Motor controller

[Dsg319]

Trying to figure out a control circuit and make sure I am correct in my head lol. Would appreciate any insight or correction. Say I have a pump motor draining a tank when it gets full. Just a small 480v low hp motor. Motor controller is hand,off,auto style with its own control transformer which makes a 120volt control circuit. And to control the 120volt coil is going to be a low and high level switch. Also in the controller will be a 120volt relay for the high level switch and one for the low. The low level switch will activate the relay as a stop button. And the high level switch activate the relays as a start button , if that can make senses. If I am wiring both level switch devices on normally open . The low level should always remained in the close position until dumped below it and once that is done should go back to open and in doing so opening the 120volt control Circuit Deenergizing the motor. And when fluid is back up again to the low it will close Essentially getting power up into the point of the stop button, once to the high level it will close the high level relay closing the entire 120vcontrol circuit energizing the motor. Also forgot to mention both level switches and both relays Will be wired in the n/o position.

 

[ActionDave]

You have the sequence correct. Are you not understanding why it functions that way?

 

[Dsg319]

No was just wanting to make sure I had the way it worked correctly in my head lol

 

[Dsg319]

You have the sequence correct. Are you not understanding why it functions that way?

In what sequence would I need to wire if it was a fill tank instead of a drain tank. I know the high level switch would activate the stop relay and the lo level the start relay. But for some reason having a heck of a time in my head figuring wether the wiring should be on N/O or N/C on both the start and stop relays and also the level switches.

 

[ptonsparky]

We put small TDR in the sequence to make sure the pump Doesn’t short cycle should one of thr level switches get stuck.

 

[ptonsparky]

The overloads would trip and prevent motor failure. Eventually found the stuck start switch. It had been cycling on the stop long enough to ruin the starter contacts. Our tank was fairly large so it would be 1-2 days before crashing again.

 

[ptonsparky]

Draw out a standard start stop with remote PBs. Replace the remote NO start with the NO float or relay contacts. Repeat with NC contacts of the stop.

 

[Dsg319]

Thanks I appreciate it!

 

[tom baker]

Typically there will be a latching relay to hold the pump on after the hi float switch closes- which opens when the pump starts. When the level drops to the lo float that drops the holding relay out. I'll see if I can draw it up.

 

[Inrush Jeff]

Yeah, the latching circuit is critical to prevent chatter while the level is bouncing around at the exact level of either switch. A standard motor start/stop circuit is perfect for this since momentary signals will trigger the on and offs.

 

[Dsg319]

Thanks guys

 

[Russs57]

You can make this as simple as one float switch and no relays. Look at the type of float switch that is used with 120 VAC sump pumps for elevators/basements. The float's cord is tethered to the discharge pipe of the pump. The length of the free end determines on/off points.

Or you can have one relay and two float switches. Put the two float switches in series going to a DPDT relay coil. Wire one contact from hot to the pump motor starter coil. The other contact will go across the high level float to create a "holding" circuit. This holding circuit will keep the relay coil energized when the high level float opens and allow the pump to run until the low level float opens.

If you want to get fancy add another float for an alarm with horn and half wave flasher for the light. Add another relay if you want to silence the audible alarm. Add a HOA switch. Wire it so hand bypasses all floats (and maybe even phase monitor). Add a phase monitor and put it in series with overload relay contacts. Indicator lights are nice and can make the system self trouble shooting. At this point it would be a shame not to have a second pump with an alternator relay

 

[ptonsparky]

You can make this as simple as one float switch and no relays. Look at the type of float switch that is used with 120 VAC sump pumps for elevators/basements. The float's cord is tethered to the discharge pipe of the pump. The length of the free end determines on/off points.

Or you can have one relay and two float switches. Put the two float switches in series going to a DPDT relay coil. Wire one contact from hot to the pump motor starter coil. The other contact will go across the high level float to create a "holding" circuit. This holding circuit will keep the relay coil energized when the high level float opens and allow the pump to run until the low level float opens.

If you want to get fancy add another float for an alarm with horn and half wave flasher for the light. Add another relay if you want to silence the audible alarm. Add a HOA switch. Wire it so hand bypasses all floats (and maybe even phase monitor). Add a phase monitor and put it in series with overload relay contacts. Indicator lights are nice and can make the system self trouble shooting. At this point it would be a shame not to have a second pump with an alternator relay

At this point you need to do a bit of browsing at AD. Even the lowest priced PLC combined with the proper Touch screen will make this small project stand out. When the plant manager gets a text telling him this pump has exceeded the expected number of starts per hour and a second by second data File as proof, you will know success.