Re: Allegro 2961 uptdate

>
> One way - I have something like this on my servo amps - is to have
> the motor DC power interlocked to the logic power. There is a fail-

safe

> relay in the safety chain of the CNC system in each servo amp.
> When there is no logic power, the relay is de-energized, which

equals

> the fault state. (Normally open contacts are wired in series for

all

> the fault relays.) Only when power is OK, there is no blown fuse or
> overcurrent condition, then the relay energizes, closing the

contacts.

> When all relays in the chain are closed, then the computer is able

to

> command the system to come out of e-stop. When it does that, it
> closes a set of sequential relays that charge the cap bank in the

servo

> amps through a resistor and then closes a direct contactor to supply
> DC to the amps. The charge-direct relay circuit is on my web page

at

> http://pico-systems.com/EMC.html as the 2nd schematic. (The first
> is the safety control, but it is somewhat specific for the Servo-to-

Go

> card and its very wierd watchdog timer.)
>
> I needed all this complexity because I have some fairly large caps

right

> on the servo amps, and because the high-side current sensing

resistor

> is BEFORE the cap. So, if I just closed a contactor to the DC

supply, it

> would look like a short while the cap charged up, and trip the

overcurrent

> shutdown. It would also fry the relay contacts. This circuit also

does

> the reverse on power down, removing the direct connection and then
> connecting an energy dump resistor. This resistor will brake the

motors

> in an emergency stop condition or power failure.
>
> Jon

Thanks again Jon, great info and ideas.
Lonnie