in the battery. Ordinary car batteries won't last
very long, if you "deep discharge" them all the time. A
car battery works best, if you only use a small percentage
of the ampere-hours, and then charge them up again. There
are batteries designed for "deep discharge", but they're
more expensive. Perhaps run your car battery, between
75% and 100% charge level. It means setting the ampere-hours
of the battery you buy, to about 4X what the project needs.
It is also possible, for a person to build custom power regulation
solutions, using "brick" converters, but the above adapter is
a ready made solution, and more likely to do what you want.
This company makes "bricks". I worked on a few different
projects, where the power was provided by this style of
brick.
http://www.vicr.com/cms/home/products/brick
You can get info on charging batteries, from a site like this.
http://www.batteryuniversity.com/partone-13.htm
I prefer to use a "battery hydrometer", to test a car battery, to
determine the state of charge. That will work, if the car battery
has removable caps on it. The fluid inside the battery is sulphuric
acid, which ruins cotton instantly (so don't get it on your jeans
or your skin). The density of the H2SO4 changes as the battery charges,
and the hydrometer can measure that. I got my hydrometer at an automotive
parts store. ( *Every* pair of jeans I owned in university, had
holes in them, from sulphuric acid. I never wore a lab coat
in chem lab :-) ) Sulphuric acid is that nasty. A one second
contact is enough. You cannot neutralize the acid fast
enough, to protect your jeans.)
http://en.wikipedia.org/wiki/Hydrometer
A sealed lead acid battery, reduces the odds of coming in contact
with the contents. Sealed lead acid batteries are used in
uninterruptable power supplies (UPS) or for emergency lighting.
There will be a lot less explosive gas released by an SLA.
If you're going to use the car battery, *always* charge it
outdoors, not in the house! My next door neighbor had
an explosion, with a car battery, and the result
was not a pretty sight. If you're going to use car
batteries, while charging, they stay outdoors in the
open air. If you aren't charging them, you can bring them
inside (because they won't be releasing gas then). If storing
a car battery on your basement floor, put something
underneath it, to catch acid residue. The car battery
can make a mess of your floors too. They're really
just better off, outside.
The SLA, by comparison, will be a cleaner solution, but
given enough abuse, could also spell trouble. Batteries
like this, are no joke.
http://www.jaycar.com.au/images_uploaded/slabatts.pdf
(Always cover the battery terminals, to prevent
accidental contact. I had a friend who got burned, because
of ignoring that advice. A lead acid battery can pump
a *lot* of current, if you short the terminals together.
Remove any personal jewelry, before working around
a battery. My friend got his wrist watch strap in contact
with the battery, and ended up with a "watch strap
burn mark" on his wrist. Remove your watch and rings
or the like, before working around the battery. And
keep screwdrivers or wrenches away from the battery
as well. A brand new car battery comes with terminal caps,
to keep the battery safe. Terminal caps help prevent
accidents, when you're not using the battery.)
Good luck and stay safe,
Paul