V3c dubbio sulle masse

Da superrobin Gio 4 Feb 2010 - 8:33

L'amministratore non me ne voglia se apro un nuovo topic riproponendo una domanda già fatta nel mio topic precedente

Ho un dubbio sulle masse, sull'SMPS tra il GND della 220 e il GND della +-Vcc misuro 20 milli ohm, e in effetti quando è acceso tra il ground della Vcc e la terra misuro una differenza di potenziale di circa 0,1 millivolt

è ok così o farei meglio a collegare a terra anche il GND della Vcc?
premetto che quello sul lato 220 è collegato alla terra della spina insieme a tutto il cabinet

è la prima volta che maneggio un alimentatore switching e amp ad alimentazione duale, non vorrei fare qualche cavolata, o quantomeno creare un famigerato anello di massa

grazie

Da Cristi Ven 5 Feb 2010 - 11:49

the smps protective Earth pin 3 of the mains connector is connected to secondary GND through a small resistor and capacitor. you can find them behind one of the big capacitors, close to the heatsink. the reason why i connect like this is to avoid GND loops and noise. if you experience noise, you can increase the value of the reistor up to 10R. do not leave the smps without this connection because not only will alter the noise ratio and increase EMI, but it will create flux imbalance in the transformer and lead to staircase saturation which can trigger the over-current protection or even damage the smps in some cases.

Da superrobin Ven 5 Feb 2010 - 12:40

Ok Cristi, so if I've understood well, I connect to earth ground just only the smps main GND (220 supply site) and NOT the GND on the +-Vcc side

Thanks

P.S.

I'm going to separate coupling cap and pot department from amp with an iron plate; while I was aware of EMI contaminations issue on big coupling cap, I've probably underestimated the magnitude, and this issue could lead to the lack of transparency and precision the I've noticed, without any signal input I can ear a little hiss coming out from the tweeter ...

Da Cristi Ven 5 Feb 2010 - 13:06

the secondary GND is connected to Earth, not primary GND. let's not create a confusion. is not allowed to connect the mains GND to secondary GND, since this will carry the mains voltage and can lead to electric shock hazard and possible damage for the amplifier.

Da superrobin Ven 5 Feb 2010 - 14:22

ehmm

just to avoid a possible misunderstanding, I connected to the earth ground only the GND pin on the main 220V side; the cabinet also is connected to ground

My concern was if should be better to connect to earth also GND pin on the Vcc side, but in this way I would put in contact the two GND on the smps, and I'm afraid is not a good thing

Thanks Cristi

Da Cristi Ven 12 Feb 2010 - 4:51

i think i don't understand what you mean. the idea is simple:
there are 2 GND's one in primary side and one in secondary side and one Earth. the secondary GND is connected to Earth though a resistor and capacitor. primary GND should be NEVER connected to secondary GND or earth.

Da Fabio Ven 12 Feb 2010 - 9:39

Cristi ha scritto:i think i don't understand what you mean. the idea is simple:
there are 2 GND's one in primary side and one in secondary side and one Earth. the secondary GND is connected to Earth though a resistor and capacitor. primary GND should be NEVER connected to secondary GND or earth.

Excused me for a question.
I dont speak, and write, english well, and probably I have not understood something.
Is the primary GND connected to the earth or secondary GND inside SMPS in some electric way? or is smps circuit class II isolation certified?