Electromagnet analog control
Electromagnet analog control
(OP)
I need to control the force of 3 electromagnets wired in parallel to pick up steel discs that are piled up in a stack.
Discs range from 4" to 42" in diameter of various thicknesses (0.075" to 0.25"). 1/2 lb to 85lbs. About 30 different format total.
One stack is composed of only identical discs (diameter, thickness, finish) up to 50 pcs for small sizes.
I'm designing the machine that will pick up the discs.
The goal is to pick up only one disc at a time and thus my need to adjust the voltage that will power the electromagnets. I'll set them up to produce a bit more power than needed to lift one disc but less power than for 2.
The PLC running the system will "know" which discs are next and will have the settings for each disc pre programmed (50% power for medium disc, 85% for large discs for example).
Note: I will setup 3 sets of 3 magnets to match different diameter/force requirements. PLC will control which set is needed at which power.
My PLC (P2000 Automation Direct) can output a 0-10V signal to control the power needed.
Strongest electromagnets used are 24VDC, 0.37A, 420N 8.9W each.
I did some research and was surprised I couldn't find a power supply or a standalone MOSFET Board I could use with 0-10V input to power the EM 0-24VDC. I'm looking for 2A power supply min to have some buffer.
I found a complete machine that does exactly what I need and they are dealing with the 0-10V signal to 0-24VDC output with a custom proprietary board. ;(
I have been toying around the idea of using a DC motor drive that will receive the O-10V input and output a PWM signal to the EM.
What do you guys think?
Any other ideas?
It's a 1 off project.
Thanks a bunch!
Sylvain.
Discs range from 4" to 42" in diameter of various thicknesses (0.075" to 0.25"). 1/2 lb to 85lbs. About 30 different format total.
One stack is composed of only identical discs (diameter, thickness, finish) up to 50 pcs for small sizes.
I'm designing the machine that will pick up the discs.
The goal is to pick up only one disc at a time and thus my need to adjust the voltage that will power the electromagnets. I'll set them up to produce a bit more power than needed to lift one disc but less power than for 2.
The PLC running the system will "know" which discs are next and will have the settings for each disc pre programmed (50% power for medium disc, 85% for large discs for example).
Note: I will setup 3 sets of 3 magnets to match different diameter/force requirements. PLC will control which set is needed at which power.
My PLC (P2000 Automation Direct) can output a 0-10V signal to control the power needed.
Strongest electromagnets used are 24VDC, 0.37A, 420N 8.9W each.
I did some research and was surprised I couldn't find a power supply or a standalone MOSFET Board I could use with 0-10V input to power the EM 0-24VDC. I'm looking for 2A power supply min to have some buffer.
I found a complete machine that does exactly what I need and they are dealing with the 0-10V signal to 0-24VDC output with a custom proprietary board. ;(
I have been toying around the idea of using a DC motor drive that will receive the O-10V input and output a PWM signal to the EM.
What do you guys think?
Any other ideas?
It's a 1 off project.
Thanks a bunch!
Sylvain.
Talk To Other Members
RE: Electromagnet analog control
It also means you get to use a junky unregulated 24ish-Vdc supply that will take a beating-and-keep-on-giving.
PWM that out thru the magnets. Include flybacks which will cause a general averaging of the PWM into something akin to an analog magnetic field.
Look at Solid State Relays - the DC variety.
dc ssr1
dc ssr2
Crydom DC SSR AppNote
Automation Direct SSR that includes DC outputs (three in the middle of the table)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electromagnet analog control
Ok for PWM.
You mentioned the SSR.
The PLC doesn't have a PWM function per say but it can be done in the ladder in few rungs (time proportional control). What period would you recommend? 50ms?
I'll get the SSR and wire a diode to protect from the inrush current (following your Crydom link do I need a fast recovery diode in my case?).
What are your thoughts of using the DC drive (PWM) that will receive the analog 0-10V from the PLC as input? Is it a viable option or overkill? Might be easier to implement.
Thank you,
Sylvain.
RE: Electromagnet analog control
Not clear what DC PWM drive you're referring to.
As for using a motor drive. Small drives like those used in RC and quad-copter like stuff would probably work but you can't use the ones for brushless motors as they need to see three phase things back from the motor. You'd have to use one for a brushed motor. Also, they look for that RC-servo signal which is digital in nature. Simple but digital. It's easy to come up with. Often they're rated at 20A some to 80A and they're really cheap. You could snag one and experiment.
Brushed ESC
A BUNCH more
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electromagnet analog control
https://www.automationdirect.com/adc/Shopping/Cata...
it runs on a potentiometer but can also take 0-10V as input signal.
Thx,
Sylvain.
RE: Electromagnet analog control
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electromagnet analog control
Thanks for the help Keith.
I ordered the SSR and I am sourcing the diode right now.
DC driver ordered as well as option B.
Sylvain.
RE: Electromagnet analog control
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electromagnet analog control
1st method:
Using the Drive made to run DC motors works well with the electromagnets. The PWM does the job fine. I just use the potentiometer of the drive to test the electromagnets in parallel under 0V-24VDC. I shouldn't see any issues using the 0-10V output from the PLC to replace the potentiometer and run the drive remotely from the PLC.
2nd method:
I tried with the PLC as well running few lines to output the PWM signal.
One variable takes care of the period, another one the ON/OFF time withing that period in %.
Keith, you mentioned starting at 5ms. It seems it's going to be too small for the PLC to keep up and have a clean signal.
I'll probably have to go 50 or 100ms. I'm testing with regular outputs at this point on a P2000. I might have to use a fast output usually dedicated to running steppers to pilot the SSD.
I'll try next week.
One thing I might have to do is reverse the voltage to get rid of any remanence. I'll run more tests as I'd like to avoid that; it just adds another thing to deal with.
I'll update as more tests are done.
Sylvain.
RE: Electromagnet analog control
I'd suggest controlling current, not voltage, as current is what actually creates the magnetic field so keeping the current constant would keep the magnetic field constant even when the coil resistance changes with temperature.
RE: Electromagnet analog control
Keith Cress
kcress - http://www.flaminsystems.com