Auto Transfer Switch Question

[benaround]

OK, Jim, explain to me what is goig to happen when the pressure on the

system falls below the set point, based on how it is now proposed.

 

[jim dungar]

OK, Jim, explain to me what is goig to happen when the pressure on the

system falls below the set point, based on how it is now proposed.

The OP has existing motor starters and control systems. He simply wanted an "automatic" method to replace the existing manual transfer switch.

 

[crossman]

I see Benaround's point. Without further information, it seems that when the pressure falls below setpoint, the transfer contactors just may be shutting off the first compressor under load. Possibly more thought needs to go into the control scheme.

 

[mkgrady]

I see Benaround's point. Without further information, it seems that when the pressure falls below setpoint, the transfer contactors just may be shutting off the first compressor under load. Possibly more thought needs to go into the control scheme.

I was thinking the pressure drop would be because the main compressor stopped running due to some malfunction. In other words, it is off. The air tank, wiich is very large, would continue to supply air until the pressure dropped below normal.

Then the pressure sensor I install, which is not part of either compressors control circuit, would tell the transfer contactor to close/open. It is my goal to stay out of the control schemes of each compressor. I just want to transfer power from the main compressor to the backup. I don't want to get a call if and when the compressors don't work, just if one of them doesn't have power.

While the contactor transfers in either direction the motor starter will be off. When the contactor is done closing it will power the normal control circuits that turn on the backup compressor. So upon closing or opening of these two interlocked contactors they are not doing so under load. Am I wrong?