I just want a simple start and stop of a large 10 hp AC electric motor, and possibly some feedback that it is running. I've attached the wiring diagram of the current switch box. I've was thinking i'd be able to use a relay where the start and stop buttons are currently. But i'm not sure how big of a relay i'll need. Also is there a senor that I could use in conjunction w/ the relay's that will let me know that the motor is running or not?
many thanks,
20160705090351.pdf (239 KB)
What you have here is a 3 phase motor starter, using 2 phases to start the motor and one phase as a current seal in. I don't know what size starter it is. If it is a smaller starter, a 10 amp relay should hold the coil in.
Up to a NEMA Size 4 contactor at 230VAC it should take less than 5 amps (inrush) to pull the relay in and a lot less to keep it held in. If you have a larger starter, you may need a larger relay with a interposing relay to pull it in (I've found it difficult to find more than a 10 amp relay board that can be tied to the Arduino).
As far as feedback that the motor is running, I would try to pick that up down stream of the stop button. The voltage is 230 VAC at this point, so you would need to get it down to a DC signal that will not blow up your arduino. If the starter has an AUX contact, it is possible to get the run feedback through that, but a 5VDC signal would be very prone to interference from the starter.
If I were to wire up the circuit, I would parallel a N.O. relay with the start button and place a N.C. relay in series with the stop button. That would allow the local start and stop button to work. Since the coil seals itself in, the relays would be momentary.
The circuit ringed is not a 3-phase anything.
MarkT:
The circuit ringed is not a 3-phase anything.
Nope, but the starter shown is a three phase starter wired for single phase use.
nathancamp:
Nope, but the starter shown is a three phase starter wired for single phase use.
Not if it has thermal overloads built into the contactor. If the overload trip is part of the contactor arrangement then it is essential that all three contact sets carries the load current otherwise the device will trip on what it "thinks" is the loss of a phase.
jackrae:
Not if it has thermal overloads built into the contactor. If the overload trip is part of the contactor arrangement then it is essential that all three contact sets carries the load current otherwise the device will trip on what it "thinks" is the loss of a phase.
I looked at the schematic again and you are right, the drawing shows only one thermal overload.
In any case, I think a 10 amp relay should pull the contactor in.
so would something like this work?
I wouldn't trust a large expensive installation like that to those cheap "toy" relays. Do you have a link or part nr for that starter? If its all built into a "block" with inaccessible internal connections, it may be a problem, can you post some pictures?
Also if the remote station is not within sight of the motor, you have to think about safety, you should have a local / remote switch and an emergency stop switch local to the motor.
I agree on using quality components, but i have no idea what quality is.... Here are some pics that should help put the rest in perspective.
Well, all that stuff is very familiar, how about a picture of the front of that Telemech button.
it is a centrifugal fan....
