Electronics > Beginners
Grounding Bench Power Supplies (connecting GND to mains PE)
janoc:
--- Quote from: Benta on March 01, 2019, 09:42:18 pm ---
--- Quote from: magic on March 01, 2019, 09:02:18 pm ---Is it a good idea to disconnect GND from PE in a PSU which was designed that way?
--- End quote ---
A very good point and one that I didn't mention. ATX supplies have a precisely defined function.
Using a modified ATX supply in a lab environment is questionable at least, but defensible when you know what you're doing.
My feeling is that it's not the case here.
In general: confusing/mixing PE with ground is not a good idea.
--- End quote ---
Yep, definitely no messing with the ATX supply, that's asking for a big problem. OTOH, removing the earthing strap on the output of the lab supply should be fine, that one is designed to be removed (or even moved to the other terminal, as required).
Doctorandus_P:
Same thoughts here. Do not modify the ATX by modifying the PE connection.
Your DPS modules are another concern.
They may internally have a buck or flyback topology. and the output "GND" may well be at different levels (if both modules are set to different voltages). The inputs of each of these modules should only be taken from a floating power supply.
With cheap modules such as these the current shunt is often in the GND lead.
If you short the shunt by "random" wiring between all the GND leads of your modules, at best the current measurement does not work, and at worst: "If you connect the supply power with output, the module wil be burnt". (Taken directly from DPS5005 user manual).
Lab power supplies should always be floating. Then you can make connections on the front panel as needed. Use common GND by connecting GND's together, or use them in series, or even parallel.
If the power supplies themself are floating, then you can also mak a star ground on a convenient place and connect them individually to that.
rdl:
An ATX power supply is rarely suitable for use in an electronics lab. If you need to use one, you'll know, otherwise don't.
neo2001:
Thank you all for your replies!
I realize that there isn't simple and easy right/wrong answer for this. It depends on the situation and intended application.
To be honest, I wanted to replace the ATX power supply by the other ones long ago. But I still keep it, since its provides precise and stable voltages, I often use or need. It's also nearly impossible to select the wrong voltage, since every output has it's own colored banana terminal.
janoc:
--- Quote from: neo2001 on March 05, 2019, 05:56:55 pm ---Thank you all for your replies!
I realize that there isn't simple and easy right/wrong answer for this. It depends on the situation and intended application.
To be honest, I wanted to replace the ATX power supply by the other ones long ago. But I still keep it, since its provides precise and stable voltages, I often use or need. It's also nearly impossible to select the wrong voltage, since every output has it's own colored banana terminal.
--- End quote ---
An ATX supply is pretty far from what one would consider "stable" and "precise". They are specified with about +-5% tolerance (that's 11.4 to 12.6V on the 12V rail and 4.75 to 5.25V on the 5V rail!) and the outputs tend to be full of switching noise - the ATX spec for max. ripple specifies 120mV peak-to-peak on 12V rail and 50mV on 5V rail. Many older supplies with poor quality capacitors or bottom of the barrel design are even worse than this.
120mV ripple is going to ruin your day if you are trying to power anything sensitive with it - e.g. various amplifiers or radio receivers.
Even the cheapest lab supply is going to be better than this, especially the linear ones. ATX supply is good to have on hand for things that require a lot of current - such as motors or large LEDs. However, if you need a stable, accurate and clean supply, stay away!
This is one of the reasons why almost everything in a PC has local voltage regulators - the "raw" power from the power supply is simply not good enough. **
Oh and the biggest issue of all - an ATX supply has no current limiting. It does have a short circuit protection but it will happily pump 20+A into your breadboard if you make a mistake, melting stuff or setting things on fire, without ever tripping that protection.
** The other reasons are need for different voltage rails and reducing losses from high current on the 5V and 3.3V rails - it is better to use 12V and down-regulate locally next to the load to minimize the length of the low voltage but high current connections.
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