Motor control question...

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JacksonburgFarmer

JacksonburgFarmer

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Location
Butler County Ohio
I have a customer wanting a setup as follows....
He has a 7.5 3phase motor driving a grain auger. He would rlike the following to happen. When the motor driven auger is loaded (is actually moving grain), for a small 120v 3amp pump to kick on and treat grain w/ some kind of chemical. When the 7.5 horse motor is off, OR, if the 7.5 horse motor is not loaded, (running the auger, but no grain to move), the small electric pump shuts off. When the auger is again loaded, the pump restarts. My thoughts are that to shut the pump on/off, would be done by reading amps of 7.5 motor. Could i use a overload relay, set the overloads to trip when the motor pulls more amps than at empty auger, and run a contactor w/ coil controlled by auxillary contacts of overload relay? Clear as Mud? I think it will work but thought I would ask you guys...Thanks ahead..:)
 
JacksonburgFarmer said:
Could i use a overload relay, set the overloads to trip when the motor pulls more amps than at empty auger, and run a contactor w/ coil controlled by auxillary contacts of overload relay?
Click to expand...

Many companies make current switches just for this purpose. Two that I have used are: RIB (relay in a box) and NK Technologies.

This is not a good application for an overload relay.
 
re

re

They also make a Current Sensor that is adjustable with N.O N.C output contacts, you may have to follow up on the current ratings of the contcts here is a part number


"NK TECHNOLOGIES, AS1-NOU-FT
^^SWTCH:CUR SENSING,FIXED CORE W/
FIXED CORE AC CURRENT OPERATED SWITCH, RANGE:1-150AMPS AC, OUTPUT: .15A @ 240VAC. USED IN B29 COLD ROOM ON AUX #1 CONTROL PANEL."

Just a thought...
 
What loads the grain on to the Augur?.. or is it removing grain from a silo?

Is it manual or it is a conveyer? If it is manual then current sensor is the way to go..but if it is fed by another conveyer, then AuX contact of conveyer contactor can be used to start the chemical dosing pump.

Cheers.
 
the ol relay is not the way to go Who is going to constantly reset the relay?? a relay set up with a current sensing ct under load with dry contact type ct to turn on relay when elevator is under load. This is an explosion proof installation I presume??
 
jim dungar said:
Many companies make current switches just for this purpose. Two that I have used are: RIB (relay in a box) and NK Technologies.

This is not a good application for an overload relay.
Click to expand...

How funny I was looking for one last week... Here But I too, do not think this a good application for a current switch or sensor.

acuamp_acs200_300.jpg


However - you may find this type of operation unreliable for the purpose.... May not be sensitive enough to sense other than a heavy load, or like mixing concrete varied conditions of the grain may act differently on different days due to weather etc. or what have you.... Other loads on the transformer serving this equipment may vary voltage from time to time, and then throw current and this set up out of wack. As you are looking for a very specific amp range - from unloaded to very lightly loaded. Otherwise you would not get consistant results of mercury coating on the grain at the start or end of each load.

Why not make the auger (unknown starting method?) act independantly of the poison hose of death infecting the food. Sorry... Act independantly of the chemical pump. You could have a paddle operate a limit switch in the shoot where the grain comes out of the auger - or even in the auger. Simple - effective

But if shooting for high tech.... A capacitive proximity sensor to sense the grain. Or light beam?

Check this out...


Sorry - just cant get over the use of the word "chemical" and grain(food).... Even if it being fed to pigs... I eat pigs! :cool:
 
With motors the use of just current to determine load v unloaded conditions often doesn't work. You can use a product like this for that purpose. I have used a number of them to shut down pumps on loss of flow, however they are somewhat expensive.
 
don_resqcapt19 said:
With motors the use of just current to determine load v unloaded conditions often doesn't work. You can use a product like this for that purpose. I have used a number of them to shut down pumps on loss of flow, however they are somewhat expensive.
Click to expand...

I agree that current alone is unreliable because current can change with voltage fluctuations and is unpredictable at low loads due to power factor issues. For this project, that Load Controls unit may be a bit of overkill though. There are also relatively inexpensive load monitor relays such as this:
Siemens Active Power Monitor
Active Power monitors look at the current, voltage AND power factor to calculate a direct linear response to actual shaft power load, so it is insensitive to line voltage changes and motor power factor alone. It only looks at 1 of the 3 phases (vs the Load Controls product which looks at all 3), but it is 1/4the the cost. There are 3 or 4 other similar products from small manufacturers out there like this. You can do a Google search on "Load Monitor Relays".
 
How about using an allen-bradley slick504? A small rack with i/o could easily contol the 3 phase motor, interface with the 120 spray pump, and sensing equipment. Adjusting time cycles and sensing (4 to 20 milliamp) devices are really easy. The initial installation costs may be higher but the long term flexibility usually pays off.
 
frenchelectrican said:
Lightbeam ??? I hope you relized how much dust the grain can kick out and can really screw up the lightbeam.

IMO the flow switch is better suited for this appacation.

Merci,Marc
Click to expand...
Depends really.... On how it is designed and installed. True a lot of dust caked on it directly would be a problem, but have seen installations where whatever it was (coco powder I think) - was going in a tube past windows. And the light beam goes through them....

Apparently some do better than others in dusty places?

Anyway probably a hundred ways to do it....
 
What controls the grain to the auger? If there is a gate valve install a switch there... I might even suggest a pneumatic gate valve. Open equates to flow of grain. You might also consider a Time On Delay relay to delay starting pump for the given distance of the screw. I'm guessing there is some timed system which starts the screw, this might also open the gate valve on delay and shut off the screw off delay.
 
I agree that the small ct's (pictured by e57) should not be used. We've used them for monitoring heat trace circuits and they are fairly tricky to get dialed in. May be a problem with load caused by different amounts of grain on auger at any given time.
 
080608-1629 EST

Jacksonburg:

Can you provide a photograph of the auger, its relationship to where grain is fed in, and where the spray nozzle is located?

Also can you measure power input (not VA) to the motor when no grain is present, the minimum grain that needs to be detected, and when the auger is fully loaded?

If the ratio of no-load power with auger turning to the load power with the minimum amount of grain that must be detected is reasonable and stable, then I like the power measurement method.

Assuming a balanced load from the motor you could use a single phase wattmeter because all we need are ratios. But you need to measure the voltage and current that correspond with each other. With a Y connection the current in a leg and and the voltage from that leg to neutral. In a delta load measure leg to leg voltage and the current in the path between those two legs.

.
 
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