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Electronics => Beginners => Topic started by: resistcircuitresist on May 05, 2012, 09:48:47 pm

Title: Need help with relays.
Post by: resistcircuitresist on May 05, 2012, 09:48:47 pm

I have two relay boards. One of them is standard 5v dc relay and the other is a solid state. I am trying to trigger several devices, one of them is a small 12v motor.

The solid state relay board functions normally by shorting + to input, but latches closed on device side of the relay until load is turned off or is disconnected.
Is this normal for solid state relays with inductor type devices?
http://www.sainsmart.com/sainsmart-4-channel-5v-solid-state-relay-module-board-omron-ssr-avr-dsp-arduino.html (http://www.sainsmart.com/sainsmart-4-channel-5v-solid-state-relay-module-board-omron-ssr-avr-dsp-arduino.html)


The standard relay works by shorting ground to input and releases on the device side when the input voltage is disconnected. I would have thought that both relays should  work by connecting + to input rather than ground to input.  Is there a problem with this relay board?
http://www.sainsmart.com/module/acceleromete/arduino-pro-mini.html (http://www.sainsmart.com/module/acceleromete/arduino-pro-mini.html)

Title: Re: Need help with relays.
Post by: TerminalJack505 on May 06, 2012, 05:00:19 am

First, the SSR has a "zero cross" feature.  This implies that the source on the load side must be AC.  DC won't work since 0V will never be crossed.

Second, if this happens only with inductive loads then be aware that it doesn't look like the PCB maker followed Omron's advice (datasheet (http://www.components.omron.com/components/web/PDFLIB.nsf/0/F1D420C93E86CDB685257201007DD5BA/$file/G3MB_0609.pdf) pg 386) regarding inductive loads.

The datasheet says "No overvoltage absorption element is built in. Therefore, if the G3MB is connected to an inductive load, be sure to connect the overvoltage absorption element."

I see a fuse on the load side but that's not the same thing. 

The PCB maker very likely expects the user to do this since it is very load-specific and would likely interfere with non-inductive loads.

If the SSR will shut off for resistive loads but not for inductive loads then you might follow Omron's advise in the SSR Design Considerations (http://media.digikey.com/pdf/Other%20Related%20Documents/Omron%20Other%20Doc/SSR%20Design%20Considerations.pdf) booklet, pg 831.

They advise the use of varistors, zeners, RC snubbers, etc., depending on the various factors.

Title: Re: Need help with relays.
Post by: resistcircuitresist on May 12, 2012, 03:35:55 am

Thanks for the information. Having trouble finding a 2 channel relay module that i can use with I/O pins, by sending high signal to close relay.  Can be powered by 0-12v.

Title: Re: Need help with relays.
Post by: dfnr2 on May 12, 2012, 03:03:21 pm

Assuming you share a common ground, you should be able to drive either with an I/O pin.