Mach3 5 Axis China BoB: 5 V Versorgung

warumm nutzt du denn nicht einen einfachen stepdown wandler
LM65xx reicht
oben linke im bild
12V und 5V
a 2Euro

General:
Printer port works with 5v but has no +5v supply on the plugs.
The ic's getting signals from pc to drive the step/dir need a supply(5v best)
The easiest way for the manufacturer is to have USB port so there 5v can be feed in. Me personally preferes to get them from pc supply. (There ares different ways to do it, using a double typ A cabe is easiest. And as the stepper drivers are normally quite neat to the job and also galvanic isolated 5v are emv save enough.

Another story is the reading of contacts. They are influenced by higher emv as longer distances are requested. I've only seen them realized by optocouplers. Therefore u need a second and better higher voltage. That's why you always find additional borns to supply external +. ( Also used to allow a 0-10v output swing, that would otherwise not be cheapo to do)
The grounding is a bit of philosophy. As boards are often cheepo, both negative supplies are often connected so you have no choice anyhow. But that means you easily run a "ground loop" over external supply and printer/USB cable. So try to keep these cables near to each other's.
Myself if the hw allows I always connect negative to ground only via a resistor in parrallel with a capacitor. One time to avoid high current low frequency mass loops with higher frequency short gutted and on the other side gives that the possibility to measure on the resistor if something is not good in your cabling or electronic.
If you understand these things it is not to difficult to "re-engineer" a cheapo job without good documentation.
m5c Mike

Wovon? Von der E-Box? Diagramm ist oben

Ist noch nicht viel zu sehen

Mike_Eitel wrote:

Another story is the reading of contacts. They are influenced by higher emv as longer distances are requested. I've only seen them realized by optocouplers. Therefore u need a second and better higher voltage.

Basically you are saying you have one circuit for the endstops running at a higher voltage and a board with optocouplers close to the bob to reduce EMV?

Mike_Eitel wrote:

The grounding is a bit of philosophy. As boards are often cheepo, both negative supplies are often connected so you have no choice anyhow. But that means you easily run a "ground loop" over external supply and printer/USB cable. So try to keep these cables near to each other's.

I measured the board/drivers and ground doesn't seem to be connected in the drivers. Same for endstop circuit vs digital IO part of the bob

Mike_Eitel wrote:

Myself if the hw allows I always connect negative to ground only via a resistor in parrallel with a capacitor. One time to avoid high current low frequency mass loops with higher frequency short gutted and on the other side gives that the possibility to measure on the resistor if something is not good in your cabling or electronic.
If you understand these things it is not to difficult to "re-engineer" a cheapo job without good documentation.
m5c Mike

Any values you can give me for the capacitor? I was thinking about a 1k to 10k resistor to keep the current in the mA range.

pl7i92 wrote:

warumm nutzt du denn nicht einen einfachen stepdown wandler

Der Step Down Converter hat wahrscheinlich einen gemeinsamen Ground für Input und Output Seite. Damit baust Du einen Groundloop von der Hochstromseite der Treiber zur Digitalseite der Treiber. Ich habe mich mit einem Digitalelektroniker unterhalten und der hat mir das bestätigt und deutlich davon abgeraten. Deswegen arbeite ich lieber über einen extra Powersupply.

spicer wrote:

Beispiel:
Masse ist Masse (0V). Und die sollte immer über alles gleich sein (verbunden).

Ich verstehe was Du meinst, den Satz könnte aber jemand missverstehen. Masse ist immer nur ein Bezugspunkt und eben nicht immer 0V

Siehe meine Messung (der maximale Potenzialunterschied den ich gesehen habe war 6V! Und das bei einem 12V und einem 5V Netzteil)

I'm using a few hundred ohms or maybe 1k and yes as long as I see any voltage something is not OK. There should be no voltage and in fact I try mostly to avoid "high level floating charge".

The capacitor maybe 100n parallel with some small few nano ceramic. These are to shortcut the emv fx. of agressif high current stepper pulses etc. Also I use external stepper driver and sheelded cables with toroids...

Maybe a bit overdone for 24v sensorics and 75v steppers.. Plus all with superb 7i76e.

Noch eine wahrscheinlich dumme Frage: Wo kann ich denn einen Widerstand in den Ground löten, wenn ich eine externe Stromversorgung habe statt USB? Wenn ich den in den Ground der Stromversorgung löte habe ich nur ein paar hundert Millivolt auf dem Board, weil natürlich nichts über die Groundverbindung geht, weil da der Widerstand drin ist. Der Ground zum PC ist ja gar nicht zugänglich.

Die Frage ist ob Deine Stromkreise galvanisch getrennt sind oder nicht. Nur wenn ja, dann besagte Ankopplung machen um hohe floating Potentiale zu vermeiden. Es geht darum Stromschleifen zwischen Masse und Erde zu vermeiden.

Ich halt mich jetzt raus hier.
Aber ich sagte hier mal, dass Masse = Masse ist.
Was soll das Ganze.
Verschiedene Massen produzieren?
Normalerweise ist das genau das, was man vermeiden will!