Tech help

Hi David,

We should have more details to give you good advice. If they are AC relays and you are powering them with 24 VAC the capacitors will not likely do any good.  A microsecond spike to 0 volts would not be enough time to cause a relay to drop out. How are you driving these relays, switch, triac, or other relays? As much information as you can supply will get you a better , more to the point answer.

John

These relays are in a VFD motor circuit, the relays are P&B double pole plug in/socket relays located in the run circuit. We have a ups suppling power to these controls/relays. On transfer of power via the ups, from line to battery back-up, I loose the run command because the switching time of the ups drops power to the relays for a micro second, which drops out the controls. i need ride through, to allow the relays to hang in through this interruption 

I am not an engineer just a technician. You will have to pardon me if I keep asking questions. The relays that you describe are between the VFD and the motor and they control whether the motor is on or off? The circuit that decides whether these relays are energized or not is also powered by the same power source which is backed up with a UPS? If this circuit that energizes the relays has a micro processor it is likely the switch over to backup is triggering a reset of the microprocessor and thus you loose power to the relays. I may be wrong but chances are that the relays in question may be switching AC but they are more likely energized by DC. The circuit that energizes the relays has to have a power supply of its own. If we can improve this power supply with a larger capacitor or maybe even a super capacitor then the power supply to the brain that controls the relays will not reset during the switch over of the UPS. Once again I am just guessing at this point but if you focus on the circuits that energize the relays as opposed to the relays themselves you may be closer to a solution.

John

If the coil is DC and driven by a transistor on the ground side, the power side of the coil may need to have a diode in series with its power lead and a capacitor large enough to hold the relay on through the dropout period. Without the diode the capacitor would need to hold up everything connected to the power rail. The signal turning on the transistor may need a similar diode and capacitor to stay on during the dropout.

If the coil is DC and driven by a transistor on the ground side, the power side of the coil may need to have a diode in series with its power lead and a capacitor large enough to hold the relay on through the dropout period. Without the diode the capacitor would need to hold up everything connected to the power rail. The signal turning on the transistor may need a similar diode and capacitor to stay on during the dropout.