Contactor Coil Impedance

A telephone call to the original equipment manufacturer would sort this out, however, having withheld both the name of the manufacturer and the equipment type from the forum, it would appear that the best individual to make the call is still the original poster. Please update the forum with the outcome of the telephone call so that others may learn from it.

I already have telephonic discussion with OEM but they simply says that buy our contactor only, do not use any other make. It's monopoly item.

But I want to replace the contactor any break their monopoly.

Wouldn't be better to get the equipment running again, so hat it may carry out its business function in line with any warranty or maintenance contract that is in place, instead of wasting business time on a 'Don Quixote campaign'? Fit the correct contactor, and be done with it! <sigh>

What if the 'real contactor' costs $15,000.00 and the generic one costs $245.00?

Perhaps the OP will illuminate us with the salient costs?

You might be encountering a digital monopoly in the form of a chip that handshakes with the equipment to enforce this monopoly.

If you examine the failed contactor to see if there is any such chip, so you can defeat it, or wire it in to the new contactor.

Many companies hard wire little monopolies into their products. Defeating these is a permitted use under current laws.

It might also be the similarity of current flow that is detected? In that case, you need an added coil in parallel with the Schneider coil to decrease the perceived impedance to be 75 ohms - if is is that simple?

Have you considered that the PLC is actually measuring the current flow to the relay coil.

Due to the fact that I=E/R, changing the value of R means that the PLC can quite easily determine that there is a discrepancy with the expected current flow to the coil and so deduce that a fault condition exists.

Changing from the 75Ω coil to the 120Ω one produces a 37% decrease in coil current, going to the 1200Ω one produces a 94% decrease in coil current (I seriously doubt that the armature would even move at that value). The PLC is highly likely to view these values as faults and indicate so.

Measuring the resistance with a multimeter should give you an adequate value for a replacement coil.

If you can't get an original equipment replacement or information on its value, and the old coil is burnt out, then about the only way to get its resistance is to count the number of coils, translate this to a total wire length, measure the resistance of a known length, bring that up to the full length figure and then find a coil with a similar resistance. Adding resistance in series or parallel may assist in getting to a value that the PLC will accept, but be careful of wattage values.

I agree with the suggestion to use the contactor make that was specified by the OEM.

There is no easy way other than the use of a current shunt and an analog input to the PLC for the PLC to monitor the coil current draw. So... is the shunt and associated PLC input present?

If so and you are bound and determined to use other than what the OEM specified, for the contactor, the easiest, quickest and cheapest way to fix this is to find the proper variable in the PLC program and change it to what values the new contactor will present to the PLC.

Certainly this all sounds a little strange and a rather expensive way to ensure you use only an OEM specified contactor. You may be missing something else, such as timing perhaps; as in the amount of time between the command to close and the contactor actually picks up. Does the PLC get feedback from the contactor when it has closed?.

Often OEMs use methods like this to force consumers to buy a product that costs twice as much, ever buy a Keurig coffer maker that uses DRM

and how consumers fought back

There are now Keurig Hacks out there

As has been suggested, PLC may monitor current draw.

However, you have to apply the designed 110 VAC 50 Hz to find relay coil AC current draw - DC ohmmeter is no-good, since inductance may be different.

It is unlikely a current monitor registers phase - so a resistor (increase I) or capacitor (reduce I) in parallel with your substitute relay, so it draws the same current, may fool the "vampire".

Let us know if this works.

The coil of a contactor is highly inductive. Further, the inductance varies...it is small when the contactor is open, and high when it is closed. This is caused by the reduction in the airgap of the magnet. Please check the catalogues of good manufacturers who give VA and wattloss of their contactors. i find it strange that any coil current draw or inductance is monitored at all. Are you sure?

How does the machine know when the contactor has been changed to another brand

Contactors , like any other equipment, are characterised by AC3 rating, Operating voltage and a few application-specific things. A 25A contactor (for example) of any make will function very similarly to another 25A contactor of a reputable make. In all applications that i have seen, this is the case. Just like any MCB, MCCB etc. The make of the contactor should not matter to the drive in my opinion. Choice of the make is a personal preference.

That is the way it should be in a competitive world.

As you can see, this machine maker also makes contactors and has created a pathway to tie the customer to their brand of contactor going forward.

This sill lead to a class action lawsuit in the USA, at least - other areas? It is, after all, a form of fraud.

Ah i see. Yes, it is unethical. Word of mouth advertising should make this boomerang on them. But the contactor is such a negligible (costwise) component of the overall system that few people would really bother. They may pay 4 or 5 times the cost direct to the system manufacturer rather than worry about consequences. There is also CYA factor working against the maintenance engineer, even he knows that a far cheaper alternative can be used. That is monopoly in some ways. Think of all the parts in your car that are unreasonable expensive..... it is the same thing,

It is, after all, a form of fraud. Most of the world sees / accepts this as standard business practice, to be allowed for in the due diligence/ cost-of ownership decision before purchasing.

eg. few car manufacturers produce their own electrical components..ergo, a starter for a Mercedes cost more than that of a Fiat or Kia.

It isn't very logical to think the brand of the contactor is the problem. I have never come across such a problem in 40 + years doing this type of work. He might be missing a set of contacts from the old unit to the new.

Everyone is jumping to conclusions about conspiracies here.

In a lot of machine safety applications, the Safety Relay or Safety PLC (aka "Safety Controller") is REQUIRED to detect a circuit fault of any sort, and disable operation until it is corrected. One method of doing this is to set up a rather narrow window of acceptable circuit impedance in the control wiring, so that if a wire is cut or grounded, or a coil is failed or even failing, the impedance changes and the Safety Controller takes action. When that type of system is employed, it is IMPERATIVE that you ALWAYS replace like-with-like, right down to model numbers. Once the system is validated and accepted, you are NOT ALLOWED to make ANY changes without going through an entirely new Safety Evaluation process and validation.

We do NOT know the nature of his machine, not do we know the sophistication of the OP in being able to assess or understand this issue. Advice may not be attainable via an anonymous internet forum without risk of life and limb.

dhanesh.koshti, as others have said, just do what you are being told to do and stop pinching pennies and complaining about conspiracies.