choosing a bleed resistor

[m_c]

Lower resistance = faster voltage drop after power removal, but more heat generated.
Higher resistance = slower voltage drop after power removal, but less heat generated.

Once you have drives attached to the power supply, they'll help reduce the voltage. The bleed resistor is more a safety measure for if there are no drives attached, as otherwise the capacitor(s) could retain quite a high voltage for a considerable amount of time.
I've just checked what I've used previously, and for my digitiser (around 40VDC IIRC) it's a 270ohm 15W, and the mill a 680ohm 25W (around 55VDC IIRC).

[the great waldo]

Hi
Does the resitor in parallel with the caps alter the voltage coming into the controller whilst running the motors and controller at all? If so in which way?

Cheers

Andrew

[Doddy]

Hi
Does the resitor in parallel with the caps alter the voltage coming into the controller whilst running the motors and controller at all? If so in which way?

Cheers

Andrew

With an unregulated PSU, the bleed resistor will lower the terminal voltage slightly. Provided the PSU is specified sufficiently for the steppers then the resistor effect will be negligible.

I'd be looking to dissipate 2->5W just to keep the temperature down and keep the costs low.

.