How do I know if its an AT or ATX Supply?

[Tisr]

Hi Guys

For my first go at DIY electronics, I'm about to convert an old PC supply into a powersuppply for my field charger. My question is, how do I know if I've got an AT or ATX supply? I believe the conversion process is a little bit different for both...


Thanks

Dan

[Chippie]

AT power supply uses 2 plugs to connect to the motherboard...

ATX use one main one........pin outs as per picture

[Tisr]

Thanks for the reply

The wiring harness going to the motherboard does in fact have two six pin connectors (see photo). So it is an AT right?

Will a powersupply like this have the output necessary to power say a 'Swallow' or 'Hyperion' charger for my TX and small lipo packs?

Thanks

Dan

[dc812]

Yes that power supply will work just fine. I converted one a year and a half ago as a novelty, and have since used the heck out of it. This link (http://web2.murraystate.edu/andy.batts/ps/powersupply.htm) documents the conversion process well. The author runs a school lab that uses dozens of them.

I suggest that if you build one, take the extra time to install banana jacks for all of the available DC voltages in the power supply. You may not think you'll use them, but you will......I have jacks for 3.33V, 5.55V, 13V, and a negative jack. I also installed a on/off switch and a power good switch to let me know if the power is on and/or if I have un-latched it by shorting something I am working on. I have use my little power supply to run my battery charger, cut wing foam cores, check dc motors, etc....it sure is handy to have 5.5V DC power supply when all your RX batteries are drained or buried when you need to check a RX or a servo throw during a build.

So, I suggest you go for it. You'll have fun building it, it doesn't take very long, and you'll have a power supply for life that you built yourself!

DC :D


Thanks for the reply

The wiring harness going to the motherboard does in fact have two six pin connectors (see photo). So it is an AT right?

Will a powersupply like this have the output necessary to power say a 'Swallow' or 'Hyperion' charger for my TX and small lipo packs?

Thanks

Dan

[Andrew0820]

Thanks for the reply

The wiring harness going to the motherboard does in fact have two six pin connectors (see photo). So it is an AT right?

Dan

Dan --

Yours is an AT -- it will not have a 3.3v rail or soft-switched PS_ON line. The AT's were powered on through the attached pigtail and a double pole single throw switch. Generally this pigtail will have 5 wires: blue, brown, black, white and green. Blue and brown are the live and neutral feeds from the 120v power and are HOT whenever the power supply is plugged in. Black and white carry the AC feed from the switch back to the PSU -- these are hot only when the PSU is plugged in and the switch is turned on. Green or green/yellow strip is earth ground and would normally be screwed to the computer chassis.

Generally the AT form factor will power up without a load resistor, but you can usually increase the voltage on the 12v rail slightly and improve the stability of this rail under load by adding a 10 ohm load to the 5v rail (red/black).

I've attached pictures of the switch with standard wiring colors. Your layout may differ, but you want to pair up blue\brown together and black/white -- otherwise, if blue gets switched to brown, you will be unhappy.

As a precaution, be sure to meter the AC voltages just in case your supply does not follow the industry guidelines.

andrew

[Tisr]

Andrew

You've described my PSU exactly. I pluged it in this morning and it powered up without any load. Putting a DMM across the black / yellow cables I got 11.96 V unloaded. What wattage resistor should I be looking for for the 5v line? 10W or 20W?

Thanks

Dan

[Andrew0820]

Dan --

10W will be fine -- it will get hot, but that's normal. ZIP tying it to the case vents with a little thermal grease will keep it cooler. Many times the wire wound resistors are sold in pairs. If so, get 10 ohm. Try one and check your output voltage. If it's still lower than you would like, hook up the second resistor in parallel to the first -- this will give a resistance of 5 ohms. The higher load will probably push the output up a tenth or so. There is little gain in reducing the resistance any farther.

andrew