Hold On and Drop Down Characteristics of DOL Starter

This is simular to the logic of a PLC, between 0 and 1 there is always a grey area on the inputs.

The energy required to pull the relay on is greater than the energy required to hold the relay, once the relay has made contact with it's corresponding contact surface the current will be lower if we are talking about an AC Coil contactor, this is due to back EMF.

Cheers

Joe

Back emf.......

What a load of Crock.

C'mon.

Are we professionals here. or what.

Cheers

Mark N.

PS. 'spose it could have been Eddy currents.....!...////...!

Excuse me Markone, but Joe is right i think ... there is a back-emf which makes the hold-in current far less than the pick-up current. Mainly due to the high inductance of the 'sealed' magnet. There are plenty of references on the web about this, here is a video also http://techtv.mit.edu/tags/1969-spark/videos/880-mit-physics-demo----back-emf-in-a-large-solenoid

Eddy currents have nothing to do with this. Designers strive to reduce eddy current and hysteresis losses in AC solenoids.

Anyway, we are now in the age of the microprocessor-controlled coils, which use pulse-width modulation to give just enough power to the moving system so that the contacts close with minimal bounce, and the consumption is extremely low.

Hi Kvsridar, Thanks for your support My Freind.

You and I know that we are both right.

Mark is wrong, and is giving wrong advise to the forum. If you look at previous threads that he has been involved in,the also make no sence.

Kvsridar, I have a a lot of respect for you and your reply in my defence!

But all of this has not answered the question that was asked directly, I will have a go at thying to answer this tomorrow.

Best Regaeds

Joe

For some reason Markone, I dont like your attidude.

Of course Back EMF is a factor, why do you think coils burn out. A lot of the time a contactor coil can burn out if if the armiture and the base have not made a good contact, this can be caused by some foreign material being trapped between the contact surfaces.

You call yourself a professional, so why did you get out of your trade couldn't you handle it. I think that you went into sales because you were washed up as a electrician. With the attidude you have I think that the best carrer move that you have done was to retire!!!!!

Best Regards

Joe

Yeh, well I suppose, if you lead with your chin, we will have someone hit us.

Fair Comment.!

But, Joe, don't presume, that which you don't know, as I, also, shall not presume anything of, or in life.

And, you have proved my point.......! "sometimes Good Electricians, don't see the Volts for the Amps."

We, all of us, aren"t perfect, in particular...Me...!

Cheers.

Mark N.

I tried it on an electro-magnetic contactor 3 times in succession and got different results,why?.

If you are doing it on an AC coil, it could be due to the point-on-wave when you give the closing command. Or when you reduce the voltage and hunt for the drop-off point. Then there are mechanical contributors...friction, spring forces... Even with DC coil, unless it is a battery supply, the ripple of rectified DC will give different results.

In any case, if you study the gate limits of IEC, they are pretty wide. The pick-up and drop-off values are not expected to be precise.

However, your query is aimed at Debasis, so he will respond too i hope.

I reckon that the control voltage you are using is DC.

You haven't stated as such in your enquiry post.

I am not going to advise of the math in the equation, but to suck it in, is a lot more than, to hold it.

Common answer to a large contactor coil, for a 100 amp contactor and above is to actually have a Dc coil, to pull him in.. Most cases the DC bit is done in the coil, ie 240vac, bridge rectifier in the coil, and so on.

The main reason, is that most control devices, timers, relays, pressure switches, etc are only rated at 10amp ac ac1, whereas to suck in a, say 400amp ac3 contactor, say using a 110vac coil:- will actually need another smally type contactor to do the "Sucking".

You really have to sit back and see what is going on.

I am an electrician, not an Author or a Teacher, but if you can understand that which I am trying to say here, will help

1. Answer your Question
2. Save you a lot heartache later on in life.

I have worked as a sales Engineer most of my life, and to acquire a solution to this problem is as hard as...................I have nearly wanted to kill..............

Normal sane electricians ( that I would Pin my Life on) have said to me, the coil pulls 20amps, and burns out the contacts in the timer, Your contactor is Faulty. I have shown them the coil operating data for the opposition stuff, and they all pull about the same current, but.......no...it was my gear that was the problem........

We sometimes don't see the Amps for the Volts. Bit Cryptic, but I hope you can understand this problem. Learn, from your Instructor......he has more than likely been Bit, B4

All the Best Cheers............Learn.

Mark N.