Supply voltage causing damage to circuit board

[rockman7892]

We have a circuit board for a VFD which keeps buring up. (Relays buring up) The supply voltage to the circuit board is coming off of a 480V to 120V control transformer and the supply voltage to the circuit board is measured at 126V.

The circuit board manufacturer has stated that this 126V is too high and that the supply voltage should be as close to 115V as possible. I have installed a Constant Voltage Transformer to keep the supply to the board at 120V exactly even during surgers.

Is there anything else that I can be overlooking here? Anything relating to grounding?

 

[Renovator1]

I'm inferring that it is the coil burning up on these relays, but I have never encountered any for 115VAC operation that are *that* sensitive the voltage... UNLESS, the coil is for *60Hz* and you are applying the higher voltage at a lower frequency, e.g. - 50Hz. Then I could just about believe there might be a problem, but it would still be a stretch.

For example, a small 115VAC relay draws 12mA at 60Hz (1.38W); at 126VAC it will draw 13mA (1.64W). This is hardly going to be the difference between 'working just fine' and 'burning up'.

What is the relay for in this VFD? Is it, by any chance, what would more properly termed a contactor (e.g. - a "large" relay?)

 

[rockman7892]

These relays are on an interface board to the VFD. They are small little contact relays used for inputs to our DCS.

I'm not sure what these small relays are rated for, but they are used for providing input feedback from the VFD.

 

[automatic2]

Had a similar problem recently but at a 230vac input.

In our case we where using a VFD to change freq/voltage into a stepdown, which was then tranx again to the 230vac control. Our only solution was to obtain the 230vac via stepdown directly from mains, bypassing the VFD.