Enlightenment in a dynamical brake scheme 1

[monsieurelec]

Hi
I finally found a way to brake dynamically a drilland i found it on a circular saw.
I've drawn the electrical scheme of its brake which work with the drill.
The problem is that I want to resize the componant to make it brake faster.
But I dont fully understand of this brake work.
So can anybody enlight me?

 

[DickDV]

I would caution you on increasing the brake intensity. The braking action is done by passing DC thru the motor while it spins. There is a limit to how much DC current the components of the motor can tolerate before being damaged.

If the existing design is at all optimized, then you are already at that safe limit and increasing it will damage the motor.

 

[monsieurelec]

Thanks for the answer
I want first to fully understand this scheme (role of the MOSFET and the thyristor, how the current is getting in the motor maybe with the capacitor) and then compute it from the drill and increase it but not much.

 

[blacksea]

What kind of motor you use?
Pay attention that dynamic brake can damage a driver also due to disabling of current protection in this mode also.

 

[BrianE22]

What's a "Bobine"? Is that the field coil? And the "interupteur", is that a circuit breaker? I'm guessing the 10 ohm resistor is the dynamic brake resistor. For quicker braking you would decrease the value of that resistance (careful, the current will go up!)

 

[monsieurelec]

Thank you for the answers
@blacksea:
It's an universal motor (8.5A,230VAC,1500W).
It's kind of experimental then when I will understand how it work I will increase the value really carefully.

@BrianE22: If it's the braking resistor then I don't know how it brake the circuit(it's a big resistor for the circuit CMS 5W).
yes the bobine is the same as coil and interrupteur means switch.

I just has tested with the Ohmmeter and i know now that when the switch is open the 3 goes to the ground and the 4(second coil) go to the node (1) of the 10 ohm resistor and the thyristor.
When it's close the 3 and 4 are connected and the node(1) is in open circuit until the switch close.

 

[monsieurelec]

Sorry but in the diagram, both the capacitors in derivation with the diodes are varistors then just protections.

 

[BrianE22]

When you say "ground" do you mean the actual motor body metal? Or maybe you mean connected to your neutral?

The basics for dynamic braking are to:

1) Remove AC power to the motor
2) Reverse the polarity of the armature relative to the field
3) Connect a resistor in series with the armature and field.

Some times there is not enough residual magnetism in the field to get the regeneration started. A common method to initiate the braking is to discharge a capacitor across the field to get some initial current flowing. This capacitor is charged up during the running mode.

I suspect that is what this circuit is doing but I haven't quite figured it out.

 

[monsieurelec]

Thank you thats what I thought too until I until I test it with a scope and see that there's some negative current at the braking time but in both the coils (even the second one connected to the neutral(yeah sorry neutral not ground)).
I don't understand how and where this current is coming from for the second coil because the switch is open and there's no contact with the big capacitor...