Thread: VFD interference problem
Well, guys, problem solved ! Guess who was right ??????????
The 5V signal to the BOB had two routes to 0V... getting the 5V from the PC solves the problem :) This is why disconnecting the PP cable was causing the noise to go away, since it would suppress one of the two 0V possible routes.
Thanks for your help !
I do have one more tiny issue:
Mach3 controls the RUN/STOP signal and spindle speed fine, but the BOB seems to output an unstable signal for the spindle speed control. When running, the frequency can't stay still and keeps going up and down by 1-2 Hz, causing the spindle to run faster/slower (you can hear a slight increase/decrease in speed).
I can bypass this issue by disabling Mach3 speed control and only do the RUN/STOP, but while I'm at it, let's fix this issue if possible :)
19-03-2016 #75It's called Crap Bob Syndrome and I doubt there's much you can do for it.!!..Clive
You dorks :D
Well, a clue could have been that when the 5V PSU was off, its power LED was slightly on (not fully, but you could see some light), indicating that power was flowing from THE PC through to BOB to the 5V PSU (receiving -5V I guess).
Anyways, problem fixed, let's now move on to cutting !!!!
Had you originally connected V- on your 5v PSU to GND ?
On your BoB the terminal marked PC GND is actually the current return path and should not be connected to GND but only to V- on the power supply. The BoB itself has a GND plane connection next to the 12-24v terminal, which is the current return path AND GND for the BoB electronics.
Last edited by cropwell; 20-03-2016 at 09:24 AM.It takes all sorts to make a world, I am just glad I am not one of them.
Yes that's what I had done. PC GND to 0V of the 5V PSU, and PC +5V to +5V of the 5VPSU.
Can you provide a quick diagram on how to do what you're explaining ?
Last edited by eurikain; 21-03-2016 at 10:10 AM.
I trust you mean PC GND to -5v on the power supply.
On your power supply check with your meter for continuity between -5v and the earth terminal. It should not be connected internally in the power supply. If it is you will have a ground loop. These power supplies are generally not connected between the -5v terminal and the Earth terminal. Also make sure that if you use the 5v power supply that -5v is connected to PC GND on the BoB and nowhere else (I am assuming that you do not have any other requirements for 5v in your control box).
The Earth connection on the power supply should be connected to the star earthing point to provide shielding for the power supply.
In a conversation with Graeme, he thought that the power supply, if under loaded, may react badly to interference from the VFD and cause all manner of effects, in fact it could go unstable by itself. So even if you get the earth and current return paths right, you may still have problems as you are only driving the optos on the BoB.
Jazz hit on a solution, and the PC USB supplying 5v to the BoB is workable, but I do not like using USB ports to provide power as they have limitations.
If it is working now don't muck about with it, but I still don't believe that we have got to the root cause of the problem.
RobIt takes all sorts to make a world, I am just glad I am not one of them.
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