Ground noise

[checonbill]

I have 3 pieces of equipment 1)2-DC electric seam welders
2)AC electric seam welder

These both operate at a very low voltage (5V) and high current (60 A 480V primary) using a high fequency firing circuit all welders have 1 side grounded.When operating the DC welders by themselves all is well. I f I operate either DC welder with the AC welder the weld is very eratic on the AC welder and fails quality tests. As a test I moved the feeder from the AC welder to a seperate source (We have 2 main services to the facility) this did not make any difference to the problem. I then removed all common ground connections to the AC welder and the problem dissapeared. Is there a good fix to this problem maybe a way of isolating the ground fron the pieces of equipment. I do believe there is noise on the ground coming from the DC welders. Any help in which direction to go would be greatly appreciated

 

[Skogsgurra]

I have reduced HF noise using ferrite toroids on the cables. It is the same technique that you see on every computer power supply cable.

The problem is that you cannot put a toroid on one cable, because it gets saturated by the high DC current. So you have to get a large aperture core that can take both + and - cables.

On the other hand, it is not 100 percent sure that it is the HF noise that is disturbing the weld. If, for instance, there is a common path for the return current to both welders, then the mutual voltage drop influence may very well do bad things to the weld. At these high currents and low voltages, half a volt can make a big difference.

Gunnar Englund

http://www.gke.org

 

[itsmoked]

Gunnar makes some very good points.

Do these welders all have two cables running to the tips and the tool fixture? Or are all the tool fixtures tied together and then back to the machines?

Are the dc machines straight 60Hz rectified? Or are they SCR controlled?

Is there any trickery like high frequency ignition on the AC unit?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[checonbill]

The welders are connected solidly by electrode rolls one on the top of the material and one on the bottom.

The DC welders are SCR controlled

The AC welder does have a firing circuit for frequency control

Thanks for any help