On Friday 15 May 2020 07:31:27 Dan Henderson wrote: > I was just testing any pin. I have two BOB’s connected to two parallel > ports. All my steppers are working on BOB zero. No issues with any of > that. BOB “1” has spindle-motion-reverse => paraport.1.pin-04-out. > From this BOB I have both + and - 5v going to Inputs of external relay > along with output of pin 04. By issuing M4, I assumed would get a > click or trigger from external relay? This could also have been setup > for coolant/air or any external device. I have not connected anything > to the business end of the relay. Not sure if that would matter. > Also, the BOB is powered by USB not sure if that matters. I have the > ability to power it with an external 5 volt source as well. > If the pix posted yesterday is the external relay in question here, its a 10 amp rated contacts relay, and coil current to activate that is going to be well beyond the bobs ability to deliver the needed currant.
The bob can probably src no more than 4ma at a logic one, and sink not more than 16 at a logic 0 before the mini-74 family of chips is destroyed. If useing 2 BoBs, you'll have 2 relays available, why not use pin 14 of bob-0 which WILL have the boosted current (and flywheel diode to protect that logic output from the coils inductance) to drive an on-off(off=braking Resistor across motor) relay, and use that on-board the bob-1 relay to switch the coil current to a 2nd external relay to reverse it, which is big enough for a smallish motor, say half a hp. For 1hp and up, I'd recommend a bigger relay with 20 amp contacts. A 1hp, at its rated voltage, probably 90 volts, will draw very close to 10 amps at full load. And if reversed under that load current flow, it will be very close to a dead short because its now spinning the wrong direction. If the controller doesn't have an active current limit, it will likely destroy the controller if your hal file does not have the logic to stop the motor first before starting it in the other direction. I have actually done this in a previous incarnation of my 7x12 lathe which does have an external 1hp 90 volt motor and a separate power supply made from the power transformer of an old blown up 1500 watt Phase Linear power amplifier, which delivers about 124 volts at a 20 amp surge, giving nominally 2 hp from that motor, and as I found, more that enough to break things if not well controlled by the hal config. Then I discovered the Pico Systems pwm-servo driver, which removed all those relays as its a full 4 quadrant controller that pulls energy back out of the motor when slowing or stopping it, running that supply up to around 165 volts while stopping the motor, and is very well protected from such self destruction with a programable current limit. A bit of hal code to profile the reversals and its happy, not to mention that with the dynamic braking, the reversals are done in 25% of the time it took with the relays. Since I useally forget I've put the head in neutral while fooling with the workpiece, then starting the motor in neutral, which could overspeed the flywheel, potentially exploding it. That would be poor form. So now I have code in the hal file that gives it 50 millisec's to output an encoder pulse after a start or it shuts the machine down. My "hey dummy, put it back in gear" reminder. What is embarrassing is how often that code saves me from myself, reminding me my wet ram has reached that forgetfull stage at 85+ years :) Stay well and safe, Dan. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
