Go Down

Topic: will it go bang (Read 926 times) previous topic - next topic

jonisonvespaa

Dec 01, 2016, 10:04 pm Last Edit: Dec 01, 2016, 10:05 pm by jonisonvespaa
ok, im 100% sure it will just checking,

im building a circuit inside a metal box, its totally shielded to mains earth to try to reduce noise

i have a power supply inside im gong to experiement with c's all over the place to try to reduce noise on the supply, im pretty sure it will if i connect a c from the 12v power supply gnd, to chassy / mains earth will it go bang?

TomGeorge

Hi,
DO NOT CONNECT IT TO MAINS SUPPLY.

If you need to ask this question and do not provide a circuit diagram and pictures, it seems to me you do not know enough to even attempt what you are proposing.

You NEVER connect AC to gnd.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

ricky101

+1


Why would you even want to connect ac to the earthed case ?  or do you really mean connecting the power supplies 0v 'ground'  rail to the earthed case ?


Enclosing a project in a sealed metal box is usually due to poor project design or layout.

You might be better detailing your project and what probems you have experienced to make you look at metal boxes and modifiying power supplies.


jonisonvespaa

#3
Dec 01, 2016, 10:41 pm Last Edit: Dec 01, 2016, 10:50 pm by jonisonvespaa
No i ment 12v gnd,

add a capacitor between this gnd to chassy gnd, ie mains earth.


Im trying to use a prosessor very close to a very  noisy frequency inverter which is why im trying lots of different things to get it to work, im kind of encasing it in a metal box inside a metal box to try to minimise noise

Southpark

#4
Dec 01, 2016, 11:15 pm Last Edit: Dec 01, 2016, 11:18 pm by Southpark
No i ment 12v gnd,

add a capacitor between this gnd to chassy gnd, ie mains earth.


I'm trying to use a processor very close to a very noisy frequency inverter which is why I'm trying lots of different things to get it to work, I'm kind of encasing it in a metal box inside a metal box to try to minimise noise
For a "DC" system, it's not unusual to have a capacitor connected to chassis ground (mains earth) if the negative rail of your electronics is also connected to mains earth. But.... if it's an AC system, it would be unusual.

jonisonvespaa

#5
Dec 01, 2016, 11:26 pm Last Edit: Dec 01, 2016, 11:27 pm by jonisonvespaa
Ok great ill experiment then with some c's

Im using an 240v in 12vdc switch mode supply so ill check to see how the gnd is connected

Thank you

Grumpy_Mike

Quote
No i ment 12v gnd,
That is fine. As long as the 12V supply is somewhere along the line isolated from the mains then no harm will come. It would be unusual for it not to be isolated.

If you think about it, when ever you make a measurement with an oscilloscope the ground signal of your probe is connected to the mains earth. So when you clip the ground of the probe to the ground of your circuit you are doing exactly the same thing.

jonisonvespaa

#7
Dec 01, 2016, 11:32 pm Last Edit: Dec 01, 2016, 11:33 pm by jonisonvespaa
I was going to experiment with low value, medum, and large c's  see if improved things,

Thanks very much

Southpark

#8
Dec 02, 2016, 12:41 am Last Edit: Dec 02, 2016, 12:52 am by Southpark
That is fine. As long as the 12V supply is somewhere along the line isolated from the mains then no harm will come. It would be unusual for it not to be isolated.

If you think about it, when ever you make a measurement with an oscilloscope the ground signal of your probe is connected to the mains earth. So when you clip the ground of the probe to the ground of your circuit you are doing exactly the same thing.
True!! Brings back memories ...... of the older days.....  like the BWD 530A, with the metal earth clip for providing the option for earthing or not-earthing the ground.

.....click here for picture.....

But then big brother stepped in and said 'hey, we know what's better for you, and your safety'.

Grumpy_Mike

Quote
But then big brother stepped in and said 'hey, we know what's better for you, and your safety'.
How true that is.  :smiley-confuse:

Before molded plugs you could disconnect the earth pin and have it hanging out of the plug to tell you it was floating.

TomGeorge

Hi,
Can you post a picture of your project and can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Most SMPS have capacitors already fitted between DC output gnd and chassis gnd.

Thanks... Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Go Up