Conveyor System Control

[paulr57]

Yes Wooly.

Your panel sounds OK. What I meant is a DOL starter circuit mounted on the front panel for the magnet, and stop start relay circuits for the inverter controls. I don't know what the magnet does so if it has to stay on, exclude it from the E.stop circuit.

Of course, if driving a large mass there should be little motor run-on. This can only be ascertained during running.

In summary you need a panel-mounted DOL start/stop plus overload,
Two stop/start relay circuits with E.stop loop
Appropriate overcurrent protection for each inverter.
Some study time with the inverter manuals!

The manuals usually contain some good diagrams illustrating FWD/REV and ESTOP
circuitry.

 

[Knobhead]

Switch the magnet supply on the AC side of the rectifier this saves having to break a DC arc. The large magnets I used to work on we couldn’t switch the AC. We used 125A AC 4 pole contactors with two contacts in series to safely break the DC. The contactors were rated at 660V AC they used to burn up switching 180V DC. Also fit a reverse bias diode across the magnet feed to prevent high voltage spikes from the collapsing field.

 

[Bobster]

Switch the magnet supply on the AC side of the rectifier this saves having to break a DC arc. The large magnets I used to work on we couldn’t switch the AC. We used 125A AC 4 pole contactors with two contacts in series to safely break the DC. The contactors were rated at 660V AC they used to burn up switching 180V DC. Also fit a reverse bias diode across the magnet feed to prevent high voltage spikes from the collapsing field.

I can't see him understanding all of that Tony if he's asking us how to set a conveyor belt system up.

 

[Robotstar5]

The only thing I remember about switching magnets was they draw a big arc when the contacts open! had to switch the DC as it was powered by a motor-generator set.

 

[Wooly]

Thanks for that really useful information RoB2, really helpful.

Robotstar5 and tony, I hadn't even thought about the magnet really. Is it really a pain to control? I feel very embarrassed to have to ask, but with magnets I haven't a clue.

 

[Bobster]

No worries .

I'm sorry but I feel like your out of your depth, if you've been in industry a long as you have, you should have delt with setting up simple systems like this up before.


If you give me a couple of days I'll throw a quick drawing together on how I'd do it.

 

[Knobhead]

You a mind reader RoB? I still don't know what's going where!

And Wooly, 10 years in engineering? This should have been done on the back of a smoke packet in 5 minutes!

 

[Wooly]

Fair comments, I suppose.

I was only trying to get things right in ny head.

After 10 years of doing the same monotonous maintenance work, and no design or installation work, I'm sorry if I can't switch into that mode instantly.

Maybe I was a bit quick to ask for help on the conveyor side, but that was mainly for the estop cct, and the more I've looked into it, the more I seemed to have overanalysed it and over complicated it, mainly due to worries about safety.

Think what you like about my ability, I'm just very rusty after years of not using my brain, and I know I am more than capable of understanding what's going on.

Except, not when it comes to magnet control.

I know I sound like a dimwit, but I rather ask a stupid question and be happy that I'm on the right lines, than not ask and be cocky and do it all wrong.

Thanks for all comments so far, good or bad.

 

[Knobhead]

As RS said and I was hinting at, when you break the magnet circuit you have to contend with the power of the colapsing magetic field. An easy way around this is a diode across the output to the magnet to divert the power. It's fitted +ve to +ve so normally it doesn't conduct. when the circuit is broken the polarity reverses and diverts through the diode. Hence it's name, reverse bias diode. The diode should be rated aprox 2 X the normal running current.