Need Help!- Gremlin or Normal?

[Mr.Chips]

I’m down to the last go round of checking everything before I get brave enough to power up and I found something that brought everything to a screeching halt.

I panic when it comes to the electronics as I fried 3 Xylotex driver cards because of a misunderstanding in wiring on the first go round on my first machine. (they are still in my junk box) I was saved by Probotix and their EXCELLENT wiring diagrams (in full color) that even a newbie can follow.

My electrical parts consist of CandCNC UBOB Kit and Gecko G251 driver cards

I was turning the X axis screw by hand and I notice every time I turned it the red LED’s on all 4 (X, Y, Z and A) of the G521’s would light up then dim off. Naturally there isn’t any power applied to any part of the control box.

I kind of would expect the X Driver card to light up because the stepper acts like a generator when it is rotated, but why all axis.

Thanks

Hager

[joshendy]

I imagine thats because the power generated goes back through the mosfets of a single drive and goes into the dc line which powers each of the 4 axis'. Therefore powering each of the drives.

If you put a multimeter on the dc input to the G540 you'd see a small amount of voltage when you turn any one of the motors.

[Mr.Chips]

Thanks Joshendy, I was hoping it was not an issue.

And welcome to the forum.

Hager

[Mariss Freimanis]

It's not an issue. The motor being back-driven becomes an alternator, its AC voltage gets full-wave rectified by the attached drive and the resulting DC voltage appears on the power supply bus. This voltage begins to light-up the other drives and loads the back-driven motor, limiting this effect to a safe voltage.

Mariss

[mlabruyere]

Yup....as the others have said this is normal. The motors act as generators when you turn them by hand.

I wonder if putting a diode in line on the stepper wires will prevent this?

[Mariss Freimanis]

Don't put any parts of any kind on the motor leads! Putting a diode across the winding will destroy a G251.

Mariss

[Mr.Chips]

BOY, that is good to know!

[mlabruyere]

Originally Posted by Mariss Freimanis Don't put any parts of any kind on the motor leads! Putting a diode across the winding will destroy a G251. Mariss

Wow....really. Why is that?

[yorkrose]

Even if the G251 was made of Kryptonite this would not work, for at least two reasons. The most basic reason is that the current must flow in a circuit. The diodes shown would never allow any significant current flow. Also, in most cases bi-directional operation is needed. The current flow needs to be supported in both directions on each wire.

Gene

[mlabruyere]

Originally Posted by yorkrose Even if the G251 was made of Kryptonite this would not work, for at least two reasons. The most basic reason is that the current must flow in a circuit. The diodes shown would never allow any significant current flow. Also, in most cases bi-directional operation is needed. The current flow needs to be supported in both directions on each wire. Gene

...................................................................................................................................................................................................ME

Yeah...not thinking....the coil has to have a flow of current....duh. And it has to be able to flow in either direction to boot....well frick.

Like I said...if it would have worked they would have built them this way.....