Did you measure the voltage under load?
You can run a stress test to test it
Where do I need to place the probes to measure under load?
Not too sure.
It's LM2596 DC-DC. I believe the specs are:
Output voltage range: 1.25V to 30V DC voltage is continuously adjustable, high efficiency (maximum 92%) of the maximum output current of 3A.
There where you soldered the capacitor.
It's measuring 4.8v.
By the way, the only load it has is an LED strip connected to the USB port and my Ender3 V2 connected to its USB port.
I would measure it at the output of the converter (to rule out the cable) and at the 5V pin.
You can use the metal housing of the usb ports as ground when you probe the pi. That way the risk of shorting something by accident with the probes should be really small.
ok. so 2 things:
- When measuring the output of the converter, it's 5.3v
- I didn't measure at the end of the cable because it's a micro USB cable and I don't know how to measure the output voltage on a micro USB cable.
That's why I would also measure the voltage at the 5V pin. Then you know what's actually being delivered to the pi.
oh, so if I measure 4.8v at the GPIO pins that means a 4.8v under load? or 4.8v regardless of load?
I'm asking because assuming I'm disconnecting the USB devices from the Pi, I wouldn't want the voltage to spike to say ~6v and fry the little Pi.
Well, that depends on whether you did the stress test or if the Pi was idle and how much the usb devices are drawing.
I guess it's a bad usb cable/plug. Both let the voltage drop at idle and probably even more under load.
But the voltage will not be higher than the one coming from the step-down converter.
I tested the voltage on the Pi without load, it's 5.15v, mind you the step-down converter is set to 5.3v.
With load, it's 4.8v on the Pi.
I thought that this is where the capacitor comes into play. To help provide constant voltage per demand (to some limit of course).
So what are my options here?
It's more for short voltage drops - not for constant undervoltage.
Well your two options are to either use another usb cable or to connect the step down directly to the pi.
If you decide to do the latter, I would recommend to reduce the voltage output of the converter to max 5.1V.
Keep in mind, that the Pi3 has a resettable fuse inline just behind the USB socket.
Once it was activated, it has a higher voltage drop than before.
Oh I didn't know that. I thought it would reset itself to the old state.
But a drop of .5V seems really high, doesn't it?
With 5.0V input the Pi would brown out really fast.
is it good to reset it?
It resets by itself.
When new, the fuse has a resistance of 0.015 Ohms. With 2 Amps current this makes a drop of 0.03 V.
Once the fuse was activated, the resistance is 0.1 Ohms. With 2 Amps current there is a drop of 0.2 V
This is the Power input circuit:
D7 is a protection diode for over voltage and activates at 6.4 V
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