REVIEW: Sparkfun ATX to benchtop supply kit.

[3v0]

While looking for a new variable voltage bench PS I ran into Sparkfun's Power Board Kit to convert an ATX supply to a bench supply. One does not need a kit to do this but fuse holders and binding posts in the kit cost nearly what the kit did so I gave it a try.

I built the PCB and mounted it to a 200W ATX PSU pulled from a 400MHz machine.



A bench supply should have short circuit protection. This unit uses 5A 125V glass fuses which run about 50 cents a pop. (pun intended)

As noted in the sparkfun comments the connectors do not use standard spacing but I do not much care about that. For reasons I do not understand there is no switch to the soft power line on the PSU, that would have been nice. The plastic spacers need to be 1/4" longer to keep the tips of the binding posts from contacting the PSU case.

My old ATX PSU has a 20 pin connector and the kit uses a 24 pin connector. It works but the latch on the connector does not line up. the 20 pin version of the PSUs have a -5V line that is a NC in the 24 pin versions.

I had a bit of a fuss getting a load that would let the PSU startup. I used a resistor on the 5V output and that worked until I plugged the PSU case fan into the PSU PCB. Removed the resistor and it did not work with the fan in place. Without the resistor, but with the fan on the 5V rail it works. So I am going with that and do not much care why. I need to remove the PCB to do a decent job of connecting the fan wire. Maybe add a switch.

I would give the kit a thumbs up, It is good so far as it goes.

 

[Sceadwian]

Umm.. ATX supplies have built in short circuit protection, why would you add it? For the price, I would expect a power switch, and active 5v SB bus LED as well., but considering it just plugs into the stock ATX MB connector it's not bad. For a real bench I'd be a little curious about what the traces on the PCB are rated for. the 5 and 12 volt supply lines of modern ATX supplies are capable of some pretty serious current.


I've heard a lot of people complain about starting up without a load, but I've never had any issues, mind you I've only done it on a couple power supplies, and from what I recall they had enough 'native' load that they would always startup.

 

[Reloadron]

I've heard a lot of people complain about starting up without a load, but I've never had any issues, mind you I've only done it on a couple power supplies, and from what I recall they had enough 'native' load that they would always startup.

Years ago the claim on early SMPS units was they needed to have a load. I don't know how much truth there was to it. The conversions I have done I generally used a 10Ω 10 Watt resistor and placed it on the 3.3 volt out with the sense lead (if the PSU had one) tied to it. Don't know that it mattered but what the hell.

Ron

 

[3v0]

My old 200w ATX supply will not start without a load as I stated in the original post. Either I have a one of kind supply or the myth is true.

The fuses are a belt and suspenders/braces thing. One down side here is that if you stick a wire or probe too far into the binding posts they contact the fuses. Depending on what you are shorting it may illustrate that the fuse or built in short circuit protections works. But once you are aware it can be avoided. I like to put my wires on solderless banana plugs so it is not a real problem.

Sceadwian what do you mean by 5v SB bus? No need to guess about the traces. Sparkfun provides the Eagle Cad files so we can look. If you want different you can modify them and etch you own. https://www.sparkfun.com/datasheets/Kits/benchtop power supply-v12.zip.

 

[Reloadron]

My old 200w ATX supply will not start without a load as I stated in the original post. Either I have a one of kind supply or the myth is true.

Guess it isn't a myth huh?

I don't have a working 200 watt PSU around here, not that I know of anyway. I have some in pieces and parts maybe.

Ron

 

[Sceadwian]

The myth is obvious true, cause you have a supply that won't start yet I have two that will, it depends on the supplies themselves. I was simply stating that my experience so far as been with supplies that do not have a starting issues, the again I wasn't monitoring the voltage under no load and when connected to a load to see if there were any stability issues during the initial application of load, your supply could have had more stringent stability requirements than mine.

The 5vSB is the ATX line that is an always on 5V supply capable of a couple amps. The 5VSB on my 350watt bench supply is listed on the side as being able to deliver 2 amps, it's either a linear supply or a very low quiescent current switcher, separate from the main 5V bus. It doesn't require the fan to be on and as long as the power supply is plugged in that 5V line is hot, the exception being that some ATX supply's have actual rocker switches on the back that switch the mains off killing the 5vSB. Mine is such a supply but many supplies don't have this rocker switch. The line goes to the motherboard and is purple. It powers a chip (possibly the bios) that allows the machine to be turned on with soft switches, and allows the bios (such as in my PC's case) to turn the PC back on and scheduled times to run applications.

 

[SABorn]

Not so pretty, but what works very well is to use a old 3.5 floppy drive and plug it into one of the power wires that it would normally plug into.

The PSU will start up every time and give good votage regulation on all power rails.

Considering you can buy a new 3.5 floppy drive for $5.00 they make it cheap and easy to put a PSU into use without even needing to open the case.

Although there is a sense wire (green by memory) in the plug that goes to the mother board that needs to be grounded to start the PSU.

Pete.

 

[3v0]

The current version of the sparkfun benchtop supply has an on/off switch as suggested by Sceadwian back in 2011.

I have been playing with the ESP8266. Needed a 5V supply for my old PIR module so I fired up the supply I used in the review. For some reason the supply would shut down when I reset the ESP. According to the specs on the PSU it should have had more then enough current for the ESP. For a while it looked like a 1000 uF cap fixed the problem but no it came back.

So I pulled the plug on the existing supply and hooked up a different one. The new one is stacked on top the ailing one but it works. Good enough for now.

The ESP is another topic.