anti reversal latch & active breaking fet

[Gavin]

simple yes or no

am i right in thinking arl is not needed with active breaking mosfet or is it advisable to keep it in there ???

cheers guys

[Bachelarius]

Re: anti reversal latch & active breaking fet

Keep it in.

Prevents Double Feeds due to reverse spin, and any other issues that may arrise (broken tappets). You may get away with not using one if you have a light spring and a really stiff motor, but it will be held still by a hope and a prayer.

[No1_sonuk]

Re: anti reversal latch & active breaking fet

Double feed shouldn't be a problem with active braking on semi.
Auto might be an issue, though. That's why I'd not remove the ARL on a setup without a cycle-completion MOSFET unit.

And what does this mean:

You may get away with not using one if you have a light spring and a really stiff motor, but it will be held still by a hope and a prayer.

The motor won't hold a main spring at all. If there was enough resistance for it to do so, you'd be wasting a lot of power driving the system.

[Bachelarius]

Re: anti reversal latch & active breaking fet

Motors work by switching current direction and using that motor's 'stiffness' or magnetic strength as a form of thrust. Try spinning a neo-based motor, you will see that the magnets are massively strong and the motor is very hard to turn by hand.

Braking 'fets makes this effect even stronger by in essence, sending a push signal (reverse current, generated by the motor's spin) to the motor when it is expecting a 'pull' signal (and vice versa), simply by shorting the motor, and in essence, slamming on the brakes. An AB fet does absolutely nothing when the motor is stationary.

All an AB 'fet really does is slow a motor down quicker when you release the motor, helping slightly with overspin. It does not remotely replace an AR lever, as it is still an unpredictable effect, which should be combated with a heavier spring and short stroking rather than an AB fet due to excess motor heat generated by the braking.

The only thing that even comes close to the effect of the AR is the latching properties of a motor and some of the beefier motors can hold a light spring, especially with torque gears, but like I said, I would not rely on it, esp if the spring happens to be fully compressed, that just won't get held at all, no matter the motor!

In short, keep it in, it's a safety mechanism which is the only thing that prevents the gears from trashing your tappet plate.

[No1_sonuk]

Re: anti reversal latch & active breaking fet

I'm an electronics engineer, and I still don't understand how you think an unpowered motor could hold against a spring, especially as the shorting action of the MOSFET is turned off after a short period to avoid potential shoot-through when the trigger is pulled again.
That means no back-EMF would be available to resist the motion.

In short:
If you have guaranteed cycle completion (and I mean by sensor feedback, not just timing like almost all MOSFET units currently available), you don't need the ARL.

[[email protected]]

Re: anti reversal latch & active breaking fet

Whether you need it or not is very debateable IMO but what is not in question is the fact that it does no harm to leave it there.

[Gavin]

Re: anti reversal latch & active breaking fet

will leave it in guys, many thanks