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Topic: Dry Contacts - timing relay (Read 960 times) previous topic - next topic

JessetheBotty

I am trying to interface the Uno with a Magnecraft timing relay that will be switching a larger 90VDC load.  The relay is set up to accept a simple dry contact closure to close the coil.  I would like to use an output pin to do this from the Arduino but am getting some extremely spotty results.  Does anyone know of the simplest way to do this?  I don't need the 5VDC output, I just need to close the contacts.  Thank you for the help!

Grumpy_Mike

You need to use a transistor to drive the relay.
Direct connection to an arduino will damage the arduino.

CrossRoads

Have arduino pin drive a transistor to close the coil contacts to get more current sink capability.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

retrolefty

#3
Jul 06, 2011, 05:48 am Last Edit: Jul 06, 2011, 05:52 am by retrolefty Reason: 1

I am trying to interface the Uno with a Magnecraft timing relay that will be switching a larger 90VDC load.  The relay is set up to accept a simple dry contact closure to close the coil.  I would like to use an output pin to do this from the Arduino but am getting some extremely spotty results.  Does anyone know of the simplest way to do this?  I don't need the 5VDC output, I just need to close the contacts.  Thank you for the help!


"set up for a dry contact" means the device is providing the voltage source needed to power the coil and all a user has to provide is a switch or relay contact to close the circuit that powers the relay coil.

So before the best interface method for using a arduino can be decided, one needs to know what coil voltage is (and if AC or DC voltage)  being used and how much current the relay coil draws at that voltage. So you can read the voltage by just taking a voltmeter reading across the 'dry contact' connections with nothing wired to them. Then reading the coil current requires reading the series current with the "dry contact circuit" completed.

With these measurement then one can decide on the several methods possible. So find out if the coil is using AC or DC voltage, it's value, and it's current consumption value and we can talk again.  ;)

Lefty

JessetheBotty

The relay is not like a typical relay as it does not need voltage to close the contacts.  It is an electronic tinge relay that has an external switch option.  Here is the link to the wiring scheme.  http://www.serelays.com/library/section5/105A_TDRPRO-5100.pdf

I think ll I really need is direct continuity and don't know how to achieve this. 

Grumpy_Mike

It needs a voltage signal greaterbthan 12V to drive it. The arduino supples only 5v so younhave to use a transistor and external power supply to generate this signal.

retrolefty

Quote
I think ll I really need is direct continuity and don't know how to achieve this. 


Well if you don't or can't provide the relay coil voltage/current values used in it's 'dry contact' control mode, (the data sheet doesn't provide that without more nameplate data from your specific unit) then you are left with only being able to use real 'dry contacts', meaning using another relay controlled by the arduino and have that relay's contacts control your timing relay.

JessetheBotty

Sorry, the voltage present on the switch contacts of the relay is 5VDC @ ~30mA.  I haven't yet payed any attention in which way I connected this to the pins (whether I tied the common to gnd or vise/versa).  This would definitely matter right?

Grumpy_Mike

The data sheet said dry contacts or a power pulse from 12v to 220v AC or DC so that is why I suggested a 12V signal. Still if it is 5V and 30 mA on those contacts I would STILL suggest running it through a transistor first.

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