Yes my initial switch was a spdt mentioned in post#1. But like I said I did not get the rate at which it stopped as expected.

 

Have a look at "Retarders" as used in coaches and lorries.

https://en.wikipedia.org/wiki/Retarder_(mechanical_engineering

The section on electrical retarders could be useful.

If you want full braking, i.e to STOP, you will need to devise a circuit that not only can sense wheel rotation, but can supply a reverse current to the motor to oppose the rotation. Remember that as your motor is being used as a generator during braking, the output will fall as it slows, so the braking force will become less until it reaches zero when stopped. By feeding a reverse power, you can ensure full braking right up to stop. At that point you need to turn it off or it will reverse.

 

In post #1 your circuit was much more complicated than needed. Also you has a 35 ohm braking resistor which would make the stopping time longer. Try the following .
Motor negative to supply negative.
Motor positive to common on the DPDT switch.
Supply positive to NO on the switch.
NC on the switch to motor negative,

Les.

 

I started off with that design but came across a problem. The negative side of the power supply is always in contact with the motor negative terminal.

 

Why is that a problem ?

Les.

 

In the OFF state as it is now seen in the schematic the back emf from the motor flows back into the power source as well which is generally blocked by a diode.

 

I created a dynamic brake circuit many years ago when I used 8-track tape drives for storing data.
I called it a negative resistance circuit. I will have to see if I can recreate the circuit.

 

The back EMF from the motor can't flow back into the supply as there is no path to the supply positive when the switch in in the off position.

Les.

 

Maybe be i understand it wrong.


The path shown in yellow, isn't that how the current flow when in the OFF position ? Pin 1 being the positive terminal and 2 Negative.

 

The source at pin 1 and 2 is a an ebay module to generate PWM pulse to control the speed of the motor. The pot on the module will be change to resistor latter.

 

Maybe be i understand it wrong.

The path shown in yellow, isn't that how the current flow when in the OFF position ? Pin 1 being the positive terminal and 2 Negative.

Power Pin 1 is open circuit in braking mode.
Max.

 

Pin 2 from the motor from which the emf flows to pin 2 on the power connector and pin on the spdt which connects to the pin 1 on the motor. So part of this emf flows to pin 2 to the power source.

Either way the motor without a load stops instaniously but with a load it takes time to do so. So I was looking for something that could gradually stop when the motor has a load.

Not sure how the circuit in post 15 works but seems to work in his video. That again is without a load.

 

Why not just build the circuit that suits your idea of how it works. Or alternativly build each one and see which works best for you. In the circuit in post #29 the braking current goes through switch contacts 1 & 2. You seem to think current can flow when there is no closed circuit.
In post #32 you say "EMF flows" EMF does not flow. Current flows.

Les.

 

Maybe be i understand it wrong.

View attachment 166921
The path shown in yellow, isn't that how the current flow when in the OFF position ? Pin 1 being the positive terminal and 2 Negative.

This path should be the only current flow in the OFF position:

 

Thank you for clearing that to me.

I was kinda lost there. Since the motor runs with a load the stop is not instantaneous, takes about 10 Seconds to come to a complete stop. I Have seen the Dremel Tool use two mosfet that works to bring the motor to complete stop instantaneously, something i think is what is mentioned in post#15.

I am not sure how it would work but seems like in the video it does seem to work.

 

So i just reverse engineered the PCB in the Dremel and this is what i found, not sure if i did it correctly. R1 and R2(4L0) are 40Ω resistors in parallel.



Looks like the FET is just a switch and the dual diodes are just blocking the back emf from the motor but where is brake part of the circuit.

Here is the remaining PCB in the dremel

 

It is probably an electromagnetic brake that is released when voltage is applied to the motor. Also I think your schematic is wrong. You show the supply positive connected (Via the switch.) to the source of an N channel mosfet.

Les.

 

I've removed everything from the PCB and here which helped with this schematic.

 

I've removed everything from the PCB and here which helped with this schematic.
View attachment 166978

View attachment 166979

For what it's worth, that one looks like it makes sense to me. I couldn't get my head around a lot of the others (though I have very, very little experience with motor control, much less braking, so my understanding or lack thereof may not be relevant!)

I'm a little surprised by the position and values of R1 and R2, but I suppose they could work in conjunction with the Vgs threshold of Q1 to create a crude current limiting system. I assumed a Dremel motor required more current than that system would allow, but I've never looked at the motor specs, so could be way off base on that part of it.

 

The Dremel like other applications uses the 775 motor rate led for 12-24v.