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Topic: Arduino and VFD (Variable Freq. Drive) (Read 1 time) previous topic - next topic

89ls1

I have an application where I am using a Teco VFD and I would like to interface and arduino as a "safety"..

The VFD has a 0-10v DC output linear to the AC motor current. I am using that as a "safety" so if a larger load was put on the motor thereby increasing the current the arduino can send a stop command to the VFD to turn off the motor.

That command is just shorting two pins on the VFD together. If I short the pins together with a wire the VFD set an Emergency Stop as it should. I am trying to recreate that short with the arduino. I have tried with a SSD Relay, 2n222 transistor and an IRF510 mosfet but am unable to get my "short" from the arduino to trigger the E-Stop on the VFD so I need help.

I will post my sketch as soon as I have it in front of me again, as currently I am in another city.

I have a 2n222 transistor hooked up currently with the gate to arduino with 1k pulldown, Collector hooked to the 24vDC pin on VFD, and Emitter attached to the other end of the NO E-Stop contact on VFD.

Not triggering E-Stop

With the SSD relay I simply hooked the 24vDC and the E-Stop pin on the relay so when I trigger the relay it should short the two together. But that did not work either, VFD still did not trigger E-Stop

I have the grounds from the VFD, Arduino, and the 12vdc power supply I had available that powers the arduino tied together.


I'm probably missing something easy that I should not be missing but I can't see the problem here. Thanks!

retrolefty

#1
Dec 18, 2012, 08:30 pm Last Edit: Dec 18, 2012, 08:33 pm by retrolefty Reason: 1
Quote
I'm probably missing something easy that I should not be missing but I can't see the problem here. Thanks!


Most SSR are for switching AC voltages only and require a zero crossing to activate conduction in addition to the input command to the SSR. Your emergency stop circuit is surely a DC circuit so a standard electromechanical relay would be the proper way to interface to the stop circuit and would not require to know or care what the DC voltage or polarity of the existing stop switch contacts are, just parallel the normally open contacts across the stop switch contacts.

So don't fool with any transistor switching arrangement where you are forced to tie the grounds of the arduino and VFD system together and know what the polarity of the switch contacts are, a simple DC relay is the correct device to interface your arduino to your VFD stop circuit. It will act just like your jumper wire experiment did.


Lefty

89ls1

Thanks Lefty, I figured it would be something simple I was just overlooking. Will go out and by a 5v coil relay and give it a shot when I get back to it.

dc42

#3
Dec 19, 2012, 12:34 am Last Edit: Dec 19, 2012, 12:37 am by dc42 Reason: 1
Try a reed relay with a 5V coil, that will be small and reliable, and the coil current should be low enough to drive from an Arduino pin without a transistor (you still need a flyback diode). Here's an example: http://uk.farnell.com/coto-technology/9007-05-00/relay-reed-sip-spst-5vdc/dp/1081682.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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