DC motor wiring

Hi,

I have to connect a DC motor (shunt wound) with a magnet contactor and I do not know what is the best way to do that. Some of my freinds said I have to cut the power of shunt with a contact and some other said that the shunt wond have to be energise any time and I just have to cut the armature power! What is the truth? What is the practice (standard)?

Thanks

Steve

Reply to
Steve et Julie
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Hire 2 professionals.

1 An english teacher so we can maybe understand your question 2 An electrician who can look at the motor and save you a lot of trouble.
Reply to
John G

in article 6iOvd.37$ snipped-for-privacy@nnrp1.ozemail.com.au, John G at snipped-for-privacy@ozemail.com.au wrote on 12/14/04 7:35 PM:

I have seen much worse English than this although it is confusing. Also this does not look like a homework problem.

The only thing I will tell you for sure is to not apply voltage to the armature without the field being energized. That is a sure way to either blow out the armature circuit at its weakest link or to rev up the motor to where it tears itself to pieces. Also watch out for dc arcs.

Bill

Reply to
Repeating Rifle

I reckon most electricians haven't seen a DC motor since apprentice days

Reply to
bob watkinson

I dunt git it. One place he says it's shunt wound, the next he implies seperate wiring for the arm and field.

Reply to
Steve Cothran

JFC!!! Hire an electrician!

I have to connect a DC motor (shunt wound) with a magnet contactor and I do not know what is the best way to do that. Some of my freinds said I have to cut the power of shunt with a contact and some other said that the shunt wond have to be energise any time and I just have to cut the armature power! What is the truth? What is the practice (standard)?

Thanks

Steve

Reply to
Brian

Shunt wound *is* separate wiring for armature and field. Both connected across the line (as opposed to series). Many DC machines bring all the winding connections out to the controller.

I've seen some large machines have the field energized all the time. Generates enough heat to keep the machine dried out. As Repeating said, be darn sure the field is applied before applying the armature. In large machines with several resistance starting steps, the main contactor is often interlocked with the resistor-cutout contactors so you can't accidently start it without the starting resistance. The field should be directly across the line, not through a starting resistor.

daestrom

Reply to
daestrom

There is no need to be nasty about this. his description is fairly well defined and questions quite valid. More then I can Say about a lot of posts here. Most Electricians I know would not be able to answer this with confidence.

In mining applications we tend to leave the shunt field permanently connected as mentioned by Daestrom. The level of current remaining in the shunt field should be below what the motor can handle without ventilation. Usually a contactor is used to short out some resistance to give you the full field level when the motor is required to operate. This achieves a couple of things. Firstly, as already mentioned, It acts as an anti-condensation heater, and secondly it keeps some field on the motor in case the sequencing is screwed up and the motor is asked to operate before proper field current is applied to the shunt field. A little bit of field is far better then none at all in a desparate situation.

If you are driving your motor with some sort of digital solid state control then the problem of sequencing becomes a lot easier to solve. These controllers usually have some sort of variable field control interlocked with a field current feedback signal to make sure it does not try to run with without field.

Seeing that you Mention Contactors I am guessing you are considering the use of these. The thing, as one of your advisors has mentioned, is that you must make sure you have shunt field current flowing before trying to run it.

Some sort of current detection device is the best.

further details really depend on the application, of which we know nothing so far

Regards Tom Grayson

Reply to
Tom Grayson

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