PSU to Bench Supply conversion - other loads to use to make it work.

[ItsMike]

Hey guys,
I know there must have been a million threads about PSU to Bench Supply conversion but still I couldn't really find an answer.

I understand that most of those PSU's must have a load in order to operate and as I have seen most people use a 10Ω 10W resistor connected between the +5 and GND rails.

I was thinking of using a more... useful load, maybe some sort of lighting ?
Anyways, can I connect the load to any rail to make the PSU work ? is it just the 5v rail or can I use the 12v one to.

Also how can I tell what kind of current the PSU need's to "latch on" ? I've read it's around 0.5A to 1A, does it change if I draw it from the 12v rail ?

Also, besides powering a huge led as a load does anyone have a different suggestion as to what "useful" load should I use ?

Thanks in advance,
Mike.

 

[3v0]

I have a nice variable voltage bench supply and needed another with fixed voltages. I had an old 250 ATX supply. I used the already existing fan for a load.

https://www.electro-tech-online.com...-review-sparkfun-atx-benchtop-supply-kit.html

**broken link removed**

 

[Reloadron]

While I have always hung a 10 ohm 10 watt resistor on the 3.3 volt line on newer PSUs it really isn't necessary, I would always include the 3.3 volt sense line at that point also. I have run plenty of ATX form factor PSUs without any load just fine. It really depends on the PSU. Worst case scenario as of the PSU design guide (2004) without any load the PSU should not start at all.

Note: If anything I would hang a 10 ohm 10 watt resistor out there on the 3.3 volt rail.

Ron

 

[SABorn]

I use to add resistor loads to psu, but now im more of an animal and just use an old 3.5 floppy drive plugged into one lead as these seem to regulate the power loading better and not draw as much current as the resistors use to.

Secondly old floppys are cheap if not free, you could gutter the floppy and just tuck the board away somwhere, but as i said im more animal like and just tape it to the side of the psu as its about the same size.

30 seconds work to have a psu up and running.

Pete.

 

[ItsMike]

While I have always hung a 10 ohm 10 watt resistor on the 3.3 volt line on newer PSUs it really isn't necessary

If it's possible to hang the load from the 3.3v line, is it also possible to hang it from the 12v line ?

 

[Reloadron]

If it's possible to hang the load from the 3.3v line, is it also possible to hang it from the 12v line ?

Sure. I used the 3.3 volt rail simply because I can buy 10 ohm 10 watt resistors at the local Radio Shack in a 2 pack for a few bucks, also because I could include the 3.3 volt sense at the load point. Additionally using the 3.3 volt line gives me 3.3 Volts / 10 Ohms = .33 Amps so .33 amps * 3.3 volts and when all is said and done just over 1 Watt. If you load the 12 volt rail with 10 ohms you get 12 volts / 10 ohms = 1.2 amps which works out to be about 14.4 watts. If I loaded the 12 volt line I would use both 10 ohm 10 watt resistors in the pack placed in series.

Pete also makes a good point in that just about anything can be used as a load depending on the PSU. For me a few resistors is convenient while for Pete tossing an old FDD on there is a good enough load.

Also, give the thread linked to by 3V0 a read.

Ron