Hey dudes

I'm working on a carton making machine and two contactors have burned out in as many days. The contactors themselves are running two belts one is a simple conveyor and the other is a chain drive, both have overloads and the convery is set for 2 amps and the chain drive 6. Before the contactors burned out (and when i say that i mean the coil is stuck out on both and wont pull in) and the coil is 24vac. I checked the circuitry and it looks like the A2 on them wasnt giving a proper return as when i measured the coil it was only giving 12 amps ac could this under voltage cause the contactor to fail? As in not enough voltage to keep the coil closed and cause it to develop an air gap and fail?

PS all the circuitry on the motors is ok 3 phases in and out and overloads trip when tested

 

Switch to solid state relays.

 

If you supply an AC contactor coil with less than rated voltage you risk the burn out due to the armature not able to fully engage.
Obviously in this case correct voltage is required, but the better solution is to always use DC coils. They do not suffer in this way.
In your case you could replace the coils with DC style and use a bridge to feed them.
Max.

 

thanks guys but changing it to dc is not straight forward the start stop station runs through a safety relay a guardmaster Minotaur MSR5T then through another relay which switches the coils on

 

But the AC circuit before the bridge would not change, just a fit the bridge local to the coil(s).
Even if you did them individually.
Most contactor manuf. supply DC or AC coils.
Max.

 

Thanks for that guys now i have another problem on this circuit. Somebody else went at it and got some cables mixed up the problem is all the control wires are the same colour and have no cable markings on them and there is no drawings for the machine NONE! so now neither conveyor will latch and run when i reconfigured the wires the best i could get was the 2 contactors to slam which obviously is wrong. i have 3 cables unaccounted for which i think go back into 13, 33 and 34 of the Minotaur saftey realy which i have attached a pic of below both coils on the contactors A1's were linked to begin with as id imagine the a2's would be as well according to the Minotaur drawing it looks like i have 13, 33, and 34 missing would i be right to assume 13 is running the a2 side of the coil and the 33 and 34 is going through the NO contacts?

https://images.search.yahoo.com/sea...a/Image%203/100_0774-800x800.JPG&action=click

 

Thanks for that guys now i have another problem on this circuit. Somebody else went at it and got some cables mixed up the problem is all the control wires are the same colour and have no cable markings on them and there is no drawings for the machine NONE!

Beautiful!

Probably the only thing left is to come up with a re-design and draw up a new system.
It does not sound like all that of a complicated system.
It looks like 13-23-33 are the main contactor feeds and the 41 is the N.C. for interlock purposes.
It also sounds like it may have been poorly designed in the first place.
You can get the data sheet and instruction from here http://uk.rs-online.com/web/p/safety-relays/1930520/
Max.

 

looked at the drawing and still a little confused is it showing that 33 and 34 would go through the normally open contactos on the contactor and that 13 would be A2?

 

There are different ways to employ it, this shows some a little better https://www.google.ca/url?sa=t&rct=...lrrGYAr4A&sig2=TMPZmVuE6LXS_alWduFPLA&cad=rja
A1-A2 are basically your L.V. control circuit and the 3 sets of contacts are your Controlled circuits.
Max.

 

Ok back at it again today and still not sure where 13 14 33 and 34 are wired back to I'm guessing the contactors on the ntmally open side so I pair 13 and 14 together and 33 and 34? Also now whereever I take my a2 from the coil either slams on and off or the coil pulls in right away bypassing the start buttons please help totally lost on this

 

Very hard to help from a distance without quite a bit more info on the present system, there are a few configurations this could be wired in, and to know exactly what you have.
If I were on the site, I would attempt to reverse engineer what is there and draw up a schematic.
Max.

 

Hi BENCASEY83,
I've just read your first post again and do not understand this statement "looks like the A2 on them wasnt giving a proper return as when i measured the coil it was only giving 12 amps ac" The coil should not take anything like this amount of current. The coils are rated at 4 VA so for a 24 volt coil that would only be about 170 mA. Are the contactors being used in latching mode ? For example with a start button and a stop button. Or are they only closed while power is being supplied to the coil ? Have you tested the suspect contactors on the bench with a 24 volt supply on A1 and A2 and a link X1 and X2 ? Are these contactors IDENTCAL to the ones they were fitted to replace ?

