Power Supply Question

I've found that my Pi-3 needs about 5.2VDC to operate properly with a WD pi-drive and regular sized keyboard and mouse.

The supply I built for testing this has an adjustable 5V output. It's a Mean Well RD-50B dual output 5V@4A and 24V@1.4A

http://www.onlinecomponents.com/mean-well-rd50b.html?p=11952931

I added a fuse and current meter to monitor what's happening.

Here's a pic

Scott

Until now, the most reliable solution to give a good power to a consistent project (like the modules I am doing for the PiIoT MuZIEum project is using ATx power supplies.

The only doubt I have is if it is reliable just to shortcut the power pin to make the unit working properly or some kind of circuit should be done, like an emulation of the logic power button on the PC

Enrico

I've used a couple of ATX power supplies like that for running extractor fans in the workshop. So far have proved reliable but are only on for a few hours at a time. I can't see why you would need a special circuit, it is just a signal line that you have to pull low.

It is true... I have read somewhere that the. Atx can be damaged just short circuit the power pin to gnd witjout a resistor... Better to solder just a cable

Enrico

It is true... I have read somewhere that the. Atx can be damaged just short circuit the power pin to gnd witjout a resistor... Better to solder just a cable

Enrico

The kit versions for adapting ATX to bananna plugs often have a space for a high current load resistor to place across the output. I believe it will help stabalise the output voltage as most of these supplies are switch mode. Best not short the outputs though!

So you confirm that a resistor should be placed between the ATX power pin (the green one) and one of the GN pins with a resistor between. What value do you suggest?

Enrico

Not sure if it is still the case or not but a number of SMPS designs used to require a minimum load on the output in order to operate correctly. I'd hazard a guess that the space for the load resistor may be for this purpose, especially if being used as a bench supply where the load may not always meet the minimum load requirement of the SMPS.

Yes, for both "switching powersupplies" and "atx power supplies" stories are going around that they require a lot to operate correctly. One of the devices where you wouldn't expect it are some MEANWELL power supplies. There it seems to me that they no longer guarantee that the output will remain within 5% of the nominal value if the output is unloaded. Not really a problem if you can tolerate say +10%. Just being able to cope with 13.2V is much cheaper in the long run than adding a load resistor.

Similarly, some old ATX power supplies would give weird results, like the 5V rising to 6V or more when only the 12V was loaded. I haven't seen such "weird" behaviour from any supply made the last two decades. (I used to say I had never seen it, but that is no longer true. A few years ago, I grabbed an older  powersupply from the pile of "old spare powersupplies" and it indeed behaved weird and required a load to be stable. That powersupply was built in 1992. )

In practice, it isn't a problem or only happens with very old/odd equipment.

Some power supplies need a load resistor on the power output to be stable, but I have re-purposed 3 PC power supplies using a custom PCB with banana sockets, fuses and switches. The card I designed has room for power resistor loads, but in every case the output voltages were accurate and stable without any load. The power switch just controls the power control signal. Maybe I will post a blog about it....

It will be very helpful ... Thanks in advance

Enrico

You can twist green and GND together or have a switch if you want.

The load is from 5v to GND.

http://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

Very clear Andy! Thank you for the precious suggestions.

Enrico