Wiring Motor Start Contactor Problem???

horrorsix

Member
Location
Harrisburg PA
IMG_3442.jpg

Attached is a picture of a motor start control assembly that we built. This is for a large conveyor system. The owner opted ,for some reason, NOT to go with the company who designed the conveyor system and get the factory built PLC control unit. Motor controls are not my specialty but these are long time customers of mine and they asked us to build this old school with contactors. On paper this should work but we're having a problem. I'll explain the problem and then how we have it wired. If anyone has any feedback that would be great.

Problem: Various contractors intermittently are not pulling in far enough and humming like hell. Not one contactor is consistently failing. It's like the all the coils are not getting enough power. Sometimes they work sometimes they don't.

Wiring: There are 15 motor control contactors. All coils are wired from the same 20A/120V circuit. All contactors are 25A 3 pole and all are wired in parallel.. There is a delay relay that turns the signal on for 5 sec. then turns all the motor start contactors on. The contactor in the picture labeled the power start is the first contactor where the emergency stops are wired through. Right now the emergency stops are jumped out and there is no power to the motors. The only thing powered are the coils. We were just testing the contactors for their operation. All contactors are engaging and the delay relay is turning the signal on and off but the the contactors are not all pulling in all the way. You can physically push them in and get them to quiet up.

Coil voltage is 122V and amp draw is .8A

Is there something I have wired wrong?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Are you sure that the coils really are for 120V?
And that the wires inside the panel are large enough to handle the inrush current of all coils simultaneously?
Each coil needs to have full voltage as the contacts are moving initially. Otherwise the momentum may not throw the contacts far enough that the pole pieces can hold them all the way against the contact spring force.

Tapatalk!
 

horrorsix

Member
Location
Harrisburg PA
Are you sure that the coils really are for 120V?
And that the wires inside the panel are large enough to handle the inrush current of all coils simultaneously?
Each coil needs to have full voltage as the contacts are moving initially. Otherwise the momentum may not throw the contacts far enough that the pole pieces can hold them all the way against the contact spring force.

Tapatalk!
I'm pretty sure the coils are 120V. That's what I ordered. I have a feeling you're right though. Is the inrush voltage listed in the contactor specs? I'll have to check into that. That's exactly what's happening though.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
How much wire and how many control devices are in the coil circuit? It sounds like excessive voltage drop. As suggested by Augie, if there is a control power transformer, it may be too small.
 
Coils are 120V. I'm getting that straight from the panel. Is that the problem? not stable enough?
What does "straight from the panel" mean?
This sure sounds like a control transformer that is too small for the simultaneous inrush from the contactors. If so, you could split them up into two or three smaller groups with some time delays. Or put a larger transformer in.

That PLC system they passed on probably avoided turning all the contactors on at once.

w piper
 

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Brewery Engineering Plant Technician - HVACR Electrical and Mechanical Systems
TDRs

TDRs

Time Delay Relays of various types are used extensively in HVACR Control Panels and they are notorious for giving the types of symptoms you are describing when they fail, or sometimes when they are applied outside of their design range. As an example ICM makes a lot of devices, and they are sensitive to milliamps within a certain range. I would look at the way the TDR is being used based on what has been described. They can be very temperamental and sensitive devices if not used in a certain envelope. Sometimes talking to Engineering for the device in question can be helpful. This kind of thing is particularly noticable in 24V control circuits where you can quickly lose the necessary VA as some would term it to pull in downstream relays.
 

kwired

Electron manager
Location
NE Nebraska
The fact you mentioned voltage is 122 and current is .8 tells me these are likely not 120 volt coils. If the supply was a transformer not sized large enough you would have a pretty significant voltage drop.

.8 amps seems pretty high for a single contactor coil on units this small @ 120 volts, but if they are not pulled all the way in current will be high.

