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3hase speed control of dc electric motor using dual thyristor

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Member level 4
Sep 25, 2012
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I am trying to design variable-frequency speed control of dc motor 10hp.180v dc.pls I need the triggering cct

A 555 timer IC can be made to vary duty cycle. Apply a varying voltage to the control pin.


The connection to ground is implied.

Thanks. The o/p of 555 timer is it connected to the gate of thyristor?I'm using six thyristor

Thyristor implies an scr or triac.
Since your supply is 180 VDC, it may be best not to connect the 555 to a thyristor, if the thyristor is connected to the supply. I'm not sure what amount of DC is able to come back through the gate of a thyristor, and harm the 555.

I was going to suggest an N-mosfet for the switching device.
10 HP converts to 7600 W. At 180V the current will be 42 A.
There are mosfets that can handle this, as long as you heat sink it sufficiently.

It what valtage range can I use the 555 timer with scr?. Yes it is 7.6kw 42amp.using mosfet is it pwm techinique.pls help me with cct. diagram .Thanks

If the motor were low power then it would be easier to design a PWM controller which is robust enough to endure the jolts.

This schematic is only a tentative theoretical design. I don't know how well it will work at the power levels you are talking about, or at the typical PWM switching speeds.

The single mosfet may really need to be a gang of mosfets.

The diode is a customary add-on when switching current through a coil. However in this case it may conduct as much as 42A when the mosfet shuts off and it creates a current loop with the motor. The diode will need to be rated to handle it. Several diodes in parallel would not necessarily conduct equally.

All this is to say, I am not responsible, etc., get a second opinion, etc., test it first at low voltage and low power levels, etc.

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