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Dc motor

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hikrish4u

New Member
hi all
i have a DC motor operating at 180vdc and at 120rpm.
i have to rotate this motor in clockwise & anti-clockwise directions for 1.75 seconds repeatedly.
if i use a microcontroller & h-bridge circuit for the rotation of the motor,how can
i get a voltage level of 180vdc,so that the motor can be rotated.
 

MikeMl

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hikrish4u

New Member
I have a power drive with me which gives me 180vdc output.
The motor is connected to this power drive,so that it gets 180vdc.
 

MikeMl

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So what is your question?
 

hikrish4u

New Member
AS stated the motor takes 180vdc for operating.
i am using a H-bridge circuit to rotate the motor in both directions.i want to know,whether the H-bridge circuit is capable of withstanding upto 180vdc.


can i directly connect the h-bridge circuit to 180vdc with the power drive i have....

if it doesn't then what is the solution.....
 

unclejed613

Well-Known Member
Most Helpful Member
for starters, use transistors rated at 200-250V, and use anti-kickback diodes across them. a motor is an inductive load and can cause huge reverse voltages across transistors when you turn them off. is this a brushless motor?, how much current? is it a stepper motor? as blueroom said, got a schematic? are you looking for constant torque or speed?
 

MikeMl

Well-Known Member
Most Helpful Member
You said:

I have a power drive with me which gives me 180vdc output.
Since the drive already produces 180V for the motor, what do you need in addition????
 

hikrish4u

New Member
it is a dc motor ... but i ve to change its direction after every 1.75 seconds.
a normal h - bridge can do this for a dc motor operating at 12v dc.

but my problem is that the dc motor which i ve operates at 180v.
and if i use that in the h-bridge circuit the transistors can be damaged ... as the h-bridge circuit is for small voltages.
plz look at the following links:
DC Motor Controlling System using PIC | electrofriends
 

Martel

New Member
For the H-bridge, you may use power MOSFETS such as the IXFX90N30 (available from Digi-Key...) 90 Amperes @ 300 Volts

But i do have two questions:

1 - What is the power of the motor (in Watts or HP) and

2 - What is the MECHANICAL load for the motor ?

Having a motor reversing it's rotation every 1.75 seconds is NOT a normal way to have a motor work. Okay, 120 RPM is quite low, but if your motor is attached to a 50 lb flywheel, it will last, say 2 - 3 minutes !

You will also need an electric brake to stop (or highly decelerate) the motor before it change direction. This is done by:

1 - Remove ALL power from the motor and

2 - Putting-in a high power low value resistor directly across the motor. When the motor power is cutoff, tho motor will continue to rotate due to it's inertia and thus becomes a generator. Putting a resistor will brake the motor and absorb/dissipate the motor's/flywheel's kinetic energy. Do NOT short-citcuit the motor. If you do so, the MOTOR will dissipate the kinetic energy and may become quite warm.

And if your motor's load inertia in very high, you may have to think about a mechanical brake.

Finally, if the motor's output power is low, you may advantagely consider a stepper motor rather than a DC one. Steppers ARE designed to continuously "stop-and-go", change their speed and change rotation sense.
 
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unclejed613

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that H-bridge isn't going to work as shown for 180V. you are going to need some kind of level shifting for the top two transistors. the reason for this is, the top two transistors are emitter followers (common collector), and the voltage at the emitter when one of these is turned on is equal to the base voltage minus 0.7V. so if you turn it on with the PIC output of 5V, the emitter voltage will be 4.3V. enough to spin a 6V motor, but not a 180V motor.

the following circuit (rough draft) is one half of the h-bridge. the low side needs no changes, but you can see how the level shifting is done on the high side.
 

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tcmtech

Banned
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Actually you can dynamic brake with an H - Bridge just turn on either both top switching devices at the same time or both bottom ones at the same time.
If its a standard PM DC motor thats geared down to 120 RPM it will fry doing a lot of uncontrolled reversing.
But if its a industrial DC servo motor that runs directly at 120 RPM it designed to do that all day long. But the Peak amps they can draw during a full reversal can be 50 - 100 times higher than the average running load!
I have Getty's DC servos that are rated at 38 amps continuous and 300 peak at 60 volts per 1000 RPM with a 3000 RPM rated top speed.
SO for that application I would need a H-Bridge and power source that has a peak capacity of 180 Volts 300 amps! Thats a 54 KW surge capacity for a 7 KW load!
 
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