Les.

 

The coil should not take anything like this amount of current. The coils are rated at 4 VA so for a 24 volt coil that would only be about 170 mA.
Les.

I have some Small contactors with 24vac coil and they measure around 5Ω, which if the contactor armature is not pulling in for some reason will account for high current and subsequent burn out and then causing even more current.

i mean the coil is stuck out on both and wont pull in

.
Max.

 

Hi Max,
Looking at the top right block diagram on the second page of this link that you posted it looks like the coil is DC. I interpret the block below the A1 and A2 terminals to be a bridge rectifier and it show the output as 24 volts DC The increase in the winding inductance when the contactor was closed would not effect the current with DC. The data table also says the 24 volts can be AC or DC.

Les.

 

I took it the A1 A2 refereed to the contactor coils which is a standard way of labeling.
The safety relay could be controlling the contactors, the DC supply to the Safety relay is normally controlled by whatever E-stop circuit is in place.
At least that is what I am surmising.
The OP is not clear on details.
Max.

 

Hi Max,
Like you I am guessing. I have never seen a contactor like these. The appear to be two contactors in series with a set of contacts that can monitor if one of the contactors is closed when it should be open. I am amazed that they can fit so much into such a small package. It is so much easier to test your view of how it works if you have the item to play with.

Les.

 

The item shown is a Safety Relay not a contactor, and is now used in place of a E-stop relay, I have been under the assumption that this is controlling the power to the contactor circuits.
The series contacts are called force-guided, and are the feature of most if not all Safety relays.
http://www.schneider-electric.us/en/faqs/FA111694/.
Max.

 

Hi guys
Sorry for late reply but got problem sorted 2 weeks ago turned out it was a relay that was shorting out intermittently between the ac and dc voltages and dragging it down. On looking at the machine i am trying to campaign to get a plc installed and get rid of most of the redundant wiring and obsolete (and discontinued relays). i have given an outlay of the machine below so just wondering what type of plc would be needed, as in how many inputs and outputs. Thanks guys

A selector switch (on/off) which is used to call cartons (normally open)
A start and stop button for on off control of an outfeed conveyor
A start and stop button for the main chain drive conveyor (which by the looks of it has a slight on delay timer on it and is run through an inverter and has a speed control pot too.
An infeed conveyor start and stop push buttons
2 reset buttons
2 emergency stops
A 2 position selector switch one is run in automatic the other is inch/jog. The inch/jog is a hand hand controller with 2 push buttons on it
A 2 position selector switch which lifts the hood of the machine up and down, (this is turning on a 3 phase contactor)


And lastly and maybe most detailed are the guard door interlocks

The doors are numbered as follows and borken down into different areas 3, 4, 5 ,6 ,7, 9 10, 14 each section has a high and low level door on it so it would be as follows

Area 3: 3 doors
Area 4: 2 doors
Area 5: 2 doors
Area 6: 1 door
Area 7: 4 doors
Area 9: 2 doors
Area 10: 6 (small) doors
Area 14: 3 doors

I know this may seem a lot but all these doors have on them are Guradmaster sensors and im guessing that all of these would be wired in parallel? As when you open a door in lets say area 7, where there are 4 doors it knocks the safety relay out weather the door is high or low level. So would these need to be all on there own inputs? How big of a PLC would be needed?

Thanks dudes

 

My favorite is Mitsubishi, I have used Allen-Bradley but they are expensive and the S/W likewise.
You need to total up all the inputs and it may need I/O expansion module.
Have you done any PLC programming so far?
You also need to draw up a schematic of sorts of the system and how it currently operates.
One of the obvious pluses with a PLC over hard wiring is one input can be used multiple times as needed in either NO or NC state.
If you have door sensors or safety interlocks they could not be wired in parallel as one closure will defeat the rest.
Max.