DC Motor Starter with Power Diode

[calvintey]

I have a 125VDC motor starter circuit having a diode across the series coil of the DC motor. I don't understand the reason for this diode. I though a flyback diode is normally across the motor itself? Attached a sketch of this circuit.
Appreciate if anyone could share their insight on this. Tq.

 

[calvintey]

Sorry... I think I missed out the attachment. Here it is.

 

[Skogsgurra]

It is the series winding that creates the inductive kick-back. So the diode sits OK across it. But I don't see that arrangement very often. Have seen something similar in an old military (tank) application. But don't remember why it was there. And not sure if it was across the series winding either.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

It gets the field off the motor quickly rather than allowing it to decay through the motor armature, which might arguably bring benefit in some circumstances.

 

[waross]

It's a series motor John. The diode may prevent a high voltage inductive kick from reaching the armature and puncturing the insulation.

Bill
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"Why not the best?"
Jimmy Carter

 

[Parchie]

The correct function of that diode is as a "free-wheeling diode". What @waross said, it clamps/drains the winding voltage on the field and protects it.

 

[Skogsgurra]

Oh? Is that so?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.