Method of decoupling the noise the contactors are causing?

[calico]

noise in power source

In my system i have some ldo regulators with outputs, 1.2V, 2.5, 3.3V and 1.8V. The input to them is 5V from a switching power source. In the system exist also two contactors and the conmutation of them cause some time a hung of the dsp in the board. The board is isolated from the rest of the system, the sensors used are hall effect, or transformers, when i need a digital input there are optocouplers,...
Do you know about an effective method of decoupling the noise the contactor are causing?

Note: to control the contactors i use a relay in serial with each, to let the current pass through their coil or cut it. And i use a phase voltage from a trifasic system of 380V RMS across them.

The power source of 5v is powerd by a phase too, and i have just tried to use different phases for both of them but nothing changed.

 

[jorgito]

Re: noise in power source

Hello calico,

First, control your grounding! Look for ground loops. Be shure that the contactor driver current and load current both close over its own path and it meets to system ground in only one point.

Second try to control noise across the contactor. Use a snubber network such as a RC and/or a varistor. Install it over the contactor if possible, this way you are limiting the area of the "antenna" formed by wiring.

Hope this helps and best regards!