That type of contactor will not have coil voltage marked on the main data information that is generally for the contacts themselves, the coil is replaceable and not marked on the main data, you need to look at the coil itself to see its rated voltage, should be marked near the coil terminals.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
.8 amps seems pretty high for a single contactor coil on units this small @ 120 volts, but if they are not pulled all the way in current will be high.
:thumbsup:
The coil current in an AC coil will be primarily inductive. Once the pole pieces in the magnetic circuit come together, the inductance becomes much higher and the current drops.

I too wonder whether the time delay relay and its wiring are adequate for the inrush current. Possibly that relay has already suffered contact damage?


Tapatalk!
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
:thumbsup:
The coil current in an AC coil will be primarily inductive. Once the pole pieces in the magnetic circuit come together, the inductance becomes much higher and the current drops.

I too wonder whether the time delay relay and its wiring are adequate for the inrush current. Possibly that relay has already suffered contact damage?


Tapatalk!
I think GoldDigger is on to something there. Can't read part numbers, but I can see the UR mark, which means these are Definite Purpose (junk) contactors, Eaton, and 25A 3 pole, so it's not hard to find that they are C25 series. Coil inrush is 74.69VA per coil, that photo shows 16 coils. If they all turn on at once, that is 1195 VA of coil power, which will amount to basically 10A of coil current. But that is 10A of INDUCTIVE current, and although most timers like that have "10A" rated contacts, that is 10A RESISTIVE, which equates to about 4-6A if it is inductive (if it doesn't say, but it says 1/2HP max, that's 5.4A inductive and if it says 1/3HP, as several do, that is only 4A inductive). So most likely you have smoked those contacts and they are now giving you high resistance, which is dropping the voltage AT the coils and making them not pull in strongly enough. Complete failure is inevitable and likely to happen very soon.

The "Sealed" VA on those coils is 5.79VA, which at 120V should be .48A; so if you are reading .8A, there's your sign...
 

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
I'm sure the other guys are right but just in case make sure you don't have any metal shavings from possibly drilling holes that may have wound up behind the coil mechanisms. This to can cause contractors to not fully pull in and make a bit of noise.
 

Besoeker

Senior Member
Location
UK
Attached is a picture of a motor start control assembly that we built.
Somewhat left of field..........
We also build control panels. So a couple of comments from that perspective.

I note that the contactors and other components are mounted directly on the back plate.
Most of what we get here at the sizes you are looking at can be DIN rail mounted. Fit the DIN rail with a couple or maybe three screws and the contactors are clipped clipped on to it.
Saves time, so cost effective, and makes a neat job.

Another thing we do differently is to use trunking for the wires. Again, it's quick, not expensive, and saves time for wiring.

Back to the topic. As others have stated, the 0.8A indicates that the contactor has not pulled in and closed. That would account for the noise. And a recipe for disaster. If the voltage is maintained at 122V then maybe you should be looking for a mechanical problem that prevents the recalcitrant contactors from closing. Or just replace them.
 

kwired

Electron manager
Location
NE Nebraska
I note that the contactors and other components are mounted directly on the back plate.
Most of what we get here at the sizes you are looking at can be DIN rail mounted. Fit the DIN rail with a couple or maybe three screws and the contactors are clipped clipped on to it.
Saves time, so cost effective, and makes a neat job.
That would be typical of IEC contactors. The ones pictured are "definite purpose" contactors. They are "UL recognized components" and most commonly found in HVAC equipment. I don't think I have seen any that mount on DIN rail, but they kind of have a standard base and you can usually replace one of same size with any other brand and mounting holes usually line up with the original.
 

Besoeker

Senior Member
Location
UK
That would be typical of IEC contactors. The ones pictured are "definite purpose" contactors. They are "UL recognized components" and most commonly found in HVAC equipment. I don't think I have seen any that mount on DIN rail, but they kind of have a standard base and you can usually replace one of same size with any other brand and mounting holes usually line up with the original.
Yes, HVAC here is also made to a price and not necessarily to the neatest standard.
We mainly serve the industrial sector and this is typical stuff - poor pics but just done for the record but it gives an idea of the different approach.

AP12775002_zpsb641908c.jpg
 
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