scottm
Hardcore RCTalk User
I have started making a power supply to power my chargers from an atx power supply. It is a great project if you have an old ps laying around. I am using a new Linkworld LPG8-350W ps, rated for 15 amps output at +12 volts. I bought it new for $30 because I couldn't find an old one. My neighbor just tossed out a pc with one in it a few weeks ago - oh well!
I am using plans from www.rcbatteryclinic.com and from the Sept 03 AMA magazine. I am going to trick it out with binding posts for 12V, 5V, and 3.3V output. 12v is for peak chargers, and 5 and 3.3 v will be good for breaking in motors and who knows what else.
It is really pretty simple, but it requires some tools and a voltmeter. Following the instructions, here is the first step:
Take it out of the case and find the PS-On and PW-OK wires (green and grey in my case). Then apply a resistor across the +5 V line and common (red and black), and measure voltage between +12v and common (yellow and black). The resistor tells the ps that the computer is on, and makes it boost output on the 12 V line. The lower the load resistor, the higher the output.
Next pick out three +12v wires and three commons (yellow and black) to solder to the binding posts. Trim off all the others, except for 5v or 3.3 v wires if you plan to use them. Install binding posts, solder it up, and put it back together.
The MARCEE instructions from batteryclinic says to use a 1 ohm resistor on the +5 v line. The AMA article says to use a 50 ohm resistor to reduce wasted power on the circuit, since a 1 ohm load at 5v will waste 25 watts of power. I tried 20 ohms, then 10 ohms, then 5 ohms, trying to get higher voltage on the 12 v output. The pic above shows it putting out 12.27 volts with a 5 ohm resistor, but that dropped to 11.6 volts with a 5 amp charger load. The AMA guy claims to get over 13V with a 50 ohm resistor, so maybe mine is a dog, I don't know. I hoped to be able to run at least two chargers off it, but not if it drops under 11 volts or so.
I am going to try a lower resistance for more voltage, then finish it with binding posts and a switch. Even if I can't get a lot more voltage out of it, it is still worth doing for a light, cheap ps. It will run one good charger at least. At this time I recommend against buying one just for this use until I figure out what is possible for output. But if you have one laying around, give it a try (just be careful, unplug it before playing inside, etc, etc).
I am using plans from www.rcbatteryclinic.com and from the Sept 03 AMA magazine. I am going to trick it out with binding posts for 12V, 5V, and 3.3V output. 12v is for peak chargers, and 5 and 3.3 v will be good for breaking in motors and who knows what else.
It is really pretty simple, but it requires some tools and a voltmeter. Following the instructions, here is the first step:
Take it out of the case and find the PS-On and PW-OK wires (green and grey in my case). Then apply a resistor across the +5 V line and common (red and black), and measure voltage between +12v and common (yellow and black). The resistor tells the ps that the computer is on, and makes it boost output on the 12 V line. The lower the load resistor, the higher the output.
Next pick out three +12v wires and three commons (yellow and black) to solder to the binding posts. Trim off all the others, except for 5v or 3.3 v wires if you plan to use them. Install binding posts, solder it up, and put it back together.
The MARCEE instructions from batteryclinic says to use a 1 ohm resistor on the +5 v line. The AMA article says to use a 50 ohm resistor to reduce wasted power on the circuit, since a 1 ohm load at 5v will waste 25 watts of power. I tried 20 ohms, then 10 ohms, then 5 ohms, trying to get higher voltage on the 12 v output. The pic above shows it putting out 12.27 volts with a 5 ohm resistor, but that dropped to 11.6 volts with a 5 amp charger load. The AMA guy claims to get over 13V with a 50 ohm resistor, so maybe mine is a dog, I don't know. I hoped to be able to run at least two chargers off it, but not if it drops under 11 volts or so.
I am going to try a lower resistance for more voltage, then finish it with binding posts and a switch. Even if I can't get a lot more voltage out of it, it is still worth doing for a light, cheap ps. It will run one good charger at least. At this time I recommend against buying one just for this use until I figure out what is possible for output. But if you have one laying around, give it a try (just be careful, unplug it before playing inside, etc, etc).
