Regenerative/Dynamic Breaking with minimal components.

LesJones

Joined Jan 8, 2017
4,174
The new schematic in post #38 looks correct. It uses the same method of braking the motor by shorting it out with the normally closed contact on the switch as the schematic in post #29. The MOSFET is only used for PWM speed control of the motor.

Les.
 

LesJones

Joined Jan 8, 2017
4,174
D1 shunts the current due to the inductance of the motor armature winding (This is NOT the same thing as the voltage generates while still spinning. It is the oposite polarity to that.) when the mosfet switches off and also when the normally open contact opens and before the normally contact closes. Without D1 there would be high voltage spikes that could damage the mosfet. It also helps to maintain the current through the motor during the PWM off time.

Les.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
549
Thank you Less.

I've just tested this without the MOSFET and i am pleased with it. The stopping time is very fast with a few sparks on the motor brushes as expected. I omitted the MOSFET circuit and connected ground directly to the supply.
Capture.PNG

Would adding a resistor in series with the M- and the Anode of D1 control the rate at which the motor stops ?
 

LesJones

Joined Jan 8, 2017
4,174
The schematic in post #44 will not give any braking. You do not need D1 as you have no mosfet that needs protecting from voltage spikes. Use the circuit from post #29 and if you want to make the braking more gentle add a resistance between connection 1 on the switch and the motor negative. To make the braking effect more severe requires applying reverse polarity to the motor until it has stopped. This will be much more complex. Why do you keep wanting to make the circuit more complex than required ?

Les.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
549
Thank you Less.

I've just tested this without the MOSFET and i am pleased with it. The stopping time is very fast with a few sparks on the motor brushes as expected. I omitted the MOSFET circuit and connected ground directly to the supply.
View attachment 167010

Would adding a resistor in series with the M- and the Anode of D1 control the rate at which the motor stops ?
If I need to regulate the braking power would it be ideal to have a 4R 5W resistor in series with M2 and D1 ?
 

LesJones

Joined Jan 8, 2017
4,174
anishkgt,
I can't answer your question as the way you have wired your circuit can't be the same as post #44 as that circuit would give no braking. You would need to show HOW IT IS ACTUALY wired. IF it was wired as in post #24 then the resistor would be inserted between contact 1 on the switch and the motor negative. With a value of 4 ohms the INITIAL braking current would be a little less than 3 amps. (12/(4 +Rm) amps Rm is the internal resistance of the motor. You will have to use a high power potentiometer (Or just try different values.) and adjust it until you get the exact stopping time you require.

Comments for ebeowulf17. The path through the diode only conducts with the back EMF due to the inductance of the winding when the power is removed. This is because this is in the opposite polarity to the supply to the motor. The EMF due to the motor continuing to rotate is the same polarity as the supply so if the diode was conducting with this polarity it would also short out the supply when the motor was running.

Les.
 

ebeowulf17

Joined Aug 12, 2014
3,307
The EMF due to the motor continuing to rotate is the same polarity as the supply so if the diode was conducting with this polarity it would also short out the supply when the motor was running.
Thanks for the clarification. I thought this EMF had the opposite polarity. So much to learn... thanks for your help!
 

Thread Starter

anishkgt

Joined Mar 21, 2017
549
anishkgt,
I can't answer your question as the way you have wired your circuit can't be the same as post #44 as that circuit would give no braking. You would need to show HOW IT IS ACTUALY wired. IF it was wired as in post #24 then the resistor would be inserted between contact 1 on the switch and the motor negative. With a value of 4 ohms the INITIAL braking current would be a little less than 3 amps. (12/(4 +Rm) amps Rm is the internal resistance of the motor. You will have to use a high power potentiometer (Or just try different values.) and adjust it until you get the exact stopping time you require.

Comments for ebeowulf17. The path through the diode only conducts with the back EMF due to the inductance of the winding when the power is removed. This is because this is in the opposite polarity to the supply to the motor. The EMF due to the motor continuing to rotate is the same polarity as the supply so if the diode was conducting with this polarity it would also short out the supply when the motor was running.

Les.
Your correct. The Diode had nothing to do with the braking. I was carried away with D1 in the Dremel schematic. So a basic SPDT switch would do the job but need to figure out a way to slow down the braking which is close 20A peak and the inrush current, 50A at 5A steady.
 
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