Re: [CAD_CAM_EDM_DRO] Re: how to safely stall a DC motor

On 19 May 2005, at 13:26, Lance Hopper wrote:

> tool turret mechanism. I'm actually reverse engineering it and then
> trying to mimic the original controls with my own as I'm installing
> new controls for everything on this machine.

Try measuring how much current the existing control puts through the
motor when it's stalled in reverse. If your replacement for it limits
the current to the same amount you shouldn't have any trouble.

> I'm still looking into more elegant ways of controlling the motor
> with H-bridge IC's etc... However, this level of electronics is way
> beyond my current knowledge/experience level.

Alan's microcontroller based solution assumes that the motor needs to
drive backwards at 100% power for a short time before reducing to low
power holding mode. If it isn't necessary to do that and full power
forward/part power backward is sufficient, then a simple DPDT
reversing relay and a current limiting resistor with a bypass diode
across it should work just as well. If you tell us the motor's
winding resistance and how much current the existing controller
supplies when it's stalled, we can work out the size of the current
limiting resistor for you.

--
------------ Alex Holden - http://www.alexholden.net/ ------------
If it doesn't work, you're not hitting it with a big enough hammer