This is a tutorial on how to construct a precision high power
high efficiency DC to DC converter.
Most equipment nowadays runs from either 5 volts or 12 volts.
The problem with 5 volts is you have to regulate the voltage
down from either 6 volts or higher. As a battery depletes the
voltage decreases and a 6 volt battery will drop to 5 volts
when that battery has over 30% of its power left to give.
So then people use 12 volts batteries to run 5 volt equipment.
But the voltage difference has to go somewhere. In most low
cost systems that use regulators such as 7805 the difference goes
out as heat. That is why you see the large aluminum heat sinks
on these devices. The more power you consume the more heat
created.
When you are running this from the AC line, this is not a problem
as you can waste energy.
But when we run from a battery you want as much power from the
battery to be available to your device not wasted as heat.
So we can't use linear regulators, they waste to much power.
So we have to use a switching power supply, but again this is much
more expensive and harder to design.
I do not know about you but I would rather spend my time doing
something else than designing power supplies. So if I go on the
Internet and look for DC to DC converters, I find that I can easily
spend $100 or more for a good switching supply. I wanted one that
could take voltage down to 9 volts and up to 16 volt input.
My electronics are important to me so I also wanted one that would
make sure that I got 5 volts exactly.
So this was a big wish list, especially because I wanted it cheap.
Well you know I would not be writing this if I had not found a solution
to the problem. So here it is.
I found multiple sources for these converters that will give me what
I want.
5 volts at up to 6 amps of current
12 volts at up to 2 amps of current
2% regulation control
Powered from 9 volt to 16 volts.
And I wanted greater than 90% efficiency so my battery goes to my project
not to heat.
All if this for $20.00
It all comes from a new breed of computer. The Carputer as their called. Small
portable computers that are designed to run in your car off of the 12 volt car
battery.
The car battery is a dirty nasty source of power never meant to run fragile
electronics. It takes a lot of cleanup to make it run a computer.
So I found this board.
It is made by a company called Morex and they can be found at
http://www.idotpc.com/thestore/pc/viewPrd.asp?idcategory=69&idproduct=311This is a DC to DC converter made to power Carputer motherboards.
It runs an entire PC comparable computer and works very well doing it.
We are taking this one and building our own DC converter that will be
powered from a 12 volt battery.
The one I am doing in this article is a little more expensive. It cost $26.00
but only gives more power.
All these boards share one thing in common. They output their power on a
standard atx power plug.
You can buy a cable for a few dollars or cut the one off a dead or old
computer power supply.
On the left side of the board is the power input. +12 volts and Ground. We will
hook this up to our 12 volt battery.
This is what my power plug looks like.
I crimped spade lugs at the ends of the wires so I can just plug it into
my battery.
Now we are going to work on the power cable.
The plug looks like this
Pin Name Color Description
1 3.3V Orange +3.3 VDC
2 3.3V Orange +3.3 VDC
3 COM Black Ground
4 5V Red +5 VDC
5 COM Black Ground
6 5V Red +5 VDC
7 COM Black Ground
8 PWR_OK Gray Power Ok
9 5VSB Purple +5 VDC Standby Voltage (max 10mA)
10 12V Yellow +12 VDC
11 3.3V Orange +3.3 VDC
12 -12V Blue -12 VDC
13 COM Black Ground
14 /PS_ON Green Power Supply On (active low).
15 COM Black Ground
16 COM Black Ground
17 COM Black Ground
18 -5V White -5 VDC
19 5V Red +5 VDC
20 5V Red +5 VDC
You will notice that most of the +5 volt outputs have a ground
next to them. We will use this.
I have no need for -5 volts, -12 volts, or 3.3 volt so you can
either cut the wires off, remove the wires from the plug, or
just cap the wires so they don't short.
To make this supply work in our application we only have to
short pin 14 to ground to turn the supply on. I used a simple
on off rocker switch to act as my power on/off button.
I wired several of the + 5 volt with their neighboring ground
to plugs that correspond to my equipment I need to power
Here is a picture of one of my power plugs on a +5 volt line.
Notice I have caps for them to be extra careful not to short
them if I am not using this one.
You see the cap off so I can plug it into my device.
I am also wiring a cigarette lighter socket because my
battery charger uses this to plug in.
So this is my completed harness plugged into the DC to
Dc converter board. This is ready to plug into a battery
and use.
Now that I have my complete converter, I can actually use
a battery that is half the size, Here is a picture of smaller
battery next to my original one.
If you have not thought about it by now, you can just
as well put a cigarette lighter plug on the input side
of this converter and run the entire system off you car
battery.
If you just want to charge your PSP you can probably recharge
your PSP for about two weeks of playing off of one charge of
this battery.
Just be careful that the plus and minus of the input is
connected correctly or you will blow your fuse.
Because the system converts DC voltage to DC voltage you can
touch the converter board without harm. It generates no heat
so you can simply put your converter in a plastic box.
There you have it a low cost high power high efficiency power
system for your portable electronics.
Have a great day !
