Frame ground vs. "neutral" for DC

Depends on the application. In power wiring code often mandates that scheme. In high frequency gear or fast digital systems that usually does not work well. And for proper shielding of LF fields such as 60Hz you need mu-metal. Expensive and you have to avoid trauma to it (sharp bends etc.). I haven't had to use mu-metal in, oh, 15 years or so.

As we've noted, they were wrong.

Not much, and without care it may actually funnel 60 Hz magnetic fields into your gear. The best defense against magneticly induced hum is to keep loop areas small.

John

Make that 10 schools of thought for the digital folks.

The NEC/UL folks have only one concern with grounds...safety. They worry about power frequency conduction paths that might put dangerous voltages on a chassis. E or H field coupling isn't a major concern, safety-wise at 60 Hz. Proper equipment operation is another thing, but the safety folks just figure you electronics folks can put in enough bypass caps and shielding to fix it.

Nope, 01. Who needs analog, given enough transistors. ;-)

That may be, OTOH, the FCC has other ideas.

I do know some on HF coz i have a tesla coil and it did some wired stuff and stuff that was next to it did not have a gnd had high voltage on it.. just had some fencing on the top that did have a gnd.. take my word for this it was hard to take a photos of it!!!!!

Hi John,

What do you think of connecting circuit ground to chassis only via a 1M resistor (and usually a 0.1uF cap in parallel with the resistor)?

regards

Ian

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Is the intent to keep the board ground at the same potential as the chassis, dc and RF? Why not use bolts?

John

John, what do you think about my control board, does its layout etc make sense to you? Note the machine screw in the middle to which all ground is bolted.

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

That is the intent. Its one of those things that worked once and has been used ever since. Specifically it helped us to pass the static discharge part of the emc tests.

Ian

A lot of the time I need to have the board not at ground potential for DC.

I sometimes do that. If emi/esd is an issue, I use several standoffs, with a bypass cap or two for each one.

John

This is true. One must differentiate between the safety ground, the shield and the return ground and design each appropriately.

how does this sound the circuit that i have for a welder has the gnd form igbt going to Frame gnd and the hole circuit to Frame gnd is a good thing or bad to hook dc- to frame gnd??????

think what would happen if you wanted to weld with DCEN, and connected the work clamp to a grounded object....

the gnd on the -dc side on the input to the igbt... if you look at the circuit

and ir has a application note on ic IR2110 and they are an easy driver setup

and i have looked in a pc power supply and dc gnd is in ac gnd and that would mean that the whole motherboards dc gnd would be on ac gnd

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so what do you think????

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I think that having one side of the welder grounded, and connecting to a grounded object with another side, (say having negative grounded and connecting to a grounded object with a positive "work clamp") creates a short. Not a very good thing at welding currents.

I personally would really appreciate if you tried to make some effort to write more clearly. I am sure that I also am often unclear, but at least I try to be clear.

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I will try to be clear

well a mig welder has the dc ground on ac ground. did you look at the circuit???? the point wear the ground is at should not get + dc

I am not sure about MIG, as MIG is done with DC electrode positive, I think. Not as big of an issue with grounding a negative side.

With DC electrode negative, like with stick or most TIG welding, or with AC (which is sometimes electrode negative and sometimes electrode positive), grounding the work clamp (positive) would result in a short.

Do you agree with that?