Computing > General Computing

PSU: Measuring Current From SATA Connection?

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DW1961:
How would I go about measuring current from the SATA power connection from the PSU? I need to make sure I'm not overloading the 4.5Amp connectors.

Is there a pass through SATA connector available I could use to connect a DMM so I can see the current?

mariush:
you could just get a molex -> sata adapter cable or a sata -> 3-4 sata extension cable , cut the 5v and/or 12v wires and solder in current sense resistors (ex 0.1 ohm or something like that)

or just cut the wire of your atx power supply if you don't care about it.

Berni:
If you have a current clamp you can just put the wire you want to measure trough it.

But for splicing into things i like to cut up various random adapters that i might have laying around. Those molex to sata power adapters are pretty common, there are some sata power splitter adapters, sometimes fan power adapters have a passtrough design having both a female and male molex/sata on it, there are some molex to 6 pin PCIe power adapter cables (for graphics cards)...etc. Old ATX power supplies can also be cannibalized for the connectors.I keep a box of random computer cables for cases like these for when i need to hack something together.

But keep in mind that adding a multimeter in series introduces extra voltage drop. Probably fine for the 12V rail but might cause too much drop on 5V or 3.3V rails if the currents are high.

David Hess:

--- Quote from: DW1961 on July 30, 2021, 04:46:33 am ---Is there a pass through SATA connector available I could use to connect a DMM so I can see the current?
--- End quote ---

There are SATA power splitters which could be used as a pass through connector.  The have a female SATA power connector on one side and a male SATA power connector on the other.

mariush:

--- Quote from: Berni on July 30, 2021, 05:43:41 am ---
But keep in mind that adding a multimeter in series introduces extra voltage drop. Probably fine for the 12V rail but might cause too much drop on 5V or 3.3V rails if the currents are high.

--- End quote ---

IF you put the multimeter in series yes, you'll have to deal with the multimeter's burden voltage and the resistance of the probes.

BUT if you solder a low value resistor with a good temperature coefficient so the value won't change significantly as it heats up from all the power going through it, then you can use the multimeter in voltage mode and measure the drop across the resistor... and you can also measure the actual voltage after the resistor with a second multimeter and then you can multiply actual voltage with current and get your power.

For example, a 1 ohm resistor will cause a 1v drop across it at 1A  of current.
But you can go down to 0.1 ohm and then you'll only have 0.1v drop across the resistor at 1A of current... and you'd just have to multiply by 10 the voltage measured across the resistor to get your current value.

It's the technique Dave's uCurrent uses ... only that device uses much lower value resistors and  a precision opamp to amplify the voltage drop across the resistor before it's measured by a multimeter

IF your device needs 5v, you can use a linear power supply, set the voltage to something like 5.2v and measure your device - I doubt your device must have 5v and really can't deal with +/- 0.25v

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