Wacky controls

[ChillerGuy]

Ran across an interesting problem with a JC P66 speed control for a condenser fan motor. Fan motor is 230/1/60 on a 460/3/60 unit. Used step down transformer to get 230 volts.Control requires 24 volt power supply for transducer.
Used 24v of of units controls which was fed from a separate power supply. Wired everything and speed control would not work. Jumped across speed control and motor ran at full speed. Replaced P66 control and still didn't work correctly. Broke down and read instructions on P66 and it said 24v had to be on same phases as motor. Installed 230/24v transformer using L1 and L3 (same as 460/230v transformer) and everything worked. My question is why the 24v from separate feed did not operate control.

 

[RadarRay]

The way I interpret what you said is the first supply from a separate source was a DC supply, but the second source you used was a 24 volt AC signal supplied by a step down transformer.

Was the first supply an AC supply or DC supply?

Even if the first supply was AC there could be issues. I don't know the specifics of the controller, but usually when you have to connect from the same supply it is because of a phasing issue. Using the same supply means the controller knows the phasing of the supply. A separate supply could be out of phase.

 

[ChillerGuy]

Both supplies were 24vac.

 

[RadarRay]

I tried a search for the JC P66 controller but found nothing. I believe it is either a phasing issue or a common issue. You would have to have a diagram of the circuit if you are going to try to figure this out.

Phasing problems were common with old DC drives. In first reading I assumed the controller was IGBT, since it is for AC but considering it is single phase it could be SCR or Triac based which would definitely bring up the phasing concern.

To understand phasing remember your facility is getting three phases supplied to it ABC. The controller may be wired to AB. Your second supply may be AC or BC, thus the phasing would be off. Note if it was connected BA, even that could be a problem. If they are specific in their instructions, that a certain power input is connected to a certain control input, (i.e. a wire to power input 1 must be connected to control input 1), then your circuit is sensitive to this type of phasing error.

 

[busbar]

It is possible that the 1ø controller used triac or SCR gating to vary the motor speed. Gating of the triac relied on a combination of 24VAC control and 230V sine waves peaking and zero-crossing at the same moment. With control voltage on another phase, the controller may not have been able to “keep up” with out-of-sync waveforms.

 

[advidana]

If soild state controls they may have sensors like a car computers to see if every thing is running right -if not it will shut down.

 

[jbartos]

Suggestion: The complete schematic diagram would be necessary to answer the question correctly.